TWI391358B - Optical glass for compression molding - Google Patents

Description

Optical glass for compression molding

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

For optical lenses such as CDs, MDs, DVDs, and other optical reading lenses for various optical disc systems, cameras, and general-purpose camera lenses, the refractive index (nd) is 1.57 to 1.62, and the Abbe number (vd) is 55. More specifically, the optical glass having a refractive index (nd) of 1.575 to 1.610 and an Abbe number (vd) of 58.5 to 62.0 is more specifically. Conventionally, lead glass having SiO ₂ -PbO-R' ₂ O (R' ₂ O is an alkali metal oxide) as a basic component has been widely used as such a glass, but in recent years, in consideration of environmental problems, It is replaced with non-lead glass such as SiO ₂ -B ₂ O ₃ -RO (RO is an alkaline earth metal oxide)-R' ₂ O system (for example, Patent Documents 1 and 2).

Patent Document 1: Japanese Laid-Open Patent Publication No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei.

These optical reading lenses and photographic lenses are formed as follows. First, the molten glass is dropped from the tip end of the nozzle, and the droplet-shaped glass is temporarily produced, and ground, washed, and washed to prepare a preformed glass. Alternatively, the molten glass is rapidly cast and the glass brick is temporarily produced, and the preformed glass is produced by grinding, grinding, and washing. Thereafter, the preformed glass in a softened state is press-formed by performing a precision-machined mold, and the surface shape of the mold is transferred onto the glass. Such a method is called a so-called compression molding method and is widely used.

The glass formed by press molding is of course required to satisfy the required optical constant (refractive index, Abbe number), and the softening point is required to be low so as not to deteriorate the mold, and it is required to be difficult to cause fusion with the mold, and High weather resistance.

Further, most of the previously non-lead-based preformed glass as described above does not have sufficient weather resistance. When the weather resistance of the glass is not sufficient, in the cutting, polishing, and washing steps, the glass component is eluted into the polishing washing water or various washing solutions to cause deterioration of the surface. As a result, devitrification is liable to occur in the forming step, and defects occur in the glass to cause mass production. Moreover, even if it is a final product, there is a problem that the glass surface is deteriorated due to prolonged exposure to a high temperature and high humidity state, which may impair reliability.

An object of the present invention is to provide an optical glass for a non-lead-type press molding which satisfies the characteristics required for an optical glass for press molding, in particular, a refractive index (nd) of 1.57 to 1.62 and an Abbe number (vd) of 55 or more (preferably, the refractive index (nd) is 1.575 to 1.610, the Abbe number (vd) is 58.5 to 62.0), and the weather resistance is excellent.

As a result of various tests conducted by the inventors of the present invention, it has been found that the above object can be attained by strictly limiting the composition of SiO ₂ -B ₂ O ₃ -RO-R' ₂ O-La ₂ O ₃ -based glass, and is proposed as the present invention.

In other words, the optical glass for press molding of the present invention contains, in mass%, 41 to 56% of SiO ₂ , 1.5 to 5% of Al ₂ O ₃ , and 7 to 16% of B ₂ O ₃ , 0.1. ~10% CaO, 0~10% BaO, 0~10% SrO, 0~5% ZnO, 1~10% Li ₂ O, 0~5% Na ₂ O, 5~15% La ₂ O ₃ .

The optical glass of the present invention has a refractive index (nd) of 1.57 to 1.62, and 55 or more used in an optical lens such as an optical reading lens of various optical disk systems such as CD, MD, and DVD, and a photographic lens of a camera or a general camera. Abbe number (vd). Further, since the softening point is low and the glass component is hard to be volatilized, there is no possibility of deterioration in molding precision and defects or contamination of the mold. Further, since the working temperature range is wide, the mass production property of the preformed glass is excellent, and the weather resistance is good, so that the physical properties are deteriorated or the surface is deteriorated during the production step or product use. Therefore, it is suitable as an optical glass for press molding.

The optical glass for press molding of the present invention contains 41 to 56% of SiO ₂ , 1.5 to 5% of Al ₂ O ₃ , 7 to 16% of B ₂ O ₃ , and 0.1 to 10% of CaO by mass%. 0 to 10% of BaO, 0 to 10% of SrO, 0 to 5% of ZnO, 1 to 10% of Li ₂ O, 0 to 5% of Na ₂ O, and 5 to 15% of La ₂ O ₃ The composition of the glass. In general, in the non-lead-based glass, a large amount of the alkaline earth metal oxide RO is contained in order to obtain a high refractive index, which is a cause of lowering the weather resistance of the glass. Therefore, the glass of the present invention contains the component La ₂ O ₃ which increases the refractive index and the component Al ₂ O ₃ which improves the weather resistance, suppresses the content of RO, and contains the essential component CaO as RO, whereby the refractive index can be maintained and improved. Weather resistance of glass. Further, when La ₂ O ₃ is contained, the Abbe number tends to decrease, but B ₂ O ₃ is contained to prevent the Abbe number from decreasing. By obtaining excellent weather resistance, refractive index (nd) of 1.57 to 1.62, Abbe number (vd) of 55 or more, especially Abbe having refractive index (nd) of 1.575 to 1.610, and 58.5 to 62.0 The number (vd) optical glass for press molding can be used as an optical lens for optical elements having less dispersion and high function and small size. Further, the optical glass for press molding of the present invention preferably has a glass softening point of 650 ° C or less (preferably 640 ° C or less, more preferably 630 ° C or less). When the softening point of the glass is lowered, it can be press-formed at a low temperature, thereby suppressing contamination of the mold caused by oxidation of the mold or volatilization of the glass component or fusion of the glass and the mold.

The reason for defining the range of each component as described above is explained.

SiO ₂ is a component of a glass skeleton and has an effect of improving weather resistance. The content is 41 to 56%, preferably 42 to 53%, and more preferably 43 to 50.5%. Further, when SiO _{2 is} increased, the refractive index is lowered or the softening point tends to increase. Moreover, the tendency to devitrification is enhanced. On the other hand, when SiO _{2 is} reduced, weather resistance such as acid resistance or water resistance is deteriorated.

The skeleton component of B ₂ O ₃ -based glass has an effect of improving resistance to devitrification. In order to increase the Abbe number and lower the softening point. Further, it has an effect of lowering the alkalinity of the glass, and has an effect of preventing fusion of the glass and the mold in the press molding. The content is 7 to 16%, preferably 9 to 16%, particularly preferably 10 to 15.5%, and more preferably 12 to 15%. Further, when B ₂ O _{3 is} increased, when the glass is melted, the volatile matter formed by B ₂ O ₃ -R' ₂ O is increased to promote the formation of streaks. Further, the weather resistance is deteriorated. On the other hand, when B ₂ O _{3 is} small, there is a possibility that the devitrification resistance is lowered and a sufficient operating temperature range cannot be secured. Moreover, it is easy to fuse with the mold. Further, in the composition domain where SiO _{2 is} less, if the B ₂ O _{3 is} small, it is difficult to maintain the Abbe number at 55 or more.

The Al ₂ O ₃ system forms a component of a glass skeleton together with SiO ₂ and has an effect of improving weather resistance. In particular, in the SiO ₂ -B ₂ O ₃ -RO-R' ₂ O-La ₂ O ₃ -based glass, the effect of suppressing the selective elution of the alkaline component in the glass to water is remarkable, and the content thereof is 1.5 to 5%. The good is 2~4.5%, and then the better is 2.7~4.5%. Further, if there is a large amount of Al ₂ O _{3 ,} it is easily devitrified. Further, there is a possibility that the meltability is deteriorated, streaks or bubbles remain in the glass, and the required quality as a glass for a lens cannot be satisfied. On the other hand, when Al ₂ O _{3 is} small, water resistance and acid resistance are lowered, and it is difficult to obtain glass having extremely high weather resistance.

Alkaline earth metal oxides (RO) such as CaO, BaO, and SrO function as fluxing agents, and have no reduction in SiO ₂ -B ₂ O ₃ -RO-R' ₂ O-La ₂ O ₃ -based glasses. The effect of increasing the refractive index by the number of shells. The total amount of CaO, BaO, and SrO is desirably 10 to 30%, particularly 10 to 20%, and further 12 to 18%. In addition, when the amount of RO is increased, the preformed glass is melted, the devitrified material is easily precipitated in the molding step, the liquidus temperature is increased, and the working range is narrowed, which tends to be difficult to mass-produce. Further, the elution from the glass to the polishing washing water or various washing solutions is increased, and the deterioration of the glass surface in the high-temperature and high-humidity state is remarkable, and the weather resistance is likely to be deteriorated. On the other hand, if RO is reduced, problems such as a decrease in refractive index or a high softening point tend to occur.

The CaO system does not lower the Abbe number and increases the refractive index component. Further, in the high-temperature and high-humidity state, the effect of preventing precipitation on the surface of alkaline or alkaline earth is improved, and therefore it is an essential component for improving weather resistance. The content of CaO is preferably from 0.1 to 10%, particularly preferably from 0.5 to 5%, and more preferably from 1 to 4%. Further, if the CaO is increased, the liquidus temperature rises and the devitrification is likely to occur.

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

SrO is a component that increases the refractive index. Moreover, compared with BaO, the amount of precipitation from the surface of the glass in a high temperature and high humidity state is small. Therefore, by actively using SrO, a product excellent in weather resistance can be obtained. The content is 0 to 10%, preferably 0.5 to 9%, and more preferably 3 to 8%. Further, when SrO increases, the liquidus temperature rises and the working range tends to be narrow.

Further, in addition to CaO, BaO, or SrO, in order to increase the refractive index, MgO may be added. When MgO is added, the content is preferably from 0 to 5%, particularly preferably from 0 to 3%. When MgO increases, it is easily devitrified.

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

An alkali metal oxide (R' ₂ O) such as Li ₂ O or Na ₂ O is used to lower the softening point component. The total amount of Li ₂ O and Na ₂ O is preferably 5 to 12%, preferably 6 to 11%, and more preferably 7 to 10%. Further, R _'2 O increases the liquidus temperature tends to rise, the working temperature range is narrowed. At this time, there is a possibility that the mass production property is adversely affected and the weather resistance is deteriorated. Conversely, if R' ₂ O decreases, the softening point increases.

Among R' ₂ O, the effect of lowering the softening point by Li ₂ O is the largest. The content is from 1 to 10%, preferably from 3 to 9%, and more preferably from 5 to 8.5%. However, since Li ₂ O has a strong phase separation property, when it is added in a large amount, the liquidus temperature becomes high and the workability tends to be deteriorated. Further, since the Li ₂ O-based Field Strength (hereinafter referred to as FS) is low and the component of the alkalinity of the glass described later is increased, it is a cause of fusion with the mold at the time of press molding. On the other hand, if Li ₂ O is decreased, the softening point is increased.

Na ₂ O has an effect of lowering the softening point. When it is contained in a large amount, the volatile matter formed by B ₂ O ₃ -R' ₂ O at the time of melting increases, and the formation of streaks is promoted. Moreover, vulcanization and mold contamination occur during compression molding, resulting in a significant reduction in mold life. The content of Na ₂ O is preferably from 0 to 5%, particularly preferably from 0.5 to 3%.

Further, 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, the content thereof is preferably from 0 to 7%, particularly preferably from 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 lowering the Abbe number, it is not necessary to contain a large amount of RO, which has an effect of improving weather resistance. Further, the La ₂ O ₃ system has an effect of improving the devitrification resistance and can expand the component in the working temperature range. However, if it is contained in a large amount, the phase separation tendency of the glass tends to be enhanced, and it is difficult to obtain a homogeneous glass. The content of La ₂ O ₃ is 5 to 15%, preferably 6 to 12%, and more preferably 7 to 10%.

Further, it is preferred to adjust the content of SiO ₂ and La ₂ O ₃ so that the value of SiO ₂ /La ₂ O ₃ is in the range of 3.2 to 15.0 based on the mass%, particularly preferably 3.2 to 10.0. Within the scope. By setting the ratio to 3.2 to 15.0 without lowering the refractive index, high devitrification resistance can be maintained. When the ratio is small, the devitrification resistance is lowered, and when the ratio is increased, 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, it is desirable to make the content of Sb ₂ O _{3 to} be 1% or less.

Furthermore, TiO ₂ and Nb ₂ O ₅ increase the refractive index of the glass, but decrease the Abbe number or increase the absorption in the ultraviolet region, reducing the transmittance of 390 to 440 nm, and hindering use as a short wavelength. The lens should be avoided from being introduced into the solid glass.

Further, for environmental reasons, since Ag and a halogen are used as a photochromic carrier, it is avoided to introduce PbO, Bi ₂ O ₃ and As ₂ O ₃ into the solid glass.

In the present invention, "avoiding introduction into the parenchyma" means that the content is 0.1% or less.

Further, in the optical glass for press molding of the present invention, in order to further prevent fusion of the glass and the mold during press molding, it is desirable to set the alkalinity of the glass to 11 or less (preferably 9.5 or less) in addition to the above characteristics. ).

Further, in the present invention, the basicity is defined as (the sum of the molar numbers of oxygen atoms/the sum of the FieId Strength of the cations) × 100, and the Field Strength (hereinafter referred to as F.S.) is obtained according to the following formula 1.

Equation 1 FS=Z/r ²

Z represents the ion valence and r represents the ionic radius. Further, the numerical values of Z and r in the present invention are based on the values of Table 1 (disclosed in the value of "Science Handbook Basics Revision 2 (issued by Maruzen Co., Ltd., 1975)"). According to the findings of the present inventors, the lower the alkalinity, the more difficult it is to fuse with the mold. The following is a description of the mechanism by which the alkalinity of the glass dominates the fusion.

Here, the method of determining the alkalinity of the glass will be described by taking SiO ₂ as an example.

First, find the number of moles of oxygen atoms. 1 mol of SiO ₂ contains 2 mol of oxygen atoms. Therefore, by multiplying the number of oxygen atoms by 2 mol by the mole % of SiO ₂ in the glass composition, the number of moles of oxygen atoms of SiO ₂ in the glass can be determined. Similarly, the number of moles of oxygen atoms of each component is obtained, and the total is referred to as "the sum of the mole numbers of oxygen atoms".

Second, find FS. The cation Si ⁴⁺ is Z=4, r=0.4, and thus FS=25. SiO ₂ contains 1 mol of Si ⁴⁺ , so the FS in the glass is 25 × 1 (mol) × (% of SiO ₂ in the composition).

F.S. was obtained for each component, and the total was taken as "the sum of F.S. of cations". Further, the value of "the sum of the molar numbers of oxygen atoms" divided by the value of "the sum of the F.S. of the cations" is multiplied by 100 as the "glass value alkalinity".

Secondly, the mechanism of the alkalinity of the glass is explained.

The alkalinity of the glass indicates an indication of how much electrons of oxygen in the glass are attracted by the cations in the glass. In glass with high alkalinity, the cations in the glass attract electrons to oxygen weakly. Therefore, when the glass having a high alkalinity is in contact with a cation (mold component) having a strong tendency to attract electrons, the cation from the mold easily enters the glass as compared with the glass having a low alkalinity. When the cation as a mold component intrudes (diffusion) into the glass, the concentration of the mold component in the glass phase near the interface increases. Thereby, the difference in composition between the glass phase and the mold phase is reduced, so that the affinity between the two is increased, and the glass is easily attached to the mold. It is generally believed that the glass is fused to the mold because of such a mechanism. Therefore, as the alkalinity is lowered, it is difficult for the mold component to intrude into the glass, and the glass and the mold are not fused.

Specifically, it is considered that if the alkalinity of the glass is 11 or less, preferably 9.5 or less, fusion does not occur. When the alkalinity of the glass exceeds 9.5, the mold tends to be fused, and if it exceeds 11, the glass is fused with the mold, which impairs the surface precision of the product, and the mass productivity tends to be remarkably deteriorated.

Next, a method of manufacturing an optical reading lens, a photographic lens or the like using the glass of the present invention will be described.

First, the glass raw material is blended in a desired composition, and then melted in a glass melting furnace.

Next, the molten glass is dropped from the tip end of the nozzle to temporarily prepare a droplet-shaped glass to obtain a preformed glass, or the molten glass is rapidly cast and cast, and the glass brick is temporarily produced, ground, polished, and washed to obtain a preformed glass.

Next, the preformed glass is poured into a mold subjected to precision machining, and is press-formed while being heated to a softened state, and the surface shape of the mold is transferred onto the glass. This forming method is called compression molding and is widely used.

An optical reading lens or a photographic lens can be obtained in this way.

Example

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, 7 to 13) and Table 3 shows comparative examples (sample Nos. 5 to 6).

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

The obtained sample was measured for its refractive index (nd), Abbe number (vd), softening point (T _s ), and weather resistance. Also, the alkalinity was calculated. These results are shown in the tables.

As shown in the table, the refractive index of each of the samples Nos. 1 to 4 and 7 to 13 of the present invention was 1.5821 to 1.6061, the Abbe number was 56.6 or more, the softening point was 648 ° C or lower, and the liquidus temperature was 887. Below °C. Further, the change in transmittance before and after the exposure test in the high-temperature and high-humidity state was as small as 1.6% or less, and the weather resistance was also good. Further, since B ₂ O _{3 is} contained in a large amount and the alkalinity is also 9.55 or less, it is generally considered that it is difficult to cause fusion with a mold.

On the other hand, in each of the samples of Comparative Examples No. 5 and No. 6, the transmittance change before and after the exposure test was as large as 3.1% or more, and the weather resistance was low.

Further, the refractive index (nd) is represented by a measured value for the d-line (587.6 nm) of the xenon lamp.

The Abbe number (vd) is the value of the refractive index of the above-mentioned 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 same hydrogen lamp, according to the Abbe number (vd)={ (nd-1)/(nF-nC)} is calculated.

The softening point T _s was measured by a fiber elongation method according to Japanese Industrial Standard R-3104.

The liquidus temperature T _L was measured by the following procedure, that is, the sample was pulverized into powders of 297 to 500 μm and classified, placed in a platinum boat, and kept in an electric furnace having a temperature gradient for 24 hours. Cooling was placed in the air, and the devitrification precipitation position was obtained by an optical microscope.

The evaluation of the weather resistance was carried out by measuring the glass transmittance before and after the exposure test in a high temperature and high humidity state by a spectrophotometer, and evaluating the difference in glass transmittance at a wavelength of 590 nm in the visible region. Further, the exposure test was carried out under the conditions of a temperature of 60 ° C, a humidity of 90%, and a temperature of 300 hours, and the glass sample was optically polished to a thickness of 30 mm to a thickness of 10 mm.

The alkalinity was calculated according to the formula (sum of the molar number of oxygen atoms/the total field strength of the cation) × 100. Furthermore, the Field Strength (hereinafter referred to as F.S.) in the formula is obtained by the following formula.

FS=Z/r ²

Z represents the ion valence and r represents the ionic radius.

The invention will be described in detail with reference to the specific embodiments thereof, and it is obvious that various changes or modifications may be made without departing from the spirit and scope of the invention.

The present application is based on a Japanese patent application filed on Apr. 5, 2006 (Japanese Patent Application No. 2006-103806), and Japanese Patent Application No. 2007-86412, filed on March 29, 2007, The contents thereof are incorporated in the present invention as a reference.

Claims (5)

An optical glass for press molding, comprising: 41 to 50.5% SiO ₂ , 1.5 to 5% Al ₂ O ₃ , 10 to 16% B ₂ O ₃ , 0.1 to 10% by mass% CaO, 0~10% BaO, 0~10% SrO, 0~5% ZnO, 1~10% Li ₂ O, 0~5% Na ₂ O and 5~15% La ₂ O ₃ . The optical glass for press molding of claim 1, wherein the total amount of Li ₂ O and Na ₂ O is 5 to 12%. The optical glass for press molding of claim 1 or 2, wherein the total amount of CaO, BaO and SrO is 10 to 20%. The optical glass for press molding according to any one of claims 1 to 3, which further contains substantially no TiO _{2 or} Nb ₂ O ₅ . The optical glass for press molding according to any one of claims 1 to 4, wherein the content of SiO ₂ and La ₂ O ₃ is 3.2 ≦ SiO ₂ /La ₂ O ₃ ≦15.0 based on the mass%.