JP2007091537A - Near-infrared light absorbing glass material lot and method for manufacturing optical element by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a near-infrared light absorbing glass material lot which can realize high performance glass optical elements each having a near-infrared light absorbing function. <P>SOLUTION: In the near-infrared light absorbing glass material lot comprising near-infrared light absorbing glass blanks containing copper, each glass material constituting the lot is characterized in that the tolerance of refractive index (n<SB>e</SB>) at a wavelength of 546.07 nm is >-0.001 and <0.01. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a near-infrared light absorbing glass material lot suitable for color correction of a semiconductor imaging device, and an optical element manufacturing method using the glass material lot.

In order to perform color correction by blocking near-infrared light incident on a semiconductor image sensor such as a CCD or CMOS, a filter made of copper-containing glass that absorbs near-infrared light is used. Such glass is disclosed in Patent Document 1, for example.
Japanese Patent Laid-Open No. 10-194777

  2. Description of the Related Art In recent years, mobile devices equipped with an imaging device such as a camera-equipped mobile phone have been required to reduce the size of the imaging optical system. Such an imaging optical system includes a lens system for forming an image of a subject on the light receiving surface of the imaging element, and the color correction filter described above. Here, if a part of the lens system is formed of near-infrared light absorbing glass, the lens function and the color correction function can be combined with a single lens, so the number of parts is reduced, and the imaging optical system is further reduced. Can be downsized.

  However, conventional near infrared light absorbing glass was not manufactured for the purpose of molding into a lens, but it was assumed that it was processed into a flat plate and used as a filter. The accuracy of the refractive index (nd) is at most 4 digits (3 digits after the decimal point), that is, ± 0.001 when the variation in the refractive index (nd) between the glass materials for making the optical element is shown by tolerance. That was all. However, in lens applications, if the accuracy of the refractive index is not high no matter how precise the lens shape is, the performance as a lens must be insufficient. In particular, there is a problem that even if an aspherical lens effective for high performance and miniaturization of the optical system is made of the glass, the performance as an aspherical lens cannot be utilized.

  Until now, for small image pickup devices such as camera-equipped mobile phones, priority has been given to downsizing, and user demand for image quality has not been strong. However, due to the widespread use of camera-equipped mobile phones and the high-definition of digital still camera images, the digital signal transmission speed, and the remarkable improvement in processing speed, users can achieve high-definition even for mobile devices such as camera-equipped mobile phones. I want to have a good image quality. Specifically, a high-definition image pickup device having several hundred thousand to over one million pixels has been mounted on a mobile device.

  An image pickup apparatus equipped with such an image pickup device having a high number of pixels requires an image pickup optical system suitable for the performance of the image pickup device.

  The present invention aims to solve the above-mentioned problems, and a near-infrared light absorbing glass material lot capable of realizing a high-performance glass optical element having a near-infrared light absorption function, and an optical element from the glass material lot. It is an object of the present invention to provide a method for manufacturing an optical element for mass production.

The present invention has been made in order to achieve the above-described object, and provides the following (1) to (12).
(1) In a near-infrared light absorbing glass material lot made of a near-infrared light absorbing glass material containing copper,
A near-infrared light-absorbing glass material lot, characterized by being composed of a glass material having a refractive index (n _e ) tolerance of less than ± 0.001 at a wavelength of 546.07 nm.
(2) Tolerance of refractive index (n _e) is a tolerance of refractive index of the glass material while cooling to 25 ° C. at 30 ° C. / hour or less in a predetermined temperature lowering rate from the glass transition temperature (n _e), The near-infrared light absorbing glass material lot described in (1) above.
(3) The near-infrared light absorbing glass material lot according to (1) or (2) above, wherein the glass material is fluorine-containing glass.
(4) The near-infrared light absorbing glass material lot according to the above (1) or (2), wherein the glass material is a preform for press molding.
(5) The near-infrared light absorbing glass material lot according to (1) or (2), wherein the glass material is a glass plate or a glass rod.
(6) A method for producing an optical element, characterized in that the optical element is mass-produced using the near-infrared light absorbing glass material lot described in any one of (1) to (5) above.
(7) The method for manufacturing an optical element according to (6), wherein the lens is mass-produced.
(8) The method for manufacturing an optical element according to (7), wherein the aspherical lens is mass-produced.
(9) The method for producing an optical element according to any one of (6) to (8), wherein the near-infrared light absorbing glass material lot is heated and press-molded.
(10) The method for manufacturing an optical element according to (9), wherein a press-molded product produced by press molding is machined.
(11) The method for producing an optical element according to any one of (6) to (8), wherein the near-infrared light absorbing glass material lot is heated and precision press-molded.
(12) The method for manufacturing an optical element according to any one of (6) to (8), wherein a near-infrared light absorbing glass material lot is machined.

  The present invention relates to a near-infrared light absorbing glass material lot that enables mass production of a glass optical element having a high-performance near-infrared light absorption function, and a method for manufacturing an optical element that mass-produces optical elements from the glass material lot. Makes it possible to provide.

  In an optical element whose optical function surface is a curved surface or a curved surface such as a lens, or an optical element whose optical function surfaces are non-parallel such as a prism, the shape and dimensions of the optical element, particularly the shape of the optical function surface, Even if the dimensions and the angles formed by the optical functional surfaces are precisely made, if the accuracy of the refractive index of the glass is insufficient, the performance of the optical element cannot be improved.

  The near-infrared light-absorbing glass containing copper contains a substance that is easily volatilized in a molten state (referred to as a volatile substance). Therefore, when the molten glass flows out and is molded, the volatile substance is removed from the glass by volatilization with time. Since it is lost, the refractive index of the molded glass fluctuates with time, and as a mass-produced glass, it is difficult to guarantee the refractive index with an accuracy of 4 digits or more (5 digits or more) after the decimal point.

  Due to such problems, it has been impossible to stably mass-produce optical elements such as lenses having a high-performance near-infrared light absorption function.

  In other words, until now, there has been no need to form a subject image on a high-definition semiconductor image sensor with a million pixels or more with near-infrared light absorbing glass, and near-infrared light suitable for the high-definition image sensor. It was difficult to procure a glass material having a refractive index with high accuracy even when trying to mass-produce a product made of an absorption glass and having no performance variation.

  In order to solve the above-mentioned novel problem, the present invention provides a glass material lot having a high refractive index and a method for mass-producing optical elements using the glass material lot, the details of which are described below. Explained.

[Near infrared light absorbing glass material lot]
The present invention is a near-infrared light absorbing glass material lot comprising a near-infrared light absorbing glass material containing copper.
It is characterized in that the tolerances of the refractive index at a wavelength of 546.07 nm _{(n e)} are constituted by a glass material of less than ± 0.001.

  Here, the glass material means glass which is a material for making a glass product. A lot is generally a collection of products of the same specification. Here, a specific specification, for example, a collection of a plurality of glass products exhibiting the same light transmission characteristics or near-infrared light absorption characteristics, or This means an important specification for use as a required near-infrared light absorbing glass, such as a collection of a plurality of glass products having a predetermined copper content.

The refractive index (n _e ) is a refractive index at a wavelength of 546.07 nm. The refractive index of optical glass is generally indicated by the refractive index (nd) at a wavelength of 587.56 nm, but in the near-infrared light absorbing glass containing copper, the transmittance at a wavelength of 587.56 nm is higher than the transmittance at a wavelength of 546.07 nm. In order to measure and manage the refractive index with high accuracy, it is desirable to specify and specify the refractive index by the refractive index (n _e ). Therefore, in the present invention, _ne is used as the refractive index, and hereinafter, the refractive index means the refractive index ( _ne ) unless otherwise specified.

Copper in the glass is responsible for near-infrared light absorption characteristics and exists as Cu ²⁺ . Examples of the glass exhibiting good near-infrared light absorption characteristics by introducing copper include fluorophosphate glass and phosphate glass. Similarly, copper-containing fluorophosphate glass has a feature that it has better weather resistance than copper-containing phosphate glass.

  Here, a glass material lot having a refractive index tolerance of less than ± 0.001 is a glass material having a refractive index difference of less than 0.002 between the largest and the smallest of the glass materials constituting the lot. Means a set of If the tolerance of the refractive index of the lot is ± 0.001 or more, even if mass production of optical elements with extremely high dimensional accuracy and shape accuracy is performed using this lot, the optical performance of the elements will vary greatly, and the performance will It becomes difficult to provide a stable imaging device. In order to provide an imaging apparatus having stable performance, a lot refractive index tolerance is less than ± 0.001, preferably within ± 0.0009, more preferably within ± 0.0008, and even more preferably ± 0.0005. , More preferably within ± 0.0004, still more preferably within ± 0.0003.

  The glass material lot is composed of a plurality of glass materials, and the number thereof is 2 or more. However, when mass-producing optical elements, 10 or more, or 100 or more, and even 1000 or more may be used. Good. Select a glass material from the lot and measure the refractive index of the selected glass material. The number of glass materials whose refractive index should be measured from a lot can be determined as follows.

  The molten glass accumulated in the melting vessel is slightly inhomogeneous, and when the molten glass flows out continuously, the refractive index of the flowing out glass may vary with time. Further, if the cooling rate at the time of cooling the molded glass varies, the refractive index varies. A technique for melting and molding optical glass with a refractive index determined with high accuracy, which is not colored in general, suppresses the refractive index fluctuation of the flowing out glass and makes the cooling rate of the molded glass constant. In this state, the main factor of the refractive index fluctuation is the temporal refractive index fluctuation of the outflowing glass. Therefore, in the individual glass raw materials, glass melting and molding equipment, how long it takes within the desired refractive index tolerance. Whether the glass material can be obtained or the number of samplings is increased, and the refractive index tolerance in the manufacturing conditions is grasped. Based on the data thus obtained, the number of glass materials whose refractive index is to be measured from the lot may be set.

  In an optical element whose optical function surface is a curved surface or a curved surface such as a lens, or an optical element whose optical function surfaces are non-parallel such as a prism, the shape and dimensions of the optical element, particularly the shape of the optical function surface, The required optical performance can be achieved by precisely making the dimensions and the angle formed by the optical functional surfaces and using the glass having the above refractive index accuracy.

  As described above, a mobile device equipped with an imaging device such as a camera-equipped mobile phone has come to be equipped with a high-definition image sensor having 500,000 pixels or more, or even 1 million pixels or more. In order to cope with such a device, it is not sufficient to combine the lens function and the color sensitivity correction function of the image sensor into one optical element, and it is necessary to improve the imaging performance as a lens. In order to improve the performance, it is not sufficient to increase the shape accuracy and dimensional accuracy of the lens, and it is necessary that the refractive index be defined with high accuracy regardless of which glass material is selected from the glass material lot. However, near-infrared light absorbing glass has been conventionally produced for flat filter applications, and the accuracy of the refractive index (nd) was at most 3 digits after the decimal point (4 significant digits). Such a situation is one of the reasons why the necessity of near-infrared light absorbing glass with high refractive index accuracy has not been recognized so far.

  Near-infrared light absorbing glass is prepared by adding the required copper based on fluorophosphate glass or phosphate glass, but it can be obtained from the molten glass surface, whether fluorophosphate glass or phosphate glass. Since some glass components decrease with time due to volatilization, the refractive index fluctuates.

In the near-infrared light absorbing glass, when the melting temperature is raised, Cu ²⁺ is reduced to Cu ⁺ and the glass changes from blue to green. If it does so, the characteristic required for the color-sensitivity correction | amendment of a semiconductor image pick-up element which enlarges absorption of near-infrared light, improving visible transmittance will be impaired. Therefore, it has been recommended not to leave the glass in a high temperature state for a long time. However, if a process for producing molten glass under such conditions is performed, molten glass containing a large amount of volatile substances will flow out and be molded, and the glass composition will be kept constant from the beginning to the end of the outflow of glass. And the refractive index fluctuates.

  In order to reduce such composition fluctuations due to volatilization, at least a clarification step is performed while flowing a dry gas, preferably a dry inert gas, in a closed container that accumulates glass, and in this step, volatile substances are sufficiently volatilized. Just do it. The closed container is provided with an exhaust port to exhaust the gas flowing in the container to the outside of the container. The exhausted gas is purified by a purification device and then discharged to the outside.

  By reducing the volatile substances from the glass, the content of some components, such as fluorine and alkali, decreases, but the glass raw material may be weighed and prepared in advance to compensate for the decrease. Such composition correction may be performed by performing test melting so that the refractive index of the test sample approaches the target refractive index.

  The upper limit of the refractive index tolerance is as described above, but the extent to which the tolerance should be reduced may be determined in consideration of the specifications of the target optical element. Even if only the tolerance of the refractive index is reduced, the performance of the optical element is determined by comprehensive conditions including shape accuracy and dimensional accuracy, and the performance of only the optical element made of near-infrared light absorbing glass is improved. Even so, if the performance of other optical elements does not match that, it will result in excessive specifications. Considering such points and manufacturing costs, it is sufficient that the accuracy of the refractive index is five digits after the decimal point.

  If it is such a glass material lot, if the refractive index indicated by five digits after the decimal point is labeled and sent to the optical element manufacturing process, optical elements with uniform performance can be mass-produced. Alternatively, even when a glass material lot is sold, a glass material is designated by a predetermined product name, product number, etc., and the refractive index of the product name, product number can be displayed with 4 digits or more, preferably 5 digits or more after the decimal point. it can. A person who has purchased a lot can produce an optical element having the desired performance regardless of the glass material in the lot.

  In addition, the glass formed from the molten glass remains strained unless it is sufficiently cooled, and due to the influence, the original refractive index of the glass is determined with high accuracy, but the apparent refractive index varies. Sometimes. For example, when a preform for press molding (including a precision press-molding preform) is molded directly from molten glass, stress is generated in the preform that has been quenched and molded, and the stress is generated by annealing over time. It is difficult to accurately evaluate the tolerance of the refractive index without relaxing the above. In such a case, if the refractive index after the glass material is cooled to 25 ° C. at a slow speed of 30 ° C./hour or less from the glass transition temperature and measured at a predetermined speed, it is due to strain in the glass material. It is possible to evaluate the refractive index inherent in the glass material with reduced influence as well as the tolerance of the refractive index in the lot.

  A preferred embodiment of the present invention is composed of a glass material having a refractive index tolerance of less than ± 0.001 in a state in which the glass material is cooled to 25 ° C. at a predetermined temperature decrease rate of 30 ° C./hour or less from the glass transition temperature. It is a near-infrared light absorbing glass material lot characterized by being. Here, in the case of a glass material with a small volume or a thin sheet-like glass material, cooling proceeds while the glass is adapted to the ambient temperature, but in the case of a glass material with a large volume or a thick glass material, cooling inside the glass material In this case, the rate of temperature decrease is made smaller (cooled more slowly). Here, in the same lot, the refractive index of each glass material is measured at a constant temperature drop rate. If the temperature drop rate varies between glass materials of the same lot, it will cause a variation in refractive index, so the above points should be fully noted. The preferable tolerance range of the refractive index is as described above.

  As the near-infrared light absorbing glass, there are copper-containing fluorophosphate glass, copper-containing phosphate glass, and the like. However, since copper-containing fluorophosphate glass has the property of being excellent in weather resistance, its utility value is high. On the other hand, there is a problem that the refractive index variation is large because fluorine containing extremely high volatility is contained. However, according to the present invention, the tolerance of the refractive index can be made small enough to be compatible with a high-definition image sensor having one million pixels or more, so that a high-performance optical element having excellent weather resistance can be stably mass-produced.

  Examples of the glass material include forms such as a glass plate and a glass rod in addition to a press molding preform such as a precision press molding preform as described above. A glass plate or a glass rod can be cut to an appropriate size, and the surface can be ground and polished to finish the preform, or the cut glass piece can be ground and polished to finish an optical element.

Next, the preferable aspect of the glass of this invention is explained in full detail.
The first aspect is a glass having a Cu ²⁺ content of 0.5 to 13 cation%. Hereinafter, unless otherwise specified, the cation component content and the total content are expressed as cation%, and the anion component content is expressed as anion%. If the amount of Cu ²⁺ is less than 0.5%, it is difficult to obtain desired near infrared light absorption characteristics. Conversely, if it exceeds 13%, the devitrification resistance of the glass decreases.

In the glass of such an embodiment, the glass of a more preferred embodiment is
P ⁵⁺ 11-45%,
Al ³⁺ 0-29%,
Li ⁺ , Na ⁺ and K ⁺ in total 0 to 43%,
Ba ²⁺ , Sr ²⁺ , Ca ²⁺ , Mg ²⁺ and Zn ²⁺ in total 14 to 50%,
Cu ²⁺ 0.5-13%,
In addition, in anionic% display,
F ^- 17-80%,
Is included.

It is preferable that all the remaining amount of the anionic component having the above composition is O ²⁻ .

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

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

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

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

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

A preferable range of the Mg ²⁺ content is 0.1 to 10%, and a more preferable range is 1 to 8%. A preferable range of the Ca ²⁺ content is 0.1 to 20%, and a more preferable range is 3 to 15. A preferable range of the Sr ²⁺ content is 0.1 to 20%, and a more preferable range is 1 to 15%. Ba ²⁺ content preferably falls within a range of 0.1 to 20%, more preferably in the range of 1% to 15%, still more preferably in the range of 1 to 10.

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

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

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

  Note that Pb and As are not harmful because they are highly harmful.

  In this embodiment, the refractive index of the glass is in the range of 1.4700 to 1.5500, preferably 1.5000 to 1.5400, 4 digits after the decimal point (5 significant digits or more), preferably 5 digits (effective digits). It can be set in several 6 digits).

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

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

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

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

  According to the near-infrared light absorbing glass of the present invention, it has a required near-infrared light absorption characteristic and has a refractive index determined with high accuracy, so that an optical design corresponding to the refractive index becomes possible. For example, if the design of the lens shape, dimensions, etc., and the design of the angle and dimensions made by the optical functional surface of the prism are performed for a given refractive index value, various aberrations are small and lenses with excellent imaging performance An optically accurate prism can be realized.

  In forming the molten glass, it is preferable to perform the glass outflow atmosphere in a dry atmosphere, or while flowing a dry gas in the vicinity of the glass outlet at the lower end of the pipe and the outflowed glass surface. The reason is that the melting atmosphere is the same, but if water vapor is contained in the molding atmosphere, a reaction with the molten glass occurs, which causes a change in refractive index and a deterioration of the glass. Moreover, when glass flows out, it is because the wetting of the molten glass to the outer periphery of the lower end of an outflow pipe becomes remarkable. The wet glass is altered, and the altered glass is taken into the glass, causing striae.

  The preferable dryness of the atmosphere or the dry gas is preferably a dew point of −10 ° C. or lower, more preferably −20 ° C. or lower, still more preferably −30 ° C. or lower, still more preferably −40 ° C. or lower, and even more preferably −50 ° C. . Examples of the type of gas include an inert gas such as nitrogen, a mixed gas of an inert gas such as nitrogen and oxygen, and the like.

  As the compound raw material, a phosphate raw material, a fluoride raw material, a copper oxide raw material, or the like may be used.

  The molten glass thus prepared continuously flows out from the pipe connected to the container, is poured into a mold, is molded, and is slowly cooled to obtain a glass molded body having a desired shape. The shape of the mold is appropriately selected according to the shape of the target glass molded body.

  At the time of molding, high-temperature glass easily reacts with moisture in the atmosphere, and the quality of the glass is lowered by this reaction. Therefore, it is preferable that the molten glass is discharged and molded in a dry atmosphere. The amount of water in the dry atmosphere is preferably equivalent to a dew point of −30 ° C. or lower. As the type of gas, an inert gas such as nitrogen or argon, a gas obtained by mixing oxygen with the inert gas, or the like may be used.

  The glass molded body thus formed is subjected to mechanical processing such as cutting, grinding and polishing to form a glass material for press molding and a precision press molding preform described in detail below, and optical elements such as lenses, prisms and filters. Can be.

  When the glass of the present invention is precision press-molded, a precision press-molding preform made of the glass is prepared. Here, the precision 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 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.

  Copper-containing fluorophosphate glass has properties of a high degree of wear and a large thermal expansion coefficient compared to other general optical glasses. Such a property is not preferable for polishing. When the degree of wear is large, processing accuracy is lowered, and scratches during polishing are likely to remain on the glass surface. Polishing is performed while the cutting fluid is applied to the glass. However, if the cutting fluid is applied to the glass whose temperature has been increased by polishing, or if glass having scratches due to polishing on the surface is added to the cleaning liquid whose temperature has increased during ultrasonic cleaning, A fluorophosphate glass that is exposed to a large temperature change and has a large coefficient of thermal expansion is likely to break the glass due to thermal shock. Therefore, it is desirable to manufacture by a method that does not depend on polishing, whether it is a preform for precision press molding or an optical element. From this point of view, the precision press-molding preform is desirably a surface formed by solidifying glass whose entire surface is melted, and the optical element is desirably produced by precision press-molding.

  Preventing and reducing damage to the preform when it is cleaned or heated prior to precision press molding by making the entire surface of the preform a surface formed by solidifying glass in the molten state Can do.

Next, a method for producing a press-molding preform will be described.
One example of a method for producing a press-molding preform is to let molten glass flow out of a pipe, separate a molten glass lump of a desired weight, and form the glass lump into a preform made of the glass in the process of cooling the glass. .

  In this method, the molten glass is continuously applied 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. Spill. 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.

  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. In that case, it is preferable from the viewpoint of reducing and preventing striae to spray the gas on the surface of the glass lump to promote the cooling of the surface.

  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, glass outflow and preform molding should be performed in a dry atmosphere (dry nitrogen atmosphere, dry air atmosphere, nitrogen and oxygen dry mixed gas atmosphere, etc.) as described above. Is preferred.

  Another example of a method for producing a press-molding preform is a method in which molten glass is molded to produce a glass molded body, and the glass molded body is machined to produce a preform made of the glass.

  In this method, first, molten glass is continuously discharged from a 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 near-infrared absorbing glass having a certain refractive index having a certain width and thickness is obtained. The glass molded body thus obtained has reduced and suppressed surface striae.

  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, the glass is filled into the through hole, 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. Also in these methods, it is preferable to perform the outflow and shaping of the molten glass in a dry atmosphere as described above. Furthermore, also in these methods, it is effective to reduce and prevent striae by accelerating cooling by blowing a gas onto the glass surface during molding.

[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 has a near-infrared light absorption characteristic as described above and has a refractive index determined with high accuracy, it has a color sensitivity correction function of a semiconductor imaging element such as a CCD or CMOS, An optical element excellent in high-performance optical function, for example, imaging performance with small aberrations can be provided.

  For example, taking a lens as an example, the refractive index of the glass constituting the lens has an accuracy of 6 or more effective digits, preferably 7 digits. If the decenter is reduced, a lens constituting an optical system exhibiting excellent imaging performance is obtained.

  Taking advantage of such a high refractive index glass, an aspherical lens is produced using the glass of the present invention, thereby realizing a lens having excellent optical performance having near-infrared light absorption characteristics. be able to.

  In an optical element made of near-infrared light absorbing glass, the amount of absorption of near-infrared light varies depending on the optical path length in the optical element. Therefore, in the case of a lens, it is desirable to make the optical path length in the lens as close as possible to the light beam traveling on the optical axis and the light beam passing through the locus away from the optical axis. Such a requirement can be satisfied depending on where in the lens system the lens of the present invention is arranged, and can also be satisfied by making the shape of the lens a meniscus shape.

  Compared with a biconvex lens, a plano-convex lens, a biconcave lens, or a plano-concave lens, the meniscus lens has a value close to the thickness on the optical axis and the thickness away from the optical axis. Therefore, compared with a biconvex lens, a plano-convex lens, a biconcave lens, or a plano-concave lens, the meniscus lens can be said to be a lens that meets the above requirements.

  In particular, the ratio of the shortest distance connecting one point on the effective optical diameter of the first surface of the lens and one point on the effective optical diameter of the second surface to the thickness on the optical axis of the lens is in the range of 0.7 to 1.3. By doing so, the near-infrared light absorption amount of the light transmitted through the lens can be made substantially constant even if the distance from the optical axis is changed, and as a result, an image with little color unevenness can be obtained.

  By using copper-containing fluorophosphate glass as the glass constituting the optical element, it is possible to realize an optical element having higher weather resistance than phosphate glass. As a result, 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.

  From the viewpoint of application, it is suitable for an optical element constituting an imaging system having a near-infrared light absorption function, such as a digital camera lens or a camera lens of a camera-equipped mobile phone.

  A diffraction grating may be formed on the surface of the optical element to provide an optical low-pass filter function. The optical low-pass filter functions to prevent the generation of false colors and moire colors that occur when light having a high spatial frequency is incident on a single pixel of a semiconductor imaging device.

  In addition, an optical thin film such as an antireflection film may be formed on the surface of the optical element as necessary.

  Thus, when manufacturing an aspherical lens or a lens with a diffraction grating, it is less time-consuming and costly to provide an optical element formed by precision press-molding than by polishing glass.

  Hereinafter, the manufacturing method of the optical element of the present invention including the method by precision press molding will be described.

  The manufacturing method of the 1st optical element of this invention is a method of carrying out precision press molding of the said glass or the glass produced with the said manufacturing method.

  Precision press molding is also called mold optics molding, and is a well-known method in the art. 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, this aspect is suitable for manufacturing optical elements such as lenses, lens arrays, diffraction gratings, lenses with diffraction gratings, prisms, prisms with lenses, diffraction gratings and prisms with lenses, and particularly high productivity of aspherical lenses. It is suitable as a manufacturing method based on

  According to the method of this aspect, any of the optical elements having the above optical characteristics can be produced, and since the glass transition temperature (Tg) is low, the press molding temperature can be lowered. Damage to the surface is 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.

As the method of precision press molding used in the method of this embodiment, the following two methods 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.

  Although the above is the manufacturing method of the first optical element, there is also a manufacturing method of the second optical element in which, for example, glass is ground and polished to be processed into a lens other than the method described above. In this method, molten glass is flowed out to form a glass molded body, annealed and then machined to produce the optical element of the present invention. 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.
Example 1 (Example of production of a near-infrared absorbing glass material lot)
First, No. 1 having the composition shown in Table 1 using a fluoride, a metaphosphate compound, an oxide, or the like as a glass raw material. 1 and no. The raw materials were weighed so as to be glass No. 2 and mixed well, and then put into a platinum crucible sealed with a lid, and heated and melted in a dry nitrogen atmosphere while stirring at 790 to 850 ° C. in an electric furnace. A dry nitrogen gas having a dew point of −30 ° C. or lower was constantly flowed into the platinum crucible, and the gas staying in the crucible for a certain period of time was discharged outside the crucible to continuously replace the atmosphere. The exhausted gas was purified through a filter and discharged outside.

  The glass melted in such a state is clarified and homogenized while performing the atmosphere substitution described above, and the obtained molten glass is continuously flowed out from the temperature-controlled pipe at a constant flow rate and poured into a mold in a dry nitrogen atmosphere. The glass was formed into a round bar-shaped glass. Holding the molded glass near the transition temperature, reducing the temperature difference between the inside and the surface of the glass, annealing for 1 hour near the transition temperature, and gradually cooling to room temperature at a slow cooling rate of 30 ° C / hour in the annealing furnace Thus, the glass shown in Table 1 was obtained. Note that a dry air atmosphere may be used instead of the dry nitrogen atmosphere. Moreover, slight volatilization from the glass surface can be suppressed by spraying a dry gas such as dry nitrogen or dry air on the outflowed high-temperature glass surface to promote cooling of the glass surface.

  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 (ne) in wavelength 546.07nm, the refractive index (nd) in wavelength 587.56nm, and glass transition temperature (Tg) were measured as follows. The results are shown in Table 1.
(1) Refractive index (ne), Refractive index (nd)
The refractive index (ne) and refractive index (nd) were measured based on Japan Optical Glass Industry Association Standard JOGIS 01-1994 “Measurement Method of Refractive Index of Optical Glass”.
(2) Glass transition temperature (Tg)
The temperature was increased at a rate of 4 ° C./min with a thermomechanical analyzer from Rigaku Corporation.

  In this way, no. 1 and no. For each glass of No. 2, five round bars were molded and the refractive index of the sample for refractive index measurement cut out from each round bar was measured. The refractive index (ne) and refractive index (nd) are shown in Table 1. It was value.

  Next, no. 1 and no. Each glass of No. 2 was processed into a flat plate shape, and both facing surfaces were optically polished to make a sample for transmittance measurement. And the spectral transmittance of each sample was measured using the spectral transmittance measuring apparatus. From the obtained measurement results, the plate thickness at which the transmittance was 50% at a wavelength of 615 nm was determined, and the transmittances at typical wavelengths of the respective materials at the plate thickness were determined from the measurement results. In addition, even if the sample of the said plate | board thickness was produced and the transmittance | permeability measurement was performed, since it became a numerical value similar to the said conversion result, the optical homogeneity of each sample was able to be confirmed.

  In Table 2, no. 1 and no. For glass No. 2, the thickness is such that the transmittance is 50% at a wavelength of 615 nm, and the transmittance at a representative wavelength at the thickness is shown.

  Thus, no. 1 and no. It was confirmed that the glass No. 2 had good performance as glass for color sensitivity correction of the semiconductor image sensor.

Example 2 (Example of optical element production)
Next, the round bar-shaped glass obtained in Example 1 was cut perpendicularly to the longitudinal direction, ground and polished to produce spherical lenses and prisms.

  Next, the round bar-like glass obtained in Example 1 was cut perpendicularly to the longitudinal direction, ground and polished to produce a precision press-molding preform.

  Next, the mold was changed to form a sheet glass from the molten glass. Next, the glass sheet was slowly cooled, cut, ground and polished to produce optical elements such as spherical lenses and prisms. Further, the plate glass was cut, ground and polished to produce a precision press-molding preform.

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 taken out of 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 each of 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.

Next, the molten glass was continuously poured into a mold from a pipe, formed into a sheet glass in a dry nitrogen atmosphere, and slowly cooled. Next, when the inside of the glass was observed, no striae was observed.
This plate glass was cut, ground and polished to produce a spherical lens.

Next, the plate glass was cut, ground, and polished to obtain a material for press molding, and this material was heated, softened, and press molded to produce an optical element blank. The blank was annealed and then ground and polished to obtain a spherical lens.
These optical elements may be coated with an antireflection film or a near infrared light reflection film as necessary.

  Next, the molten glass was dropped from a pipe and received by a concave portion provided on a mold, and a gas was ejected from the concave portion to float and rotate the glass droplet to form a spherical glass molded body. This glass molded body was used as a preform and precision press-molded to obtain an aspheric lens made of near-infrared light absorbing glass. The spherical glass molded body was gradually cooled and then polished to obtain a glass sphere having a predetermined diameter, and this glass sphere was precision press molded as a preform to obtain an aspherical lens.

  In any of the optical elements, the refractive index is determined with an accuracy of 5 digits after the decimal point (6 effective digits), so that high-performance optical performance can be realized.

  Then, an imaging optical system is configured in combination with a lens using another optical glass, and the positions of the optical system and the imaging element are set so that the aspherical meniscus lens made of near-infrared light absorbing glass comes to the semiconductor imaging element side. Fixed. When the image pickup device used was a CCD having 2 million pixels and was photographed, it was possible to obtain a clear and well-balanced image. When the near-infrared light absorbing glass lens of the above optical system is replaced with the same kind of near-infrared light absorbing glass lens, the refractive index matches with high accuracy, so that good image quality is obtained even after lens replacement. I was able to. Even when the lens was replaced with an arbitrarily selected near-infrared light absorbing glass lens, good image quality could be obtained as before the replacement.

  According to the present invention, it is possible to obtain a near-infrared light-absorbing glass material lot that enables mass production of a glass optical element having a high-performance near-infrared light absorption function. The optical element which has can be obtained.

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

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

Claims (12)

In a near-infrared light absorbing glass material lot consisting of a near-infrared light absorbing glass material containing copper,
A near-infrared light-absorbing glass material lot, characterized by being composed of a glass material having a refractive index (n _e ) tolerance of less than ± 0.001 at a wavelength of 546.07 nm. Tolerance of refractive index (n _e) is a tolerance of refractive index of the glass material while cooling to 25 ° C. at 30 ° C. / hour or less in a predetermined temperature lowering rate from the glass transition temperature (n _e), claim 1 The near infrared light absorbing glass material lot described in 1.   The near-infrared light absorbing glass material lot according to claim 1 or 2, wherein the glass material is a fluorine-containing glass.   The near-infrared light absorbing glass material lot according to claim 1 or 2, wherein the glass material is a preform for press molding.   The near-infrared light absorbing glass material lot according to claim 1 or 2, wherein the glass material is a glass plate or a glass rod.   A method for producing an optical element, comprising mass-producing an optical element using the near-infrared light absorbing glass material lot according to any one of claims 1 to 5.   The method for manufacturing an optical element according to claim 6, wherein the lens is mass-produced.   The method for manufacturing an optical element according to claim 7, wherein aspherical lenses are mass-produced.   The manufacturing method of the optical element of any one of Claims 6-8 which heats and press-molds a near-infrared-light absorption glass material lot.   The method for manufacturing an optical element according to claim 9, wherein a press-formed product produced by press molding is machined.   The method for producing an optical element according to any one of claims 6 to 8, wherein the near-infrared light absorbing glass material lot is heated and precision press-molded.   The method for manufacturing an optical element according to claim 6, wherein the near-infrared light absorbing glass material lot is machined.

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