JP2007297269A - Optical glass for mold press molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lead-free optical glass for mold press molding which has characteristics required for optical glasses for mold press molding, especially a refractive index (nd) of 1.57-1.62 and an Abbe's number (νd) of not less than 55, while being excellent in weather resistance. <P>SOLUTION: The lead-free optical glass for mold press molding is characterized by having a composition containing, in mass%, 41-56% of SiO<SB>2</SB>, 1.5-5% of Al<SB>2</SB>O<SB>3</SB>, 7-16% of B<SB>2</SB>O<SB>3</SB>, 0.1-10% of CaO, 0-10% of BaO, 0-10% of SrO, 0-5% of ZnO, 1-10% of Li<SB>2</SB>O, 0-5% of Na<SB>2</SB>O and 5-15% of La<SB>2</SB>O<SB>3</SB>. Preferably, the composition of the optical glass further satisfies the following conditions: MgO+CaO+BaO+SrO is 10-20%, Li<SB>2</SB>O+Na<SB>2</SB>O K<SB>2</SB>O is 5-12% and SiO<SB>2</SB>/La<SB>2</SB>O<SB>3</SB>is ≥3.2 and ≤15.0. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical glass for mold press molding.

Refractive index (nd) is 1.57 to 1.62 and Abbe number (νd) for optical lenses such as optical pickup lenses for CD, MD, DVD and other various optical disk systems, video cameras and photographing lenses for general cameras. Is more than 55, more specifically, an optical glass having a refractive index (nd) of 1.575 to 1.610 and an Abbe number (νd) of 58.5 to 62.0 is used. Conventionally, lead-containing glass based on SiO ₂ —PbO—R ′ ₂ O (R ′ ₂ O is an alkali metal oxide) has been widely used as such glass. _2- B ₂ O ₃ —RO (RO is an alkaline earth metal oxide) —R ′ ₂ O-based non-lead glass is being switched (for example, Patent Documents 1 and 2).
JP-A-6-107425 JP 2000-302479 A JP 2004-328068 A

  In these optical pickup lenses and photographing lenses, molten glass is dropped from the tip of a nozzle to form a drop-shaped glass, and then preform glass or molten glass obtained by grinding, polishing, and washing is quenched and cast once. The preform glass obtained by preparing a glass block and grinding, polishing, and washing is pressed into a soft preform glass with a precision-processed mold, and the surface shape of the mold is changed to glass. A so-called mold press molding method for transferring is widely used.

  Glass molded by mold press molding not only satisfies the required optical constants (refractive index, Abbe number), but also has a low softening point so as not to deteriorate the mold, and fusion with the mold. Are required to be difficult to occur, and weather resistance is high.

  Further, the conventional lead-free preform glass as described above often does not have sufficient weather resistance. If the weather resistance of the glass is not sufficient, surface alteration occurs due to elution of the glass components into the polishing cleaning water and various cleaning solutions during the cutting, polishing and cleaning steps. As a result, devitrification is likely to occur in the molding process, and defects in the glass occur, making mass production difficult. Further, even in the final product, when exposed to a high temperature and high humidity for a long time, the surface of the glass is deteriorated and the reliability is impaired.

  The object of the present invention is to satisfy various properties required as optical glass for mold press molding, and in particular, the refractive index (nd) is 1.57 to 1.62, and the Abbe number (νd) is 55 or more (preferably the refractive index. (Nd) is 1.575 to 1.610, Abbe number (νd) is 58.5 to 62.0), and it is to provide a lead-free optical glass for mold press molding having excellent weather resistance.

As a result of various experiments, the present inventors have found that the above object can be achieved by strictly limiting the composition of the SiO ₂ —B ₂ O ₃ —RO—R ′ ₂ O—La ₂ O ₃ glass. It is proposed as the present invention.

That is, press molding for the optical glass of the present invention, in _{mass%, SiO 2 41~56%, Al} 2 O 3 1.5~5%, B 2 O 3 7~16%, CaO 0.1~10 %, BaO 0~10%, SrO 0~10 %, 0~5% ZnO, Li 2 O 1~10%, Na 2 O 0~5%, and characterized in that it contains La ₂ O ₃ 5~15% To do.

  The optical glass of the present invention has a refractive index of 1.57 to 1.62 used for optical lenses such as optical pickup lenses for CD, MD, DVD and other various optical disk systems, video cameras and photographing lenses for general cameras. nd) and an Abbe number (νd) of 55 or more. In addition, since the softening point is low and the glass component is difficult to volatilize, the molding accuracy is not lowered and the mold is not deteriorated or contaminated. In addition, the working temperature range is wide, the preform glass is excellent in mass productivity, and the weather resistance is good, so that the physical properties are not deteriorated and the surface is not deteriorated during the production process or use of the product. Therefore, it is suitable as an optical glass for mold press molding.

Press molding for the optical glass of the present invention, in _{mass%, SiO 2 41~56%, Al} 2 O 3 1.5~5%, B 2 O 3 7~16%, CaO 0.1~10%, is a glass with BaO 0~10%, SrO 0~10%, 0~5% ZnO, Li 2 O 1~10%, Na 2 O 0~5%, the basic composition of La ₂ O ₃ 5~15% . In general, lead-free glass contains a large amount of RO, which is an alkaline earth metal oxide, in order to obtain a high refractive index, which causes a decrease in the weather resistance of this glass. Therefore, in the glass of the present invention, La ₂ O ₃ which is a component for increasing the refractive index and Al ₂ O ₃ which is a component for improving weather resistance are contained to suppress the content of RO, and CaO is used as RO. By containing as an essential component, the weather resistance of the glass is improved while maintaining the refractive index. Further, when La ₂ O ₃ is contained, the Abbe number tends to decrease. However, the inclusion of B ₂ O ₃ prevents the Abbe number from decreasing. In this way, excellent weather resistance, a refractive index (nd) of 1.57 to 1.62, an Abbe number (νd) of 55 or more, particularly a refractive index (nd) of 1.575 to 1.610. , 58.5 to 62.0 Abbe number (νd) can be obtained, and can be used as an optical lens for small optical elements with high function and small color dispersion. . Moreover, the optical glass for mold press molding of the present invention preferably has a glass softening point of 650 ° C. or lower (preferably 640 ° C. or lower, more preferably 630 ° C. or lower). When the softening point of the glass is lowered, press molding at a low temperature becomes possible, and mold oxidation and mold contamination due to volatilization of glass components and fusion between the glass and the mold can be suppressed.

  The reason why the range of each component is limited as described above will be described.

SiO ₂ is a component constituting the skeleton of the glass and has an effect of improving weather resistance. Its content is 41-56%, preferably 42-53%, more preferably 43-50.5%. When SiO ₂ increases, the refractive index tends to decrease and the softening point tends to increase. In addition, the tendency to devitrification becomes stronger. On the other hand, when the amount of SiO ₂ decreases, weather resistance such as acid resistance and water resistance deteriorates.

B ₂ O ₃ is a skeletal component of glass and is effective in improving devitrification resistance. It is a component that increases the Abbe number and lowers the softening point. Further, it has the effect of lowering the basicity of the glass, and is effective in preventing fusion between the glass and the mold in mold press molding. The content is 7 to 16%, preferably 9 to 16%, particularly preferably 10 to 15.5%, and further preferably 12 to 15%. When B ₂ O ₃ increases, more volatiles are formed by B ₂ O ₃ —R ′ ₂ O during glass melting, which promotes the generation of striae. Furthermore, weather resistance deteriorates. On the other hand, when the B ₂ O ₃ is small, there is a possibility that devitrification resistance can not be secured a sufficient working temperature range decreases. Moreover, it becomes easy to fuse | melt with a metal mold | die. In yet SiO ₂ less composition range, and B ₂ O ₃ is less the Abbe number can be maintained at 55 or more is difficult.

Al ₂ O ₃ is a component constituting a glass skeleton together with SiO ₂ and has an effect of improving weather resistance. In particular, SiO ₂ —B ₂ O ₃ —RO—R ′ ₂ O—La ₂ O ₃ glass has a remarkable effect of suppressing selective elution of alkali components in the glass into water, and its content is 1 0.5 to 5%, preferably 2 to 4.5%, more preferably 2.7 to 4.5%. Incidentally easily devitrified and Al ₂ O ₃ is large. In addition, the meltability deteriorates and striae and bubbles remain in the glass, which may not satisfy the required quality as glass for lenses. On the other hand, when the Al ₂ O ₃ is less, water resistance, acid resistance is lowered, it is difficult to obtain a glass having a very high weatherability.

Alkaline earth metal oxides (RO) such as CaO, BaO, and SrO act as fluxes and lower the Abbe number in SiO ₂ -B ₂ O ₃ -RO-R ' ₂ O-La ₂ O ₃ glass Without increasing the refractive index. The total amount of CaO, BaO, and SrO is preferably 10 to 30%, particularly 10 to 20%, and more preferably 12 to 18%. When RO is increased, devitrification beads are likely to be precipitated during the melting and forming process of the preform glass, the liquidus temperature is increased, the working range is narrowed, and the mass production tends to be difficult. Further, the weather resistance is likely to deteriorate, for example, the elution of the glass into the polishing cleaning water and various cleaning solutions increases, and the glass surface changes significantly in a hot and humid state. On the other hand, when RO is decreased, inconveniences such as a decrease in refractive index and an increase in softening point are likely to occur.

  CaO is a component that increases the refractive index without decreasing the Abbe number. Moreover, since the effect which prevents precipitation to the surface of an alkali or alkaline earth in a hot and humid state becomes high, it is an essential component for a weather resistance improvement. The content of CaO is preferably 0.1 to 10%, particularly 0.5 to 5%, and more preferably 1 to 4%. In addition, when CaO increases, liquidus temperature will rise and it will become easy to devitrify.

  BaO is a component that increases the refractive index, and this glass system also has the effect of lowering the liquidus temperature and improving workability. However, the amount of precipitation from the glass surface in a high-temperature and high-humidity state is significantly larger than that of other RO components, so if it is contained in a large amount, the weather resistance of the final product may be impaired. The BaO content is preferably 0 to 10%, particularly preferably 0.5 to 9.5%, and more preferably 4 to 9%.

  SrO is a component that increases the refractive index. Moreover, compared with BaO, there is little precipitation amount from the glass surface in a hot and humid state. Therefore, a product excellent in weather resistance can be obtained by positively using SrO. Its content is 0-10%, preferably 0.5-9%, more preferably 3-8%. When SrO increases, the liquidus temperature rises and the working range tends to narrow.

  In addition to CaO, BaO, or SrO, MgO may be added to increase the refractive index. When adding MgO, the content is preferably 0 to 5%, particularly preferably 0 to 3%. It becomes easy to devitrify when MgO increases.

  ZnO has the effect of increasing the refractive index and improving the weather resistance. Moreover, since the devitrification tendency is not strong, a homogeneous glass can be obtained even if it is contained in a large amount. Its content is 0-5%, preferably 0.5-4%, more preferably 1-3%. When the amount of ZnO increases, the Abbe number tends to decrease.

Alkali metal oxides (R ′ ₂ O) such as Li ₂ O and Na ₂ O are components for lowering the softening point. The total amount of Li ₂ O and Na ₂ O is preferably 5 to 12%, particularly 6 to 11%, and more preferably 7 to 10%. When R ′ ₂ O increases, the liquidus temperature rises and the working temperature range tends to narrow. In this case, the mass productivity may be adversely affected. Moreover, there exists a tendency for a weather resistance to deteriorate. Conversely, when R ′ ₂ O decreases, the softening point increases.

Among R ′ ₂ Os, Li ₂ O has the greatest effect of lowering the softening point. Its content is 1 to 10%, preferably 3 to 9%, more preferably 5 to 8.5%. However, since Li ₂ O has a strong phase separation property, if it is added in a large amount, the liquidus temperature becomes high and the workability tends to deteriorate. In addition, since Field Strength (hereinafter referred to as FS) is low and it is a component that increases the basicity of glass described later, it causes fusion with a mold during press molding. On the other hand, when Li ₂ O decreases, the softening point increases.

Na ₂ O has an effect of lowering the softening point. However, when it is contained in a large amount, volatiles formed by B ₂ O ₃ —R ′ ₂ O at the time of melting increase and promote the formation of striae. In addition, volatilization occurs during molding, which contaminates the mold and greatly shortens the life of the mold. The content of Na ₂ O is preferably 0 to 5%, particularly preferably 0.5 to 3%.

In addition to Li ₂ O and Na ₂ O, K ₂ O may be added to lower the softening point. When K ₂ O is added, its content is preferably 0 to 7%, particularly preferably 0 to 5%. When K ₂ O increases, the weather resistance deteriorates.

Since La ₂ O ₃ has an effect of increasing the refractive index without reducing the Abbe number, it is not necessary to contain a large amount of RO and is effective in improving the weather resistance. Moreover, although it has the effect of improving devitrification resistance and can expand the working temperature range, if it is contained in a large amount, the phase separation tendency of the glass becomes strong and it becomes difficult to obtain a homogeneous glass. Content of La ₂ O ₃ 5-15%, preferably 6-12%, more preferably 7% -10%.

Also, the content of SiO ₂ and La ₂ O ₃ is such that the value of SiO ₂ / La ₂ O ₃ is in the range of 3.2 to 15.0, particularly 3.2 to 10.0 on a mass% basis. It is preferable to adjust. By setting this ratio to 3.2 to 15.0, high devitrification resistance can be maintained without lowering the refractive index. When this ratio decreases, the devitrification resistance decreases, and when it increases, the refractive index tends to decrease.

Sb ₂ O ₃ can be added as a fining agent. However, in order to avoid excessive coloring of the glass, the content of Sb ₂ O ₃ is desirably 1% or less.

TiO ₂ and Nb ₂ O ₅ are components that increase the refractive index of glass. However, they reduce the Abbe number, increase the absorption in the ultraviolet region, decrease the transmittance at 390 to 440 nm, and are used for short wavelengths. Substantial introduction to glass should be avoided as it may interfere with use as a lens.

Furthermore, since PbO, Bi ₂ O ₃ and As ₂ O ₃ are for environmental reasons, Ag and halogens are photoreversible discoloration carriers, and therefore should not be substantially introduced into glass.

  In the present invention, “avoid substantially introducing into glass” means that the content is 0.1% or less.

  Further, in the optical glass for mold press molding of the present invention, in order to prevent the glass and the mold from being fused at the time of mold press molding, in addition to the above features, the basicity of the glass is 11 or less (preferably 9). .5 or less).

  In the present invention, the basicity is defined as (total number of moles of oxygen atoms / total number of positive field strength) × 100, and field strength (hereinafter referred to as FS) is as follows. It is obtained by Equation 1.

Formula 1 F. S. = Z / r ²
Z represents an ionic valence, and r represents an ionic radius. The values of Z and r in the present invention are the values in Table 1 (values described in “Science Manual Basic Bias Revised 2nd Edition (1975 Maruzen Co., Ltd.)”). According to the knowledge of the present inventor, the lower the basicity, the harder it is to fuse with the mold. The mechanism by which the basicity of the glass controls the fusion will be described below.

Here, taking SiO ₂ as an example, how to determine the basicity of the glass will be described.

First, the number of moles of oxygen atoms is obtained. In 1 mol of SiO ₂ , 2 mol of oxygen atoms are contained. Therefore, the number of moles of oxygen atoms possessed by SiO ₂ in the glass can be obtained by multiplying the number of moles of oxygen by ₂ mol by the mole percentage of SiO ₂ in the glass composition. Similarly, the number of moles of oxygen atoms of each component is obtained, and the sum is defined as “total number of moles of oxygen atoms”.

Next, F. S. Ask for. Since the cation Si ⁴⁺ is Z = 4 and r = 0.4, F.I. S. = 25. Since 1 mol of Si ⁴⁺ is contained in SiO ₂ , F. S. Is calculated as 25 × 1 (mol) × (mol% of SiO _{2 in} the composition).

  This is calculated | required about each component and let the sum total be "the sum total of FS of a cation." Then, the value obtained by multiplying the value obtained by dividing the “total number of moles of oxygen atoms” by the “total number of FS of cation” by 100 is defined as “basicity of glass”.

  Next, a mechanism in which the basicity of the glass controls the fusion will be described.

  The basicity of the glass is an index indicating how much oxygen electrons in the glass are attracted to the cations in the glass. In a glass having a high basicity, the attraction of oxygen electrons by cations in the glass is weak. Therefore, when a glass having a high basicity is in contact with a cation (mold component) that has a strong tendency to demand electrons, a cation from the mold is more likely to enter the glass than a glass having a low basicity. . When the cation which is a mold component penetrates (diffuses) into the glass, the mold component concentration in the glass phase near the interface increases. Thereby, since the difference in composition between the glass phase and the mold phase is reduced, the affinity between the two is increased, and the glass is easily wetted by the mold. It is considered that the glass and the mold are fused by such a mechanism. Therefore, as the basicity is lowered, the mold components are less likely to enter the glass, and the glass and the mold are not fused.

  Specifically, if the basicity of the glass is 11 or less, preferably 9.5 or less, it is considered that fusion does not occur. If the basicity of the glass exceeds 9.5, a tendency to fuse with the mold appears, and if it exceeds 11, the glass and the mold are fused to impair the surface accuracy of the product, and the mass productivity is remarkably deteriorated. There is a tendency.

  Next, a method for producing an optical pickup lens, a photographing lens, etc. using the glass of the present invention will be described.

  First, after preparing a glass raw material so that it may become a desired composition, it fuse | melts in a glass melting furnace.

  Next, molten glass is dripped from the tip of the nozzle to produce a glass droplet once to obtain a preform glass. Alternatively, the molten glass is rapidly cast to prepare a glass block, which is then ground, polished and washed to obtain a preform glass.

  Then, it puts into the preform glass in the precision-processed metal mold | die, press-molding, heating until it becomes a softened state, and transfers the surface shape of a metal mold | die to glass. This molding method is called a mold press molding method and is widely used. In this way, an optical pickup lens and a photographing lens can be obtained.

  Hereinafter, the present invention will be described based on examples.

  Tables 2, 4 and 5 show examples of the present invention (sample Nos. 1 to 4 and 7 to 13) and Table 3 shows comparative examples (samples No. 5 to 6).

  Each sample was prepared as follows. First, glass raw materials were prepared so as to have the composition shown in the table, and were melted at 1400 ° C. for 3 hours using a platinum crucible. After melting, the melt was poured onto a carbon plate, and after annealing, a sample suitable for each measurement was produced.

  About the obtained sample, refractive index (nd), Abbe number (νd), softening point (Ts), and weather resistance were measured. The basicity was calculated. The results are shown in each table.

As is apparent from the table, No. 1 as an example of the present invention. Samples 1 to 4 and 7 to 13 each had a refractive index of 1.5821 to 1.6061, an Abbe number of 56.6 or more, a softening point of 648 ° C. or less, and a liquidus temperature of 887 ° C. or less. Moreover, the transmittance | permeability change before and behind the exposure test of a hot and humid state was as small as 1.6% or less, and the weather resistance was also favorable. Further, since it contains a large amount of B ₂ O ₃ and its basicity is as low as 9.55 or less, it is considered that fusion with the mold hardly occurs.

  On the other hand, No. which is a comparative example. 5 and no. Each sample of No. 6 had a large change in transmittance of 3.1% or more before and after the exposure test, and the weather resistance was low.

  The refractive index (nd) is indicated by a measured value for the d-line (587.6 nm) of a helium lamp.

  The Abbe number (νd) is the refractive index of the d-line and the refractive index of the F-line (486.1 nm) of the hydrogen lamp, and the C-line (656.3 nm) of the hydrogen lamp, and the Abbe number (νd) = It was calculated from the {(nd-1) / (nF-nC)} formula.

The softening point T _S was measured by a fiber elongation method based on Japanese Industrial Standard R-3104.
The liquid phase temperature T _L is pulverized and classified so that the powder has a powder form of 297 to 500 μm, placed in a platinum boat, held in an electric furnace having a temperature gradient for 24 hours, and then allowed to cool in air. The measurement was performed by determining the deposition position of devitrification with an optical microscope.

  The weather resistance was evaluated by measuring the transmittance of the glass before and after the exposure test in a hot and humid state with a spectrophotometer and evaluating the difference in the transmittance of the glass at a wavelength of 590 nm in the visible range. The exposure test was performed under conditions of a temperature of 60 ° C., a humidity of 90%, and 300 hours, and a glass sample having a size of 30 × 25 mm and optically polished on both sides to a thickness of 10 mm was used.

  The basicity is calculated based on the formula: (total number of moles of oxygen atoms / total number of cation field strength) × 100. The field strength (hereinafter referred to as FS) in the formula is obtained by the following formula.

F. S. = Z / r ²
Z represents an ionic valence, and r represents an ionic radius.

Claims (5)

By _{mass%, SiO 2 41~56%, Al} 2 O 3 1.5~5%, B 2 O 3 7~16%, CaO 0.1~10%, BaO 0~10%, SrO 0~10% ZnO 0 to 5%, Li ₂ O 1 to 10%, Na ₂ O 0 to 5%, La ₂ O ₃ 5 to 15%. The optical glass for mold press molding according to claim 1, wherein the total amount of Li ₂ O and Na ₂ O is 5 to 12%.   3. The optical glass for mold press molding according to claim 1 or 2, wherein the total amount of CaO, BaO and SrO is 10 to 20%. The optical glass for mold press molding according to any one of claims 1 to 3, further comprising substantially no TiO ₂ and Nb ₂ O ₅ . In press molding for optical glass according to any one of claims 1 to 4, the content of SiO ₂ and La ₂ O ₃ is, on a mass% _{basis, 3.2 ≦ SiO 2 / La 2} O 3 ≦ 15. An optical glass for mold press molding characterized by having a relationship of 0.