JP2002187735A - Optical glass for mold press forming - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical glass for mold press forming having 1.55 to 1.65 refractive index (nd), >=50 Abbe's number (νd) and <=650 deg.C softening point, hardly devitrifying during molding and having high weather resistance as well. SOLUTION: The glass has the composition of, by wt.%, 35 to 50.5% SiO2, 0 to 15% Al2O3, 1 to 12% B2O3, 0 to 10% MgO, 0 to 15% CaO, 0 to 11.5% BaO, 4.1 to 15% SrO, 0 to 10% ZnO, 3 to 12% Li2O, 0 to 10% Na2O, 0 to 9% K2O, 0 to 0.4% TiO2, 0 to 10% ZrO2, 7.1 to 15% La2O3, 0 to 10% Gd2O3, 0 to 4.5% Nb2O5, 0 to 5% Bi2O3, 10 to 30% MgO+CaO+BaO+SrO and 5 to 14.5% Li2O+Na2O+K2O.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical glass for mold press molding.

[0002]

2. Description of the Related Art A refractive index (nd) of 1.55 to 1.65 is used for an optical lens such as an optical pickup lens of a CD, MD, DVD or other various optical disk systems, and a photographing lens of a video camera or a general camera. Optical glass is used. Conventionally, as such glass, SiO ₂ —Pb
_{O-R '2 O (R} ' 2 O is an alkali metal oxide). However lead-containing glass which is based have been widely used in recent years in -RO SiO ₂ -B ₂ O ₃ from the environmental problems (RO is being switched to the divalent metal oxide) -R 'lead-free glass such as ₂ O system.

[0003]

These optical pickup lenses and photographing lenses are preform glass obtained by dropping molten glass from the tip of a nozzle to once form a glass in the form of drops, grinding, polishing, and washing. Or, the molten glass is rapidly quenched and cast to produce a glass block, and the preform glass obtained by grinding, polishing, and washing is pressed into a softened preform glass by a precision-processed mold. A so-called mold press molding method for transferring the surface shape of a mold to glass has been widely used.

However, since the above-mentioned lead-free preform glass generally has a high softening point, the mold is deteriorated and the molding accuracy is reduced, and the mold is contaminated by volatilization of the glass component. There is a problem that it is not suitable.

[0005] There is a glass for mold press molding containing a large amount of boric acid or an alkali metal oxide.
These preform glasses are not suitable for mass production because devitrification and striae are liable to occur in the melting and forming steps, so that the glass has internal defects. In addition, this internal defect directly affects the final product, and there is a problem that optical characteristics as designed cannot be obtained. Furthermore, the deterioration of the surface due to the elution of the glass components in the cleaning water and various cleaning solutions in the cutting, polishing and cleaning processes causes poor weather resistance, and the final product is exposed to high temperature and humidity for a long time. There is a problem that the surface is deteriorated and reliability is impaired.

An object of the present invention is to improve the above-mentioned problems,
Refractive index (nd) is 1.55-1.65, Abbe number (ν
d) is 50 or more, the softening point is 650 ° C. or less, and it is an object of the present invention to provide an optical glass for mold press molding, which is hardly devitrified during the molding step and has high weather resistance.

[0007]

The optical glass for mold press molding of the present invention contains 35 to 50% by weight of SiO ₂ .
5%, Al ₂ O _{3 0 to} 15%, B ₂ O ₃ 1 to 12%, M
gO 0-10%, CaO 0-15%, BaO 0
11.5%, SrO 4.1-15%, ZnO 0-10
_{%, Li 2 O 3~12%,} Na 2 O 0~10%, K 2
O 0-9%, TiO ₂ 0-0.4%, ZrO ₂₀ 0
10%, La ₂ O ₃ 7.1 to 15%, Gd ₂ O ₃ 0 to 1
0%, Nb ₂ O ₅ 0 to 4.5%, Bi ₂ O ₃ 0 to 5%,
MgO + CaO + BaO + SrO 10-30%, Li
Characterized by having a _{2 O + Na 2 O + K} 2 O 5~14.5% of the composition.

[0008]

The optical glass for mold press molding of the present invention comprises:
Since it contains 7.1% or more of La ₂ O ₃ , it has a high refractive index, a low softening point and a working range (forming temperature-liquidus temperature) of 5%.
Since it is as wide as 0 ° C. or more, it is hard to be devitrified in a molding process and is suitable for mass production of preform glass. In addition, La ₂ O ₃ suppresses the elution of glass components into polishing and washing water and various cleaning solutions in the cutting, polishing, and cleaning steps, and particularly causes deterioration of the glass surface when exposed to a high temperature and high humidity state in a final product for a long time. Has the effect of suppressing.

The reasons for limiting the composition range will be described below.

[0010] SiO ₂ is a component constituting the skeleton of glass, and has the effect of improving the weather resistance. Its content is 3
It is 5-50.5%, preferably 36-50.5%.
If SiO ₂ exceeds 50.5%, the refractive index becomes too low, or the softening point exceeds 650 ° C. On the other hand, 35%
If the amount is less than the above, weather resistance such as acid resistance and water resistance is remarkably deteriorated.

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, in the case of SiO ₂ —B ₂ O ₃ —RO—R ′ ₂ O—La ₂ O ₃ system glass, the effect of suppressing the selective elution of alkali components in the glass into water is remarkable, and the content is 0%. ~ 15%,
Preferably it is 1 to 10%. If the content of Al ₂ O ₃ exceeds 15%, the glass tends to be devitrified, the melting property is remarkably deteriorated, striae and bubbles remain in the glass, and the required quality as glass for lenses cannot be satisfied.

B ₂ O ₃ is essential as a component for increasing the Abbe number (νd). Also has the effect of lowering the softening point,
Its content is 1 to 12%, preferably 3 to 9.5%. When B ₂ O ₃ exceeds 12%, B ₂ O ₃ −
R 'becomes large volatiles formed by ₂ O, resulting in promoting the generation of striae. In addition, volatilization also occurs during molding and contaminates the mold, greatly shortening the life of the mold. Further, the weather resistance is significantly deteriorated. On the other hand, if B ₂ O ₃ is less than 1%, the Abbe number becomes smaller than 50.

[0013] MgO, CaO, BaO and SrO act as fluxing agents, and SiO ₂ -B ₂ O ₃ -RO-R ' ₂
In O-La ₂ O ₃ based glass, an effect of increasing the refractive index without lowering the Abbe number. The total amount is 10-30
%, Preferably 14 to 27. If it exceeds 30%,
During the melting and forming steps of the preform glass, devitrified debris easily precipitates, the liquidus temperature rises, the working range becomes narrow, and mass production becomes difficult. Further, elution from the glass into polishing and washing water and various cleaning solutions becomes severe, and the quality of the glass surface in a high-temperature and high-humidity state becomes remarkable, and the weather resistance is remarkably deteriorated. On the other hand, if it is less than 10%, the refractive index becomes too low or the softening point exceeds 650 ° C.

Although MgO is a component that increases the refractive index, it has a high phase separation property and tends to increase the liquidus temperature. Therefore, its content is desirably 10% or less, particularly preferably 5% or less.

CaO is a component for increasing the refractive index.
Compared with O, the phase separation is not so strong that it can be contained up to 15%. Preferably it is 3 to 10%.

BaO is a component that raises the refractive index. In this glass system, it also has the effect of lowering the liquidus temperature and improving workability. However, since the amount of precipitation from the glass surface in a high-temperature and high-humidity state is significantly larger than other RO components,
If it is contained in a large amount, the weather resistance of the final product will be significantly impaired. Therefore, its content is desirably 11.5% or less, preferably 10% or less.

SrO is an essential component for increasing the refractive index, and has an effect of lowering the liquidus temperature as compared with other RO components, so that the working range is widened. Further, compared to BaO, the degree of precipitation from the glass surface in a high-temperature and high-humidity state is small, and the weather resistance is excellent. Its content is 4.1 to 15%, preferably 4.1 to 13%. If SrO exceeds 15%, the liquidus temperature rises and the working range becomes narrow. On the other hand, 4.1
%, The refractive index becomes too low or the softening point is 6%.
If the temperature exceeds 50 ° C., desired characteristics cannot be obtained.

Li ₂ O, Na ₂ O and K ₂ O are components for lowering the softening point, and their total amount is 5 to 14.5.
%, Preferably 6.5 to 14.5%. 14.5%
If the temperature exceeds the above range, the liquidus temperature rises remarkably, the working range becomes narrow, which has an adverse effect on mass productivity, and the weather resistance deteriorates remarkably. On the other hand, if it is less than 5%, the softening point becomes high.

Li ₂ O is an essential component because it has the effect of lowering the softening point most among the R ′ ₂ O components. Its content is 3 to 12%, preferably 3 to 10%. 12%
If it exceeds, the phase separation is strong, the liquidus temperature becomes high, and the workability deteriorates. On the other hand, if it is less than 3%, the softening point exceeds 650 ° C.

The Na ₂ O, K ₂ O is are effective to lower the softening point, B with ₂ O _3, during melting of the glass B ₂ O ₃ -
R 'becomes large volatiles formed by ₂ O, resulting in promoting the generation of striae. In addition, volatilization also occurs during molding and contaminates the mold, greatly shortening the life of the mold. Therefore, the content of Na ₂ O is desirably 10% or less, and particularly desirably 5% or less. Similarly, the content of K ₂ O is preferably 9% or less, particularly preferably 5% or less.

La ₂ O ₃ is an essential component for ensuring a sufficient working range without lowering the Abbe number without increasing the refractive index and suppressing the rise in softening point. It also has the effect of improving weather resistance. Its content is 7.1 to 15
%, Preferably 7.1 to 14%. If it exceeds 15%, the phase separation becomes strong, the liquidus temperature rises, and the workability is greatly reduced. On the other hand, if the content is less than 7.1%, the above effect cannot be obtained, and particularly, the working range becomes extremely narrow.

Gd ₂ O ₃ is a component that increases the refractive index.
Since the phase separation is strong and the liquidus temperature tends to increase, the content is desirably 10% or less, particularly preferably 5% or less.

[0023] ZrO _2, ZnO, Nb ₂ O ₅ is a component for improving the refractive index, the content is ZrO ₂ is 0-10%,
Preferably 0.1 to 5%, ZnO is 0 to 10%, preferably 0 to 5%, Nb ₂ O ₅ is 0 to 4.5%, preferably 0 to ₅ %.
~ 3%. If each component exceeds the range, the Abbe number (νd) decreases, a desired optical constant cannot be obtained, the tendency to devitrification increases, and a homogeneous glass cannot be obtained.

Bi ₂ O ₃ is a component that increases the refractive index, and is effective in preventing fusion between glass and a mold in mold press molding. However, Bi ₂ O ₃ is more likely to be colored by heating during molding. The amount is desirably 0 to 5%, preferably 3% or less.

In addition to the above, the optical glass of the present invention can
_{Since 2} O ₅ has an effect of lowering the liquidus temperature, its content is 5% or less. However, since water resistance is lowered, it is particularly desirable to be 3% or less. As an adjustment component of the optical constant, TiO ₂ is
0% to 0.4%, and Sb ₂ as a fining agent
O ₃ or the like can be added. PbO or As ₂ O ₃
It is not desirable to use them because they are not environmentally desirable.
Further, Ag and halogens are preferably not contained since they become photoreversible discoloration carriers.

The glass having the above composition has a refractive index (n
d) is 1.55 to 1.65, Abbe number (νd) is 50 or more, softening point is 650 ° C. or less, ΔT = ｛forming temperature (10
(Temperature at ^2.5 poise) -Liquid phase temperature 以上 is 50 ° C. or more, weight loss by water resistance in powder method according to JOGIS standard of Japan Optical Glass Industry Association is less than 0.10%, weight loss in acid resistance by powder method is 0 .35%.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments.

Tables 1 to 6 show Examples (Sample Nos.) Of the present invention.
1 to 12) and Comparative Examples (Sample Nos. 13 to 22).

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

[0032]

[Table 4]

[0033]

[Table 5]

[0034]

[Table 6]

A sample was prepared as follows. First, a glass raw material was prepared so as to have the composition shown in the table, and was melted at 1400 ° C. for 4 hours using a platinum crucible. After melting, the melt was poured out onto a carbon plate, and after annealing, samples suitable for each measurement were prepared.

For the obtained sample, the refractive index (nd),
Abbe number (νd), softening point (Ts), water resistance, acid resistance,
The molding temperature (T _W ) and liquidus temperature (T _L ) were measured. The results are shown in each table.

As is clear from the table, the No. 1 of the embodiment of the present invention. Each of the samples 1 to 12 has a refractive index (nd) of 1.
5662 to 1.6361, and an Abbe number (νd) of 5
It was 4.4 or more, and the softening point (Ts) was 644 ° C. or less. In addition, the water resistance was 0.09% or less in weight loss, and the acid resistance was 0.33% or less in acid resistance, and the weather resistance was good. Further, since the difference (ΔT) between the molding temperature and the liquidus temperature was 67 ° C. or more, workability was excellent.

On the other hand, in Comparative Example No. 13,1
Nos. 5, 16, 21, and 22 have poor weather resistance and have a small working range because ΔT is smaller than 50 ° C. Sample No. 22 had a high softening point of 658 ° C. No. 14 had poor weather resistance. No. Sample No. 17 had a high softening point of 650 ° C. or higher. N
o. 18 had a low Abbe number of 50 or less. No.1
Nos. 9 and 20 have a low refractive index of 1.55 or less and a softening point of 65.
It was as high as 0 ° C or higher.

The refractive index (nd) is shown by a measured value with respect to the d line (587.6 nm) of a helium lamp. The Abbe number is calculated based on the refractive index of the d-line and the F-line (48
6.1 nm) and the C line of the hydrogen lamp (656.3 n)
m), the Abbe number (νd) = ｛(nd)
-1) / (nF-nC)}. The softening point is
It was measured by a fiber elongation method based on Japanese Industrial Standard R-3104. Water resistance and acid resistance are
A glass sample was crushed to a particle size of 420 to 590 μm based on the Japan Optical Glass Industry Association Standard 06-1975, its specific gravity gram was weighed and placed in a platinum basket, which was placed in a flask containing a reagent and placed in a boiling water bath for 60 hours. The weight loss (weight%) of the powdered glass after the treatment was calculated. The reagent used in the water resistance evaluation was pure water adjusted to pH 6.5 to 7.5, and the reagent used in the acid resistance evaluation was 0.01 N
It is a nitric acid aqueous solution adjusted to. Forming temperature T _W is measured by a platinum ball pulling method was determined as a temperature corresponding to 10 ^2.5 poise. The sample is pulverized and classified into a liquid state having a liquidus temperature T _L of 297 to 500 μm, placed in a platinum boat, kept in an electric furnace having a temperature gradient for 24 hours, then allowed to cool in air, and The measurement was performed by obtaining the deposition position of devitrification with a microscope. The working range was determined as the difference between the molding temperature _TW and the liquidus temperature _TL .

[0040]

As described above, the optical glass of the present invention is excellent in mass productivity of preform glass used for mold press molding, and can be used for optical pickup lenses, video cameras, and the like for CD, MD, DVD and other various optical disk systems. It has a refractive index (nd) of 1.55 to 1.65 and an Abbe number (νd) of 50 or more, which are used for an optical lens such as a photographing lens of a general camera. In addition, it has good weather resistance, and does not cause deterioration of physical properties or deterioration of the surface during the manufacturing process or use of the product. Moreover, since the glass component has a low softening point, it is difficult for the glass component to volatilize, so that the molding accuracy is not lowered, and the mold is not deteriorated or contaminated.

Continued on the front page F-term (reference) 4G062 AA04 BB01 DA05 DA06 DB01 DB02 DB03 DB04 DC03 DC04 DD01 DE01 DE02 DE03 DF01 EA03 EA04 EB01 EB02 EB03 EC01 EC02 EC03 ED01 ED02 ED03 EE01 EE02 EE03 EE04 EF03 EF03 EF03 EF03 EF04 FC02 FC03 FD01 FE01 FF01 FG01 FG02 FG03 FH01 FJ01 FK03 FK04 FL01 GA01 GA02 GA03 GA10 GB01 GC01 GD01 GE01 HH01 HH03 HH05 HH07 HH09 HH11 HH13 HH15 HH17 HH20 JJ01 KK03 NN10 KK05 KK07 KK10

Claims (3)

[Claims] 1. 35% to 50.5% by weight of SiO ₂ ,
Al ₂ O _{3 0 to} 15%, B ₂ O ₃ 1 to 12%, MgO
0-10%, CaO 0-15%, BaO 0-11.5
%, SrO 4.1 to 15%, ZnO 0 to 10%, L
_{i 2 O 3~12%, Na 2} O 0~10%, K 2 O 0
_{~9%, TiO 2 0~0.4%,} ZrO 2 0~10
%, La ₂ O ₃ 7.1 to 15%, Gd ₂ O ₃ 0 to 10
_{%, Nb 2 O 5 0~4.5%} , Bi 2 O 3 0~5%, M
gO + CaO + BaO + SrO10-30%, Li ₂ O
_{+ Na 2 O + K 2 O} 5~14.5% of mold press molding an optical glass characterized by having a composition. 2. a refractive index (nd) of 1.55 to 1.65;
Abbe number (νd) of 50 or more, softening point of 650 ° C. or less,
△ T = {molding temperature (temperature at 10 ^2.5 poise) - liquidus temperature} is 50 ° C. or higher, Japanese Optical Glass Industrial Standard JOGIS
2. Mold press molding according to claim 1, wherein the weight reduction in water resistance by the powder method is less than 0.10% and the weight loss in the acid resistance by the powder method is less than 0.35%. For optical glass. 3. The optical glass for mold press molding according to claim 1, which is used for an optical pickup lens or a photographing lens.