JP5327956B2 - Optical glass composition, preform and optical element - Google Patents

Description

  The present invention relates to an optical glass composition, a preform, and an optical element. In particular, the present invention relates to an optical glass composition suitable as a material for an optical element such as a lens element included in a photographing lens system of a digital still camera or a digital video camera (hereinafter simply referred to as a digital camera), and press molding the optical element. The present invention relates to a preform for manufacturing according to the above, and an optical element thereof.

  In recent years, various types of digital cameras have been proposed ranging from popular types to high-end types according to consumer needs. Among such digital cameras, in particular, high-end cameras are strongly required not only to be thin for improving portability but also to have high performance such as wide angle and high magnification.

  In order to reduce the thickness of a digital camera, it is essential to reduce the thickness of a photographic lens system that occupies a relatively large volume. To reduce the thickness of the photographic lens system, it is effective to reduce the number of lens elements. However, in recent years, the optical performance required for photographic lens systems has improved, and there is a limit to the reduction in the number of lens elements, particularly in order to increase the magnification. Therefore, in order to reduce the thickness of the photographing lens system, it is necessary to reduce the thickness of individual lens elements included in the photographing lens system.

In order to reduce the thickness of the lens element, it is effective to increase the refractive index of the glass material constituting the lens element. It is preferred that the dispersion be relatively low. For example, Patent Document 1 proposes an optical glass in which such a glass material having a high refractive index and relatively low dispersion is taken as an example.
JP 2003-267748 A

  In a photographic lens system, when a glass material having a high refractive index and relatively low dispersion is used, for example, as the most object side negative lens element of a lens group having a negative power, or the positive lens element of a lens group arranged on the image side. It is considered that high performance such as wide angle and high magnification can be realized in combination with thinning. In the imaging lens system, it is necessary to correct aberrations. Usually, aberration is obtained by variously combining the optical constants such as the refractive index (nd) and dispersion (νd: Abbe number) of the lens element and the shape of the lens element. Is corrected. Therefore, in order to reduce the thickness and improve the performance of the photographic lens system and to sufficiently correct aberrations, among glass materials having a high refractive index and a relatively low dispersion, a high refractive index within a predetermined range can be obtained. It is desirable to appropriately arrange lens elements obtained by adjusting the power, shape, etc., using a glass material having an Abbe number in a predetermined range.

  Patent Document 1 shows an optical glass having a refractive index of 1.80 to 1.90 and an Abbe number of 35 to 50, and further having an optical constant in which these refractive index and Abbe number are defined under predetermined conditions. Is disclosed. The optical glass has such a high refractive index as described above, but its dispersion ranges widely from low to high dispersion. In order to obtain a photographic lens system that can be thinned and improved in performance and capable of sufficient aberration correction, for example, it is obtained from a glass material having an Abbe number of around 45 for a high refractive index of around 1.85. However, Patent Document 1 discloses a glass material that has such a specific combination of refractive index and Abbe number, and excellent meltability, workability (droplet properties), crystallinity, and the like. Is not specifically described.

  In view of the above problems, the present invention has a refractive index (nd) with respect to the d-line in a high refractive index region of around 1.85, and an Abbe number (νd) with respect to the d-line of around 45. An object of the present invention is to provide a high refractive index-low to medium dispersion type optical glass composition having excellent properties (droplet properties), crystallinity, etc., and a preform and an optical element comprising the optical glass composition. And

  The above object is achieved by the following optical glass composition, preform, and optical element.

That is, the present invention
(1) In mol% display
SiO ₂ is 5.0% or more and 25.0% or less,
B ₂ O ₃ 40.0% or less 20.0% or more,
ZnO is 13.2 % or more and 15.0% or less,
ZrO ₂ is 2.7 % to 5.0%,
La ₂ O ₃ is 10.0% or more and 25.0% or less,
Including Ta ₂ O ₅ 3.4 % or more and 5.0% or less, and Gd ₂ O ₃ 5.0% or more and 20.0% or less,
SiO ₂ / B ₂ O ₃ (mol ratio) is 0.25 or more and 0.90 or less,
Substantially free of Li ₂ O,
An optical glass composition having a refractive index (nd) for d-line of 1.83 or more and 1.87 or less, an Abbe number (νd) for d-line of 43 or more and 47 or less, and a liquidus temperature of 1300 ° C. or less. ,
(2) A preform comprising the optical glass composition described in the above item (1) and softened by heating and used for at least press molding, and (3) the optical glass composition described in the above item (1) The present invention relates to an optical element.

  According to the present invention, the refractive index (nd) for the d-line is in a high refractive index region of 1.83 to 1.87, and the Abbe number (νd) for the d-line is in the range of 43 to 47, In addition, a high refractive index-low to medium dispersion optical glass composition having a liquidus temperature of 1300 ° C. or lower can be provided.

  According to the present invention, the refractive index (nd) for the d-line is in a high refractive index region of 1.83 to 1.87, and the Abbe number (νd) for the d-line is in the range of 43 to 47. In addition, it is possible to provide a preform for producing, by press molding, an optical element made of a high refractive index-low to medium dispersion type optical glass composition having a liquidus temperature of 1300 ° C. or lower.

  Further, according to the present invention, the refractive index (nd) for the d-line is in a high refractive index region of 1.83 to 1.87, and the Abbe number (νd) for the d-line is in the range of 43 to 47. In addition, an optical element made of a high refractive index-low to medium dispersion type optical glass composition having a liquidus temperature of 1300 ° C. or lower can be provided.

(Embodiment 1)
First, the optical glass composition according to Embodiment 1 of the present invention will be described in detail. The optical glass composition has the following composition.

That is, the optical glass composition according to the first embodiment is expressed in mol%, SiO ₂ is 5.0% to 25.0%, B ₂ O ₃ is 20.0% to 40.0%, ZnO is 13.2 % to 15.0%, ZrO ₂ is 2.7 % to 5.0%, La ₂ O ₃ is 10.0% to 25.0%, Ta ₂ O ₅ is 3. 4 % or more and 5.0% or less, and Gd ₂ O ₃ is contained by 5.0% or more and 20.0% or less, and SiO ₂ / B ₂ O ₃ (mol ratio) is 0.25 or more and 0.90 or less, Substantially free of Li ₂ O. From the optical glass composition, the refractive index (nd) for d-line is 1.83 or more and 1.87 or less, and the Abbe number (νd) for d-line is in the range of 43 or more and 47 or less, and the liquidus temperature is It is possible to obtain a more stable optical glass having a high refractive index-low to medium dispersion type at 1300 ° C. or lower.

  Next, each component constituting the optical glass composition will be described in detail. Hereinafter, the content of each component is expressed in mol%.

SiO ₂ functions as a network forming component and is an essential component that improves devitrification resistance. However, when the amount of SiO ₂ exceeds 25.0%, the solubility is deteriorated and it is difficult to produce stably, and the liquidus temperature rises, making the production difficult. On the contrary, when the amount of SiO ₂ is less than 5.0%, the devitrification resistance is deteriorated or the glass becomes unstable. A preferable amount of SiO ₂ is 8.0% or more and 23.0% or less.

B ₂ O ₃ functions as a network forming component and expresses the effect of lowering the temperature range for ensuring meltability and viscous flow. However, if the amount of B ₂ O ₃ exceeds 40.0%, the refractive index is too low. Conversely, if the amount of B ₂ O ₃ is less than 20.0%, the temperature range for securing meltability and fluidity becomes too high. A preferable amount of B ₂ O ₃ is 26.0% or more and 39.0% or less.

ZnO has the effect of improving devitrification resistance and lowering the temperature of viscous flow. However, if a large amount of ZnO is used, it becomes difficult to adjust the refractive index (nd) and the Abbe number (νd) to the desired ranges. Therefore, the amount of ZnO is 15.0% or less, preferably 14 .5% or less. Incidentally, to improve devitrification resistance, in order to express sufficiently the effect of lowering the temperature of the viscous flow, shall be the amount of the ZnO 13.2% or more.

ZrO ₂ improves the refractive index and also exhibits the effect of improving devitrification resistance. However, when the ZrO ₂ is used in a large amount, the devitrification resistance is lowered and the solubility is deteriorated. Therefore, the amount of ZrO ₂ is 5 . 0% or less, preferably 3 . 0% or less. Incidentally, the refractive index is improved, in order to sufficiently exhibit the effect of improving resistance to devitrification, the amount of the ZrO ₂ you 2.7% or more.

La ₂ O ₃ is one of the most important components for improving the refractive index and controlling the Abbe number. When the amount of La ₂ O ₃ is less than 10.0%, it is difficult to adjust the Abbe number to a desired range. On the other hand, when the amount of La ₂ O ₃ exceeds 25.0%, devitrification resistance is lowered, so that the glass becomes unstable and production becomes difficult. A preferable amount of La ₂ O ₃ is 11.0% or more and 22.0% or less.

Similar to La ₂ O ₃ , Ta ₂ O ₅ is one of components that improve the refractive index and control the Abbe number. However, if Ta ₂ O ₅ is used in a large amount, the meltability is lowered and the production becomes difficult, so the amount of Ta ₂ O ₅ is 5 . 0% or less, preferably 4 . 0% or less. In order to sufficiently exhibit the effect of improving the refractive index, it shall be the amount of the _Ta 2 _{O 5} 3.4% or more.

Gd ₂ O ₃ is one of components that improve the refractive index and control the Abbe number, like La ₂ O ₃ . However, when the amount of Gd ₂ O ₃ exceeds 20.0%, the devitrification resistance is lowered, so that it becomes unstable as glass, and the production becomes difficult. On the contrary, if the amount of Gd ₂ O ₃ is less than 5.0%, the refractive index is not sufficiently improved. A preferable amount of Gd ₂ O ₃ is 9.0% or more and 19.0% or less.

In order to suppress a decrease in devitrification resistance, the molar ratio of SiO ₂ to B ₂ O ₃ (SiO ₂ / B ₂ O ₃ ) is 0.25 or more, preferably 0.27 or more. Adjust to. Moreover, in order to adjust the liquidus temperature to a desired range and suppress the devitrification resistance from decreasing, the molar ratio is adjusted to 0.90 or less, preferably 0.80 or less.

Moreover, Li ₂ O reduces the glass transition temperature (hereinafter referred to as “Tg”) and exhibits the effect of improving the meltability, but also prevents the liquidus temperature from decreasing, and also reduces the devitrification resistance and the refractive index. Since it also causes a decrease, it is not substantially included.

Further, K ₂ O and Na ₂ O also exhibit the effect of lowering Tg and improving the meltability like Li ₂ O, but K ₂ O and Na ₂ O are also resistant to devitrification. In the case of using K ₂ O and Na ₂ O, the content is made 0% or more and 6.0% or less, respectively.

GeO ₂ can be replaced with SiO ₂ and functions as a network forming component. However, when a large amount of GeO ₂ is used, the devitrification resistance may be lowered. Therefore, the amount of GeO ₂ may be 0% or more and 16.0% or less, and more preferably 0% or more and 8.0% or less. preferable.

  BaO is a component that improves manufacturability, and can be used in an amount of 0% to 6.0%. In addition, when alkaline earth metal oxide R′O (wherein R ′ is at least one of Sr, Ca and Mg) excluding BaO is used in a large amount, devitrification resistance tends to deteriorate. Therefore, it is preferable not to use it. Therefore, when R′O is used, the total content is preferably 10.0% or less.

Nb ₂ O ₅ is one of components that improve the refractive index and control the Abbe number, like La ₂ O ₃ . Further, by replacing the La ₂ O _3, also express the effect of improving resistance to devitrification. However, if a large amount of Nb ₂ O ₅ is used, it becomes difficult to adjust the Abbe number to a desired range. Therefore, the amount of Nb ₂ O ₅ is 0% or more and 3.0% or less, preferably 0% or more. 2.0% or less. In order to fully develop the effect of improving the refractive index and devitrification resistance, the amount of Nb ₂ O ₅ is preferably 0.5% or more.

TiO ₂ controls the refractive index and Abbe number and also exhibits the effect of improving devitrification resistance. However, when a large amount of TiO ₂ is used, it becomes difficult to adjust the Abbe number to a desired range. Therefore, the amount of TiO ₂ is 0% to 3.0%, preferably 0% to 2.0%. It is as follows. In order to fully develop the effect of improving the refractive index and devitrification resistance, the amount of TiO ₂ is preferably 0.5% or more.

Y ₂ O ₃ and Yb ₂ O ₃ are components that improve the refractive index and control the Abbe number, similarly to La ₂ O ₃ . However, if these Y ₂ O ₃ and Yb ₂ O ₃ are used in a large amount, the devitrification resistance is lowered, so that the glass becomes unstable and the production becomes difficult. Therefore, when these Y ₂ O ₃ and Yb ₂ O ₃ are used by substituting with La ₂ O ₃ , it is preferable that the content be 0% or more and 3.0% or less.

WO ₃ is a component for improving the high devitrification property of La ₂ O ₃ and adjusting the refractive index and the Abbe number to a desired range. However, if a large amount of WO ₃ is used, the transmittance in the blue region tends to deteriorate, so the amount of WO ₃ is 0% to 3.0%, preferably 0% to 2.0%. . In addition, in order to improve the devitrification property of La ₂ O ₃ and to fully exhibit the effect of adjusting the refractive index and the Abbe number to a desired range, the amount of WO ₃ is set to 0.5% or more. It is preferable.

Al ₂ O ₃ can be used to adjust the refractive index, but the amount is preferably about 0% to about 10%. Ga ₂ O ₃ and In ₂ O ₃ can also be used in amounts up to about 10% in order to adjust the refractive index. However, it is desirable not to use them in large quantities because the use of these materials may deteriorate the devitrification resistance.

In addition to the above components, Sb ₂ O ₃ and SnO ₂ that are generally used as fining agents can be used. The amounts of Sb ₂ O ₃ and SnO ₂ are each preferably about 0% or more and about 2% or less. However, it is preferable not to use As ₂ O ₃ having a strong action as a clarifying agent because it is toxic.

  In addition, it is desirable not to use Pb and its compounds, radioactive materials such as U and Th, etc. from the viewpoint of safety, such as Te, Se, Cd. Moreover, it is desirable not to use substances that cause coloring such as Cu, Cr, V, Fe, Ni, and Co.

  By adjusting each component to have the ratio as described above, the refractive index (nd) for the d-line is 1.83 or more and 1.87 or less, and the Abbe number (νd) for the d-line is 43 or more and 47 or less. In addition, a high refractive index-low to medium dispersion type optical glass composition having a liquidus temperature of 1300 ° C. or lower can be obtained.

  The liquidus temperature of the optical glass is generally preferably lower from the viewpoints of meltability, workability (droplet properties), crystallinity, etc. when the glass is handled in a softened and melted state. As described above, the liquidus temperature of the optical glass composition according to 1 is 1300 ° C. or lower, preferably 1295 ° C. or lower.

(Embodiment 2)
Next, the preform and the manufacturing method thereof according to Embodiment 2 of the present invention will be described in detail. The preform is softened by heating and used at least for press molding, and the mole and shape of the preform are appropriately determined according to the size and shape of the final press-formed product. The preform according to the second embodiment is made of the optical glass composition according to the first embodiment, and can be obtained without impairing various characteristics of the optical glass composition according to the first embodiment.

  A preform made of the optical glass composition according to Embodiment 1 will be described below. The preform means a glass preform that is heated and used for precision press molding. Preforms are roughly classified into gob preforms that are manufactured by molding a glass material from a molten state, and polishing preforms that are manufactured by physically polishing a glass material. The optical glass composition according to Embodiment 1 is applicable to both gob preforms and polishing preforms.

  Hereinafter, the preform manufacturing method will be described. First, a glass raw material (each of the above components) for obtaining the optical glass composition according to Embodiment 1 above is weighed, prepared, and subjected to steps such as dissolution, defoaming, clarification, homogenization, and the like so that no foreign matter is inherent. A new molten glass. Next, when the molten glass is allowed to flow out from an outflow pipe (hereinafter referred to as a nozzle) made of platinum alloy or the like, the temperature condition in the vicinity of the nozzle is set strictly within a range in which the glass is not devitrified. The molten glass that flows out is cast into a receiving mold having a receiving surface such as a flat shape, a concave shape, or a convex shape, or a mold having an enclosure around each of the flat surface, the concave surface, and the convex surface, and is formed into a desired shape. Hereinafter, a suitable molding method will be exemplified.

  The first molding method is an example of a gob preform manufacturing method. First, on a plurality of receiving molds arranged below the nozzle, a molten glass lump having a weight matching the final molded product or a desired weight added for secondary processing of the final molded product is dropped. Next, it cools, shaping | molding a glass lump, and obtains a gob preform.

  The second molding method is another example of a gob preform manufacturing method. The second molding method is suitable for producing a relatively large weight preform. First, the tip of the molten glass flowing out from the nozzle is brought into contact with the mold surface, and the molten glass is cut by quickly pulling the receiving mold away from the molten glass every time the desired weight is reached. Molding is performed. Next, if necessary, press molding is performed to cool the molten glass lump, and a desired shape is given to obtain a gob preform.

  The third molding method is an example of a method for producing a polishing preform. First, a desired shape is imparted to the glass lump by the same method as the first and second molding methods. At this time, the glass lump is added with a weight necessary for finishing all the surfaces including the optical functional surface of the final product (for example, a lens) by machining. Next, this glass lump is cut and polished by machining to obtain a polished preform.

  Any of the preforms obtained by the first and second molding methods can be used for precision press molding as it is as a press molding preform. In the third molding method, a polishing preform can be produced. In order to prevent the preform from being damaged at the time of handling, for example, a three-dimensional cooling method, an optimum cooling rate, an annealing treatment, and the like can be selected according to the shape and weight.

  As described above, by using the optical glass composition according to Embodiment 1, a press-molding preform and a polishing preform having a desired weight can be obtained. In the case of a press-molding preform, it is preferable to adjust the surface roughness of the receiving mold surface or form a release film for the purpose of releasing during molding. In the case of a polishing preform, it is preferable to apply HBN (boron-based release agent) in order to further facilitate the release.

(Embodiment 3)
Next, an optical element according to Embodiment 3 of the present invention will be described. The optical element according to the third embodiment has an optical constant determined by the composition of the optical glass composition according to the first embodiment. That is, the refractive index (nd) for the d-line is 1.83 to 1.87, the Abbe number (νd) for the d-line is 43 to 47, and the liquidus temperature is 1300 ° C. or lower. The optical element also has a characteristic that the amount of light absorption due to coloring is small in the visible region. The optical element using the optical glass composition according to Embodiment 1 is an optical element suitable for an optical system such as a digital camera, a video camera, or a mobile device.

  Examples of the optical element according to the third embodiment include a prism, a diffraction grating, and the like in addition to a spherical lens, an aspherical lens, a microlens, and the like. Furthermore, an optical element bonded to an optical element formed of a different optical material including a glass material can also be exemplified.

  Next, a method for manufacturing the optical element according to Embodiment 3 will be described. The optical element according to the third embodiment can be manufactured by putting the preform according to the second embodiment into a mold, softening it by heating, press-molding, and further polishing as necessary.

  The press molding method for obtaining the optical element can be roughly classified into two methods. The method is selected according to the means for forming an optical functional surface for entering and exiting light.

  The first means is a means called precision press molding. The mold surface of the press mold is precisely processed in a reverse shape with respect to the optical function surface of the optical element that is the final molded product, and if necessary, release to prevent fusion between the preform and the mold A film is formed, and the shape of the molding surface is precisely transferred to a press molding preform softened by heating by press molding. According to this means, it is not necessary to grind and polish the optical functional surface, and the optical element can be manufactured only by press molding. The press molding is performed in an inert atmosphere such as nitrogen gas. However, when a press-molding preform with a weight added to the final molded product is used, an amount corresponding to the weight added can be centered by grinding for a lens, for example.

  The second means is means for press-molding using a polishing preform that approximates the shape of the optical element that is the final molded product and is larger than the optical element. The molded press-molded product includes an optical functional surface, and the surface of the optical element is formed by machining. In press-molded products, it is necessary to minimize residual distortion in order to withstand machining and prevent glass breakage, and in order to set the required optical constant, a suitable annealing treatment is necessary. . With this means, press molding in the atmosphere is possible, and use of the release agent is also possible.

  Note that, regardless of which of the first and second means is selected, the refractive index (nd) and Abbe number (νd) of the obtained optical element slightly change depending on the thermal history in the manufacturing process. . When producing an optical element having a precisely defined optical constant, in consideration of changes in the refractive index (nd) and Abbe number (νd), adjustment of components of the optical glass composition, It is possible to appropriately select heat history adjustment, adjustment to incorporate the change amount into the optical design, if necessary. As described above, an optical element that has a desired optical constant and excellent transmittance and is particularly suitable as an optical component of a device on which a solid-state imaging device or the like is mounted can be obtained.

  Next, embodiments of the present invention will be described in more detail with reference to the following examples. However, the embodiments are not limited to these examples.

  The operation in each example and comparative example is as follows. First, a raw material mixture composed of a predetermined amount of each oxide and carbonate was put in a platinum crucible, and the raw material mixture was melted while being stirred intermittently at 1350 to 1450 ° C. for 1 hour. Next, the melt is poured into a preheated mold, held for 1 hour in an electric furnace set higher than the expected Tg, and then cooled in a furnace at a cooling rate of 30 ° C./hour to optical glass block. Got. Then, the refractive index (nd), dispersion (νd: Abbe number), and liquid phase temperature were measured using a polished sample cut out from the optical glass block. The compositions (component ratios) of the glass in Examples and Comparative Examples are shown in the following tables.

In each table, the following points are added.
(1) Each component ratio in the composition column in each table is represented by mol% calculated from the batch raw material.
(2) nd and νd are the refractive index and Abbe number at room temperature.
(3) The liquidus temperature is a value obtained by maintaining in a devitrification tester having a temperature gradient of 1000 to 1400 ° C. for 1 hour and observing the presence or absence of crystals with a microscope having a magnification of 40 times.

  As apparent from Tables 1 to 4, the optical glass compositions in the examples are in a high refractive index region where the refractive index (nd) with respect to d-line is 1.83 or more and 1.87 or less, and Abbe with respect to d-line. It can be seen that the number (νd) is in the low to medium dispersion region of 43 to 47 and the liquidus temperature is as low as 1300 ° C. or less.

  The optical glass composition of the present invention is suitable as a material for an optical element such as a lens element included in a photographing lens system of a digital camera. Further, it can be used for an optical pickup optical system lens element used in an optical head device, an illumination optical system used in a projection projector, a projection optical system lens element, or the like, and the performance of these devices can be improved.

Claims (3)

In mol% display
SiO ₂ is 5.0% or more and 25.0% or less,
B ₂ O ₃ 40.0% or less 20.0% or more,
ZnO is 13.2 % or more and 15.0% or less,
ZrO ₂ is 2.7 % to 5.0%,
La ₂ O ₃ is 10.0% or more and 25.0% or less,
Including Ta ₂ O ₅ 3.4 % or more and 5.0% or less, and Gd ₂ O ₃ 5.0% or more and 20.0% or less,
SiO ₂ / B ₂ O ₃ (mol ratio) is 0.25 or more and 0.90 or less,
Substantially free of Li ₂ O,
An optical glass composition having a refractive index (nd) for d-line of 1.83 or more and 1.87 or less, an Abbe number (νd) for d-line of 43 or more and 47 or less, and a liquidus temperature of 1300 ° C. or less. .   A preform comprising the optical glass composition according to claim 1 and softened by heating and used for at least press molding.   An optical element comprising the optical glass composition according to claim 1.