JP5072942B2 - Optical glass, press-molding preform and manufacturing method thereof, and optical element and manufacturing method thereof - Google Patents

Description

  The present invention relates to a fluorophosphate optical glass, a press-molding preform and a manufacturing method thereof, and an optical element and a manufacturing method thereof.

  The fluorophosphate optical glass is very useful as a low dispersion glass. As such a fluorophosphate optical glass, a glass as described in Patent Document 1 is known.

Japanese National Patent Publication No. 3-500162

  When the glass raw material is heated and melted, and the resulting molten glass is molded, fluorine in the glass is volatilized from the surface of the high-temperature glass, which is called striae on the surface layer of the resulting glass molded body. An optically nonuniform portion is generated.

  In the molding of glass, molten glass flows out of a pipe and casts into a mold or the like, and the higher the glass outflow temperature, the greater the volatilization of fluorine, and the more striae occurs. To reduce the occurrence of striae, it is necessary to lower the glass outflow temperature, but this increases the viscosity at the outflow, making it difficult to achieve good separation when separating the molten glass lump from the molten glass stream. There was a problem of becoming.

  In order to solve such a problem, a glass having a viscosity suitable for molding at a low temperature is required. Such glass not only has a low molten glass molding temperature, but also lowers the glass transition temperature. Therefore, it is possible to produce an optical element having a relatively complicated shape such as an aspherical lens with high productivity without using grinding or polishing. It is also suitable for precision press molding that can be originally provided.

  This invention is made | formed in view of the said situation, and it aims at providing the low dispersion optical glass suitable for shape | molding high quality glass from molten glass, and also suitable for precision press molding.

  Another object of the present invention is to provide a press-molding preform made of the glass and a production method thereof, and to provide an optical element made of the glass and a production method thereof.

The present invention for achieving the above object
(1) a fluorophosphate glass,
As an essential cation component, P ⁵⁺ and Al ³⁺ , two or more divalent cation components (R ²⁺ ) selected from Mg ²⁺ , Ca ²⁺ , Sr ²⁺ and Ba ²⁺ , and Li ⁺ are included,
In cation% display,
P ⁵⁺ 10-45%,
Al ³⁺ 5-30%,
Mg ²⁺ 0-20%,
Ca ²⁺ 0-25%,
Sr2 ⁺ 0-30%,
Ba ^{2+ 0 to} 33%,
Li ⁺ 25% or less,
Na ⁺ 0-10%,
K ⁺ 0-10%,
Y ³⁺ 0-5%,
B ³⁺ 0-15%,
And containing
A molar ratio of the content of F ^{− to} the total amount of F ⁻ and O ^{2 −} is F ⁻ / (F ⁻ + O ^{2 −} ) having a fluorophosphate glass of 0.25 to 0.85,
The refractive index (Nd) is 1.40 to 1.58, the Abbe number (νd) is 67 to 90, the glass transition temperature is 470 ° C. or lower, and the temperature indicating the viscosity of 30 dPa · s is 700 ° C. or lower. Optical glass,
(2) Optical glass as described in said (1) containing 1-30 cation% Li ^<+> .
(3) The optical glass according to (1) or (2), which is used for precision press molding,
(4) A preform for press molding comprising the optical glass according to any one of (1) to (3) above,
(5) A preform for press molding according to the above (4), comprising a fluorophosphate optical glass having a glass transition temperature of 450 ° C. or lower, and used for precision press molding,
(6) The preform for press molding according to the above (4) or (5), wherein the entire surface is a surface formed by solidifying molten glass.
(7) The preform according to any one of (4) to (6) above, in which molten glass is flown out of a pipe, a molten glass lump having a desired weight is separated, and the glass is cooled by the glass. A method for producing a press-molding preform, characterized in that
(8) The method for producing a preform for press molding according to (7) above, wherein the preform surface is removed by etching after the preform is molded,
(9) The method for producing a preform for press molding according to (7), wherein the preform surface is removed by polishing after the preform is molded,
(10) A glass molding is produced by molding molten glass, and the glass molding is machined to produce the preform described in (4) or (5) above. Renovation manufacturing method,
(11) An optical element comprising the optical glass according to any one of (1) to (3) above,
(12) The preform described in any of (4) to (6) above or the preform prepared by the method described in any of (7) to (10) above is heated and precision press-molded. A method for producing an optical element,
(13) The optical element manufacturing method according to (12) above, wherein the preform is introduced into a press mold, the press mold and the preform are heated together, and precision press molding is performed, and (14) preheating The method for producing an optical element according to (12) above, wherein a heated preform is introduced into the pressed mold and precision press molding is performed.
It consists of

ADVANTAGE OF THE INVENTION According to this invention, the low dispersion optical glass suitable for shape | molding high quality glass from molten glass, and also suitable for precision press molding can be provided.
Moreover, the preform for press molding consisting of the said glass and its manufacturing method can be provided, and the optical element consisting of the said glass and its manufacturing method can be provided.

It is the schematic of the precision press molding apparatus used in the Example of this invention.

[Optical glass]
The first aspect of the optical glass of the present invention (referred to as optical glass I) is a divalent cation component selected from P ⁵⁺ and Al ³⁺ and Mg ²⁺ , Ca ²⁺ , Sr ²⁺ and Ba ²⁺ as essential cation components. (R ²⁺ ) containing 2 or more types and Li ⁺ ,
P ⁵⁺ 10-45%,
Al ³⁺ 5-30%,
Mg ²⁺ 0-20%,
Ca ²⁺ 0-25%,
Sr2 ⁺ 0-30%,
Ba ^{2+ 0 to} 33%,
Li ⁺ 1-30%,
Na ⁺ 0-10%,
K ⁺ 0-10%,
Y ³⁺ 0-5%,
B ³⁺ 0-15%,
And containing
A molar ratio of the content of F− to the total amount of F ⁻ and O ²⁻ F ⁻ / (F ⁻ + O ²⁻ ) is fluorinated glass having a ratio of 0.25 to 0.85,
The refractive index (N _d ) is 1.40 to 1.58, and the Abbe number (ν _d ) is 67 to 90.

The optical glass I of the present invention preferably contains two or more of Ca ²⁺ , Sr ²⁺ and Ba ²⁺ as the divalent cation component (R ²⁺ ).
The optical glass I of the present invention preferably has a total content of 1 cation% or more of Mg ²⁺ , Ca ²⁺ , Sr ²⁺ and Ba ²⁺ which are divalent cation components (R ²⁺ ), Mg ²⁺ , Ca More preferably, the contents of ²⁺ , Sr ²⁺ and Ba ²⁺ are each 1 cation% or more.

  Hereinafter, the composition of the optical glass I will be described in detail. The ratio of each cation component is expressed as a cation% based on the molar ratio, and the ratio of each anion component is also expressed as an anion% based on the molar ratio. And

In the optical glass I, the molar ratio F ⁻ / (F ⁻ + O ²⁻ ) to the total amount of F ⁻ and O ²⁻ is 0.50 to 0.85, and the Abbe number (ν _d ) is 75. To 90 optical glass Ia and a molar ratio F ⁻ / (F ⁻ + O ^{2 −} ) of 0.25 to 0.50 (excluding 0.50) and an Abbe number (ν _d ) of 67 to 75 ( However, except for 75), it is roughly divided into optical glass Ib, and the preferred content range of each cation component in obtaining these optical glasses Ia and Ib is different between optical glass Ia and optical glass Ib.

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 10 to 45%. In the case of obtaining the optical glass Ia, 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 ⁺ when obtaining the optical glass Ib 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 volatile, which hinders stable production and is preferably introduced as a phosphate.

Al ³⁺ is a component that improves the stability of the fluorophosphate glass. If it is less than 5%, the stability is lowered, and if it exceeds 30%, the glass transition temperature (T _g ) and the liquidus temperature (LT) are greatly increased. For this reason, since the molding temperature rises and striae due to surface volatilization at the time of molding occurs strongly, a homogeneous glass molded body, particularly a press molding preform cannot be formed. Therefore, the amount is 5 to 30%. In the case of obtaining the optical glass Ia, 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 the optical glass Ib is 5 to 20%, more preferably 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 Mg ²⁺ and Ba ²⁺ particularly lower the stability. However, since Ba ²⁺ is a component capable of realizing a high refractive index while maintaining low dispersion, it is preferably introduced in a large amount within a range not impairing stability. Therefore, the amount of Mg ²⁺ is 0 to 20%, but when obtaining the optical glass Ia, the amount of Mg ²⁺ is preferably 1 to 20%, more preferably 3 to 17%, and further preferably 3 to 15%. More preferably, 5 to 15%, particularly preferably 5 to 10%, and when obtaining the optical glass Ib, the amount of Mg ²⁺ is preferably 0 to 15%, more preferably 0 to 12%, still more preferably. 1 to 10%.

Moreover, although the amount of Ca < ²⁺ > is 0 to 25%, when obtaining the optical glass Ia, the amount of Ca ^<2+ > is preferably 1 to 25%, more preferably 3 to 24%, still more preferably 3 to 20%. Further, it is more preferably 5 to 20%, particularly preferably 5 to 16%, and when obtaining the optical glass Ib, the amount of Ca ²⁺ is preferably 0 to 15%, more preferably 1 to 10%.

Furthermore, although the amount of Sr ²⁺ is 0 to 30%, when obtaining the optical glass Ia, the amount of Sr ²⁺ is preferably 1 to 30%, more preferably 5 to 25%, still more preferably 7 to 25%. More preferably, it is 8 to 23%, still more preferably 9 to 22%, particularly preferably 10 to 20%. When obtaining the optical glass Ib, the amount of Sr ²⁺ is preferably 0 to 15%, more preferably Is 1 to 15%, more preferably 1 to 10%.

The amount of Ba ²⁺ is 0 to 33%, but when obtaining the optical glass Ia, the amount of Ba ²⁺ is preferably 0 to 30%, more preferably 0 to 25%, still more preferably 1 to 25%, and more. More preferably 1 to 20%, still more preferably 3 to 18%, still more preferably 5 to 15%, particularly preferably 8 to 15%. When obtaining the optical glass Ib, the amount of Ba ²⁺ is preferably It 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 (T _g ) without impairing stability, but if it is less than 1%, the effect is not sufficient, and if it exceeds 30%, the durability of the glass is impaired and at the same time workability is also achieved. descend. Therefore, the amount is 1 to 30%, preferably 2 to 30%, more preferably 3 to 30%, and further preferably 4 to 30%. When obtaining the optical glass Ia, the amount of Li ⁺ is preferably 4 to 25%, more preferably 5 to 25%, still more preferably 5 to 20%. When obtaining the optical glass Ib, the amount of Li ⁺ is Preferably it is 5 to 30%, more preferably 10 to 25%.

Na ⁺ and K ⁺ have the effect of lowering the glass transition temperature (T _g ), respectively, like Li ⁺ , but at the same time, the thermal expansion coefficient tends to be larger than that of Li ⁺ . Moreover, since NaF and KF have much higher solubility in water than LiF, the water resistance is also deteriorated. Therefore, the amounts of Na ⁺ and K ⁺ are 0 to 10%, respectively. In any of the optical glasses Ia and Ib, the preferable ranges of Na ⁺ and K ⁺ are both 0 to 5%, and it is more preferable not to introduce 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 (T _g ) also greatly increases. And When obtaining the optical glass Ia, the amount of Y ³⁺ is preferably 0 to 3%, more preferably 0.5 to 3%. When obtaining the optical glass Ib, the amount of Y ³⁺ is preferably 0 to 4%. More preferably, it is 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. 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 made 0 to 15%. However, BF ₃ tends to volatilize during melting and causes striae, so in any glass of optical glass Ia, Ib, the amount is preferably 0-10%, 0-5% More preferably. When priority is given to reducing the volatility of glass, the content is preferably 0 to 0.5%, and more preferably not introduced.

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

  The optical glass I of the present invention can contain lanthanoids such as Ti, Zr, Zn, La, Gd and the like as a cation component in addition to the above-described cation component as long as the object of the present invention is not impaired.

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 optical glasses Ia and Ib, the amount of Si ⁴⁺ is preferably 0 to 10%, more preferably 0 to 8%, and further preferably 0 to 5%. .

As the ratio of the anion component, in order to obtain an optical glass having excellent stability while realizing desired optical characteristics, the molar ratio of the content of F− to the total amount of F ⁻ and O ²⁻ F ⁻ / (F ⁻ + O ²⁻ ) is set to 0.25 to 0.85, but is set to 0.50 to 0.85 in the optical glass Ia, and 0.25 to 0.50 (however, 0.50 in the optical glass Ib). ), Preferably 0.27 to 0.45, more preferably 0.3 to 0.45. Moreover, in any of the optical glasses Ia and Ib, the total amount of F ⁻ and O ²⁻ in the anion is preferably 100%.

The optical glass I of the present invention has a refractive index (N _d ) of 1.40 to 1.58 and an Abbe number (ν _d ) of 67 to 90, preferably 70 to 90. In the optical glass Ia, the Abbe number (ν _d ) is 75 to 90, preferably 78 to 89. In the optical glass Ib, the Abbe number (ν _d ) is 67 to 75 (however, excluding 75). ).
The optical glass I of the present invention exhibits high transmittance in the visible light region except when a colorant is added. The optical glass of the present invention has a transmittance at a wavelength of 400 nm to 2000 nm (excluding reflection loss on the sample surface) 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. ) Exhibits a light transmittance characteristic of 80% or more, preferably 95% or more.

Since the optical glass I of the present invention contains a predetermined amount of Li ⁺ , its glass transition temperature (T _g ) is 470 ° C. or lower, preferably 430 ° C. or lower.
In addition, since the optical glass I of the present invention positively contains Li ⁺ among alkali metal ions, the coefficient of thermal expansion is relatively small and the water resistance is relatively excellent. Accordingly, the glass surface can be polished and processed into a press-molding preform, or the optical element can be processed into a smooth and high-quality glass surface.

  Since the optical glass I of the present invention exhibits excellent water resistance and chemical durability, the surface of the preform is altered even if it is stored for a long period from the preparation of the press molding preform to the press molding. There is nothing. 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 optical glass I of the present invention, the glass melting temperature can be lowered by about 50 ° C. compared to a glass having an optical constant equivalent to that of the optical glass I of the present invention and not containing Li, Problems such as coloring of glass, mixing of bubbles and striae due to platinum melting from the container during melting 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 weight 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 optical glass I of the present invention lowers the temperature suitable for molding molten glass, so that the temperature exhibiting a predetermined viscosity is lower than that of a conventional fluorophosphate glass. The composition is determined. 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. The glass composition is adjusted so that the glass transition temperature is in the above range.

In addition, by lowering the glass transition temperature, it is possible to reduce the heating temperature of the glass in preform press molding, particularly precision press molding, and the reaction between the glass and the press mold is alleviated. It is also possible to obtain an effect such as extending the life.
Therefore, the optical glass I of the present invention is suitable as a glass material for press molding, particularly as a glass material for precision press molding.
The optical glass of the present invention uses phosphate raw materials, fluoride raw materials, and these raw materials are weighed, prepared and supplied to a platinum alloy melting vessel, heated, melted, clarified, homogenized, It can be obtained by flowing out of a pipe and molding.

Next, a second embodiment (referred to as optical glass II) of the optical glass of the present invention will be described.
The optical glass II of the present invention is a fluorophosphate glass, and is characterized in that a temperature showing a viscosity of 30 dPa · s is 700 ° C. or lower.

Also in the optical glass II, a glass containing 1 to 30 cation% Li ⁺ is preferred, a glass containing 2 to 30 cation% Li ⁺ is more preferred, and a glass containing 3 to 30 cation% Li ⁺ is more preferred, Even more preferred is a glass containing 4-30 cation% Li ⁺ .

  The preferred glass composition and optical constant of the optical glass II are the same as the glass composition and optical constant of the optical glass I. Accordingly, the types of glass components suitable for the optical glass II, their contents, optical constants, and other characteristics are also the same as those of the glass components of the optical glass I described above, their contents, optical constants, and other characteristics. To do. The optical glass II may not necessarily satisfy all the requirements for the types and contents of each glass component of the optical glass I, but any of the types of glass components constituting the optical glass I and the contents thereof. It is preferable to satisfy the requirements, and it is more preferable to satisfy all the requirements.

  According to the optical glass II of the present invention, problems such as stringing and striae during molding of molten glass are solved.

  The stringing at the time of molding can be eliminated by increasing the preform molding temperature (the temperature of the glass immediately after flowing out) and decreasing the viscosity of the glass. On the other hand, in order to reduce or prevent striae during molding, it is better to lower the preform molding temperature. Conventional fluorophosphate glasses have difficulty meeting these two requirements. However, the present inventors have found that the lower limit of the preform molding temperature (the temperature of the glass immediately after flowing out) that can prevent stringing corresponds to a temperature indicating a viscosity of 30 dPa · s. By providing an optical glass having a temperature of 700 ° C. or lower, it is possible to reduce and prevent the occurrence of striae while preventing stringing.

  In the optical glass I, a glass having a viscosity of 30 dPa · s is preferably 700 ° C. or lower, and a glass having a viscosity of 30 dPa · s is preferably 680 ° C. or lower for both the optical glasses I and II.

[Preform for press molding and its manufacturing method]
The first aspect (referred to as preform I) of the press-molding preform of the present invention is characterized by comprising the optical glass of the present invention described above.

  Here, the press-molding preform is obtained by pre-molding glass having a weight equal to the weight of the press-molded product into a shape suitable for press molding.

  For example, when producing a press-molded product that has one rotational symmetry axis such as a lens and is symmetric with respect to an arbitrary rotation angle around this symmetry axis, the shape of the preform also has one rotational symmetry axis. It is preferable that it is symmetrical with respect to an arbitrary rotation angle around this symmetry axis, or spherical. Also, during press molding, press molding is performed in a state where atmospheric gas is confined between the molding surface of the press mold and the preform surface, so that the accuracy of the shape of the press molded product does not deteriorate. It is desirable to determine the curvature in consideration of the curvature of the molding surface of the press mold. The press molding preform of the present invention is particularly suitable for precision press molding. When used as a precision press-molding preform, various known films having a function for allowing the glass to sufficiently spread in the press mold during precision press molding and various known films for improving mold release properties are used. It may be formed on the entire surface of the preform.

  The second aspect of the press molding preform of the present invention (referred to as Preform II) is made of a fluorophosphate optical glass having a glass transition temperature of 450 ° C. or lower, and is used for precision press molding. It is what. In the preform II of the present invention, the glass transition temperature is preferably 440 ° C. or less, more preferably 430 ° C. or less, further preferably 420 ° C. or less, and even more preferably 410 ° C. or less. Preferably, the temperature is 400 ° C. or lower.

  The fluorophosphate glass is generally a glass having a low glass transition temperature, but the fluorophosphate glass constituting the preform II is a glass having a particularly low glass transition temperature. Up to now, fluorophosphate glass is generally a glass with a low glass transition temperature, so it was considered to be a glass that does not particularly hinder precision press molding, but it produces optical elements with high yield by precision press molding. It was difficult. This is because the glass transition temperature of a general fluorophosphate glass is more than 460 ° C. and not more than 600 ° C., but such a fluorophosphate glass has a narrow temperature range suitable for precision press molding. This is because if the temperature of the glass at the time of press molding is slightly lowered, the glass is cracked. On the other hand, if the temperature is slightly elevated, the glass is foamed and a high-quality optical element cannot be obtained.

  On the other hand, according to the preform II of the present invention, since the glass transition temperature is suppressed to 450 ° C. or lower, the temperature setting range at the time of precision press molding can be widened, and an optical element free from cracks and foaming Can be produced stably.

  Furthermore, the annealing temperature after precision press molding can be kept low by lowering the glass transition temperature. Since the optimum temperature during annealing is in the range of −10 to −50 ° C. with respect to the glass transition temperature, it changes in conjunction with the glass transition temperature. When the annealing temperature is high, some of the fluorine present on the surface of the precision press-molded product is replaced with oxygen in the atmosphere, and the refractive index of the optical element surface increases slightly. This phenomenon is caused by the high and low annealing temperatures. It will be influenced. When an optical multilayer film such as an antireflection film is formed on an optical element, the actual optical multilayer film coating is optimal due to the refractive index change of the surface layer, even if the optical multilayer film is optimally designed according to the optical characteristics of the glass. It will deviate from anything.

However, by using the preform II of the present invention, the annealing temperature can be lowered, the substitution of fluorine and oxygen can be suppressed, and the refractive index of the optical element surface can be kept unchanged. Based on the characteristics, the design of the optical multilayer film can be optimized. Furthermore, the temperature during precision press molding can be lowered by using Preform II, so the time required for temperature rise of the preform before precision press molding and temperature drop of the glass molded product after precision press molding is shortened. And productivity can be improved. In the preform II of the present invention, in order to suppress the glass transition temperature to 450 ° C. or less, it is preferable to introduce Li cations as a glass component, and it is more preferable that the amount introduced be 1 to 30 cations. Further, F ^- and ^{O 2-F} to the total amount of ^- the molar ratio ^F of the content of ^{- / (F - + O 2-} ) that determines the distribution of anionic components such that 0.25 to 0.85 desirable. In addition, the fluorophosphate optical glass constituting the preform II of the present invention preferably has any requirement regarding the constituent components of the optical glass I of the present invention, and more preferably has all the requirements.

Preform II is preferably one having the structure of Preform I, that is, one made of the optical glass of the present invention.
The entire surfaces of the preforms I and II are preferably surfaces formed by solidifying molten glass.

  By forming preforms I and II with fluorophosphate glass having a transmittance characteristic that the external transmittance is 80% or more in the entire wavelength range of 370 to 700 nm when converted to a thickness of 10 mm, lenses, prisms, and diffraction gratings A colorless and transparent optical element suitable for such an optical element can be manufactured by precision press molding.

Next, the manufacturing method of the press molding preform of this invention is demonstrated.
According to a first aspect of the method for producing a press-molding preform of the present invention (preform production method I), molten glass is flown out of a pipe, a molten glass lump having a desired weight is separated, and the glass lump is separated. In the process of cooling the glass, it is formed into a preform made of the above-described optical glass of the present invention.

The production of the molten glass is as described above. The molten glass is continuously discharged at a constant flow rate from a platinum alloy or platinum pipe heated to a predetermined temperature by an electric heating method, a high frequency induction heating method, or a heating method combining these two heating methods. The molten glass lump having a weight obtained by adding the weight of one preform or the weight of one preform to the weight of the removal portion described later is separated from the molten glass that has flowed out. When separating the molten glass lump, it is desirable to avoid the use of a cutting blade so as not to leave a cut mark. For example, the molten glass is dropped from the outlet of the pipe, or the molten glass flow tip flowing out is supported by the support. It is preferable to use a method in which the molten glass lump is separated from the front end of the molten glass flow by using the surface tension of the molten glass by suddenly dropping the support at a timing at which the molten glass lump of the target weight can be separated.
In the case of glass having a viscosity of 30 dPa · s and a temperature of 700 ° C. or lower, no stringing phenomenon was observed due to the separation of the molten glass lump even when the glass outflow temperature was 700 ° C. or lower.

  The separated molten glass lump is formed into a desired shape in the process of cooling the glass on the recess of the preform mold. At that time, in order to prevent wrinkles on the preform surface or breakage in the glass cooling process called can cracking, it is preferable to mold the glass lump in a state of being lifted by applying upward wind pressure to the glass block.

After the temperature of the glass is lowered to a temperature range that does not deform even when an external force is applied to the preform, the preform is taken out from the preform mold and gradually cooled.
In order to reduce the volatilization of fluorine from the glass surface, it is preferable to perform glass outflow and preform molding in a dry atmosphere (dry atmosphere having a dew point of −50 ° C. or lower).

The optical glass of the present invention described above is less likely to cause striae, but when the striae slightly occur on the preform surface, the striae are localized in the preform surface layer, so that the surface layer is etched or polished. Can be removed and finished into an optically highly homogeneous preform without striae.
When the etching is performed, the preform is immersed in an acid or alkali etching solution, or the etching solution is uniformly applied to the preform surface to remove the surface layer on the entire surface of the preform. After etching, the preform is washed and dried.

Even when the surface layer is removed by polishing, it is desirable to remove the surface layer over the entire surface of the preform. The polishing process is suitable for a spherical preform or a preform having a flat surface, and the etching can correspond to various shapes regardless of the shape.
In both cases of etching and polishing, it is desirable to separate a molten glass lump having a weight added to the weight of the preform to be removed and to achieve the target weight after the surface layer is removed.

  A second aspect of the method for producing a press-molding preform of the present invention (preform production method II) is a method of forming a glass molded body by molding a molten glass, and machining the glass molded body. It is the manufacturing method of the preform for press molding which produces the preform which consists of optical glass of invention.

  Here, the production of the molten glass is as described above. The method of removing the entire surface of the preform in the manufacturing method I of the preform by polishing also corresponds to the manufacturing method II of the preform for machining the glass molded body. Here, a method other than that described in the preform manufacturing method I will be described.

  First, molten glass is continuously discharged from the pipe and poured into a mold disposed below the pipe. As the mold, a flat bottom and a side wall that surrounds the bottom from three sides and one side of which is open are used. The side walls that sandwich the opening side and bottom from both sides face each other in parallel, and the mold is placed, fixed, and poured into the mold so that the center of the bottom is positioned vertically below the pipe and the bottom is horizontal. The molten glass is spread so as to have a uniform thickness in the region surrounded by the side walls, and after cooling, the glass is drawn out horizontally from the opening on the side surface of the mold at a constant speed. The drawn glass molded body is sent into an annealing furnace and annealed. In this way, a plate-like glass molded body made of the optical glass of the present invention having a certain width and thickness is obtained.

  Next, the plate-like glass molded body is cut or cleaved and divided into a plurality of glass pieces called cut pieces, and these glass pieces are ground and polished to finish a preform for press molding with a target weight.

As another method, a mold having a cylindrical through-hole is disposed and fixed vertically below the pipe so that the central axis of the through-hole faces the vertical direction. At this time, it is preferable to arrange | position a casting_mold | template so that the central axis of a through-hole may be located in the vertically downward direction of a pipe. Then, molten glass is poured from the pipe into the mold through-hole at a constant flow rate to fill the through-hole with glass, and the solidified glass is drawn vertically downward from the lower end opening of the through-hole at a constant speed and gradually cooled. A cylindrical rod-shaped glass molded body is obtained. After annealing the glass molded body thus obtained, a plurality of glass pieces are obtained by cutting or cleaving from a direction perpendicular to the central axis of the cylindrical bar. Next, the glass piece is ground and polished to finish a preform for press molding with a desired weight.
Preform production methods I and II are suitable as a method for producing a preform for precision press molding because a preform having high quality and high weight accuracy can be produced.

[Optical element and manufacturing method thereof]
The optical element of the present invention is characterized by comprising the optical glass of the present invention. Since the optical element of the present invention is made of the above-described optical glass of the present invention, an optical element utilizing low dispersion characteristics can be provided. Moreover, since it consists of glass excellent in water resistance and chemical durability, it is possible to provide an optical element that does not cause problems such as clouding of the surface even after long-term use.

  The type and shape of the optical element are not particularly limited, but are suitable for aspherical lenses, spherical lenses, microlenses, lens arrays, prisms, diffraction gratings, prisms with lenses, lenses with diffraction gratings, and the like. Specific examples of the aspherical lens and the spherical lens include a convex meniscus lens, a concave meniscus lens, a biconvex lens, a biconcave lens, a planoconvex lens, and a planoconcave lens.

From the viewpoint of application, it is suitable for an optical element constituting an imaging system, for example, a digital camera lens, a camera lens for a camera-equipped mobile phone, an optical pickup lens, a collimator lens, and the like.
If necessary, an optical thin film such as an antireflection film may be formed on the surface of the optical element.

Next, the manufacturing method of the optical element of this invention is demonstrated.
The optical element of the present invention is characterized by heating and precision press-molding a press-molding preform produced by the press-molding preform of the present invention or the press-molding preform of the present invention. is there.

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.

According to the method for producing an optical element of the present invention, it is possible to produce an optical element having any of the above optical characteristics, and since the glass transition temperature (T _g ) is low, the press molding temperature can be lowered. Damage to the molding surface of the press mold can be reduced, and the life of the mold can be extended. Further, since the glass constituting the preform has high stability, devitrification of the glass can be effectively prevented even in the reheating and pressing steps. Furthermore, a series of steps for obtaining a final product from glass melting can be performed with high productivity.

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 preferable, and a carbon-containing film or the like can be used as the release film. In view of durability and cost, a carbon film is particularly preferable.
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.

  The above is the method for manufacturing the optical element of the present invention. In addition to the method described above, for example, the glass molded body is formed by flowing out the molten glass, annealed, and then machined to manufacture the optical element of the present invention. You can also For example, the cylindrical rod-shaped glass molded body described above can be sliced from a direction perpendicular to the cylinder axis, and the obtained cylindrical glass can be ground and polished to produce optical elements such as various lenses.

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

  As the glass raw material, phosphates and fluorides corresponding to the respective glass components are used, and the raw materials are weighed so that the glass has the composition shown in Table 1 and mixed sufficiently, and then put into a platinum crucible. The mixture was heated and melted in the air over 1 to 3 hours while stirring in the temperature range of 850 to 950 ° C. in an electric furnace. The homogenized and clarified glass melt was cast into a 40 × 70 × 15 mm carbon mold. The cast glass is allowed to cool to the transition temperature and immediately put in an annealing furnace, annealed for 1 hour near the transition temperature, and gradually cooled to room temperature in the annealing furnace, as shown in Table 1-1 and Table 1-2. Each optical glass was obtained.

When each obtained glass was magnified and observed with a microscope, no precipitation of crystals or unmelted raw material was observed.
About the obtained optical glass, the refractive index (N _d ), Abbe number (ν _d ), glass transition temperature (T _g ), and temperature showing a viscosity of 30 dPa · s were measured as follows. It is shown in 1.
(1) Refractive index (N _d ) and Abbe number (ν _d )
It measured about the optical glass obtained by making slow cooling temperature-fall rate -30 degreeC / hour.
(2) Glass transition temperature (T _g )
The temperature was increased by a thermomechanical analyzer (Thermo Plus TMA 8310) manufactured by Rigaku Denki Co., Ltd. at a heating rate of 4 ° C./min.
(3) Temperature showing a viscosity of 30 dPa · s The measuring method is as follows.
The viscosity was measured using a coaxial double-rotating cylindrical rotational viscometer (manufactured by Tokyo Kogyo Co., Ltd., high-temperature viscosity measuring device RHEOTRONIC II (improved type)) according to the viscosity measuring method of JIS standard Z8803. In obtaining the temperature indicating the viscosity of 30 dPa · s, the temperature of each glass is changed, the viscosity at each temperature is measured, and a graph showing the relationship between the viscosity and the temperature is created. The method of reading the temperature which shows the viscosity of this is simple.

  As shown in Table 1-1 and Table 1-2, each optical glass has a desired refractive index, Abbe number, and glass transition temperature, exhibits excellent low-temperature softening properties and meltability, and is used for precision press molding. It was suitable as an optical glass.

  Next, the clarified and homogenized molten glass having each composition shown in Table 1-1 and Table 1-2 was temperature-adjusted to a temperature range in which stable outflow was possible without devitrification of the glass. The weight of the target preform by a method in which the molten glass flows out from a platinum alloy pipe at a constant flow rate and supports the molten glass flow tip using a drop or a support, and then the support is rapidly lowered to separate the glass lump. The molten glass ingot was separated. Next, each of the obtained molten glass lumps was received in a receiving mold having a gas outlet at the bottom, and gas was ejected from the gas outlet and molded while the glass lumps were floated to prepare a press molding preform. The shape of the preform was made spherical or flat spherical by adjusting and setting the separation interval of the molten glass. The weights of the obtained preforms precisely matched the set values, and all of the preforms had a smooth surface.

  Next, in order to ensure that no striae remain in the preform, the entire preform that has been molded and annealed is immersed in an etching solution comprising a hydrochloric acid solution to remove the entire surface layer of the preform, washed, dried, and optically Homogeneous preform was obtained.

  As another method, the entire surface of the molded spherical preform was polished by a known method, and the entire surface layer was removed to obtain an optically homogeneous preform.

  Separately, molten glass is cast into a mold, formed into a plate-like glass or cylindrical rod shape, annealed, and then the surface of the glass piece obtained by cutting the glass is ground and polished, so that the entire surface is smooth. Got a renovation.

The preform obtained as described above was precision press-molded using the press apparatus shown in FIG. 1 to obtain an aspheric lens. Specifically, after the preform 4 is placed between the lower mold 2 and the upper mold 1 of the press mold composed of the upper mold 1, the lower mold 2 and the body mold 3, the inside of the quartz tube 11 is placed in a nitrogen atmosphere to form a heater 12. Was energized to heat the inside of the quartz tube 11. The temperature inside the press mold is set to a temperature at which the glass to be molded exhibits a viscosity of 10 ⁸ to 10 ¹⁰ dPa · s, and while maintaining the same temperature, the push bar 13 is lowered and the upper mold 1 is pressed to form. The preform set in the mold was pressed. The press pressure was 8 MPa, and the press time was 30 seconds. After pressing, the pressure of the press is released, and the glass molded product that has been press-molded is kept in contact with the lower mold 2 and the upper mold 1 until the viscosity of the glass reaches 10 ¹² dPa · s or more. It was cooled and then rapidly cooled to room temperature, and the glass molded product was removed from the mold and an aspherical lens was obtained. The obtained aspherical lens had extremely high surface accuracy.

  In FIG. 1, reference numeral 9 is a support rod, reference numeral 10 is a lower mold, a barrel holder, and reference numeral 14 is a thermocouple.

  An aspherical lens obtained by precision press molding was provided with an antireflection film as required.

Next, the same preform as the above preforms was precision press-molded by a method different from the above method. In this method, first, the preform was preheated to a temperature at which the viscosity of the glass constituting the preform was 10 ⁸ dPa · s while the preform floated. On the other hand, a press mold having an upper mold, a lower mold, and a body mold is heated to a temperature at which the glass constituting the preform exhibits a viscosity of 10 ⁹ to 10 ¹² dPa · s, and the preheated preform is pressed. It was introduced into the mold cavity and precision press-molded 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 lens had extremely high surface accuracy.

An aspherical lens obtained by precision press molding was provided with an antireflection film as required.
In this way, a glass optical element with high internal quality could be obtained with high productivity and high accuracy.

  According to the present invention, it is possible to obtain an optical glass having a low dispersion and a low glass transition temperature and capable of precision press molding, and having a low-temperature softening property. Optical elements such as various lenses can be manufactured.

DESCRIPTION OF SYMBOLS 1 ... Upper type | mold 2 ... Lower type | mold 3 ... Body type | mold 4 ... Preform 9 ... Supporting rod 10 ... Lower type | mold, body type | mold holder 11 ... Quartz tube 12 ... Heater 13 ... Push rod 14 ... Thermocouple

Claims (14)

A fluorophosphate glass,
As an essential cation component, P ⁵⁺ and Al ³⁺ , two or more divalent cation components (R ²⁺ ) selected from Mg ²⁺ , Ca ²⁺ , Sr ²⁺ and Ba ²⁺ , and Li ⁺ are included,
In cation% display,
P ⁵⁺ 10-45%,
Al ³⁺ 5-30%,
Mg ²⁺ 0-20%,
Ca ²⁺ 0-25%,
Sr2 ⁺ 0-30%,
Ba ^{2+ 0 to} 33%,
Li ⁺ 25% or less,
Na ⁺ 0-10%,
K ⁺ 0-10%,
Y ³⁺ 0-5%,
B ³⁺ 0-15%,
And containing
A molar ratio of the content of F ^{− to} the total amount of F ⁻ and O ^{2 −} is F ⁻ / (F ⁻ + O ^{2 −} ) having a fluorophosphate glass of 0.25 to 0.85,
The refractive index (Nd) is 1.40 to 1.58, the Abbe number (νd) is 67 to 90, the glass transition temperature is 470 ° C. or lower, and the temperature indicating the viscosity of 30 dPa · s is 700 ° C. or lower. Optical glass characterized. The optical glass of claim 1, comprising 1-30 cation% Li ⁺ .   The optical glass according to claim 1 or 2, which is used for precision press molding.   A preform for press molding comprising the optical glass according to any one of claims 1 to 3. The preform for press molding according to claim 4, which is made of a fluorophosphate optical glass having a glass transition temperature of 450 ° C or lower and is used for precision press molding.   The preform for press molding according to claim 4 or 5, wherein the entire surface is a surface formed by solidifying molten glass.   The molten glass is flowed out from the pipe, a molten glass lump having a desired weight is separated, and the glass lump is molded into the preform according to any one of claims 4 to 6 in the process of cooling the glass. A method for producing a press-molding preform.   The method for producing a press-molding preform according to claim 7, wherein the preform surface is removed by etching after molding the preform.   The method for producing a press-molding preform according to claim 7, wherein the preform surface is removed by polishing after the preform is molded.   A method for producing a preform for press molding, comprising forming a glass molded body by molding a molten glass, and machining the glass molded body to produce the preform according to claim 4 or 5.   An optical element comprising the optical glass according to claim 1.   A method for producing an optical element, wherein the preform produced by the preform according to any one of claims 4 to 6 or the preform produced by the method according to any one of claims 7 to 10 is heated and precision press-molded.   The optical element manufacturing method according to claim 12, wherein the preform is introduced into a press mold, the press mold and the preform are heated together, and precision press molding is performed.   The method for producing an optical element according to claim 12, wherein the heated preform is introduced into a preheated press mold and precision press molding is performed.

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