JP2958919B2 - Optical lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical lens using an optical glass having a high refractive index, a high Abbe number and a low yield point temperature and suitable for precision press molding.

[0002]

BACKGROUND ART refractive index (n _d) from 1.65 to 1.75,
Glasses having an Abbe number (ν _d ) having an optical constant in a range of 50 or more include shot catalog names such as SSK and LaK. These high-refractive low-dispersion glasses are indispensable when making an optical imaging system consisting of a plurality of lenses used in cameras and video cameras, etc., and by using an aspheric lens using this glass, It is well known that it is possible to create an imaging system having an unprecedented imaging characteristic and a small number of lenses.

However, it is expensive and inefficient to manufacture an aspheric lens by the conventional grinding and polishing method.
In recent years, precision press molding technology for directly forming a lens by press-molding softened glass has been actively developed. This method is an epoch-making manufacturing method suitable for mass-producing precision optical elements such as lenses, but the molding temperature is high, and therefore, the shape of the surface of the mold used for molding is severely deteriorated, and frequent In addition, rework of the mold is required, which raises the cost of the product. Also,
When performing precision pressing, if the working temperature is 600 ° C. or higher, the durability of the mold material is rapidly deteriorated, and the working efficiency is also deteriorated. Therefore, it is desired to perform the precision pressing at a temperature of 600 ° C. or lower. In order to cope with this, it is necessary to lower the temperature at which the glass softens, and to carry out molding at a temperature as low as possible.

[0004]

In general, the refractive index (n _d )
Is relatively high in refractive index and low dispersion and has an optical constant in the range of 1.65 to 1.75 and Abbe number (ν _d ) of 50 or more. It belongs to a glass which is relatively difficult to perform precision press molding, such as liable to cause phenomena such as fusion with a mold and breakage of the glass.

As an example of a glass having a low softening point in such a region, B ₂ O ₃ —La ₂ O ₃ —ZnO—Li ₂ O—S
b ₂ O ₃ based glass has been proposed in some composition in JP-A-62-100449.

However, in precision press molding of glass at high temperatures, there is no problem if Sb ₂ O ₃ is contained only in a very small amount in the glass composition, but if Sb ₂ O ₃ is contained in several percent or more, it volatilizes, and the surface of the mold and It causes clouding on the surface of the precision-pressed glass element, or reacts with the mold on the surface of the mold to cause a reduction in the durability of the mold.

In order to lower the softening point of the glass, it is common practice to add an alkali metal oxide such as Li ₂ O into the composition. However, adding a large amount of an alkali metal oxide significantly deteriorates the chemical durability of glass and makes it difficult to maintain optical performance.

Accordingly, in view of the above-mentioned circumstances, the present invention has an optical constant having a refractive index (n _d ) of 1.65 to 1.75 and an Abbe number (ν _d ) of 50 or more. It is an object of the present invention to provide an optical glass suitable for precision press molding, which realizes softening properties at a low temperature while maintaining excellent chemical durability and has good releasability from a mold material.

Another object of the present invention relates to an optical glass formed by precision press working using the optical glass described above.

[0010]

The optical glass according to the present invention has the following components and the following contents. Ingredient content _{(wt%) SiO 2 5~25 B 2 O} 3 16~40 However _{SiO 2 + B 2 O 3 30~50} Li 2 O 2~ 8 Na 2 O 0~10 K 2 O 0~10 Cs 2 O 0 However _{Na 2 O + K 2 O +} Cs 2 O 0~15 MgO 0~10 CaO 0~30 SrO 0~30 BaO 0~20 ZnO 1~20 However CaO + SrO + BaO + ZnO 5~40 Al 2 O 3 0~10 ZrO 2 0. 5 to 15 La ₂ O ₃ 22 to 40 According to the present invention, SiO ₂ —ZrO ₂ —B ₂ O ₃ —La ₂ O ₃ —Z
An optical glass having an nO—Li ₂ O composition has the advantages of high chemical durability, low softening point, high refractive index, and low dispersion glass.

The reasons for defining the component ranges of the optical glass according to the present invention as described above are as follows.

SiO ₂ is a main component constituting a glass network and has effects of improving chemical durability and suppressing devitrification. However, if the amount is less than 5% by weight, the above effect cannot be sufficiently obtained. If the amount is more than 25% by weight, the yield point temperature becomes high, and it becomes difficult to obtain desired optical performance. The yield point is defined as a sufficiently annealed, 50 mm long, 4 m diameter.
The thermal expansion curve of the glass by accurately measuring the elongation and temperature of the sample when heated uniformly at a constant temperature of 4 ° C. per minute under a load of 50 g in the axial direction of the sample glass rod of m length. On this thermal expansion curve, the sample apparently stops elongating and then starts shrinking due to deformation due to the softening of the glass with an increase in temperature. This is the transition point from the apparent expansion to the contraction.

B ₂ O ₃ constitutes a glass network like SiO _2, and is effective as a low-dispersion component when used in an amount of 16% by weight or more. However, if it exceeds 40% by weight, the chemical durability deteriorates and the tendency of devitrification increases.

In order to maintain the stability and low dispersibility (abbe number of 50 or more) of the glass, SiO ₂ and B ₂ O ₃
Is required to be 30% by weight or more, and in order to maintain a low softening property and a high refractive index (n _d = 1.65 or more), Si is required.
The total amount of O ₂ and B ₂ O ₃ must be less than 50% by weight.

Here, the Abbe number (ν _D ) is

[0016]

(Equation 1) (N _D , n _F , n _C are the sodium d lines (587.56n
m), hydrogen F line (486.13 nm), hydrogen C line (65
6.28 nm). ) Indicates the degree of the difference in the refractive index depending on the wavelength of light. When the Abbe number is small, the difference in the refractive index depending on the wavelength is large, that is, when the chromatic dispersion is large, and when the Abbe number is large, the reverse is true. It is.

Li ₂ O can drastically lower the yield point temperature of glass by making it an essential component.
Meltability is improved. In particular, in order to reduce the yield point temperature to 560 ° C. or less, 2% by weight or more is required. On the other hand, if the amount of Li ₂ O is too large, the chemical durability deteriorates, the thermal expansion coefficient becomes too large, and a desired optical constant cannot be obtained.

The _{Na 2 O, K 2 O,} Cs 2 O is similar to the Li ₂ O, the effect of lowering the yield point temperature is remarkable. However, if each exceeds 10% by weight and the total amount exceeds 15% by weight, desired optical constants cannot be obtained.

MgO is effective for stabilizing glass,
If it exceeds 10% by weight, a desired optical constant cannot be obtained.

Although CaO, SrO and BaO are effective for stabilizing the glass in order to obtain a desired optical constant,
If the content of O and SrO exceeds 30% by weight and the content of BaO exceeds 20% by weight, the chemical durability of the glass deteriorates and the tendency of devitrification increases. ZnO is highly effective in improving chemical durability and stabilizing glass, and also has a favorable effect on lowering the yield point temperature. To achieve these effects, an amount of at least 1% by weight is required.
However, since this component has a strong tendency to highly disperse the optical performance of glass, the maximum amount is set to 20% by weight.

However, CaO, SrO, BaO, ZnO
When the total amount exceeds 40% by weight, the chemical durability of the glass is deteriorated and the tendency of devitrification is increased. When the total amount is less than 5% by weight, a sufficient effect cannot be obtained.

[0022] Although Al ₂ O ₃ is a effective in improving the chemical durability, sag temperature of the glass increases exceeds 10 wt%.

ZrO ₂ has remarkable effects of suppressing the devitrification phenomenon of glass and improving the chemical durability.
It is an essential component in the present invention. However, if the content is less than 0.5% by weight, the effect cannot be obtained. Also, 15
If the content exceeds 10% by weight, the desired optical constants cannot be obtained, the yield point temperature of the glass increases, the devitrification phenomenon is easily induced,
The adverse effects such as appear.

La ₂ O ₃ is an essential component for a glass having a high refractive index and a low dispersion as in the present invention, and requires a minimum of 22% by weight. It is extremely difficult to suppress.

[0025]

Further, as the optical glass of the present invention, a more preferable composition from the viewpoint of preventing the tendency to devitrify is as follows: Component content (% by weight) SiO ₂ 5 to 20 B ₂ O ₃ 20 to 35 SiO ₂ + B ₂ O _{3 30~45 Li 2 O 2~ 7 Na 2} O 0~ 5 K 2 O 0~ 5 Cs 2 O 0~ 5 except _{Na 2 O + K 2 O +} Cs 2 O 0~10 MgO 0~ 5 CaO 0~15 SrO 0~15 a BaO 0 to 15 ZnO 2 to 12 provided that CaO + SrO + BaO + ZnO 5~20 Al 2 O 3 0~10 ZrO 2 1~10 La 2 O 3 25~35 However SiO ₂ + ZrO ₂ 10~25.

[0027]

Embodiments of the present invention will be described below with reference to the drawings.

First, Table 1 shows Examples 1 to 10 and Comparative Examples 1 to
About 3 of total 13 kinds of glass, the composition (in the table, values are weight%), refractive index (n _d), Abbe number ([nu _d), sag temperature (At), and shows the water resistance.

Glass is made of a raw material consisting of oxides, carbonates, and nitrates, and has a glass amount of 2 for each composition.
The desired volume ratio was calculated and blended to 50 ml. The prepared glass raw material mixture is mixed in advance so as to be sufficiently homogeneous, and the mixture is mixed in a 300 ml platinum crucible.
After melting at 0 to 1300 ° C. for about 3 hours, the glass is homogenized by stirring with a platinum rod, and after clarification, the molten glass is poured into a preheated carbon mold to obtain a glass block. Was gradually cooled. To confirm the properties of the glass, cut out small measurement specimen glass from the glass block thus produced, the refractive index (n _d), Abbe number ([nu _d), sag temperature (At), and water resistance of the measurement Was done. The water resistance was evaluated as follows based on the Japan Optical Industry Association Standard (JOGIS Standard). That is, 420-
The glass crushed to a size of 590 μm is divided by the specific gravity of the glass ×
An amount of 1 g is put into a platinum elution basket, put into a quartz glass round bottom flask containing pure water, and treated in a boiling water bath for 60 minutes. After the treatment, the weight loss of the powdered glass (%) Was calculated.

Next, the produced glass block was cut out and processed to obtain a ball-shaped glass material for precision press. This glass material was finished so that the surface roughness Rmax was 0.01 μm or less. This surface roughness is Zy
Using a GOIM MAXIM surface roughness tester, 10 locations of 0.2 × 0.2 mm surface were measured per location for one material. The PV value was 20 nm or less. The PV value is the difference between the highest value (peak value) and the lowest value (valley value) of the measured values.

Using this glass material, a molding experiment was performed using the mold materials shown in Table 2. FIG. 1 is a diagram showing a state before molding, in which 1 is an upper mold, 2 is a lower mold, and 3 is a glass material. The upper mold 1 and the lower mold 2 each have an Rmax of 0.0
Processing was performed to an accuracy of 1 μm or less, and the same material was used for the upper mold 1 and the lower mold 2 in the experiment.

For molding, first, the glass material 3 is placed on the lower mold 2 and the inside of the molding machine is evacuated to 10 −2 Torr or less. Then, when the material of the mold is non-oxide, nitrogen gas is introduced. A nitrogen gas atmosphere was used, and for those containing oxides, a mixed gas atmosphere of nitrogen gas and oxygen gas was used so as to have a constant oxygen partial pressure. Thereafter, the glass and the mold were heated according to the schedule shown in FIG. 3, and after reaching a predetermined molding temperature (T ₀ ), the glass and the mold were kept as they were for 5 minutes.
The upper mold 1 was pressed at a pressure of 00 kg / cm ² for 5 minutes to perform molding. After the pressure molding is completed and the pressure is removed, cooling is performed at a cooling rate of −5 ° C./min to a temperature (T ₁ ) lower by 50 ° C. than the glass transition temperature, and thereafter, the cooling rate is −20 ° C./min or more. After cooling at a speed, a lens-shaped glass sample 4 was taken out at a temperature of 200 ° C. or lower. Incidentally, the glass having different compositions, in order to make the molding conditions is constant, the molding was carried out at a temperature at which the viscosity of each of the glass corresponding to 10 ^9.5 poise. The molding experiment was performed 10 to 100 times for one glass-mold combination.

As a result, in the glass having the composition of Comparative Example 1,
Since the molding temperature was high, the mold surface of the carbide or metal mold material was greatly deteriorated, and the glass having the composition of Comparative Example 2 caused clouding of the mold surface and the lens surface due to volatile components from the glass. Further, with respect to the glass having the composition of Comparative Example 3, occurrence of fogging on the lens surface and deterioration of the mold surface were observed. In contrast, the first embodiment according to the present invention
With respect to the glasses having the compositions of Nos. 1 to 10, good molding was performed without fogging on the surface of the mold or lens surface, deterioration of the mold surface, fusion of the glass and the mold, and the like.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

[Table 3]

[0037]

According to the present invention, in sag temperature (At) is 560 ° C. or less, refractive index (n _d) of 1.65 to 1.7
5. Abbe number (ν _d ) maintains an optical constant of 50 or more,
An optical glass suitable for precision press molding, which has sufficient chemical durability and good releasability from a mold material, can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an arrangement of a mold and a glass material before press molding in a molding experiment of the present invention.

FIG. 2 is a cross-sectional view of a mold after press molding and a molded lenticular glass.

FIG. 3 is a diagram illustrating a temperature schedule during press molding.

[Explanation of symbols]

 Reference Signs List 1 upper mold 2 lower mold 3 glass material before molding 4 molded lens-shaped glass sample

Claims (3)

(57) [Claims] 1. A yield point consisting of the following components having the following contents :
An optical lens formed by precision press working using optical glass having a temperature of 560 ° C. or lower . Ingredient content _{(wt%) SiO 2 5~25 B 2 O} 3 16~40 However _{SiO 2 + B 2 O 3 30~50} Li 2 O 2~8 Na 2 O 0~10 K 2 O 0~10 Cs 2 O 0 However _{Na 2 O + K 2 O +} Cs 2 O 0~15 MgO 0~10 CaO 0~30 SrO 0~30 BaO 0~20 ZnO 1~20 However CaO + SrO + BaO + ZnO 5~40 Al 2 O 3 0~10 ZrO 2 0. 5-15 La ₂ O ₃ 22-40 2. A refractive index (n _d) from 1.65 to 1.75,
2. The optical lens according to claim 1, wherein the Abbe number (v _d ) has an optical constant within a range of 50 or more. 3. A yield point consisting of the following components having the following contents :
An optical lens formed by precision press working using optical glass having a temperature of 560 ° C. or lower . Ingredient content _{(wt%) SiO 2 5~20 B 2 O} 3 20~35 However _{SiO 2 + B 2 O 3 30~45} Li 2 O 2~ 7 Na 2 O 0~ 5 K 2 O 0~ 5 Cs 2 O 0-5 except _{Na 2 O + K 2 O +} Cs 2 O 0~10 MgO 0~ 5 CaO 0~15 SrO 0~15 BaO 0~15 ZnO 2~12 However CaO + SrO + BaO + ZnO 5~20 Al 2 O 3 0~10 ZrO 2 1~ 10 La ₂ O ₃ 25 to 35 where SiO ₂ + ZrO ₂ 10 to 25