KR101452479B1 - Preform for Precision Press Molding and Process for Producing Optical Element - Google Patents

Abstract

The present invention provides an oxide glass preform containing a fluorine component 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.

The present invention relates to a precision press molding preform made of an oxide glass having a different light reflectance on two surfaces opposite to each other with respect to the center of the preform and containing a fluorine component, A precursor for precision press molding made of an oxide glass containing fluorine components and having different surface free energies on two surfaces facing each other, and an optical element manufacturing an optical element by precision press molding a glass preform The present invention also provides a method for producing an optical element using the preform for precision press molding.

Preform, oxide glass, optical element, precision press molding, light reflectance

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a preform for precision press molding,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a preform for precision press molding and a method of manufacturing an optical element, and more particularly to a glass preform used for manufacturing an optical element such as a lens by a precision press molding method and a manufacturing method of the optical element using the preform .

A precision press forming method is known as a method for efficiently producing a glass aspherical lens. In the precision press-molding method, as described in Patent Document 1, preformed optical glass preforms in a shape suitable for press molding are used.

Optical glasses having various optical properties have been used depending on the purpose of use. Among them, one having a high utility value has a low dispersion property such as glass fluorophosphate.

[Patent Document 1] JP-A-8-277132

However, the precision press molding of this fluorophosphoric acid glass has the following problems. The press forming temperature of the fluorophosphoric acid glass is low as compared with other composition system glasses, for example, B ₂ O ₃ -La ₂ O ₃ based glass. However, because of the presence of fluorine, the reaction between the press-molding die and the glass tends to occur, and the reaction tends to cause problems such as cloudiness and fog on the glass surface. Therefore, in order to reduce such a risk, press molding at a lower temperature has been required.

However, when the press molding temperature is lowered, the viscosity of the glass is increased, which causes a problem that the glass is hardly elongated at the time of pressing. Most of the lenses produced by precision press molding are formed by using molds having different areas of a pair of opposed molding surfaces for pressing a preform such as a top mold and a bottom mold. For example, when the effective diameter of the convex lens surface of the meniscus lens is equal to that of the concave lens surface, the area of the mold surface that presses the lens surface having the small absolute value of the radius of curvature is smaller than the area of the mold surface Area. The difference in area between the pair of mold forming surfaces is large in the case of both convex lenses and double concave lenses as well as meniscus lenses.

In the precision press molding of such a lens, it is necessary to further elongate the glass along the mold surface having a larger area. That is, in order to stretch the preforms disposed at the center of the forming mold before pressing along the mold shaping surface by pressing, and to transfer the entire mold shaping surface onto the glass, one of the pair of opposing molds It was necessary to extend the glass significantly along the molding surface.

However, in the state where the viscosity is high, there arises a problem that radial scratches are formed on the obtained lens surface, for example, the elongation of the glass becomes insufficient or the friction at the interface between the glass and the molding surface becomes large. In order to solve such a problem, the above-described problems have occurred when the press forming temperature is raised.

As described above, in the precision press molding of the fluorine-containing glass, there has been a problem that if the molding conditions of one lens surface are made appropriate, the molding of the other lens surface is hindered.

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

The inventors of the present invention have conducted intensive studies in order to achieve the above object, and as a result, obtained the following discoveries.

As described above, on the side where the area formed by transferring the molding surface into the two lens surfaces is large, it is necessary to largely extend the glass along the molding surface in the precision press molding. Therefore, it has been noted that the above problem can be solved by making it easier for the glass on the larger mold surface area to extend along the mold surface. Therefore, the present inventors have considered a means for increasing the lubricity of one surface of the preform and the mold-forming surface to be greater than the lubricity of the other surface and the mold-shaping surface.

As a result, the present inventors have found that, in the fluorine component-containing oxide glass, the lubricity between the glass and the mold surface is changed by the fluorine concentration of the surface layer at the most, and the surface having good lubricity with the mold surface is a Shaped mold surface side to be precisely press-molded.

In order to make such a preform, it is important to keep the fluorine concentration locally large or small in the surface, although the fluorine concentration can be increased or decreased in a part of the surface of the preform. Local changes in fluorine concentration become a factor to deteriorate the optical performance.

Further, in order to change the fluorine concentration in the vicinity of the surface without generating fogging, since the oxide glass containing the fluorine component in the molten state exhibits very high volatility, the volatility of the glass is lowered to a controllable level The fluorine near the surface can be reduced by volatilization so as to prevent the formation of droplets.

The present invention has been completed on the basis of this finding.

That is,

(1) A preform for precision press molding, characterized by comprising an oxide glass having a different light reflectance on two surfaces facing opposite to each other with respect to the center of the preform and containing a fluorine component,

(2) a first curved surface including one rotational symmetry axis and one of two intersecting points of the symmetry axis and the surface, and a second curved surface including the other intersecting point, The preform for precision press molding described in (1) above, wherein the reflectance and the light reflectance on the second curved surface are different from each other,

(3) A preform for precision press molding, characterized in that the surface free energy of two surfaces facing opposite to each other with respect to the center of the preform is different and is composed of an oxide glass containing a fluorine component,

(4) An optical scanning device having a first curved surface including one rotational symmetry axis and one of two intersection points of the symmetry axis and the surface, and a second curved surface including the other intersection point of the intersection, The preform for precision press molding according to the above (3), wherein the free energy 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), wherein the curvature radius of the first curved surface is different from the curvature radius of the second curved surface,

(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 the molten glass,

(7) A method for producing a preform for glass for manufacturing a precision press molding, which is used for precision press molding,

Separating the molten glass mass including the lower end of the molten glass flowed out from the pipe and injecting gas from a gas ejection port provided in the recessed portion on the concave portion of the mold to flip up and down while applying wind pressure, , And the glass is an oxide glass containing a fluorine component

And a method for producing a preform for precision press molding,

(8) A method of manufacturing an optical element for producing an optical element by precision press-molding a glass preform,

The production of an optical element characterized by using the precision press molding preform according to any one of (1) to (6) above, or the precision press molding preform manufactured by the method described in (7) Way

.

According to the present invention, it is possible to provide a fluorine-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 by using the preform.

There are two aspects of the preform for precision press forming of the present invention. The first aspect is characterized in that the preform for precision press molding (hereinafter referred to as " precise press forming preform ") is characterized in that the preform for optical element has a different value of light reflectance on two surfaces facing to the opposite sides with respect to the center of the preform and is made of an oxide glass containing a fluorine component Press forming preform I), and the second aspect is characterized in that the surface free energy of two surfaces opposite to each other with respect to the center of the preform is different and is composed of an oxide glass containing a fluorine component (Hereinafter referred to as " preform II for precision press molding ").

Two faces opposite to each other with respect to the center of the preform are pressed to be pressed by the press forming die in the precision press forming mode. However, in the preform made of oxide glass containing a fluorine component, In the press surface, the surface reflectance is small and the surface free energy is large on the fluorine-rich pressed surface side. Further, the fluorine-rich pressed surface tends to be elongated along the mold surface. Therefore, by changing the values of the light reflectance and the surface free energy of the two surfaces facing opposite to each other with respect to the center of the preform, a slip between the two press surfaces with the mold-forming surface during precision press- It is possible to perform good precision press forming even when the difference in area between a pair of mold forming surfaces is large.

In order to produce the preforms I and II having such properties, as described in the above-mentioned [Problem Solution], the present inventors have found that the fluorine concentration near the surface of the preform can be changed For this purpose, since the oxide glass containing the fluorine component in a molten state exhibits very high volatility, the volatility of the glass is lowered to a controllable level in advance in the production of the preform, and then fluorine near the surface is volatilized And the like.

[Volatility Reduction Operation of Molten Glass]

It is considered that, when melting an oxide glass containing a fluorine component, a fluorine compound having a very high volatility and a fluorine compound having a not very high volatility are produced by a melting reaction. By flowing an inert gas such as nitrogen gas in a dry state to the molten atmosphere, the volatilization of the highly volatile product is promoted, and the concentration of the product in the molten glass is lowered. By such an operation, the volatility of the molten glass can be lowered. The fluorine component in the glass which has sufficiently lowered the volatility is derived from a product having a low volatility.

However, since the fluorine component in the glass is reduced by this operation, it is necessary to introduce a large amount of the fluorine component such as reduced by the volatilization at the time of the raw material combination.

It is preferable that the above-described operation is performed during the fining process in which the temperature of the glass is highest during the fusing process. By carrying out the above operation at a higher temperature, volatilization of the volatile product can be further promoted. Whether or not the volatility has sufficiently decreased can be confirmed by the following method.

The preform for precision press molding is made of optical glass whose refractive index is defined with high accuracy. The refractive index of the glass reflects the composition, and the refractive index also changes with the change of composition. The composition changes slightly depending on the volatilization of the volatile product. In an optical glass having a high refractive index, this slight compositional change can also be monitored as a refractive index change.

Whether or not the glass obtained by cooling and solidifying the molten glass is obtained by lowering the volatility can be found by reheating the glass and re-melting the glass, and examining the refractive index changes before and after the glass. When the refractive index difference between before and after re-melting is high, a large amount of volatile products remains in the glass before re-melting. When the refractive index difference is small, the volatile products It becomes small.

The refractive index difference before and after re-melting is correlated with the magnitude of the refractive index difference before and after the re-melting, and more specifically, the absolute value of the refractive index difference before and after re-melting is set to a predetermined value or less , It is possible to judge that the volatility of the glass has been lowered to such an extent that the molten iron is eliminated.

Specifically, the refractive index of the glass is n _d ⁽¹⁾ , the glass is re-melted in a nitrogen atmosphere at 900 ° C for 1 hour, cooled to a glass transition temperature, and then cooled to 25 ° C at a cooling rate of 30 ° C when the refractive index after the La value ^{_{n d (2), n d}} (1) and n _d ⁽²⁾ is substantially equal to be understood that the volatility is reduced.

Here, the fact that n _d ⁽¹⁾ and n _d ⁽²⁾ are substantially equal means that n _d ⁽¹⁾ and n _d ⁽²⁾ are approximated so that no fringing occurs in the optical glass. it is preferable that the absolute value of _d ⁽²⁾ -n _d ⁽¹⁾ is 0.00300 or less. If the absolute value of n _d ⁽²⁾ -n _d ⁽¹⁾ exceeds 0.00300, the molten glass is generally fumed on the surface of the preform when it is molded into a preform. When the absolute value is 0.00300 or less, a glass material capable of preventing fogging can be provided.

A more preferable range of the absolute value is 0.00200 or less, more preferably 0.00150 or less, still more preferably 0.00100 or less. In fluorine-containing oxide glass, since fluorine relatively decreases the refractive index of glass ^, the value of n _d ⁽²⁾ -n _d ⁽¹⁾ is generally positive.

The atmosphere at the remelting performed for measuring n _d ⁽²⁾ is nitrogen gas in order to prevent the refractive index of the glass from being affected by factors other than the volatilization due to the reaction of the glass with the atmosphere. The re-melting is carried out under predetermined conditions at 900 DEG C for 1 hour, and then cooled to the glass transition temperature. Since the value of n _d ⁽²⁾ is influenced by the cooling rate at the time of cooling, the cooling is carried out at a predetermined cooling rate of 30 ° C / hour and cooled to 25 ° C.

The refractive index can be measured by a known method, and it is preferable to measure the refractive index with a precision of six digits of the number of significant digits (five digits after the decimal point). As an example of the measurement of the refractive index, JOGIOS 01-1994 "Method of measuring refractive index of optical glass" of Japan Optical Glass Industry Association can be applied.

Depending on the shape and volume of the glass, for example, in the case where the glass is formed into a small spherical shape or a thin lens, the glass can not be processed with the sample of the shape and dimensions specified in the above standard. In this case, the glass is heated, softened, press molded, and annealed to form a prism shape in which the two planes intersect at a predetermined angle. Further, the refractive index is measured based on the same measurement principle as the above standard. Since the heating temperature at the time of preparing the preform by press molding is high enough to soften the glass and is much lower than the temperature at which the glass is melted, the influence on the concentration of the volatile substance is negligible, Since the amount of change in refractive index before and after is ignored, there is no problem.

The glass constituting the preform of the present invention preferably has the above properties in terms of volatility.

[Preparation of preform for precision press molding]

Subsequently, the molten glass subjected to the volatility reduction operation is discharged in this manner, and the atmosphere in contact with the surface to lower the fluorine concentration is always replaced with a new atmosphere. Volatile products are volatilized from the glass surface at a high temperature even if the glass has lowered volatility. Since the concentration of the volatile product in the atmosphere is always kept low by performing the atmosphere substitution, the rate of volatilization per unit area is almost determined by the temperature of the glass. On the other hand, in the case where the atmosphere substitution is not performed, the concentration of the volatile product in the atmosphere increases and the volatilization rate per unit area tends to be lower than that in the case of performing the atmosphere substitution.

By substituting the atmosphere only for a part of the surface of the molten glass in this manner, the fluorine concentration near the surface of the portion can be lowered. When the glass is cooled in this state, the distribution of the fluorine concentration is fixed.

Using this principle, the preform of the present invention can be produced by several methods.

A first method is a method of separating molten glass blocks containing a lower end of a molten glass flow out of a pipe and discharging gas from a gas ejection port provided in the recessed portion of the molten glass mass on a concave portion of a molding die, And the preform is formed without being flipped upside down while being levitated. Specifically, the molten glass with reduced volatility flows out of the pipe and supports the lower end of the molten glass flow out. As a result of this operation, a shrinkage portion is generated between the pipe outlet side and the lower end of the molten glass by surface tension. Next, the support is removed, or the support supporting the lower end of the molten glass is dived, and the molten glass is separated by the surface tension in the contracted part. The molten glass mass including the lower end is separated in this way and molded into a preform on the concave portion of the mold. In the concave portion, a large number of gas ejection openings are provided over the whole surface for supporting the glass, and gas is blown out from these gas ejection openings to apply wind pressure to the glass and float on the concave portion to perform molding. It is preferable to use a gas that does not contain fluorine as the gas (floating gas). For example, a rare gas such as nitrogen gas or argon gas can be used. By blowing out gas through the entire surface of the concave portion to float the glass, the glass is molded into a preform without being vertically inverted. Therefore, the lower surface of the preform on the concave portion is always supplied with the new floating gas, and the aforementioned atmosphere substitution is performed. On the other hand, since the upper surface of the preform is not blown with the floating gas, the atmosphere containing volatile products volatilized from the glass is formed in a state of staying. Thus, a preform having a high fluorine concentration and a low fluorine concentration can be produced.

In the second method, molten glass having reduced volatility is flowed out from the pipe, and melted glass droplets are taken from an inverted conical mold called a venturi tube and molded into a preform.

The venturi tube is made to decrease the inner diameter toward the bottom, and a gas outlet for blowing up the floating gas is installed at the bottom. The gas is jetted from the gas jet port to apply an upward wind pressure to the glass. From the shape of the Venturi tube, the glass floats due to strong upward wind pressure toward the bottom, but it rolls along the inverted conical slope because the upward wind pressure weakens due to the float, and repeats the upward and downward movement to rise again. By this movement, the glass is formed into a spherical preform while rotating in a random direction. In this method, the entire surface of the glass undergoes the substitution of atmosphere to lower the fluorine concentration. Next, when a part of the surface of the preform is removed by polishing, etching, or the like, the surface layer in which the fluorine concentration is lowered is removed and a surface having a high fluorine concentration appears. Thus, a preform having different fluorine concentration can be formed.

In addition, it is also possible to use a glass in which volatility is lowered and no fogging is used to promote partial volatilization of the glass surface, or to remove part of the glass surface uniformly lowering the fluorine concentration, And then exposing the portion as a surface, thereby making a desired preform. It goes without saying that the inside of the glass in which the fluorine concentration in the vicinity of the surface is lowered by volatilization is in a state of higher fluorine concentration than the surface.

The concentration difference between the high fluorine concentration and the low fluorine concentration may be slightly different. At the time of precision press molding, the preforms are pressed into a pair of opposed forming members, for example, upper and lower molds. If the lubrication between the mold surface and the glass having a larger area of the mold surface is better than that of the other surface of the mold, the glass smoothly spreads into the mold and an optical element with high surface accuracy can be molded. Direct measurement of such a small concentration of fluorine is disadvantageous in terms of measurement accuracy, labor and cost. Further, the surface layer having a low fluorine concentration is considered to be very thin, and it is considered difficult to measure its 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 the surface free energy on the surface of the preform.

For example, in a fluorine-containing oxide glass such as fluorophosphoric acid glass, fluoroboric acid glass, and fluorosilicic acid glass, the refractive index is lowered when the fluorine concentration is higher and conversely, the refractive index is increased when the fluorine concentration is lower. This is because the oxygen-rich glass has a higher refractive index than the fluorine-rich glass when the anion component is noted.

Since the refractive index sensitively reflects the fluorine concentration in this way, the fluorine concentration near the surface can be indirectly managed by the refractive index of the glass. However, since it is difficult to measure the refractive index of a very thin portion of the surface, the light reflectance on the surface can be measured instead. The relationship between the light reflectance on the surface of the preform and the refractive index of the glass surface is related by an equation called the Fresnel equation.

When the fluorine concentration on the surface of the preform is lowered, the refractive index near the surface increases and the ray reflectance increases. On the contrary, when the fluorine concentration increases, the refractive index near the surface decreases and the reflectance decreases.

The preform I for precision press molding, which is the first aspect of the present invention, is based on this finding.

[Precursor for preform press molding I]

As described above, the preform I for precision press forming according to the first aspect has a structure in which the optical reflectance of two surfaces opposite to each other with respect to the center of the preform is different and an oxide glass containing a fluorine component .

As a preform for molding an optical element having rotational symmetry such as a lens, it is preferable that a preform having a rotationally symmetric axis and a first curved surface including one of two intersection points of the symmetry axis and the surface and a second curved surface including the other intersection It is preferable that the preform has a second curved surface and the light ray reflectance on the first curved surface and the light ray reflectance on the second curved surface have different values. This preform can be produced by the first method described above.

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

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

For example, it is preferable to measure the light reflectance at three wavelengths of wavelengths of 500 nm, 600 nm, and 700 nm so that the difference in reflectance of the light is preferably 0.03% or more, and more preferably 0.05% or more. However, if the difference in the light beam reflectance is increased more than necessary, the performance of the optical element is deteriorated, and the prerequisite conditions of the present invention for obtaining an optically homogeneous preform by fogging of the preform by the manufacturing method may collapse. Therefore, it is preferable that the difference in the light reflectance is all 1.0% or less, more preferably 0.7% or less.

≪ Measurement of light reflectance on the surface of preform >

The light reflectance of the surface of the preform is measured as follows.

The surface of the preform is often a curved surface. Since the light reflectance depends on the incident angle of the measurement light on the measurement surface, if the curvatures of the measurement surface are different, even if the refractive indexes of the surfaces of the preforms are the same, the reflectance becomes different values and the refractive index of the preform surface layer may not be accurately reflected. Therefore, by making the reflectance measuring region narrow to the extent that the measuring surface is seen as a plane, the reflectance accurately reflects the refractive index of the surface layer of the preform.

Concretely, although it depends on the curvature of the surface of the preform, it is preferable to condense the measurement beam so that the diameter of the measurement beam becomes 1 mm or less on the measurement surface, more preferably 0.5 mm or less, And it is more preferable to condense light so as to be 100 mu m or less. Is reduced to 100 mu m or less, preferably 80 mu m or less, and the measurement light flux is incident perpendicularly on the measurement surface, and the reflected light is measured. In order to carry out such measurement, for example, it is preferable to use a lens reflectance measuring instrument (model name " USPM-RU ") manufactured by Olympus Kogaku Corporation.

1 is an explanatory diagram showing a principle of measurement of a light reflectance on a surface of a preform.

The measuring principle of the measuring instrument will be described with reference to Fig. 1, the optical system from the light source (halogen lamp) to the field tightening FS-a 2 illuminates the FS-a 2. The light tightening AS 1 is disposed in the optical path thereof. The light flux passing through the opening of the FS-a 2 becomes a parallel light flux in the collimator lens 3 and is reflected by the half mirror 4 to be incident on the measurement surface of the sample 6 in the objective lens 5 And the light is condensed on the measurement surface to a size of 50 mu m in diameter. The focusing on the measurement surface can be performed by observing the light reflected by the half prism 8 using the eyepiece lens 9 and adjusting the distance between the objective lens 5 and the measurement surface of the sample 6 .

The light reflected from the measurement surface returns to the original optical path and passes through the half mirror 4, the image forming lens 7 and the half prism 8 and passes through a field tightening FS-b 10 having a flare- Respectively. The reflected light having passed through the FS-b 10 passes through the two-dimensional cut filter 11 and is then diffracted by a diffraction grating 12 called a flat field grating and reflected by the mirror 13 to be received by the line sensor 14 (Light receiving surface).

Since the spectrally reflected light is incident on another position on the line sensor light receiving surface by the wavelength, the spectral spectrum of the reflected light is measured. In this device, the spectral spectrum can be measured over a wavelength range of 380 to 780 nm.

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

Reference numeral 15 denotes a lamp for flare fastening illumination, and 16 denotes a rotating mirror.

[Precursor for preform molding II]

As described above, the preforms II for precision press molding of the second aspect have surface free energies different from each other on two curved surfaces facing opposite to each other with respect to the center of the preform, .

In the fluorine component-containing oxide glass, the surface free energy increases with the surface of the glass having a high fluorine concentration, and the surface free energy decreases with the surface of the glass having a low fluorine concentration. The surface free energy also reflects the fluorine concentration on the glass surface in the same manner as the reflectance.

This preform II also has, for the same reason as the preform I, a first curved surface including one rotational symmetry axis and one of two intersection points of the symmetry axis and the surface, and a second curved surface including the other intersection It is preferable that the preform for precision press forming has a curved surface and the surface free energy on the first curved surface and the surface free energy on the second curved surface show different values. In this type of preform, it is required to measure the surface free energy of the first curved surface and the second curved surface near the intersection. These portions have a maximum radius of curvature as described above, and therefore, the influence of the surface shape of the preform can be reduced when the surface free energy is measured, which is preferable.

In order to achieve the object of the present invention in the present invention, the difference in surface free energy between the two surfaces is preferably 2.0 mJ / m ² or more, and more preferably 4.0 mJ / m ² or more. However, if the surface free energy difference is increased more than necessary, the performance of the optical element is deteriorated, and the prerequisite conditions of the present invention in which the preform is spun in accordance with the manufacturing method and an optically homogeneous preform is obtained, . Therefore, the surface free energy difference is preferably 40 mJ / m ² or less, and more preferably 30 mJ / m ² or less. This preform can also be produced by the first method described above.

≪ Measurement of surface free energy on the surface of the preform &

The surface free energy of the surface of the preform is measured as follows.

In the present invention, wetness (wetting angle) is measured by dropping each liquid onto the surface of a preform by using pure water and _two liquids of CH ₂ I ₂ (diiodomethane) for measurement of surface free energy, From the results, the surface free energy is calculated using the Owens-Wendt-Kaelble method. The surface free energy? Is given by the sum of the dispersion force? ^D of the solid or liquid and the polar or interaction force? ^P of the solid or liquid, as shown in the following equation (1).

Considering Equation (1) as the surface free energy (? _S ) of a solid, Equation (2) is obtained. Here, subscript s denotes solid. Equation (1) for Equation (1) is given by Equation (3), and subscript L represents Liquid (liquid).

? =? ^d +? ^p

γ _s = γ _s ^d + γ _s ^p

γ _L = γ _L ^d + γ _L ^p

When the liquid on the glass surface is dropped and the contact angle? Of the liquid is measured, a well-known relationship as shown in Equation (4) holds between? And the surface free energy.

? _L × (1-cos?) / 2

= (γ _s ^d + γ _L ^d ) ^1/2 + (γ _s ^p + γ _L ^p ) ^1/2

Further, in the by known data, pure water ^{_{γ L d = 21.8 mJ / m}} 2, γ L p = 51 mJ / and m _^2, CH ² I ² in ^{_{γ L d = 50.8 mJ / m}} 2, γ L p = 0 mJ / m ^2. Therefore, supposing that the contact angles θ W (pure water) and θ _C (CH ₂ I ₂ ) of the two kinds of liquids dropped onto the surfaces of the same amount of preforms, (5) and (6), respectively.

72.8 x (1-cos? W) / 2

= (粒_s ^d + 21.8) ^1/2 + (粒_s ^p +51) ^1/2 ... (5)

50.8 占 (1-cos? _C ) / 2

= (粒_s ^d + 50.8) ^1/2 + (粒_s ^p + 0) ^1/2 ... (6)

Substituting a measured value in θw, θ _C, equation (5), equation (6) can be won two simultaneous equations for the γ _s ^d, γ _s ^p as unknowns, easily calculate the unknowns. Substituting this result into the equation (2), the surface free energy? _S on the surface of the preform can be calculated.

In addition, since the light reflectance and surface free energy can not be measured accurately unless it is a clean surface, it is important to perform a cleaning and drying process at the time of measurement to make the surface of the preform clean.

The preforms I and II for precision press forming all have one rotational symmetry axis and a first curved surface including one of the two intersecting points of the symmetry axis and the surface and a second curved surface including the other intersecting point, It is preferable that the curvature radius of the first curved surface is different from the curvature radius of the second curved surface.

Although the light reflectance and the surface free energy of the first curved surface and the second curved surface are different, it is difficult to distinguish the first curved surface and the second curved surface from each other only by the difference of these characteristics at first glance.

Therefore, by making the preform so that the radius of curvature of the first curved surface is different from that of the second curved surface, it is possible to easily determine which side is the surface with a high reflectance or which side has a large surface free energy.

It is preferable that the measurement site of the surface free energy be a portion near the center of the first and second surfaces, that is, a portion centered on each intersection between the rotational symmetry axis and the surface.

Hereinafter, the sign of the radius of curvature of the glass surface including the preform is defined as positive when it is convex outside, and is defined as negative when it is concave.

When the first and second curved surfaces are all preforms having a convex shape toward the outside of 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 smaller than the light reflectance of the second curved surface (I.e., the surface free energy of the first curved surface is smaller than the surface free energy of the second curved surface). By associating the characteristics of the two curved surfaces with the magnitude of the radius of curvature as described above, it is possible to easily discriminate the surface with good lubricity when mass production of the optical element is performed by using a plurality of preforms. This preform can be manufactured by setting the side wall of the molding concave portion by the first method and making the radius of curvature of the glass bottom on the concave portion smaller than the radius of curvature of the upper surface.

In other cases, the surface of the first curved surface is made smaller than the reflectance of the second curved surface (i.e., the surface free energy of the first curved surface is made larger than the surface free energy of the second curved surface) .

In order to make such a preform, the first method is to make the molten glass mass smaller and at the same time to make the concave portion of the molding die almost flat so that the radius of curvature of the lower surface of the glass on the concave portion becomes larger than the radius of curvature of the upper surface. Such a molten glass ingot can reduce the radius of curvature of the upper surface by the surface tension.

Although the first and second curved surfaces have been described with respect to the outwardly convex preforms, the present invention is applicable to preforms having one convex curved surface and the other convex concave shape, or concave convex shapes on both curved surfaces. to be.

In the preform of the present invention, it is preferable that the entire surface is formed by cooling and solidifying the molten glass. Since the fluorine component-containing glass has a property of being low in hardness and easily scratched among the oxide glass, it is preferable to manufacture the fluorine component glass by the above-described process rather than by polishing. In addition, the preform produced by the above process is air-cooled and has excellent mechanical impact resistance.

In the present invention, the two faces opposite to each other with respect to the center of the preform have different slip properties between the mold-formed faces. By using this point, it is possible to perform good precision press molding even when the difference in area between a pair of mold forming surfaces is large. In order to enjoy such an effect, the preform may be precisely press-molded in a state in which the glass is exposed without being coated, but it may be a preform on which a coating has been applied to more reliably prevent fusion of glass and mold-forming surface. If the surface of the preform is coated, it may be thought that the effect is weaker than in the case of non-coating, but if the coating is coated on a glass surface with a slightly different light transmittance or surface free energy, , A surface having a low light transmittance, that is, a surface having a large surface free energy, has good slipperiness with the mold surface even when coated. Therefore, even when the preform is coated on the surface, the effect of the present invention can be obtained. It is preferable to set the film thickness of the coating to 7 nm or less in order to increase the influence of the glass surface of the base and obtain the above effect. In order to increase the releasability of the glass, it is preferable to set the film thickness to 0.5 nm or more. As the coating on the surface of the preform, a carbon-containing film and the like are preferable.

As a film forming method which easily reflects the state of the glass surface, for example, difference in light reflectance or surface free energy, a film forming method involving a surface reaction such as a CVD method (chemical vapor phase reaction method) And a carbon-containing film is formed on the glass surface by decomposition).

[Oxide glass containing fluorine component constituting the preform]

Next, an oxide glass containing a fluorine component constituting the preform of the present invention will be described.

Among the oxide glass containing a fluorine ingredient, and P ^5+, and Al ³⁺ A preferred glass is a phosphate glass as a fluoride, in particular essential cationic component of claim ^{1, Mg 2+, Ca 2+,} Sr 2+ and Ba ²⁺ (R < ^{2 +} >) selected from the group consisting of Li ⁺ and Li ⁺ .

An example of such a glass as cation percentages, P ⁵⁺ 10 to 45%, Al ³⁺ 5 to 30%, Mg ²⁺ 0 to 20%, Ca ²⁺ 0 to 25%, Sr ²⁺ 0 to 30%, Ba ²⁺ 0 to 33%, Li ⁺ 1 to 30%, Na ⁺ 0 to 10%, K ⁺ 0 to 10%, Y ³⁺ 0 to 5%, and at the same time contain 0 to 15% of B ^3+, The molar ratio F ^- / (F ^- + O ^2- ) of the content of F ^- to the total amount of F ^- and O ^2- is preferably 0.25 to 0.85, and Mg ²⁺ , Ca ²⁺ , Sr ²⁺ and Ba ^{2 And} a divalent cation component (R < ^{2 + &} gt ^; ) selected from the group consisting of ⁺ and -.

This fluorophosphoric acid glass is preferable as an optical glass which realizes optical characteristics having a refractive index (n _d ) of 1.40 to 1.58 and an Abbe number (v _d ) of 67 to 90.

Among them, the divalent cationic components (R ²⁺⁾ as Ca ^2+, Sr ²⁺ and Ba ²⁺ is a fluorinated phosphate glass is preferable, and a divalent cationic components (R ^2+), including two or more of Mg ^{2 +} , A total content of Ca ²⁺ , Sr ²⁺ and Ba ²⁺ of 1 cation% or more is more preferable.

The fluorophosphorous glass has a molar ratio F ^- / (F ^- + O ^2- ) of the content of F ^- to the total amount of F ^- and O ^2- , preferably 0.50 to 0.85, and Abbe number (v _d ) A glass b having a molar ratio F ^- / (F ^- + O ^2- ) of preferably less than 0.25 to 0.50 and an Abbe number (v _d ) of less than 67 - 75, The preferable content range of each cation component is different between glass a and glass b.

Hereinafter, the content of each cation component is expressed in terms of cation%.

P ⁵⁺ is an important cationic component as a network former of glass. When it is less than 10%, stability of glass is deteriorated. When it exceeds 45%, P ⁵⁺ needs to be introduced as an oxide raw material, Characteristics. Therefore, the amount thereof is preferably 10 to 45%. When the glass a is obtained, the preferable range of P ⁵⁺ is 10 to 40%, more preferably 10 to 35%, still more preferably 12 to 35%, still more preferably 20 to 35% The range is 20 to 30%. Further, in the case of obtaining the glass b, the preferable range of P ^{5 +} is 25 to 45%, more preferably 25 to 40%, still more preferably 30 to 40%. In addition, the use of PCl ₅ in the introduction of P ^{5 +} is not suitable because it destabilizes stable production because of erosion of platinum and high volatility, and is preferably introduced as a phosphate.

Al ^{3 +} is a component that improves the stability of fluoride, phosphate glass, is less than 5% stability is degraded, and a 30% excess is due to the glass transition temperature (Tg) and the liquidus temperature (LT) greatly increase, the forming temperature And the maceration due to the volatilization of the surface during molding is strongly generated, so that it is impossible to produce a homogeneous glass molded article, particularly a preform for press molding. Therefore, it is preferable that the amount thereof is 5 to 30%. When the glass a is obtained, the preferred range of Al ³⁺ is 7 to 30%, more preferably 8 to 30%, still more preferably 10 to 30%, still more preferably 15 to 25%. Further, in the case of obtaining the glass b, the preferred range of Al ³⁺ is 5 to 20%, more preferably 5 to 12%.

The introduction of Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , and Ba ²⁺ as divalent cation components (R ²⁺ ) contributes to improvement of stability, but two or more of them, more preferably Ca ²⁺ , Sr ²⁺ and Ba ²⁺ are introduced. In order to further increase the effect of introducing the divalent cation component (R ²⁺ ), it is preferable that the total content of Mg ²⁺ , Ca ²⁺ , Sr ²⁺ and Ba ²⁺ is 1 cation% or more. In addition, when the respective upper limits are exceeded, the stability sharply decreases. Ca ²⁺ and Sr ²⁺ can be introduced in a comparatively large amount, but the introduction of Mg ²⁺ and Ba ^{2+ in} a large amount lowers stability in particular. However, since Ba ²⁺ is a component capable of realizing a high refractive index while maintaining low dispersion, it is preferable to introduce a large amount of Ba ²⁺ within a range that does not impair the stability. Therefore, it is preferable that the amount of Mg ²⁺ is 0 to 20%, but when the free glass a is obtained, the amount of Mg ²⁺ is preferably 1 to 20%, more preferably 3 to 17% Is preferably 3 to 15%, more preferably 5 to 15%, particularly preferably 5 to 10%, and in the case of obtaining free b, the amount of Mg ²⁺ is preferably 0 to 15% , Preferably 0 to 12%, and more preferably 1 to 10%.

The amount of Ca ²⁺ is preferably 0 to 25%, but in the case of obtaining free a, the amount of Ca ²⁺ is preferably 1 to 25%, more preferably 3 to 24% Is preferably 3 to 20%, more preferably 5 to 20%, particularly preferably 5 to 16%, and in the case of obtaining free b, the amount of Ca ²⁺ is preferably 0 to 15% And more preferably 1 to 10%.

The amount of Sr ²⁺ is preferably 0 to 30%, but when the free glass a is obtained, the amount of Sr ²⁺ is preferably 1 to 30%, more preferably 5 to 25% Is preferably 7 to 25%, more preferably 8 to 23%, still more preferably 9 to 22%, particularly preferably 10 to 20%, and when glass b is obtained, the amount of Sr ²⁺ Is preferably 0 to 15%, more preferably 1 to 15%, and still more preferably 1 to 10%.

The amount of Ba ²⁺ is preferably 0 to 33%, but in the case of obtaining free a, the amount of Ba ²⁺ is preferably 0 to 30%, more preferably 0 to 25%, further preferably 1 To 25%, still more preferably from 1 to 20%, further preferably from 3 to 18%, still more preferably from 5 to 15%, particularly preferably from 8 to 15% , The amount of Ba ²⁺ is preferably 0 to 30%, more preferably 10 to 30%, further preferably 15 to 30%, still more preferably 15 to 25%.

Li ⁺ is an important component for lowering the glass transition temperature (Tg) without impairing stability. However, if it is less than 1%, its effect is not sufficient. If it exceeds 30%, durability of glass is deteriorated and workability is lowered. Accordingly, the amount thereof is preferably 1 to 30%, more preferably 2 to 30%, further preferably 3 to 30%, and still more preferably 4 to 30%. In the case when obtaining the glass a there, and the amount of Li ⁺ by preferably 4 to 25%, more preferably 5 to 25%, more preferably from 5 to 20%, to obtain a glass b, of Li ⁺ The amount is preferably 5 to 30%, more preferably 10 to 25%.

Na ^+, K ^+, but the effect of lowering the same glass transition temperature (Tg) and the Li ^+, respectively, tends to more greatly as compared with the same coefficient of thermal expansion to Li ^+. Since the solubility of NaF and KF in water is much larger than that of LiF, the water resistance also deteriorates. Therefore, the amounts of Na ⁺ and K ⁺ are preferably 0 to 10%, respectively. In any of the glasses a and b, the preferable ranges of Na ⁺ and K ⁺ are all 0 to 5%, and it is more preferable that they are not introduced.

Y ³⁺ has the effect of improving the stability and durability of the glass. However, if it exceeds 5%, the stability deteriorates to the contrary and the glass transition temperature (Tg) also increases greatly, so that the amount thereof is preferably 0 to 5% . When the free glass a is obtained, the amount of Y ³⁺ is preferably 0 to 3%, more preferably 0.5 to 3%, and in the case of free glass b, the amount of Y ³⁺ is preferably 0 4%, more preferably 0 to 3%, and still more preferably 0.5 to 3%.

Since B ³⁺ is a vitrification component, it has an effect of stabilizing the glass. Excessive introduction causes deterioration of durability, and also increases O ^{2- in the} glass as B ³⁺ increases. Therefore, , It is preferable to set the amount thereof to 0 to 15%. However, since BF _{3 is} easily volatilized during melting and causes fogging, the amount of BF ₃ is preferably 0 to 10%, more preferably 0 to 5% in any glass of glass a and glass b Do. When the volatility reduction of the glass is prioritized, the content is preferably 0 to 0.5%, more preferably not introduced.

In order to stably produce high-quality optical glass, P ⁵⁺ , Al ³⁺ , Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ²⁺ , Li ⁺ and Y ³⁺ is preferably more than 95%, more preferably more than 98%, more preferably more than 99%, and even more preferably 100% by cationic%.

All of the glasses a and b may contain a lanthanide such as Ti, Zr, Zn, La, and Gd as a cation component in addition to the cation component.

Si ^{4 +} can be introduced for the purpose of stabilizing the glass, but since the melting temperature is too low, excessive introduction may lead to generation of dissolution residues or volatilization during dissolution, thereby impairing 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 even more preferably 0 to 5%.

As a ratio of the anion component, a molar ratio F ^- / (F ^- + O ^2- ) of the content of F ^- to the total amount of F ^- and O ^2- is set so as to satisfy the following equation But it is preferably from 0.50 to 0.85 in the case of the glass a and from 0.25 to 0.50, more preferably from 0.27 to 0.45, and still more preferably from 0.3 to 0.45 in the glass b. In any of the glasses a and b, the total amount of F ^- and O ^{2 - in} the anion is preferably 100%.

The refractive index (n _d ) of each of the glasses a and b is about 1.40 to 1.58 and the Abbe number (v _d ) is about 67 to 90, preferably 70 to 90. The Abbe number (v _d ) of the glass a is about 75 to 90, preferably 78 to 89, and the Abbe number (v _d ) of the glass b is about 67 to 75 or less.

The glasses a and b exhibit a high transmittance in the visible range, except when a colorant is added. Specifically, when a sample having a thickness of 10 mm, both surfaces of which are flat and parallel to each other, is irradiated with light from a direction perpendicular to the both surfaces, the transmittance at a wavelength of 400 to 2000 nm (excluding reflection loss at the surface of the sample) ) Exhibits a light transmittance characteristic of usually not less than 80%, preferably not less than 95%.

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

In addition, since the positive ions a and b positively contain Li ⁺ in the alkali metal ions, the coefficient of thermal expansion is relatively small and the water resistance is relatively excellent. Therefore, by polishing the glass and processing it into a preform, it is possible to obtain a preform having smooth surface and high quality.

Since the glasses a and b exhibit excellent water resistance and chemical durability, the surface of the preform does not deteriorate even after being stored for a long period of time between the production of the preform and the use thereof for press molding. Further, since the surface of the optical element is also hard to be deteriorated, the optical element can be used in a good state in which the surface is not fogged for a long period of time.

In addition, according to the glasses a and b, the glass melting temperature can be lowered by about 50 ° C as compared with a glass having equivalent optical characteristics and not containing Li. Therefore, Coloring, incorporation of bubbles, and defects called fritters can be reduced and eliminated.

Fluorophosphate glass generally has a high viscosity at the time of spouting, and when the molten glass mass of the target mass is separated from the molten glass to be discharged and molded, the glass is finely entangled in the separating portion as a thread, There is a defect that remains on the glass lump surface to form protrusions. In order to solve this drawback by lowering the outlet viscosity, the outflow temperature of the glass has to be increased. As a result, the volatilization of fluorine from the glass surface is promoted as described above, and the problem of sparkle becomes significant.

In order to solve the above problem, the glasses a and b determine the glass composition so that the temperature showing the predetermined viscosity becomes lower than that of the conventional fluorophosphate glass in order to lower the temperature suitable for molding the molten glass. Although the glass transition temperature is much lower than the molding temperature of the molten glass, since the glass having a low glass transition temperature can lower the molding temperature, problems such as thread formation and spoilage during molding can be reduced and eliminated It is effective to adjust the glass composition so that the glass transition temperature is within the above range.

In addition, by lowering the glass transition temperature, it is possible to lower the heating temperature of the glass in the precision press molding of the preform, to relax the reaction between the glass and the press mold, or to extend the life of the press mold And so on.

Glass a and b can be obtained by weighing and combining these raw materials by using phosphoric acid raw material, fluoric raw material, etc., supplying them to the melting vessel, heating, melting, purifying, homogenizing them as described above,

A second preferred example of an oxide glass containing a fluorine component is a glass fluorophosphate containing Cu ²⁺ . This glass functions as near-infrared absorbing glass. This glass is particularly preferable as a filter for color correction of a semiconductor image pickup device such as a CCD or a CMOS. In the case where the glass is used for the above use, the content of Cu ²⁺ is preferably 0.5 to 13 cation%.

A particularly preferred composition of the glass is 11 to 45%, P ⁵⁺ as a cationic percentages, Al ³⁺ of 0 to 29%, Li ^+, Na ^+, and 0 to 43% of the K ⁺ in total, Mg ^2+, Ca ²⁺ 14 to 50% in total of Sr ²⁺ , Ba ²⁺ and Zn ²⁺ , 0.5 to 13% of Cu ²⁺ , and F ^- 17 to 80% in terms of anion%.

It is preferable that the remaining amount of the anion component in the above composition is all O ^2- . Hereinafter, the content of the cation component and the total content thereof are expressed in terms of% by cation.

In the above composition, P ⁵⁺ is a basic component of the glass fluorophosphate and is an important component that leads to absorption of the infrared of Cu ²⁺ . When the content of P ⁵⁺ is less than 11%, the color deteriorates to become green. On the contrary, when the content exceeds 45%, weatherability and devitrification 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 insolubility and heat resistance, thermal shock resistance, mechanical strength and chemical durability of fluorophosphate glass. However, if it exceeds 29%, the near infrared absorption characteristic deteriorates. Therefore, the content of Al ³⁺ is preferably 0 to 29%, more preferably 1 to 29%, further preferably 1 to 25%, still more preferably 2 to 23% Do.

Li ⁺ , Na ⁺ and K ⁺ improve the meltability and devitrification resistance of the glass and improve the transmittance in the visible range. However, when the total amount exceeds 43%, durability and workability of the glass deteriorate. Therefore, the total content of Li ⁺ , Na ⁺ and K ⁺ is preferably 0 to 43%, more preferably 0 to 40%, and even more preferably 0 to 36%.

Among the alkali components, Li ⁺ is excellent in the above-mentioned 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 for improving the resistance to devitrification, durability and workability of glass. However, since devitrification is reduced by excessive introduction, Mg ²⁺ , The total amount of Ca ²⁺ , Sr ²⁺ , Ba ²⁺ and Zn ²⁺ is preferably 14 to 50%, more preferably 20 to 40%.

The Mg ²⁺ content is preferably 0.1 to 10%, more preferably 1 to 8%.

The preferred range of the Ca ²⁺ content is 0.1 to 20%, more preferably 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%.

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

Cu ²⁺ is the mainstay of near-infrared light absorption characteristics. If the amount is less than 0.5%, the near infrared absorption is small, and conversely, when the amount exceeds 13%, the resistance to devitrification is deteriorated. 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%, still more preferably 1 to 5%.

F ^- is an important anion component that lowers the melting point of glass and improves weatherability. By containing F ^- , the melting temperature of the glass can be lowered and the reduction of Cu ^{2 +} can be suppressed to obtain desired optical characteristics. If it is less than 17%, the weatherability deteriorates. On the other hand, if it exceeds 80%, the content of O ^{2 -} is decreased, resulting in coloration of around 400 nm due to monovalent Cu ⁺ . Therefore, the content of F < ^- > is desirably set to 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 all of the remaining anion component except for F ^- is composed of O ^2- component. Therefore, a preferable amount of O ^2- becomes a range obtained by subtracting the preferable amount of F ^- from 100%. When O ^{2 -} is too small, bivalent Cu ^{2 +} is reduced to form monovalent Cu ⁺ , so that absorption in a short wavelength region, particularly around 400 nm, becomes green, resulting in green. On the contrary, when the glass transition temperature is excessively high, the viscosity of the glass is high and the melting temperature is high, so that the transmittance is deteriorated.

Further, Pb and As are highly hazardous, so it is preferable not to use them.

Preferable transmittance characteristics of the Cu-containing glass are as follows.

The spectral transmittance at a wavelength of 400 to 1200 nm in terms of a thickness of 615 nm which shows a transmittance of 50% at a spectral transmittance of a wavelength of 500 to 700 nm is as follows.

It is preferably 78% or more, more preferably 80% or more, further preferably 83% or more, still more preferably 85% or more,

It is preferably 85% or more at the wavelength of 500 nm, more preferably 88% or more, even more preferably 89% or more,

At a wavelength of 600 nm is preferably 51% or more, more preferably 55% or more, further preferably 56% or more,

The wavelength is preferably 12% or less at 700 nm, more preferably 11% or less, further preferably 10% or less,

Is preferably 5% or less, more preferably 3% or less, further preferably 2.5% or less, still more preferably 2.2% or less, still more preferably 2% or less,

Is preferably 5% or less, 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,

Is preferably 7% or less, more preferably 6% or less, still more preferably 5.5% or less, still more preferably 5% or less, still more preferably 4.8%

The wavelength is preferably 12% or less, more preferably 11% or less, further preferably 10.5% or less, still more preferably 10% or less,

Is preferably 23% or less, more preferably 22% or less, further preferably 21% or less, and still more preferably 20% or less at a wavelength of 1200 nm.

That is, absorption of near infrared rays at a wavelength of 700 to 1200 nm is large, and absorption of visible light at a wavelength of 400 to 600 nm is small. Here, the transmittance refers to a transmittance of a light beam emitted from the other side of the plane, when assuming a glass sample having two planes parallel to each other and optically polished, and when light is vertically incident on one side of the plane, By the intensity before the sample is incident, and it is also referred to as an external transmittance.

With this characteristic, it is possible to perform color correction of a semiconductor imaging element such as a CCD or a CMOS well.

In addition, the present invention can be applied to fluorinated boric acid glass, fluorosilicic acid glass, and fluorinated borosilicate glass.

[Manufacturing method of optical element]

Next, a method for manufacturing an optical element of the present invention will be described.

The method for producing an optical element according to the present invention is characterized by using any of the above-described preforms for precision press molding in a method of manufacturing an optical element for producing an optical element by precision press molding a glass preform.

The precision press molding is also referred to as mold-optics molding, and is a method well known in the art. In the optical element, a surface that transmits, refracts, diffracts, or reflects a light beam is called an optically functional surface (a lens surface, such as an aspheric surface of an aspheric surface lens or a spherical surface of a spherical lens, However, according to the precision press molding, an optical functional surface can be formed by press molding by precisely transferring the molding surface of the press-molding mold to glass. In order to finish the optically functional surface, mechanical processing such as grinding or polishing .

Therefore, the method for producing an optical element of the present invention is suitable for manufacturing optical elements such as a lens, a lens array, a diffraction grating, and a prism, and is particularly suitable as a method for producing an aspherical lens with high productivity.

In the preform used in the present invention, the light reflectance or surface free energy on two surfaces facing opposite sides with respect to the center of the preform has different values. The fluorine concentration in the layer near the surface is lower than that in the other surface and the inside of the preform, as compared with the surface having a larger light reflectance than the other surface, that is, a surface having a smaller surface free energy than the other surface. Therefore, the surface having a low fluorine concentration is superior in lubricating property to the molding surface having the other surface. A fluorine-low-concentration surface of the preform is called a fluorine-low-concentration surface. A pair of opposing types used in precision press molding, for example, a top mold and a bottom mold, It is preferable to introduce the preform into the mold. The preforms are pressed in a pair of opposed shapes, but it is necessary that the mold forming surface having a larger area than the one of the pair of opposed molds is elongated along the molding surface than the other. Therefore, by arranging the fluorine-low-concentration surface so as to be in contact with the mold surface having a large area, it is easy to largely extend the glass.

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

As the press forming die used for precision press forming, there can be used a die known in the art, for example, a die having a mold-releasing film provided on a molding surface of a heat-resistant ceramic molding such as silicon carbide, zirconia or alumina. Among them, desirable.

In the precision press molding, in order to maintain the molding surface of the press-molding mold in a good state, it is preferable that the atmosphere during molding is a non-oxidizing gas. As the non-oxidizing gas, a mixed gas of nitrogen and nitrogen and hydrogen is preferable.

Next, as an aspect of the precision press molding used in the manufacturing method of the optical element of the present invention, two modes of precision press molding 1 and 2 shown below can be shown.

≪ Precise press forming 1 >

In the precision press molding 1, the preform is introduced into a press mold, and the press mold and the preform are heated together to perform precision press molding.

In this precision press molding 1, it is preferable that the temperature of the press mold and that of the preform are both heated to a temperature at which the glass constituting the preform exhibits a viscosity of 10 ⁶ to 10 ¹² dPa · s to perform precision press molding.

Further, the glass is cooled to a temperature of preferably 10 ¹² dPa · s or more, more preferably 10 ¹⁴ dPa · s or more, and even more preferably 10 ¹⁶ dPa · s or more, and then the precision press-molded product is pressed It is preferable to take it out of the mold.

According to the above conditions, the shape of the press-formed molding surface can be precisely transferred by the glass, and the precision press-molded product can be taken out without being deformed.

≪ Precise Press Forming 2 >

In the precision press forming method 2, a preheated preform is introduced into a preformed press mold to perform precision press forming.

According to this precision press molding 2, since the preform is heated in advance before introduction into the press mold, an optical element having good surface precision without surface defects can be manufactured while shortening the cycle time.

The preheating temperature of the press-molding die is preferably set to be lower than the preheating temperature of the preform. By reducing the pre-heating temperature of the press-molding die in this manner, consumption of the press-molding die can be reduced.

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

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

It is also preferable to start the cooling of the glass at the same time as the start of the press or during the press. Also, the temperature of the press-molding die is adjusted to a temperature lower than the pre-heating temperature of the preform, but the temperature may be based on the temperature at which the glass exhibits a viscosity of 10 ⁹ to 10 ¹² dPa · s.

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-molding die and slowly cooled as required. When the molded article is an optical element such as a lens, an optical thin film may be coated on the surface as required.

<Examples>

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples at all.

Example 1

The raw materials were weighed so as to be a glass having the compositions of Nos. 1 and 2 shown in Table 1 by using phosphates, fluorides and the like corresponding to the respective glass components as raw materials for the glass, and they were sufficiently mixed to prepare a combined raw material.

The combined raw materials were dissolved in a platinum crucible at 850 ° C for 1 hour, quenched and crushed, and used as a rough melt cullet. 10 kg of this rough melt cullet was put into a platinum crucible closed with a lid and melted by heating at 900 캜. Subsequently, sufficient dry gas was introduced into the platinum crucible to refine the molten glass at 1100 DEG C for 2 hours while maintaining the dry atmosphere. Examples of the type of the dry gas include an inert gas such as nitrogen, a mixed gas of inert gas and oxygen, and oxygen.

After the clinking, the temperature of the glass was lowered to 850 占 폚 lower than the temperature at the time of refining, and then the glass was flowed out from the pipe connected to the bottom of the crucible. Further, the gas introduced into the crucible was purified through a filter and discharged to the outside. In each of the above steps, the glass in the crucible was stirred to obtain a homogeneous glass.

The obtained molten glass was injected into a carbon mold in a dry nitrogen atmosphere. The injected glass was allowed to cool to the transition temperature and immediately put in an annealing furnace. The glass was annealed at a transition temperature for 1 hour, and then slowly cooled to room temperature in the annealing furnace to obtain optical glasses No. 1 and No. 2 shown in Table 1.

As a result of observation of each of the obtained optical glasses No. 1 and No. 2 by a microscope, no precipitation of crystals or a residue of dissolution of the raw material was observed.

The refractive index (n _d ), the Abbe number (v _d ) and the glass transition temperature (Tg) of the obtained optical glass Nos. 1 and 2 were measured as follows. The measurement results are shown in Table 1.

(1) The refractive index (n _d ) and the Abbe number (v _d )

The refractive index (n _d ) and the Abbe number (v _d ) were measured on the optical glass obtained by slow cooling and cooling at -30 ° C / hour.

In addition, as for the refractive index n _d, the refractive index of the optical glass of each index value of No.1, 2 measured in the condition n _d ^(1), and after re-melting, cooling of the glass No.1, 2 n _d ^{( 2)} was measured as follows.

30 g each of the glass of the above Nos. 1 and 2 was charged into a glassy carbon crucible in a 2 liter capacity quartz glass chamber into which 2 liters / minute of dry nitrogen gas was introduced, And remelted at that temperature for 1 hour. Thereafter, the glass substrate was cooled to the vicinity of the glass transition temperature in the chamber, and then cooled to a room temperature of 25 deg. C at a cooling rate of 30 deg. C each hour. Further, refractive indices n _d ⁽²⁾ of the thus obtained Glass Nos. 1 and 2 were measured.

The absolute values of n _d ⁽²⁾ -n _d ⁽¹⁾ and n _d ⁽²⁾ -n _d ⁽¹⁾ for optical glasses No. 1 and 2 are shown in Tables 1 to 3.

(2) Glass transition temperature (Tg)

The glass transition temperature (Tg) was measured by a thermomechanical analyzer of Rigaku Denki Co., Ltd. at a heating rate of 4 ° C / min.

As shown in Table 1, optical glasses Nos. 1 and 2 exhibited excellent refractive index, Abbe number and glass transition temperature, excellent low-temperature softening property and solubility, and were suitable as optical glasses.

Also, the absolute values of n _d ⁽²⁾ -n _d ⁽¹⁾ and n _d ⁽²⁾ -n _d ⁽¹⁾ were all less than 0.00300.

Next, each molten glass composed of the glass of the optical glass Nos. 1 and 2 was flowed out at a constant flow rate from a platinum alloy pipe whose temperature was adjusted to a temperature range in which the glass did not melt and could flow out stably, After supporting the glass bottom end, the support was dipped down to separate the molten glass mass corresponding to one preform. Subsequently, each obtained molten glass lump was received in a male mold having a concave portion made of a porous material, pressurized dry nitrogen gas was supplied to the back surface of the porous material, dry nitrogen gas was blown out from the entire surface of the concave portion through the porous material, Was molded into a preform for precision press molding, and was taken out from the mold and slowly cooled.

The preform was molded from the molten glass lump and molding was carried out without inverting the upper and lower surfaces of the glass ingot until the preform was taken out from the mold.

Thus, one preform having a rotational symmetry axis and a shape symmetrical with respect to an arbitrary rotational angle around the 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 another intersection is referred to as a second surface. The first surface corresponds to the upper surface in the male mold and the second surface corresponds to the lower surface in the male 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 has a flat shape compared to the second surface.

As a result of observing the preform with a naked eye and an optical microscope, McGrill and Silou were not confirmed. Also, the surface of the preform was smooth and the scratches were not seen. After the preform was washed and dried, the following measurements were carried out.

The light reflectance of the first surface and the second surface of the preform was measured using a lens reflection measuring instrument (model name &quot; USPM-RU &quot;) manufactured by Olympus Kogaku Kogyo, and the center of the first and second surfaces, And the reflectance near the intersection was measured. The spectral spectrum of the reflected light was measured over a range of wavelengths of 380 to 780 nm and the spectral spectrum of the reflected light of the reference sample surface was measured at a wavelength of 500 nm, The reflectance of the surface of the preform at each wavelength of 600 nm and 700 nm was calculated. The results are shown in Table 1.

Subsequently, pure water and CH ₂ I ₂ (diiodomethane) were used to drop each of the liquids in an equal amount to the center of each of the first and second surfaces of the preform, that is, near the two intersections, And the surface free energy of the first surface and the second surface was measured by the above-described method.

Thus, a precision preform for preforms having different light reflectances from the first and second surfaces and different surface free energies of the two surfaces was obtained.

Example 2

Precision press molding was carried out using the preforms made of the glasses No. 1 and No. 2 prepared in Example 1. The precision press-molding mold is for molding an aspherical convex meniscus lens, and is composed of an upper mold, a lower mold, and a torus mold. Each shape was made of SiC, and the mold surface was coated with a carbon film. The upper die forming surface is convex, the lower die forming surface is concave, the area of the upper die forming surface is larger than the area of the lower die forming surface, that is, the deformation amount of the press side on the upper die forming surface of the glass, Side.

First, the preform is placed at the center of the lower mold surface so that the second surface is downward, and the preform and the precision press mold are heated together to form a preform and a mold at a temperature of 10 ⁸ to 10 ¹⁰ dPa The temperature was maintained and pressed at a pressure of 8 MPa for 30 seconds. After pressing, the press pressure was released, the press-molded glass article was brought into contact with the lower mold and the upper mold, and then slowly cooled to a temperature at which the glass had a viscosity of 10 ¹² dPa · s or more. And an aspherical convex meniscus lens was obtained from the mold. The obtained aspherical lenses consisted of glass Nos. 1 and 2, respectively, and had very high surface accuracy, and no fog or turbidity was observed on the lens surface. The series of steps was performed in a nitrogen atmosphere. Also, the optical performance of the obtained lens was a desired performance.

In addition, although the above example is the production of the lens by the precision press molding 1, the precision press molding 2 may be applied. In this method, the preform is preheated to a temperature at which the glass constituting the preform has a viscosity of 10 ⁸ dPa · s while floating the preform. On the other hand, the precision press-molding die is heated so that the glass constituting the preform is at a temperature showing a viscosity of 10 ⁹ to 10 ¹² dPa · s. The preheated preform is introduced into a cavity of a precision press- And press-formed. After the start of the press, the cooling of the glass and the press mold was started. After the molded glass was cooled to a viscosity of 10 ¹² dPa · s or more, the molded product was released to obtain an aspherical lens. The resulting aspherical convex meniscus lens had a very high surface accuracy, and no cloudiness or turbidity was observed on the surface.

Example 3

Next, an aspherical concave meniscus lens was molded using the preform obtained in Example 1. The configuration of the precision press-molding die used is almost the same as that of the second embodiment, but the shapes of the upper molding surface and the lower molding surface are different. In this mold, the area of the upper molding surface is larger than the area of the lower molding surface.

Next the second side of the preform placing the preform at the center of the molding surface the lower die face-down on and heated with the preform and the precision press mold and the preform at a temperature that indicates the viscosity of the glass 10 ⁸ to 10 ¹⁰ dPa · s The mold was kept at the temperature and pressed at a pressure of 8 MPa for 30 seconds. After the press, the pressure of the press is released, and the press-molded glass article is brought into contact with the lower mold and the upper mold to slowly cool to a temperature at which the viscosity of the glass becomes 10 ¹² dPa · s or more, The molded article was taken out from the molding die to obtain an aspherical concave meniscus lens. The obtained aspherical lenses consisted of glass Nos. 1 and 2, respectively, and had very high surface accuracy, and no fog or turbidity was observed on the lens surface. The series of steps was performed in a nitrogen atmosphere. Also, the optical performance of the obtained lens was a desired performance.

In addition, although the above example is the production of the lens by the precision press molding 1, the precision press molding 2 may be applied. In this method, the preform is preheated to a temperature at which the glass constituting the preform has a viscosity of 10 ⁸ dPa · s while floating the preform. On the other hand, the precision press-molding die is heated so that the glass constituting the preform is at a temperature showing a viscosity of 10 ⁹ to 10 ¹² dPa · s. The preheated preform is introduced into a cavity of a precision press- And press-formed. After the start of the press, cooling of the glass and the press-molding die was started. After the molded glass was cooled to a viscosity of 10 ¹² dPa · s or more, the molded product was released to obtain an aspherical lens. The resulting aspherical concave meniscus lens had a very high surface accuracy, and no cloudiness or turbidity was observed on the surface.

In each of the above embodiments, when the glass surface of the preform is exposed, that is, when precision molding is performed without coating the surface of the preform, the carbon-containing film is coated on the surface of the preform by CVD by thermal decomposition of acetylene, When molded, good results can be obtained.

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

1 is an explanatory diagram showing a principle of measurement of a light reflectance on a surface of a preform.

Description of the Related Art

1 person tightening AS

2 Field tightening FS-a

3 collimator lens

4 half mirror

5 objective lens

6 samples

7 imaging lens

8 half prism

9 eyepiece

10 Field tightening FS-b

11 Two-dimensional cut filter

12 diffraction grating

13 Mirror

14 line sensor

15 Flare Fastening Lamp

16 rotation mirror

Claims (10)

As a preform for producing a lens having a different area of two faces by precision press molding, Wherein the preform comprises an oxide glass having a different light reflectance on two surfaces facing opposite sides to the center of the preform and containing a fluorine component. The light reflectance on the two surfaces facing opposite to each other with respect to the center of the preform has different values, And an oxide glass containing a fluorine component, The refractive index value of the glass is n _d ⁽¹⁾ , the glass is re-melted at 900 ° C for 1 hour in a nitrogen atmosphere to cool it to the glass transition temperature and then cooled to 25 ° C at a cooling rate of 30 ° C And n _d ⁽²⁾ , the absolute value of n _d ⁽²⁾ -n _d ⁽¹⁾ is 0.00300 or less. 3. The semiconductor device according to claim 1 or 2, further comprising: a first curved surface including one rotational symmetry axis and one of two intersecting points of the symmetry axis and the surface; and a second curved surface including the other intersecting point, Wherein the light reflectance on the first curved surface is different from the light reflectance on the second curved surface. The preform for precision press forming according to claim 1 or 2, wherein the surface free energy on the two surfaces has different values. The precursor for precision press forming according to claim 1 or 2, wherein the curvature radius of the first curved surface is different from the curvature radius of the second curved surface. The preform for precision press molding according to claim 1 or 2, wherein the entire surface is formed by cooling and solidifying the molten glass. A method of producing a preform for glass precursor for producing a glass preform for use in precision press molding from molten glass, The refractive index value of the glass is n _d ⁽¹⁾ , the glass is re-melted at 900 ° C for 1 hour in a nitrogen atmosphere to cool it to the glass transition temperature and then cooled to 25 ° C at a cooling rate of 30 ° C when the LA n _d ^(2), the absolute value of ^{_{n d (2) -n d (}} 1) is such that less than 0.00300, and the outflow molten glass is subjected to a volatile reduction operation in advance from the pipe, Separating the molten glass mass including the lower end of the molten glass flowed out from the pipe and injecting gas from a gas ejection port provided in the recessed portion on the concave portion of the mold to flip up and down while applying wind pressure, Shaping into preforms, and Wherein the glass is an oxide glass containing a fluorine component Wherein the preforms are preformed using a preform. 8. The method of producing a preform for precision press forming according to claim 7, wherein an inert gas in a dry state is caused to flow in a molten atmosphere to melt the fluorine-containing oxide glass, thereby lowering the volatility of the molten glass. A method of manufacturing an optical element for producing an optical element by precision press molding a glass preform, A preform for precision press molding according to any one of claims 1 to 7, or a preform for precision press molding produced by the method according to claim 7 or 8 is used. The method of manufacturing an optical element according to claim 9, wherein the aspherical convex meniscus lens or the aspherical concave meniscus lens is molded.

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