JP2008105928A - Preform for precision press molding and method for producing optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxide glass preform containing a fluorine component which is useful for producing a good optical element, such as a lens, by precision press molding, and to provide a method for producing the good optical element by using the preform. <P>SOLUTION: The preform for precision press molding is characterized in that light reflectance on two faces mutually facing opposite sides with respect to the center of the preform have different values and is formed of oxide glass containing a fluorine component, and the preform for precision press molding is characterized in that surface free energies at two faces mutually facing opposite sides with respect to the center of the preform have different values and is formed of oxide glass containing a fluorine component. In a method for producing an optical element by precision press molding a glass preform, the method for producing the optical element uses the preform for precision press molding. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a precision press-molding preform and a method for producing an optical element, and more specifically, a glass preform used when an optical element such as a lens is produced by a precision press molding method, and the optical using the preform. The present invention relates to a method for manufacturing an element.

  As a method for efficiently producing a glass aspheric lens, a precision press molding method is known. In the precision press molding method, an optical glass preform preformed in a shape suitable for press molding as described in Patent Document 1 is used.

Optical glasses having various optical properties are prepared according to the purpose of use. Among them, one having high utility value is one having low dispersion characteristics such as fluorophosphate glass.
JP-A-8-277132

However, precision press molding of this fluorophosphate glass has the following problems.
The press-molding temperature of fluorophosphate glass is lower than that of other glass compositions such as B ₂ O ₃ —La ₂ O ₃ glass. However, since it contains fluorine, the reaction between the press mold and the glass tends to occur, and the reaction tends to cause problems such as cloudiness and spiders on the glass surface. Therefore, in order to reduce such a risk, press molding at an even lower temperature is required.

  However, when the press molding temperature is lowered, the viscosity of the glass increases, and there is a problem that the glass is difficult to stretch during pressing. In particular, most lenses produced by precision press molding are molded using molding tools having different areas of a pair of opposed molds that pressurize a preform, such as an upper mold and a lower mold. For example, when the effective diameters of the convex lens surface and the concave lens surface of the meniscus lens are equal, the area of the mold molding surface that presses the lens surface having a small absolute value of the radius of curvature is larger than the area of the other mold molding surface. In the case of not only a meniscus lens but also a biconvex lens and a biconcave lens, the area difference between the pair of mold surfaces may be large in this way.

  In precision press molding of such a lens, it is necessary to stretch the glass more along a molding surface having a larger area. In other words, the preform placed at the center of the mold before pressing is stretched along the mold surface by pressing and the entire area of the mold surface is transferred to glass, so the area of the mold surface of the pair of opposed molds is larger. It is necessary to stretch the glass much more along the larger mold surface.

  However, when the viscosity is high, there is a problem such as radial scratches on the obtained lens surface due to insufficient elongation of the glass or increased friction at the interface between the glass and the molding surface. Arise. If the press molding temperature is raised in order to solve such a problem, the aforementioned problem occurs.

  Thus, in precision press molding of fluorine-containing glass, there has been a problem that if the molding condition of one lens surface is made appropriate, the molding of the other lens surface is hindered.

  Under such circumstances, the present invention is good by using the oxide component preform containing fluorine component for producing an optical element such as a good lens by precision press molding, and the preform. It is an object to provide a method for manufacturing a simple optical element.

  As a result of intensive studies to achieve the above object, the present inventors have obtained the following knowledge.

  As described above, on the side having a large area formed by transferring the molding surface of the two lens surfaces, it is necessary to greatly stretch the glass along the molding surface in precision press molding. Therefore, it has been noted that the above problem can be solved by making the glass on the side having the larger area of the molding surface easy to extend along the molding surface. Therefore, the present inventor has considered a means for making the lubricity of one surface of the preform and the molding surface greater than the lubricity of the other surface and the molding surface.

  As a result, the present inventors have found that in the oxide glass containing a fluorine component, the lubricity between the glass and the molding surface varies depending on the fluorine concentration of the extreme surface layer, and the surface having good lubricity between the molding surface and the molding surface. It has been found that precision press-molding may be performed so as to face the molding surface side of a larger area.

  In order to make such a preform, it is only necessary to increase or decrease the fluorine concentration uniformly on a part of the surface of the preform, but the fluorine concentration does not increase or decrease locally in the plane. It is important to be careful. The local change in the fluorine concentration becomes a striae and causes a decrease in optical performance.

In order to change the fluorine concentration in the vicinity of the surface without causing striae, the molten fluorine-containing oxide glass exhibits extremely high volatility. It was found that the fluorine in the vicinity of the surface should be reduced by volatilization so as to prevent striae, after lowering to a controllable level.
The present invention has been completed based on this finding.

That is, the present invention
(1) Preform for precision press molding characterized in that it has different values of light reflectance on two surfaces facing opposite sides with respect to the center of the preform and is made of oxide glass containing a fluorine component ,
(2) having one rotational symmetry axis, a first curved surface including one of the two intersections of the symmetry axis and the surface, and a second curved surface including the other intersection of the intersections; The precision press-molding preform according to (1) above, wherein the light reflectance on the curved surface of 1 and the light reflectance on the second curved surface are different from each other,
(3) Preform for precision press molding characterized in that it has different values of surface free energy on two surfaces facing opposite sides with respect to the center of the preform and is made of oxide glass containing a fluorine component. ,
(4) having one rotational symmetry axis, a first curved surface including one of the two intersections of the symmetry axis and the surface, and a second curved surface including the other intersection of the intersections; The precision press-molding preform according to (3) above, wherein the surface free energy on the first curved surface and the surface free energy on the second curved surface are different from each other,
(5) The precision press-molding preform according to (2) or (4) above, wherein the curvature radius of the first curved surface and the curvature radius of the second curved surface are different.
(6) The precision press-molding preform according to any one of (1) to (5) above, wherein the entire surface is formed by cooling and solidifying molten glass.
(7) In a method for producing a precision press-molding preform for producing a glass preform for use in precision press-molding,
The molten glass lump including the lower end of the molten glass flow flowing out of the pipe is separated, and the molten glass lump is floated on the concave portion of the mold by jetting gas from the gas outlet provided in the concave portion and applying wind pressure. Molding into a preform without turning upside down,
And the glass is an oxide glass containing a fluorine component,
And (8) a method for producing an optical element for producing an optical element by precision press-molding a glass preform,
It is characterized by using the precision press-molding preform described in any one of the above items (1) to (6) or the precision press-molding preform produced by the method described in (7) above. A method of manufacturing an optical element,
Is to provide.

  According to the present invention, there is provided a fluorine component-containing oxide glass preform for producing an optical element such as a good lens by precision press molding, and a method for producing a good optical element using the preform. Can be provided.

  The precision press-molding preform of the present invention has two aspects. The first aspect is a precision press-molding characterized in that the light reflectance on two surfaces facing opposite sides with respect to the center of the preform has different values and is made of an oxide glass containing a fluorine component. Preform (hereinafter referred to as “Preform I for precision press molding”), the second aspect has different values of surface free energy on two surfaces facing opposite sides with respect to the center of the preform. In addition, a precision press-molding preform (hereinafter referred to as “Precision Press Molding Preform II”) characterized by comprising an oxide glass containing a fluorine component.

  Two surfaces facing opposite sides with respect to the center of the preform are pressed surfaces pressed by a press mold at the time of precision press molding, but in a preform made of oxide glass containing a fluorine component, Of the two pressed surfaces, the fluorine-rich pressed surface has lower light reflectance and higher surface free energy. Further, the glass rich in the pressed surface rich in fluorine tends to extend along the molding surface. Therefore, by differentiating the values of the light reflectance and surface free energy of the two surfaces facing away from each other with respect to the center of the preform, the molding surface at the time of precision press molding between the two pressed surfaces Thus, even when the area difference between the pair of molding surfaces is large, good precision press molding can be performed.

In order to produce the precision press-molding preforms I and II having such properties, as described in the above [Means for Solving the Problems], the present inventor does not generate striae. Therefore, it is only necessary to change the fluorine concentration in the vicinity of the surface of the preform. For this purpose, the oxide glass containing the fluorine component in the molten state exhibits extremely high volatility. It was found that the fluorine in the vicinity of the surface should be reduced by volatilization so as to prevent striae after reducing the property to a controllable level.
[Operation for reducing volatility of molten glass]
When melting an oxide glass containing a fluorine component, it is considered that a fluorine compound having extremely high volatility and a fluorine compound having low volatility are generated by a melting reaction. By flowing an inert gas such as nitrogen gas in a dry state in the molten atmosphere, volatilization of a highly volatile product is promoted, and the concentration of the product in the molten glass decreases. By such an operation, the volatility of the molten glass can be reduced. The fluorine component in the glass having sufficiently reduced volatility is derived from a product that is not highly volatile.

  However, since the fluorine component in the glass is reduced by this operation, a larger amount of a component such as a fluorine component that is reduced by volatilization at the time of raw material preparation should be introduced.

It is preferable to perform the said operation in the refining process in which the temperature of glass is the highest during a melting process. Volatilization of the volatile product can be further promoted by performing the above operation at a higher temperature.
Whether the volatility is sufficiently lowered can be confirmed by the following method.

  The precision press molding preform is fortunately made of optical glass whose refractive index is determined with high accuracy. The refractive index of glass reflects the composition, and the refractive index changes with the change of the composition. Although the composition slightly changes due to the volatilization of the volatile product, such slight composition change can be monitored as a change in refractive index in the optical glass whose refractive index is determined with high accuracy.

  Whether or not the glass obtained by cooling and solidifying the molten glass is obtained by reducing the volatility can be determined by reheating and re-melting the glass and examining the refractive index change before and after that. If the refractive index of the glass is accurately measured before and after remelting, and the refractive index difference between before and after remelting is large, a large amount of volatile products remain in the glass before remelting. In addition, if the difference in refractive index is small, there will be less volatile products in the glass before remelting.

  Relating the difference in refractive index before and after remelting and the possibility of canceling the understanding of the pulse, making the refractive index substantially the same before and after remelting, more specifically, the difference in refractive index before and after remelting It is possible to determine that the volatility of the glass has been reduced to such an extent that the striae is eliminated by setting the absolute value of the value to a predetermined value or less.

Specifically, the refractive index value of the glass is n _d ⁽¹⁾ , the glass is remelted in a nitrogen atmosphere at 900 ° C. for 1 hour, cooled to the glass transition temperature, and then cooled at a rate of 30 ° C. per hour. when the value of the refractive index after cooling to 25 ° C. was ^{_{n d (2), n d}} (1) and n _{d ⁽²⁾} and may be understood as volatile if Kere substantially like drops .

Here, n _d ⁽¹⁾ and n _d ⁽²⁾ are substantially equal to each other so that n _d ⁽¹⁾ and n _d ⁽²⁾ are approximated so that no striae occur in the optical glass. However, as a specific measure, it is preferable that the absolute value of n _d ⁽²⁾ −n _d ⁽¹⁾ is 0.00300 or less. If the absolute value of ^{_{n d (2) -n d (}} 1) is more than 0.00300, when molding the glass melt to preform typically striae occurs preform surface. When the absolute value is 0.00300 or less, a glass material capable of preventing striae can be provided.

A more preferable range of the absolute value is 0.00200 or less, a further preferable range is 0.00150 or less, and an even more preferable range is 0.00100 or less. In the fluorine-containing oxide glass, since fluorine is a component that relatively lowers the refractive index of the glass, the value of n _d ⁽²⁾ −n _d ⁽¹⁾ is generally positive.

The atmosphere during remelting performed to measure n _d ⁽²⁾ is nitrogen gas so that the refractive index of the glass is not affected by factors other than volatilization due to the reaction between the glass and the atmosphere. The remelting is performed under a predetermined condition at 900 ° C. for 1 hour, and then cooled to the glass transition temperature. Since the value of n _d ⁽²⁾ is also affected by the cooling rate during cooling, the cooling is performed at a predetermined cooling rate of 30 ° C. per hour and cooled to 25 ° C.

  A known method can be used for measuring the refractive index, and it is desirable to measure with an accuracy of 6 significant digits (5 digits after the decimal point). As an example of measuring the refractive index, Japanese Optical Glass Industry Association Standard JOGIOS 01-1994 “Measurement Method of Refractive Index of Optical Glass” can be applied.

  Depending on the shape and volume of the glass, for example, if the glass is small spherical or molded into a thin lens, the glass cannot be processed into a sample with the shape and dimensions specified in the above standards There is also. In that case, the glass is heated, softened, press-molded, and annealed to form a prism shape in which two planes intersect at a predetermined angle. Then, based on the same measurement principle as the above standard, the refractive index is measured. The heating temperature at the time of preform production by press molding is a temperature range that can soften the glass at most, and is extremely lower than the temperature at which the glass melts, so the influence on the concentration of volatile substances is negligible. The amount of change in refractive index before and after heating can be ignored.

The glass constituting the preform of the present invention preferably has the above properties with respect to volatility.
[Preparation of Preform for Precision Press Molding]
Next, the molten glass subjected to the volatility reducing operation in this manner is flowed out, and the atmosphere in contact with the surface where the fluorine concentration is to be reduced is always replaced with a new atmosphere. Even for glasses with reduced volatility, volatile products are slightly volatilized from the hot glass surface. Since the concentration of volatile products in the atmosphere is always kept low by performing the atmosphere substitution, the volatilization speed per unit area is almost determined by the glass temperature. On the other hand, in terms of not performing atmosphere replacement, the concentration of volatile products in the atmosphere increases, and the volatilization speed per unit area tends to be lower than when atmosphere replacement is performed.

Thus, by replacing the atmosphere only on a part of the surface of the molten glass, the fluorine concentration in the vicinity of the surface of that part can be reduced. If the glass is cooled in this state, the distribution of the fluorine concentration is fixed.
By utilizing such a principle, the preform of the present invention can be produced by several methods.

  The first method is to separate a molten glass lump including a lower end of a molten glass flow flowing out from a pipe, and to blow the molten glass lump from a gas outlet provided in the recessed part on a recessed part of a molding die to generate wind pressure. To form a preform without floating upside down. Specifically, the molten glass having reduced volatility flows out from the pipe, and the lower end of the outflowing molten glass flow is supported. By this operation, constriction occurs due to surface tension between the pipe outlet side and the lower end of the molten glass flow. Next, the support is removed, or the support supporting the lower end of the molten glass flow is rapidly lowered, and the molten glass flow is separated by surface tension at the constriction. The molten glass lump including the lower end is separated in this manner and formed into a preform on the concave portion of the mold. The recess is provided with a large number of gas jets over the entire surface supporting the glass, and molding is performed while gas is jetted from these gas jets and wind pressure is applied to the glass to float on the recess. As the gas (referred to as a floating gas), it is desirable to use a gas that does not contain fluorine. For example, a rare gas such as nitrogen gas or argon gas may be used. By ejecting gas over the entire surface of the recess to float the glass, the glass is formed into a preform without being inverted upside down. Therefore, the lower surface of the preform on the recess is always supplied with a new floating gas, and the atmosphere replacement described above is performed. On the other hand, since the floating gas is not sprayed on the upper surface of the preform, the preform is molded in a state where an atmosphere containing a volatile product volatilized from the glass remains. Thus, a preform having a surface with a high fluorine concentration and a surface with a low fluorine concentration can be produced.

  In the second method, molten glass with reduced volatility is flown out and dropped from a pipe, and the molten glass droplet is received by an inverted conical mold called a venturi tube and formed into a preform.

  The venturi tube is formed so that the inner diameter decreases toward the lower part, and a gas outlet for ejecting floating gas is provided at the bottom. Gas is ejected from this gas outlet and upward wind pressure is applied to the glass. From the shape of the Venturi tube, the glass rises by receiving a strong upward wind pressure as it goes to the bottom, but the upward wind pressure weakens due to the rise, so it rolls along an inverted conical slope and repeats the up-and-down motion of rising again. By this movement, the glass is formed into a spherical preform while rotating in a random direction. In this method, the entire glass surface is subjected to atmosphere substitution and the fluorine concentration is lowered. Next, when a part of the surface of the preform is removed by polishing or etching, the surface layer having a reduced fluorine concentration is removed, and a surface having a high fluorine concentration appears. In this way, preforms having surfaces with different fluorine concentrations can be produced.

  In addition, using glass in a state where striae cannot be reduced due to reduced volatility, the volatilization of a part of the glass surface is promoted, or a part of the glass surface whose fluorine concentration is uniformly reduced is removed. Thus, a desired preform can be produced by exposing a portion in a state before the fluorine concentration is lowered as a surface. In addition, it cannot be overemphasized that the inside of the glass which reduced the fluorine density | concentration of the surface vicinity by volatilization is in the state whose fluorine density | concentration is higher than the surface.

  The difference in density between the surface with a high fluorine concentration and the surface with a low fluorine concentration may be slight. During precision press molding, the preform is pressed with a pair of opposing mold members, for example, an upper mold and a lower mold. If the lubricity between the mold molding surface with the larger mold molding surface and the glass is slightly better than the other, the glass will spread smoothly into the mold and an optical element with high surface accuracy can be molded. . It is not a good idea to directly measure such a small fluorine concentration in terms of measurement accuracy, labor, and cost. Further, the surface layer with a low fluorine concentration is considered to be extremely thin, and it is considered difficult to measure the concentration. Therefore, in the present invention, instead of directly managing the fluorine concentration, the fluorine concentration is indirectly managed by managing the light reflectance and surface free energy on the preform surface.

  For example, in a fluorine-containing oxide glass such as fluorophosphate glass, fluoroborate glass, or fluorosilicate glass, the refractive index decreases when the fluorine concentration is high, and conversely, the refractive index increases when the fluorine concentration is low. This is because the oxygen-rich glass has a higher refractive index than the fluorine-rich glass when focusing on the anion component.

  Thus, since the refractive index sensitively reflects the fluorine concentration, the fluorine concentration in the vicinity of the surface may be indirectly managed by the refractive index of the glass. However, since it is difficult to measure the refractive index of the extremely thin portion of the surface, the light reflectance at the surface may be measured instead. The relationship between the light reflectance at the preform surface and the refractive index at the glass surface is related by an equation called the Fresnel formula.

  When the fluorine concentration on the preform surface decreases, the refractive index near the surface increases and the light reflectivity increases. Conversely, when the fluorine concentration increases, the refractive index near the surface decreases and the light reflectivity decreases.

The precision press-molding preform I which is the first aspect of the present invention is made based on such knowledge.
[Preform I for precision press molding]
As described above, the precision press molding preform I according to the first aspect has different values of light reflectance on two surfaces facing opposite sides with respect to the center of the preform, and contains a fluorine component. It is characterized by comprising an oxide glass.

  As a preform for molding an optical element having rotational symmetry such as a lens, one rotational symmetry axis, a first curved surface including one of the two intersections of the symmetry axis and the surface, It is preferable that the preform has a second curved surface including the other intersection among the intersections, and the light reflectance on the first curved surface and the light reflectance on the second curved surface are different from each other. This preform can be produced by the first method described above.

  In this preform, since the radius of curvature is maximized in the vicinity of the intersection of the first surface and the second surface, the influence of the surface shape of the preform can be reduced when the refractive index is indirectly managed by the reflectance. It is convenient.

  In the present invention, in order to achieve the object of the invention, it is preferable to provide 0.03% or more, more preferably 0.05% or more, of the difference in light reflectance at a wavelength of 500 nm between the two surfaces. In the present invention, the difference in light reflectance is provided at a plurality of wavelengths, and it is desirable that the surfaces having a large reflectance be the same surface at any of these wavelengths.

For example, the light reflectance at three wavelengths of 500 nm, 600 nm, and 700 nm is measured, and in any case, the difference in light reflectance is preferably 0.03% or more, and more preferably 0.05% or more. However, if the difference in the light reflectance is increased more than necessary, the performance of the optical element is degraded, and depending on the production method, striations occur in the preform, and the precondition of the present invention is that an optically homogeneous preform is obtained. There is a risk of collapse. Accordingly, the difference in the light reflectance is preferably 1.0% or less, and more preferably 0.7% or less.
<Measurement of light reflectance of preform surface>
The light reflectance of the preform surface is measured as follows.

  The preform surface is often a curved surface. Since the light reflectivity depends on the incident angle of the measurement light on the measurement surface, if the curvature of the measurement surface is different, even if the refractive index of the preform surface is the same, the reflectivity will be different, and the refractive index of the preform surface layer There is a risk that it will not accurately reflect. Therefore, the reflectivity accurately reflects the refractive index of the preform surface layer by narrowing the reflectivity measurement region to such an extent that the measurement surface can be regarded as a flat surface.

  Specifically, although depending on the curvature of the preform surface, it is preferable that the measurement light beam is condensed so that the diameter of the measurement light beam is 1 mm or less, more preferably 0.5 mm or less, more preferably 200 μm. It is more preferable to collect light so as to be below, and it is even more preferable to collect light so that it becomes 100 μm or less. The light beam is narrowed down to 100 μm or less, preferably 80 μm or less, and a measurement light beam is incident perpendicularly to the measurement surface to measure reflected light. In order to perform such measurement, it is preferable to use, for example, a lens reflectometer (model name “USPM-RU”) manufactured by Olympus Optical Co., Ltd.

FIG. 1 is an explanatory view showing the principle of measuring the light reflectance of the preform surface.
The measurement principle of the measuring machine will be described with reference to FIG. In FIG. 1, an optical system from a light source (halogen lamp) to a field stop FS-a2 illuminates FS-a2, and an aperture stop AS1 is disposed in the optical path. The light beam that has passed through the opening of the FS-a2 becomes a parallel light beam by the collimator lens 3, is reflected by the half mirror 4, and is irradiated perpendicularly to the measurement surface of the sample 6 by the 10 × objective lens 5, and has a diameter on the measurement surface. Light is condensed to a size of 50 μm. The focusing on the measurement surface may be performed by observing the light reflected by the half prism 8 using the eyepiece 9 and adjusting the distance between the objective lens 5 and the measurement surface of the sample 6.

  The light reflected by the measurement surface returns to the original optical path, passes through the half mirror 4, the imaging lens 7, and the half prism 8, and is condensed on the field stop FS-b10 having a flare prevention function. The reflected light that has passed through the FS-b 10 passes through the two-dimensional cut filter 11 and is dispersed by the diffraction grating 12 called a flat field grating, is reflected by the mirror 13, and enters the light receiving surface of the line sensor 14.

  Since the spectrally reflected light is incident on different positions on the light receiving surface of the line sensor depending on the wavelength, the spectral spectrum of the reflected light is measured. With this apparatus, a spectrum can be measured over a wavelength range of 380 to 780 nm.

  In addition, a measurement surface having a known reflectance is used as a reference sample surface, and a spectrum of the reference sample surface is measured to obtain a reference spectrum. The reflectance of the preform surface is calculated from the spectral spectrum of the light reflected from the preform surface and the reference spectrum.

Reference numeral 15 denotes a flare diaphragm illumination lamp, and 16 denotes a rotating mirror.
[Preform II for precision press molding]
Preform II for precision press molding which is the second embodiment has different values of surface free energy on two curved surfaces facing opposite sides with respect to the center of the preform as described above, and contains a fluorine component. It is characterized by comprising an oxide glass.

  In the oxide glass containing a fluorine component, the surface free energy increases as the surface of the glass having a higher fluorine concentration, and conversely, the surface free energy decreases as the surface of the glass having a lower fluorine concentration. The surface free energy sensitively reflects the fluorine concentration on the glass surface as well as the reflectance.

  For the same reason as the preform I, this preform II also has one rotational symmetry axis, a first curved surface including one of the two intersections of the symmetry axis and the surface, and the other of the intersections. It is preferable that the preform is a precision press-molding preform having a second curved surface including the intersection of the surface and having different values of the surface free energy on the first curved surface and the surface free energy on the second curved surface. In the preform having such a shape, it is desired to measure the surface free energy of the first curved surface and the second curved surface in the vicinity of the intersection. As described above, since the curvature radius becomes maximum at these portions, the influence of the surface shape of the preform can be reduced when measuring the surface free energy.

In the present invention, from above to achieve the object of the invention, the preferably provided 2.0 mJ / ^{m 2} or more the difference in surface free energy in the two surfaces, it is more preferable to 4.0 mJ / ^{m 2} or more. However, if the difference in surface free energy is increased more than necessary, the performance of the optical element deteriorates, and depending on the production method, striae occurs in the preform, and the precondition of the present invention is that an optically homogeneous preform is obtained. There is a risk of collapse. Therefore, it is preferred that the difference in the surface free energy below 40 mJ / ^{m 2,} and more preferably below 30 mJ / ^{m 2.} This preform can also be produced by the first method described above.
<Measurement of surface free energy of preform surface>
The surface free energy of the preform surface is measured as follows.

In the present invention, two kinds of liquids, pure water and CH ₂ I ₂ (diiodomethane), are used for measuring the surface free energy, each liquid is dropped on the surface of the preform, and the wetting angle is measured. The surface free energy is calculated using the Wendt-Kaelble method. The surface free energy (γ) is given by the sum of the dispersion force γ ^d of solid or liquid and the polar interaction force γ ^{p of} solid or liquid as shown in the equation (1). It is done.

When formula (1) is considered in terms of solid surface free energy (γ _s ), formula (2) is obtained. Here, the subscript s represents Solid. Similarly, when formula (1) is considered for the liquid, it is represented by formula (3), and the subscript L represents Liquid (liquid).

γ = γ ^d + γ ^p (1)
γ _s = γ _s ^d + γ _s ^p (2)
γ _L = γ _L ^d + γ _L ^p (3)
When a liquid on the glass surface is dropped and the contact angle θ of the liquid is measured, a well-known relationship such as equation (4) is established between θ and the surface free energy.

γ _L × (1-cos θ) / 2
= (Γ _s ^d + γ _L ^d ) ^1/2 + (γ _s ^p + γ _L ^p ) ^1/2 (4)
Further, according to known data, in pure water, γ _L ^d = 21.8 mJ / m ² , γ _L ^p = 51 mJ
/ ^{M 2,} because _CH 2 _{I 2} in ^{_{γ L d = 50.8mJ / m 2}} , a gamma _L ^p = 0 mJ / ^{m 2,} when the two kinds of liquid was added dropwise to an equal amount preform surface, respectively When the contact angles are θ _W (pure water) and θC (CH ₂ I ₂ ), the equation (4) becomes the equations (5) and (6) for the two liquids, respectively.

72.8 × (1-cos θ _W ) / 2
= (Γ _s ^d +21.8) ^1/2 + (γ _s ^p +51) ^1/2 (5)
50.8 × (1-cos θ _C ) / 2
= (Γ _s ^d +50.8) ^1/2 + (γ _s ^p +0) ^1/2 (6)
theta _W, by substituting the measured values into theta _C, (5) formula (6) is two-way simultaneous equations to unknowns γ _{s ^d,} γ _s ^p, it is possible to easily calculate the unknowns . By substituting this result into equation (2), the surface free energy γ _s on the preform surface can be calculated.

  In addition, since the light reflectance and surface free energy cannot be measured accurately unless the surface is clean, it is important to keep the preform surface clean by performing washing and drying processes. .

  Preforms I and II for precision press molding both have one rotational symmetry axis, a first curved surface including one of the two intersections of the symmetry axis and the surface, and the other intersection of the intersections. It is preferable that the first curved surface has a radius of curvature different from that of the second curved surface.

  Although the light reflectance and surface free energy of the first curved surface are different from those of the second curved surface, it is difficult to distinguish the first curved surface from the second curved surface only at a glance.

  Therefore, by making a preform so that the curvature radii of the first curved surface and the second curved surface are different, it is possible to easily determine which surface has a high reflectance or which surface has a large surface free energy. be able to.

  Note that the surface free energy measurement site is desirably a site near the center of the first surface and the second surface, that is, a site centered on each intersection of the rotational symmetry axis and the surface.

  Hereinafter, the sign of the radius of curvature of the surface of the glass including the preform is defined as positive in the case of a convex shape on the outside and negative in the case of a concave shape.

  In the case of a preform in which both the first and second curved surfaces have a convex shape outside the preform, the curvature radius of the first curved surface is smaller than the curvature radius of the second curved surface, and the light reflectance of the first curved surface Is larger than the light reflectance of the second curved surface (that is, the surface free energy of the first curved surface is smaller than the surface free energy of the second curved surface). Thus, by associating the characteristics of the two curved surfaces with the curvature radius, it is possible to easily determine a surface with good lubricity when mass-producing optical elements using a large number of preforms. Such a preform can be produced by raising the side wall of the mold recess by the first method so that the radius of curvature of the lower surface of the glass on the recess is smaller than the radius of curvature of the upper surface.

  As another case, the light reflectance of the first curved surface is made smaller than the light reflectance of the second curved surface (that is, the surface free energy of the first curved surface is made larger than the surface free energy of the second curved surface). By doing so, it is possible to easily determine a surface with good lubricity.

  In order to make such a preform, the first method is to reduce the molten glass lump and make the concave portion of the mold close to flat so that the curvature radius of the lower surface of the glass on the concave portion is larger than the curvature radius of the upper surface. You can do it. Such a molten glass lump can reduce the curvature radius of the upper surface by surface tension.

  Up to this point, the first and second curved surfaces have been explained as convex outwardly. However, the present invention can be applied to a preform in which one curved surface is convex and the other is concave, and both curved surfaces are concave. Needless to say.

  In the preform of the present invention, the entire surface is preferably formed by cooling and solidifying molten glass. Since the fluorine component-containing glass has the properties of being low in hardness and easily damaged among oxide glasses, it is preferable to produce the glass through the above-described steps rather than by grinding. Further, the preform produced by the above process is reinforced with air cooling, and is excellent in mechanical impact resistance.

  In the present invention, the two surfaces facing away from each other with respect to the center of the preform have different slidability between the molding surfaces. Using this point, even when the area difference between the pair of molding surfaces is large, good precision press molding can be performed. To enjoy these effects, precision press molding may be performed with the glass exposed without coating the preform, but a coating is applied to more reliably prevent the glass and the molding surface from fusing together. Preformed preform may be used. If the preform surface is coated, the above effect may appear to be less than when the coating is not applied. However, if the glass surface is coated with a slightly different light transmittance or surface free energy, the difference in the substrate will be affected. A surface having a small light transmittance, that is, a surface having a large surface free energy, has a better slidability with the molding surface even when coated. Therefore, even when the preform surface is coated, the effect of the present invention can be obtained. In order to increase the influence of the underlying glass surface and obtain the above effects, it is preferable that the thickness of the coat is 7 nm or less. Moreover, it is preferable that the said film thickness shall be 0.5 nm or more from the viewpoint of improving the mold release property of glass. As the coating applied to the preform surface, a carbon-containing film or the like is preferable.

Examples of film formation methods that easily reflect differences in the state of the glass surface, such as light reflectance and surface free energy, include film formation methods that involve surface reactions such as CVD (chemical vapor reaction) (for example, heating acetylene gas) An example is a method of decomposing and forming a carbon-containing film on a glass surface.
[Oxide glass containing fluorine component constituting preform]
Next, an oxide glass containing a fluorine component constituting the preform of the present invention will be described.

Among the oxide glasses containing this fluorine component, the first preferred glass is fluorophosphate glass, particularly P ⁵⁺ and Al ³⁺ , Mg ²⁺ , Ca ²⁺ , Sr ²⁺ and Ba ²⁺ as essential cation components. A fluorophosphate glass containing two or more selected divalent cation components (R ²⁺ ) and Li ⁺ .

Examples of such glasses are P ⁵⁺ 10-45%, Al ³⁺ 5-30%, Mg ²⁺ 0-20%, Ca ²⁺ 0-25%, Sr ²⁺ 0-30%, Ba, in terms of cation%. ^{2+ 0 to} 33%, Li ⁺ 1 to 30%, Na ⁺ 0 to 10%, K ⁺ 0 to 10%, Y ³⁺ 0 to 5%, B ³⁺ 0 to 15%, F ⁻ and O F to the total amount of ^{2 -} molar ratio of the content of ^F - ^/ (F - ^{+ O 2-)} is preferably 0.25 to ^.85, Mg ^2+, Ca 2+, from ^{Sr 2+} and ^{Ba 2+} This is a fluorophosphate glass containing two or more selected divalent cation components (R ²⁺ ).

This fluorophosphate glass is preferable as an optical glass that realizes optical characteristics having a refractive index (n _d ) of 1.40 to 1.58 and an Abbe number (ν _d ) of 67 to 90.

Of these divalent cationic components ^{(R 2+)} as ^Ca 2+, it is preferred fluorophosphate glass comprising two or more of ^{Sr 2+} and ^{Ba 2+, Mg} 2+ are divalent cationic components ^{(R 2+),} Ca 2+, ^{Sr 2+} Further, fluorophosphate glass having a total content of Ba ²⁺ of 1 cation% or more is more preferable.

The fluorophosphate glass, F ^- and ^{O 2-F} to the total amount of ^- the molar ratio of the content of ^{F - / (F - + O} 2-) is preferably at 0.50 to 0.85, an Abbe number ( The glass a having a νd) of about 75 to 90 and the molar ratio F ⁻ / (F ⁻ + O ²⁻ ) is preferably less than 0.25 to 0.50 and the Abbe number (νd) is about 67 to less than 75. The glass b is roughly divided, and the preferable content range of each cation component is different between the glass a and the glass b.
Hereinafter, the content of each cation component is expressed as cation%.

P ⁵⁺ is an important cation component as a glass network former. If it is less than 10%, the stability of the glass is lowered, and if it exceeds 45%, P ⁵⁺ needs to be introduced as an oxide raw material, so the oxygen ratio increases. Does not meet the target optical characteristics. Therefore, the amount is preferably 10 to 45%. In the case of obtaining glass a, the preferred range of P ⁵⁺ is 10 to 40%, more preferred range is 10 to 35%, still more preferred range is 12 to 35%, still more preferred range is 20 to 35%, and still more preferred range. Is 20-30%. Moreover, the preferable range of P5 ^{+ in} the case of obtaining glass b is 25 to 45%, a more preferable range is 25 to 40%, and a further preferable range is 30 to 40%. When introducing P ^5+, the use of PCl 5 is not appropriate because it erodes platinum and is highly volatile and hinders stable production, and is preferably introduced as a phosphate.

Al ³⁺ is a component that improves the stability of the fluorophosphate glass, and if it is less than 5%, the stability decreases, and if it exceeds 30%, the glass transition temperature (Tg) and the liquidus temperature (LT) increase greatly. Further, since the molding temperature rises and striae due to surface volatilization at the time of molding occurs, a homogeneous glass molded body, particularly a press molding preform cannot be formed. Therefore, the amount is preferably 5 to 30%. When obtaining glass a, the preferable range of Al ³⁺ is 7 to 30%, the more preferable range is 8 to 30%, the still more preferable range is 10 to 30%, and the still more preferable range is 15 to 25%. Moreover, the preferable range of Al3 ^{+ in} the case of obtaining glass b is 5 to 20%, More preferably, it is 5 to 12%.

A divalent cation component ^{(R 2+) Mg 2+, Ca} 2+, Sr 2+, the introduction of ^{Ba 2+} is contributes to the improvement of stability, two or more of these, more preferably ^Ca 2+, ^{Sr 2+} and Ba Two or more of ²⁺ are introduced. In order to further enhance the effect of introducing the divalent cation component (R ²⁺ ), the total content of Mg ²⁺ , Ca ²⁺ , Sr ²⁺ and Ba ²⁺ is preferably 1 cation% or more. Moreover, when it introduces exceeding each upper limit, stability will fall rapidly. Ca ²⁺ and Sr ²⁺ can be introduced in a relatively large amount, but the introduction of a large amount of Mg ²⁺ and Ba ²⁺ particularly decreases the stability. However, since Ba ²⁺ is a component that can achieve a high refractive index while maintaining low dispersion, it is preferably introduced in a range that does not impair the stability. Therefore, the amount of Mg ²⁺ is preferably 0 to 20%. However, when obtaining glass a, the amount of Mg ²⁺ is preferably 1 to 20%, more preferably 3 to 17%, and still more preferably 3 to 3. When obtaining glass b, the amount of Mg ²⁺ is preferably 0 to 15%, more preferably 0 to 12%, still more preferably 15%, even more preferably 5 to 15%, particularly preferably 5 to 10%. Is 1 to 10%.

The amount of Ca ²⁺ is preferably 0 to 25%, but when obtaining glass a, the amount of Ca ²⁺ is preferably 1 to 25%, more preferably 3 to 24%, and still more preferably 3 to 3. 20%, more preferably 5 to 20%, particularly preferably 5 to 16%. When obtaining glass b, the amount of Ca ²⁺ is preferably 0 to 15%, more preferably 1 to 10%. .

Furthermore, although the amount of Sr ²⁺ is preferably 0 to 30%, when obtaining glass a, the amount of Sr ²⁺ is preferably 1 to 30%, more preferably 5 to 25%, and still more preferably 7 to 25%, more preferably 8-23%, still more preferably 9-22%, particularly preferably 10-20%, and when obtaining glass b, the amount of Sr ²⁺ is preferably 0-15%, more Preferably it is 1 to 15%, more preferably 1 to 10%.

The amount of Ba ²⁺ is preferably 0 to 33%, but when obtaining glass a, the amount of Ba ²⁺ is preferably 0 to 30%, more preferably 0 to 25%, and even more preferably 1 to 25%. , More preferably 1 to 20%, still more preferably 3 to 18%, still more preferably 5 to 15%, particularly preferably 8 to 15%. When obtaining glass b, the amount of Ba ²⁺ is preferably Is 0 to 30%, more preferably 10 to 30%, still more preferably 15 to 30%, and still more preferably 15 to 25%.

Li ⁺ is an important component that lowers the glass transition temperature (Tg) without impairing stability, but if it is less than 1%, its effect is not sufficient, and if it exceeds 30%, the durability of the glass is impaired and the workability is also reduced. To do. Therefore, the amount is preferably 1 to 30%, more preferably 2 to 30%, still more preferably 3 to 30%, and still more preferably 4 to 30%. When obtaining glass a, the amount of Li ⁺ is preferably 4 to 25%, more preferably 5 to 25%, still more preferably 5 to 20%, and when obtaining glass b, the amount of Li ⁺ is preferably 5 to 30%, more preferably 10 to 25%.

Na ⁺ and K ⁺ have the effect of lowering the glass transition temperature (Tg), respectively, similarly to Li ⁺ , but at the same time, the thermal expansion coefficient tends to be larger than that of Li ⁺ . Moreover, since NaF and KF have a very high solubility in water compared to LiF, the water resistance is also deteriorated. Therefore, the amounts of Na ⁺ and K ⁺ are preferably 0 to 10%, respectively. In any of the glasses a and b, the preferable range of Na ⁺ and K ⁺ is 0 to 5%, and it is more preferable not to introduce each of them.

Y ³⁺ has the effect of improving the stability and durability of the glass, but if it exceeds 5%, the stability deteriorates conversely and the glass transition temperature (Tg) increases greatly, so the amount is 0-5%. It is preferable to do. When obtaining glass a, the amount of Y ³⁺ is preferably 0 to 3%, more preferably 0.5 to 3%, and when obtaining glass b, the amount of Y ³⁺ is preferably 0 to 4%, more Preferably it is 0 to 3%, More preferably, it is 0.5 to 3%.

Since B ³⁺ is a vitrification component, it has an effect of stabilizing the glass. However, excessive introduction leads to deterioration of durability, and as the B ³⁺ increases, O ^{2− in} the glass also increases, so that the target optical characteristics are obtained. Therefore, the amount is preferably 0 to 15%. However, since it is likely to volatilize during melting as BF3 and cause striae, the amount of glass a or b is preferably 0 to 10%, preferably 0 to 5%. Is more preferable. When priority is given to reducing the volatility of glass, the content is preferably 0 to 0.5%, and more preferably not introduced.

From the viewpoint of stably producing a high-quality optical glass, in any of the glasses a and b, P ⁵⁺ , Al ³⁺ , Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ²⁺ , Li ⁺ and Y ³⁺ The total amount of cation is preferably more than 95% in terms of cation%, more preferably more than 98%, still more preferably more than 99%, and still more preferably 100%.

  Both the glasses a and b can contain lanthanoids such as Ti, Zr, Zn, La, and Gd as cation components in addition to the cation component described above.

In addition, Si ⁴⁺ can be introduced for the purpose of stabilizing the glass. However, since the melting temperature is low, if it is introduced excessively, it will cause melting residue or increase volatilization during melting and impair the production stability. . Therefore, in any of the glasses a and b, the amount of Si ⁴⁺ is preferably 0 to 10%, more preferably 0 to 8%, and further preferably 0 to 5%.

The proportion of the anionic components, while realizing the desired optical properties, in order to obtain an optical glass having excellent stability, F ^- and O ^2-F to the total amount of ^- the molar ratio of the content of F ^- / (F ⁻ + O ²⁻ ) is preferably 0.25 to 0.85, but is preferably 0.50 to 0.85 in glass a, and 0.25 to 0.50 in glass b. Is preferably 0.27 to 0.45, more preferably 0.3 to 0.45. Moreover, in any of glass a and b, it is preferable that the total amount of F ⁻ and O ²⁻ in the anion is 100%.

Both the glasses a and b have a refractive index (n _d ) of about 1.40 to 1.58, and an Abbe number (ν _d ) of about 67 to 90, preferably 70 to 90. Further, in glass a, the Abbe number (ν _d ) is about 75 to 90, preferably 78 to 89, and in glass b, the Abbe number (ν _d ) is about 67 to less than 75.

  Glasses a and b exhibit high transmittance in the visible light region except when a colorant is added. Specifically, the transmittance (excluding reflection loss on the sample surface) at a wavelength of 400 nm to 2000 nm when light is incident on a sample having a thickness of 10 mm that is flat on both sides and parallel to each other from a direction perpendicular to the both sides. The light transmittance characteristics are usually 80% or more, preferably 95% or more.

Since the glasses a and b contain a predetermined amount of Li ⁺ , their glass transition temperature (Tg) is usually 470 ° C. or lower, preferably 430 ° C. or lower.

Further, the glasses a and b positively contain Li ⁺ among the alkali metal ions, so that the coefficient of thermal expansion is relatively small and the water resistance is relatively excellent. Therefore, a high-quality preform with a smooth surface can be obtained by polishing the glass and processing it into a preform.

  Furthermore, since the glasses a and b exhibit excellent water resistance and chemical durability, the preform surface does not deteriorate even if it is stored for a long period from the preparation of the preform to the press molding. In addition, since the surface of the optical element is hardly changed, the optical element can be used in a good state where the surface is not clouded for a long time.

  Moreover, according to the glass a and b, since glass melting temperature can be reduced about 50 degreeC compared with the glass which has an equivalent optical characteristic and does not contain Li, the glass by the platinum melt | dissolution from the container at the time of melting Problems such as coloring, foam mixing, and striae can be reduced or eliminated.

  Fluorophosphate glass generally has a high viscosity at the time of outflow, and when a molten glass lump of a desired mass is separated from the outflowing molten glass and molded, the glass draws a thin thread at the separated portion, and the filamentous portion is formed. Problems such as formation of protrusions remaining on the glass lump surface occur. When trying to solve such problems by lowering the efflux viscosity, the effluent temperature of the glass must be raised, and as mentioned above, the volatilization of fluorine from the glass surface is promoted and the striae becomes significant. .

  In order to eliminate such problems, the glasses a and b reduce the temperature suitable for forming molten glass. Therefore, the glass composition is set so that the temperature showing a predetermined viscosity is lower than that of the conventional fluorophosphate glass. Has been decided. Although the glass transition temperature is much lower than the molding temperature of molten glass, glass with a low glass transition temperature can also lower the above molding temperature, thus reducing and eliminating problems such as stringing and striae during molding. For this, it is effective to adjust the glass composition so that the glass transition temperature is in the above range.

  In addition, by lowering the glass transition temperature, it is possible to lower the glass heating temperature in precision press molding of the preform, and the reaction between the glass and the press molding die is alleviated and the life of the press molding die is extended. It is also possible to obtain an effect such as

  Glasses a and b use phosphate raw materials, fluoride raw materials, etc., weigh and prepare these raw materials, supply them to the melting vessel, heat and melt them as described above, clarify, homogenize, flow out of the pipe It can be obtained by molding.

The 2nd preferable example in the oxide glass containing a fluorine component is a fluorophosphate glass containing Cu ²⁺ . This glass functions as a near infrared absorbing glass. This glass is particularly suitable as a color correction filter for a semiconductor image sensor such as a CCD or CMOS, and when used for the above-mentioned purposes, the content of Cu ²⁺ is preferably 0.5 to 13 cation%.

A particularly preferred composition of this glass is expressed in terms of cation%, P ⁵⁺ 11 to 45%, Al ^{3+ 0 to} 29%, Li ⁺ , Na ⁺ and K ⁺ in total 0 to 43%, Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ²⁺ and Zn ²⁺ are included in a total of 14 to 50%, Cu ²⁺ is included in a range of 0.5 to 13%, and F ⁻ 17 to 80% is included in terms of anionic%.

In the above composition, the remaining amount of the anionic component is preferably O ²⁻ . Hereinafter, the cation component content and the total content are expressed as cation%.

In the above composition, P ⁵⁺ is a basic component of fluorophosphate glass and an important component that brings about absorption of Cu ^{2+ in} the infrared region. If the content of P ⁵⁺ is less than 11%, the color deteriorates to be greenish. Conversely, if it exceeds 45%, the weather resistance and devitrification resistance deteriorate. Therefore, the content of P ⁵⁺ is preferably 11 to 45%, more preferably 20 to 45%, and still more preferably 23 to 40%.

Al ³⁺ is a component that improves the devitrification resistance, heat resistance, thermal shock resistance, mechanical strength, and chemical durability of fluorophosphate glass. However, if it exceeds 29%, the near infrared absorption characteristics deteriorate. Therefore, the content of Al ³⁺ is preferably 0 to 29%, more preferably 1 to 29%, further preferably 1 to 25%, and even more preferably 2 to 23%. preferable.

Li ⁺ , Na ⁺ and K ⁺ are components that improve the meltability and devitrification resistance of the glass and improve the transmittance in the visible light region, but if the total amount exceeds 43%, the durability of the glass, Workability deteriorates. Therefore, the total content of Li ⁺ , Na ⁺ and K ⁺ is preferably 0 to 43%, more preferably 0 to 40%, and still more preferably 0 to 36%.

Among the alkali components, Li ⁺ is excellent in the above action, and the amount of Li ⁺ is preferably 15 to 30%, more preferably 20 to 30%.

Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ^2+, and Zn ²⁺ are useful components that improve the devitrification resistance, durability, and workability of the glass. However, since the devitrification resistance decreases due to excessive introduction, Mg The total amount of ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ²⁺ and Zn ²⁺ is preferably 14 to 50%, more preferably 20 to 40%.

A preferable range of the Mg ²⁺ content is 0.1 to 10%, and a more preferable range is 1 to 8%.

A preferable range of the Ca ²⁺ content is 0.1 to 20%, and a more preferable range is 3 to 15.

A preferable range of the Sr ²⁺ content is 0.1 to 20%, and a more preferable range is 1 to 15%.

A preferable range of the Ba ²⁺ content is 0.1 to 20%, a more preferable range is 1 to 15%, and a further preferable range is 1 to 10.

Cu ²⁺ is a bearer of near-infrared light absorption characteristics. If the amount is less than 0.5%, the near-infrared absorption is small. Therefore, the content of Cu ²⁺ is preferably 0.5 to 13%, more preferably 0.5 to 10%, still more preferably 0.5 to 5%, and even more preferably 1 to 5%.

F ⁻ is an important anion component that lowers the melting point of the glass and improves the weather resistance. By containing F ⁻ , the melting temperature of the glass can be lowered, the reduction of Cu ²⁺ can be suppressed, and the required optical characteristics can be obtained. If it is less than 17%, the weather resistance deteriorates. On the other hand, if it exceeds 80%, the content of O ²⁻ decreases, so that coloring near 400 nm with monovalent Cu ⁺ occurs. Therefore, the content of F ⁻ is preferably 17 to 80%. In order to further improve the above characteristics, the amount of F ⁻ is more preferably 25 to 55%, and further preferably 30 to 50%.

O ²⁻ is an important anion component, and it is preferable that the entire remaining amount excluding F ^{− of the} total anion component is composed of the O ²⁻ component. Therefore, the preferable amount of O ²⁻ is a range obtained by subtracting the preferable amount of F ⁻ from 100%. If the amount of O ²⁻ is too small, divalent Cu ²⁺ is reduced to monovalent Cu ⁺ , so that the absorption in the short wavelength region, particularly near 400 nm, becomes large, and the color becomes green. On the other hand, if the amount is excessive, the viscosity of the glass is high and the melting temperature is high, so that the transmittance is deteriorated.

Note that Pb and As are not harmful because they are highly harmful.
The preferable transmittance | permeability characteristic of the said Cu containing glass is as follows.

  The spectral transmittance at a wavelength of 500 to 700 nm is converted into a thickness at which the wavelength showing a transmittance of 50% is 615 nm, and the spectral transmittance at a wavelength of 400 to 1200 nm exhibits the following characteristics.

78% or more is preferable at a wavelength of 400 nm, more preferably 80% or more, still more preferably 83% or more, still more preferably 85% or more,
85% or more is preferable at a wavelength of 500 nm, more preferably 88% or more, still more preferably 89% or more,
51% or more is preferable at a wavelength of 600 nm, more preferably 55% or more, still more preferably 56% or more,
12% or less is preferable at a wavelength of 700 nm, more preferably 11% or less, still more preferably 10% or less,
5% or less is preferable at a wavelength of 800 nm, more preferably 3% or less, still more preferably 2.5% or less, still more preferably 2.2% or less, still more preferably 2% or less,
5% or less is preferable at a wavelength of 900 nm, more preferably 3% or less, still more preferably 2.5% or less, still more preferably 2.2% or less, still more preferably 2% or less,
7% or less is preferable at a wavelength of 1000 nm, more preferably 6% or less, still more preferably 5.5% or less, still more preferably 5% or less, still more preferably 4.8% or less,
12% or less is preferable at a wavelength of 1100 nm, more preferably 11% or less, still more preferably 10.5% or less, still more preferably 10% or less,
It is preferably 23% or less at a wavelength of 1200 nm, more preferably 22% or less, still more preferably 21% or less, and even more preferably 20% or less.

  That is, absorption of near-infrared light having a wavelength of 700 to 1200 nm is large, and absorption of visible light having a wavelength of 400 to 600 nm is small. Here, the transmittance is assumed to be a glass sample having two planes that are parallel to each other and optically polished, and when light is incident on one of the planes perpendicularly, the intensity of the light emitted from the other of the planes is expressed as follows. It is a value divided by the intensity of the incident light before entering the sample, and is also called external transmittance.

  With such characteristics, color correction of a semiconductor image sensor such as a CCD or CMOS can be performed satisfactorily.

In addition, the present invention can be applied to fluoroborosilicate glass, fluorosilicate glass, and fluoroborosilicate glass.
[Method for Manufacturing Optical Element]
Next, the manufacturing method of the optical element of this invention is demonstrated.

  The optical element manufacturing method of the present invention is characterized in that in the optical element manufacturing method for producing an optical element by precision press molding a glass preform, any one of the above precision press molding preforms is used. To do.

  The precision press molding is also called mold optics molding, and is a well-known method in the technical field. In an optical element, a surface that transmits, refracts, diffracts, or reflects light is an optical functional surface (a lens surface such as an aspherical surface of an aspherical lens or a spherical surface of a spherical lens is taken as an example of a lens). It corresponds to the optical function surface), but according to precision press molding, the optical function surface can be formed by press molding by precisely transferring the molding surface of the press mold to glass, and the optical function surface is finished. Therefore, it is not necessary to add machining such as grinding and polishing.

  Therefore, the optical element manufacturing method of the present invention is suitable for manufacturing optical elements such as lenses, lens arrays, diffraction gratings, and prisms, and is particularly suitable as a method for manufacturing aspherical lenses with high productivity. Yes.

  The preform used in the present invention has different values of light reflectance or surface free energy on two surfaces facing away from each other with respect to the center of the preform. A surface having a higher light reflectivity than the other surface, that is, a surface having a smaller surface free energy than the other surface, has a lower fluorine concentration in the layer near the surface than the other surface and the inside of the preform. . For this reason, the surface with a lower fluorine concentration is more excellent in lubricity with the molding surface than the other surface. If the surface of the preform with a low fluorine concentration is called a low-fluorine concentration surface, a pair of opposed molds used for precision press molding, for example, the upper mold and the lower mold, the larger the mold molding area, the lower the fluorine content. It is desirable to introduce the preform into the mold so that the concentration surface faces. The preform is pressed by a pair of opposed molds, but the glass needs to be stretched along the molding surface more greatly on the molding surface having a larger area than one. Therefore, the glass can be greatly stretched easily by disposing the fluorine low-concentration surface so as to face the molding surface having a large area.

  The method for producing an optical element of the present invention is particularly suitable for producing a lens having a lens surface area ratio of 1 to 2 times, and more suitable for producing a lens having a ratio of 1.2 to 1.8 times. According to the method for producing an optical element of the present invention, it is possible to produce a fluorine component-containing oxide glass optical element having good surface accuracy while keeping the press molding temperature low.

  As a press mold used for precision press molding, known molds such as silicon carbide, zirconia, alumina and other heat-resistant ceramic molds provided with a release film can be used. A silicon press mold is preferred.

  In precision press molding, it is desirable that the molding atmosphere be a non-oxidizing gas in order to keep the molding surface of the press mold in a good state. The non-oxidizing gas is preferably nitrogen or a mixed gas of nitrogen and hydrogen.

Next, as the modes of precision press molding used in the method for producing an optical element of the present invention, the following two modes of precision press molding 1 and 2 can be shown.
<Precision press molding 1>
The precision press molding 1 is one in which the preform is introduced into a press mold, the press mold and the preform are heated together, and precision press molding is performed.

In this precision press molding 1, the temperature of the press mold and the preform may be heated to a temperature at which the glass constituting the preform exhibits a viscosity of 10 ⁶ to 10 ¹² dPa · s. preferable.

The glass is preferably cooled to a temperature showing a viscosity of 10 ¹² dPa · s or more, more preferably 10 ¹⁴ dPa · s or more, and even more preferably 10 ¹⁶ dPa · s or more. It is desirable to remove from the mold.

Under the above conditions, the shape of the molding surface of the press mold can be accurately transferred with glass, and the precision press molded product can be taken out without being deformed.
<Precision press molding 2>
In the precision press molding method 2, a heated preform is introduced into a preheated press mold and precision press molding is performed.

  According to this precision press molding 2, since the preform is preheated before being introduced into the press mold, it is possible to manufacture an optical element having a good surface accuracy without surface defects while shortening the cycle time. it can.

  The preheating temperature of the press mold is preferably set lower than the preheating temperature of the preform. Thus, by lowering the preheating temperature of the press mold, it is possible to reduce the wear of the press mold.

In the precision press molding 2, it is preferable that the glass constituting the preform is preheated to a temperature exhibiting a viscosity of 10 ⁹ dPa · s or less, more preferably 10 ⁹ dPa · s.

The preform is preferably preheated while floating, more preferably preheated to a temperature at which the glass constituting the preform exhibits a viscosity of 10 ^5.5 to 10 ⁹ dPa · s ^. It is more preferable to preheat to a temperature showing a viscosity of ⁵ dPa · s or more and less than 10 ⁹ dPa · s.

Moreover, it is preferable to start cooling the glass simultaneously with the start of pressing or in the middle of pressing.
The temperature of the press mold is adjusted to a temperature lower than the preheating temperature of the preform, and the temperature at which the glass exhibits a viscosity of 10 ⁹ to 10 ¹² dPa · s may be used as a guide.

In this method, it is preferable that after the press molding, the glass is cooled to a viscosity of 10 ¹² dPa · s or more and then released.

  The precision press-molded optical element is taken out from the press mold and gradually cooled as necessary. When the molded product is an optical element such as a lens, an optical thin film may be coated on the surface as necessary.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
Example 1

ガラスの原料として、各ガラス成分に相当するリン酸塩、フッ化物などを使用し、表１に示すＮｏ．１、２の組成を有するガラスとなるように前記原料を秤量し、十分混合し調合原料とした。

As raw materials for glass, phosphates and fluorides corresponding to the respective glass components were used. The raw materials were weighed so as to be glass having compositions 1 and 2, and mixed well to prepare a blended raw material.

  The prepared raw material was melted at 850 ° C. for 1 hour using a platinum crucible, then rapidly cooled and pulverized, and used as a rough melt cullet. 10 kg of this rough melt cullet was put into a platinum crucible sealed with a lid, heated to 900 ° C. and melted. Next, a sufficient amount of dry gas was introduced into the platinum crucible and the molten glass was clarified at 1100 ° C. for 2 hours while maintaining a dry atmosphere. Examples of the dry gas include an inert gas such as nitrogen, a mixed gas of an inert gas and oxygen, oxygen, and the like.

  After clarification, the temperature of the glass was lowered to 850 ° C., which is lower than the temperature at the time of clarification, and then the glass was caused to flow out from the pipe connected to the bottom of the crucible. The gas introduced into the crucible was cleaned through a filter and discharged outside. In each of the above steps, the glass in the crucible was stirred to obtain a homogeneous glass.

  The obtained molten glass was cast into a carbon mold in a dry nitrogen atmosphere. The cast glass was allowed to cool to the transition temperature and immediately placed in an annealing furnace, annealed for 1 hour near the transition temperature, and gradually cooled to room temperature in the annealing furnace. 1 and 2 optical glasses were obtained.

  Each optical glass No. When 1 and 2 were magnified and observed with a microscope, no crystal precipitation or unmelted raw material was observed.

The obtained optical glass No. For 1 and 2, the refractive index (n _d ), Abbe number (ν _d ), and glass transition temperature (Tg) were measured as follows. The measurement results are shown in Table 1.
(1) Refractive index (n _d ) and Abbe number (ν _d )
The refractive index (n _d ) and Abbe number (ν _d ) were measured for the optical glass obtained at a slow cooling rate of −30 ° C./hour.

In addition, regarding refractive index _nd , optical glass No. measured on the said conditions. The refractive index values of 1 and 2 are n _d ⁽¹⁾ . The refractive indexes n _d ⁽²⁾ after remelting and cooling the glasses 1 and 2 were measured as follows.

No. above. 30 g of each of the glasses 1 and 2 is put into a glassy carbon crucible in a quartz glass chamber with a capacity of 2 liters / minute of dry nitrogen gas, and the whole chamber is heated to 900 ° C. at that temperature. Remelted for 1 hour. Then, it cooled to glass transition temperature vicinity in a chamber, and cooled to room temperature 25 degreeC with the temperature-fall rate of 30 degreeC / hour after that. And glass No. obtained in this way. Each refractive index n _d ^{(2) of 1} and ² was measured.

Optical glass No. Tables 1 to 3 show the absolute values of n _d ⁽²⁾ -n _d ⁽¹⁾ and n _d ⁽²⁾ -n _d ⁽¹⁾ for ^{1 and 2} .
(2) Glass transition temperature (Tg)
The glass transition temperature (Tg) was measured using a thermomechanical analyzer manufactured by Rigaku Corporation with a heating rate of 4 ° C./min.

  As shown in Table 1, optical glass no. Both 1 and 2 had a desired refractive index, Abbe number, and glass transition temperature, exhibited excellent low-temperature softening properties and meltability, and were suitable as optical glasses.

In addition, the absolute values of n _d ⁽²⁾ -n _d ⁽¹⁾ and n _d ⁽²⁾ -n _d ⁽¹⁾ were both smaller than 0.00300.

  Next, optical glass no. Each molten glass consisting of one or two glasses is allowed to flow out at a constant flow rate from a platinum alloy pipe whose temperature has been adjusted to a temperature range where stable outflow is possible without devitrification of the glass, and a support is used. After supporting the lower end of the molten glass flow, the support was rapidly lowered to separate a molten glass lump corresponding to the amount of one preform. Next, each molten glass lump obtained is received in a receiving mold having a recess made of a porous material, and dry nitrogen gas is supplied to the back surface of the porous material, and dry nitrogen is supplied from the entire surface of the recess through the porous material. A gas was blown to form a precision press-molding preform while the glass lump floated, and the glass was taken out from the receiving mold and gradually cooled.

  A preform was formed from the molten glass lump and molded without inverting the upper and lower surfaces of the glass lump until the preform was taken out from the receiving mold.

  In this way, a preform having one rotational symmetry axis and having a shape symmetric with respect to an arbitrary rotation angle around this symmetry axis was obtained. The preform surface has a convex shape on the outside. The symmetry axis intersects the preform surface at two points, and the surface including one of the intersections is referred to as a first surface, and the surface including the other intersection is referred to as a second surface. The first surface corresponds to the upper surface on the receiving mold, and the second surface corresponds to the lower surface on the receiving mold. The radius of curvature of the first surface is larger than the radius of curvature of the second surface, that is, the first surface is flatter than the second surface.

  When the preform was observed visually and with an optical microscope, striae and devitrification were not observed. The preform surface was smooth and no scratches were seen. After the preform was washed and dried, the following measurements were performed.

  The light reflectance of the first surface and the second surface of the preform is measured using the lens reflection measuring machine (model name “USPM-RU”) manufactured by Orion Pass Optics Co., Ltd. The reflectance at the center, that is, near the two intersections was measured. The objective lens used was 10 times, the diameter of the measurement light on the preform surface was 50 μm, the spectral spectrum of the reflected light was measured over a wavelength range of 380 to 780 nm, the wavelength from the spectral spectrum of the reflected light on the reference sample surface was 500 nm, The reflectance of the preform surface at each wavelength of 600 nm and 700 nm was calculated. The results are shown in Table 1.

Next, pure water and CH ₂ I ₂ (diiodomethane) are used, and each liquid is added in equal amounts to the center of each of the first and second surfaces of the preform, that is, in the vicinity of the two intersections, and contacted. The angle was measured, and the surface free energy of the first surface and the second surface was measured by the method described above.

In this way, it was possible to obtain a precision press-molding preform in which the light reflectance of the first surface and the second surface are different and the surface free energy of the two surfaces is also different.
Example 2
No. 1 prepared in Example 1. Precision press molding was performed using a preform made of one or two glasses. The precision press mold is a mold for molding an aspherical convex meniscus lens, and includes an upper mold, a lower mold, and a body mold. Each mold material is made of SiC, and the mold molding surface is coated with a carbon film. The upper mold surface has a convex shape and the lower mold surface has a concave shape. The area of the upper mold surface is larger than the area of the lower mold surface. The deformation amount on the lower mold surface is larger than the deformation amount on the press side.

First, the preform is placed in the center of the lower mold surface so that the second surface is below, the preform and the precision press mold are heated together, and the viscosity of the glass is 10 ⁸ to 10 ¹⁰ dPa · s. The temperature of the preform and mold was maintained at the indicated temperature and pressed at a pressure of 8 MPa for 30 seconds. After pressing, the pressure of the press is released, and the glass molded product that has been press-molded is gradually cooled to a temperature at which the viscosity of the glass reaches 10 ¹² dPa · s or more with the lower mold and the upper mold in contact with each other. Then, it was rapidly cooled to room temperature, and the glass molded product was taken out of the mold and an aspherical convex meniscus lens was obtained. Each of the obtained aspherical lenses has a glass No. It consisted of 1 and 2 and had extremely high surface accuracy, and no fog or cloudiness was observed on the lens surface. The series of steps was performed in a nitrogen atmosphere. In addition, the optical performance of the obtained lens was a desired performance.

In addition, although the said example is preparation of the lens by the precision press molding 1, the precision press molding 2 can also be applied. In this method, first, the preform is preheated to a temperature at which the viscosity of the glass constituting the preform becomes 10 ⁸ dPa · s while the preform floats. On the other hand, the precision press mold is heated to a temperature at which the glass constituting the preform has a viscosity of 10 ⁹ to 10 ¹² dPa · s, and the preheated preform is introduced into the cavity of the dense press mold. Then, precision press molding was performed at 10 MPa. Cooling of the glass and the press mold was started at the start of pressing, and the glass was cooled until the viscosity of the molded glass reached 10 ¹² dPa · s or more, and then the molded product was released to obtain an aspheric lens. The obtained aspherical convex meniscus lens has extremely high surface accuracy, and no cloud or cloudiness was observed on the surface.
Example 3
Next, an aspheric concave meniscus lens was molded using the preform obtained in Example 1. The configuration of the precision press mold used was almost the same as that of Example 2, but the shapes of the upper mold surface and the lower mold surface were different. In this mold, the area of the upper mold surface is larger than the area of the lower mold surface.

Next, the preform is placed in the center of the lower mold surface so that the second surface of the preform faces downward, and the preform and the precision press mold are heated together, and the viscosity of the glass is 10 ⁸ to 10 ^10. The temperature of the preform and the mold was maintained at a temperature indicating dPa · s, and pressed at a pressure of 8 MPa for 30 seconds. After pressing, the pressure of the press is released, and the glass molded product that has been press-molded is gradually cooled to a temperature at which the viscosity of the glass reaches 10 ¹² dPa · s or more with the lower mold and the upper mold in contact with each other. Then, it was rapidly cooled to room temperature, and the glass molded product was taken out of the mold and an aspherical concave meniscus lens was obtained. Each of the obtained aspherical lenses has a glass No. It consisted of 1 and 2 and had extremely high surface accuracy, and no fog or cloudiness was observed on the lens surface. The series of steps was performed in a nitrogen atmosphere. In addition, the optical performance of the obtained lens was a desired performance.

In addition, although the said example is preparation of the lens by the precision press molding 1, the precision press molding 2 can also be applied. In this method, first, the preform is preheated to a temperature at which the viscosity of the glass constituting the preform becomes 10 ⁸ dPa · s while the preform floats. On the other hand, the precision press mold is heated to a temperature at which the glass constituting the preform has a viscosity of 10 ⁹ to 10 ¹² dPa · s, and the preheated preform is introduced into the cavity of the dense press mold. Then, precision press molding was performed at 10 MPa. Cooling of the glass and the press mold was started at the start of pressing, and the glass was cooled until the viscosity of the molded glass reached 10 ¹² dPa · s or more, and then the molded product was released to obtain an aspheric lens. The obtained aspherical concave meniscus lens has extremely high surface accuracy, and no cloud or cloudiness was observed on the surface.

  In each of the above examples, when the preform glass surface is exposed, that is, when precision press molding is performed without coating the preform surface, the preform surface is coated with a carbon-containing film by a CVD method by thermal decomposition of acetylene. In the case of precision press molding, good results can be obtained.

  The precision press-molding preform of the present invention is made of an oxide glass containing a fluorine component, and is suitably used for producing an optical element such as a good lens by precision press molding.

It is explanatory drawing which shows the measurement principle of the light reflectivity of the preform surface.

Explanation of symbols

1 Brightness stop AS
2 Field stop FS-a
3 Collimator lens 4 Half mirror 5 Objective lens 6 Sample 7 Imaging lens 8 Half prism 9 Eyepiece 10 Field stop FS-b
11 Two-dimensional cut filter 12 Diffraction grating 13 Mirror 14 Line sensor 15 Flare stop lamp 16 Rotating mirror

Claims (8)

  A precision press-molding preform characterized in that it has different values of light reflectance on two surfaces facing away from each other with respect to the center of the preform and is made of an oxide glass containing a fluorine component.   A first curved surface having one rotational symmetry axis, a first curved surface including one of the two intersections of the symmetry axis and the surface, and a second curved surface including the other intersection of the intersections. The precision press-molding preform according to claim 1, wherein the light beam reflectance in the second curved surface and the light reflectance on the second curved surface are different from each other.   A precision press-molding preform characterized in that the surface free energy on two surfaces facing opposite sides with respect to the center of the preform has different values and is made of an oxide glass containing a fluorine component.   A first curved surface having one rotational symmetry axis, a first curved surface including one of the two intersections of the symmetry axis and the surface, and a second curved surface including the other intersection of the intersections. The precision press-molding preform according to claim 3, wherein the surface free energy at and the surface free energy at the second curved surface are different from each other.   The precision press-molding preform according to claim 2 or 4, wherein the curvature radius of the first curved surface and the curvature radius of the second curved surface are different.   The preform for precision press molding according to any one of claims 1 to 5, wherein the entire surface is formed by cooling and solidifying molten glass. In the manufacturing method of a precision press-molding preform for producing a glass preform for use in precision press molding,
The molten glass lump including the lower end of the molten glass flow flowing out of the pipe is separated, and the molten glass lump is floated on the concave portion of the mold by jetting gas from the gas outlet provided in the concave portion and applying wind pressure. Molding into a preform without turning upside down,
And the glass is an oxide glass containing a fluorine component,
A method for producing a precision press-molding preform. In the optical element manufacturing method for producing an optical element by precision press molding a glass preform,
A precision press-molding preform according to any one of claims 1 to 6, or a precision press-molding preform produced by the method according to claim 7, wherein an optical element is produced. Method.

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