JP2003292336A - Glass composition and optical element using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a glass composition which has low Tg, is suitable for mold forming and excellent in heat resistance. <P>SOLUTION: The glass composition comprises each component, by weight, of 18-65% of SiO<SB>2</SB>, 5-50% of B<SB>2</SB>O<SB>3</SB>, 3-35% of Al<SB>2</SB>O<SB>3</SB>, 10-15% of Li<SB>2</SB>O, 1-15% of K<SB>2</SB>O and 1-10% of Na<SB>2</SB>O, wherein Li<SB>2</SB>O+K<SB>2</SB>O+Na<SB>2</SB>O is 19-30%. Preferably, in terms of further lowering Tg and performing efficient deaeration, the glass composition further comprises one or more of the components of 0-5% of ZnO and 0-25% of BaO+SrO+CaO, and further comprises 1 wt.% or less of Sb<SB>2</SB>O<SB>3</SB>relative to the total weight of the above described glass components. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glass composition and an optical element, and more specifically, a glass composition having excellent heat resistance and capable of being molded at low temperature, and an optical obtained by molding the glass composition. It is related to the element.

[0002]

2. Description of the Related Art The use of a free-form surface mirror as an illuminating optical system mirror for liquid crystal projectors, digital televisions, etc. is being studied because it can reduce the illuminance distribution, achieve high brightness, and realize a compact optical design.
However, the free-form surface shape is very difficult to process, and it is very difficult to reduce the production cost.

Molding method (precision press molding method) is a technique for relatively easily producing glass of such a difficult-to-process shape. When the glass is molded by the molding method, it is necessary to bring the press die to a temperature near the glass transition temperature (hereinafter sometimes referred to as “Tg”) or higher. The surface of the mold is oxidized and the metal composition is changed, resulting in severe deterioration of the mold and shortening the mold life. As a measure for suppressing the mold deterioration, controlling the molding atmosphere to an inert atmosphere such as nitrogen can be considered, but this causes an increase in production cost. Therefore, it is desirable that the glass used in the molding method has Tg as low as possible.

On the other hand, in an apparatus such as a liquid crystal projector or a digital television, an illumination optical system mirror arranged near a high heat source is heated to about 200 ° C. while the apparatus is in use, while the apparatus is powered off. When it is turned on, it is cooled to room temperature. Therefore, high heat resistance is required for the illumination optical system mirror in which such a kind of heating-cooling cycle is repeated many times.

However, glass having a low Tg has a low strain point (generally, it is said that the strain point is lower than Tg by about 150 ° C.), so that a glass having a low Tg suitable for the molding method has poor heat resistance. There was a problem.

As a prior document, Japanese Patent Laid-Open No. 2000-327365 discloses a glass composition similar to the present invention as a glass composition having a high specific elastic modulus, but Tg is not particularly noted, and The examples do not disclose a glass composition having a Tg of less than 480 ° C. and a Young's modulus (E) of less than 100 GPa. Similarly, Japanese Patent Application Laid-Open No. 2000-103636 discloses glass and glass-ceramics having a high specific elastic modulus, but the Tg is extremely high at 555 ° C. or higher and is not suitable for the molding method. . Japanese Patent Application Laid-Open No. 60-77144 discloses a glass composition range similar to the present invention as an ultraviolet transmitting glass, but since it contains a fluorine component as an essential component, the moldability of the glass is poor and Tg and Young's modulus (E ) Etc. are not disclosed at all. On the other hand, no commercially available glass has a low Tg and is excellent in heat resistance.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of such conventional problems, and an object thereof is a glass composition having a low Tg, suitable for a molding method, and excellent in heat resistance. To provide.

Another object of the present invention is to provide an optical element having a small linear expansion coefficient, excellent heat resistance and high productivity.

[0009]

The glass composition of the present invention which achieves the above-mentioned objects, in wt%, is SiO ₂ : 18 to 65%, B ₂ O ₃ : 5 to 50%, Al ₂ O ₃ : 3. _{~35%, Li 2 O: 10~15} %, K 2 O: 1~15%, Na 2 O: 1~10%, _{however, Li 2 O + K 2 O} + Na 2 O: containing 19 to 30% of each component It is characterized by doing. In the following, "%" means "wt%" unless otherwise specified.

From the viewpoint of further lowering Tg and performing efficient defoaming, ZnO: 0 to 5%, BaO +
SrO + CaO: It is preferable that one or more components of 0 to 25% are further contained, and Sb ₂ O ₃ is further contained by 1 wt% or less based on the total weight of the glass components.

From the viewpoint of further improving moldability and heat resistance, the glass transition temperature (Tg) is 480 ° C.
Below, Young's modulus (E) of 75 to 95 GPa, Poisson's ratio (ν) of 0.3 or less, coefficient of linear expansion α (30 to 200 ° C)
Is 115 or less, and the tensile stress (σ) calculated from the equation (1) is preferably 20 × 10 ⁵ GPa or less. σ = 2 · E · α · (T _l −T _s ) / 3 (1−ν) (1) where T _{l is the} glass internal temperature and T _{s is the} glass surface temperature.

The optical element of the present invention is characterized by being obtained by molding the glass composition described in any of the above.

Here, the optical element is preferably any one of a reflection mirror, a lens, a prism and a diffraction grating.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Breakage of glass due to a rapid change in temperature is caused by the generation of stress due to the temperature difference between the surface of the glass and the inside. For example, when glass is rapidly cooled from high temperature, the temperature of the glass surface becomes lower than that of the inside, and if the coefficient of linear expansion is positive, tensile stress is generated on the glass surface and compressive stress is generated on the inside. The tensile stress on the glass surface promotes the extension of cracks existing on the glass surface and breaks the glass. Therefore, as the evaluation of the heat resistance of glass, the magnitude of the tensile stress generated on the surface in the operating temperature range can be used as an index.

The smaller the value of the tensile stress σ, the smaller the stress caused by the temperature change, and the higher the heat resistance.
As is clear from the equation (1), in order to reduce the tensile stress σ, the Young's modulus E is small, the linear expansion coefficient α is small,
The Poisson's ratio ν should be reduced. Therefore, in the glass composition of the present invention, the Young's modulus E is in the range of 75 to 95 GPa and the linear expansion coefficient α (30 to 200 ° C.) is 115 or less by optimizing the combination and content of the glass components.
When Poisson's ratio ν is 0.3 or less, tensile stress σ is 20
Succeeded in suppressing to less than × 10 ⁵ GPa. Since the illumination optical system mirror used in a device such as a liquid crystal projector or a digital television may be heated to about 200 ° C., the heat resistance temperature range is set to 30 ° C. (normal temperature) to 200 ° C. in the present invention. ing.

The reasons why each component of the glass composition of the present invention is limited will be described below. First, SiO ₂ is an essential component of the present invention and a component that forms a glass network.
It also has the effect of reducing the linear expansion coefficient and Young's modulus. If the content of SiO ₂ is less than 18%, the linear expansion coefficient and Young's modulus cannot be suppressed within the desired ranges, while if the content exceeds 65%, the Tg becomes 480 ° C. or higher and the meltability increases. Getting worse. Therefore, the content of SiO ₂ is set in the range of 18 to 65%. More preferable content is 2
It is in the range of 0 to 64%.

Like SiO ₂ , B ₂ O ₃ is an essential component of the present invention and a component for forming a glass network, and has the effect of lowering the Tg of glass. If the B ₂ O ₃ content is less than 5%, the Tg will be higher than the desired range, while if the content exceeds 50%, the linear expansion coefficient will be higher than the desired range. Therefore, the content is set in the range of 5 to 50%. A more preferable content is in the range of 5 to 48%.

Al ₂ O ₃ is an essential component of the present invention and has the effects of improving chemical durability and reducing the linear expansion coefficient. If the content of Al ₂ O ₃ is less than 3%, such an effect cannot be obtained. On the other hand, when the content exceeds 35%, the devitrification tendency increases. Therefore, the content is set in the range of 3 to 35%.

Li ₂ O is an essential component of the present invention and has a Tg of
Has the effect of dramatically lowering the Li ₂ O content is 10
If it is less than%, such effects cannot be sufficiently obtained.
On the other hand, if the content exceeds 15%, the stability of the glass decreases. Therefore, the content is set in the range of 10 to 15%. A more preferable content is in the range of 11 to 15%.

K ₂ O and Na ₂ O are essential components of the present invention and have the effect of dramatically lowering Tg, and Li ₂
When used together with O, it also has the effect of increasing the stability of the glass. If the respective contents of K ₂ O and Na ₂ O are less than 1%, such an effect cannot be obtained. On the other hand, if the respective contents exceed 15% and 10%, the stability of the glass decreases.
Therefore, the content of each of K ₂ O is set in the range of 1 to 15% and that of Na ₂ O is set in the range of 1 to 10%. More preferable content is K ₂
O is in the range of 1 to 13% and Na ₂ O is in the range of 1 to 8%.

However, Li ₂ O + K ₂ O + Na ₂ O is 19
It is important to be ~ 30%. This is because if the total amount of these alkali metal oxides is less than 19%, the desired Tg cannot be obtained, while if the total amount exceeds 30%, the stability of the glass decreases. More preferable total amount is 19-
It is in the range of 29%.

In the glass composition of the present invention, ZnO
And alkaline earth metal oxides (BaO + SrO + Ca
If necessary, one or more specific amounts of the glass component (O) may be further contained. ZnO has the effect of lowering the glass transition point, but if the content exceeds 5%, the devitrification tendency of the glass increases. Therefore, the content is preferably in the range of 5% or less.

Alkaline earth metal oxide (BaO + SrO
+ CaO) has the effect of improving the stability of the glass, but if the total amount exceeds 25%, the coefficient of thermal expansion becomes larger than the predetermined range and the chemical durability of the glass deteriorates. Therefore, the total amount of alkaline earth metal oxides is preferably 25% or less.

Sb ₂ O ₃ may be contained as a fining agent in the range of 1 wt% or less based on the total weight of the glass components. The reason why the content is 1 wt% or less is that a sufficient fining action can be obtained by including 1 wt%.
A more preferable content is 0.5 wt% or less.

If necessary, Gd ₂ O ₃ , P ₂ O ₅ , Y
₂ O ₃ , TiO ₂ , MgO, WO ₃ , BiO ₂ , Ta ₂ O ₅ ,
Naturally known glass components and additives such as La ₂ O ₃ may be added as long as the effects of the present invention are not impaired.

The optical composition can be produced by the known production method using the glass composition of the present invention, and the optical element is preferably produced by molding. As mold molding that can be used here,
For example, direct press molding in which molten glass is dropped from a nozzle into a mold heated to a predetermined temperature and molded, or preform material is placed in the mold and heated above the glass softening point to perform press molding. Any method such as heat molding may be used. According to such a method, the polishing and grinding steps are unnecessary and the productivity is improved.

The optical element produced by using the glass composition of the present invention is suitably used in a portion where heat resistance is particularly required. For example, as a light source reflection mirror, lens, prism, diffraction grating of a liquid crystal projector or a digital television. Used.

[0028]

EXAMPLES The present invention will be described more specifically below with reference to examples. The present invention is not limited to these examples.

Examples 1 to 14 and Comparative Example 1 Using general glass raw materials such as oxide raw materials, oxide hydrates, carbonates and sulfates, glass compositions were prepared so that the target compositions shown in Table 1 were obtained. The raw materials were blended and thoroughly mixed with powder to prepare a blended raw material. This is put into a platinum crucible in an electric furnace heated to 900 to 1,300 ° C., melted and clarified, stirred and homogenized, cast into a preheated iron or carbon mold, and slowly cooled to obtain each sample. Manufactured. The glass transition temperature (Tg) and the glass deformation temperature (A
t), linear expansion coefficient (α), Young's modulus (E) and Poisson's ratio (ν) were measured, and the tensile stress (σ) was calculated from them. The measurement results are also shown in Table 1. In addition, Tg, A
The t and α were measured using TMA. Comparative Example 1
Is a copy of Example 3 described in Japanese Patent Laid-Open No. 2000-327365.

[0030]

[Table 1]

Examples 1 to 1 which are glass compositions of the present invention
Sample No. 4 has a Tg of less than 480 ° C. and is suitable for molding, and has a Young's modulus (E) of 75 to 95.
GPa, Poisson's ratio (ν) is 0.3 or less, linear expansion coefficient α
(30 to 200 ° C.) was 115 or less, and the tensile stress calculated from these was as small as 20 × 10 ⁵ GPa or less and was excellent in heat resistance. On the other hand, Comparative Example 1
The sample of No. ₂ has a low Li ₂ O content of 6.0% and contains no K ₂ O at all.
It was as high as 8 ° C and was not suitable for molding.

[0032]

With the glass composition of the present invention, SiO ₂ , B ₂
Since each glass component of O ₃ , Al ₂ O ₃ , Li ₂ O, K ₂ O, and Na ₂ O was contained in a specific amount, and the total amount of alkali metal oxides was set in a specific range, Tg was as low as less than 480 ° C. It is suitable for molding and has a small tensile stress (σ) of 20 × 10 ⁵ GPa or less, which is excellent in heat resistance.

ZnO and (BaO + SrO + Ca)
If one or more of O) is further contained in a specific amount, Tg can be further lowered. Further, if Sb ₂ O ₃ is further contained in a specific amount, efficient defoaming can be performed.

Since the optical element of the present invention is obtained by molding the above glass composition, it has excellent heat resistance and high productivity.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G02B 5/18 G02B 5/18 F term (reference) 2H049 AA39 AA45 AA70 4G062 AA04 BB01 DA04 DA05 DA06 DB03 DB04 DB05 DC03 DC04 DC05 DD01 DE01 DE02 DE03 DF01 EA04 EB03 EC03 EC04 ED01 EE01 EE02 EE03 EE04 EF01 EF02 EF03 EF04 EG01 EG02 EG03 EG04 FA01 FB01 FC01 FD01 FE01 FF01 FG01 FH01 FJ01 FK01 FL01 GA01 GA10 GB01 GC01 GD01 GE01 HH01 HH03 HH05 HH09 HH11 HH13 HH15 HH17 HH20 JJ01 JJ03 JJ04 JJ05 JJ07 JJ10 KK01 KK03 KK05 KK07 KK10 MM02 NN32 NN33

Claims (5)

[Claims] 1. A in _{wt%, SiO 2: 18~65%} , B 2 O 3: 5~50%, Al 2 O 3: 3~35%, Li 2 O: 10~15%, K 2 O: 1 to 15%, Na ₂ O: 1 to 10%, but Li ₂ O + K ₂ O + Na ₂ O: 19 to 30%, respectively, The glass composition characterized by containing. 2. Further, one or more components of ZnO: 0 to 5%, BaO + SrO + CaO: 0 to 25%, and Sb ₂ O ₃ with respect to the total weight of the glass components. 2. The glass composition according to claim 1, further containing 1 wt% or less. 3. A glass transition temperature (Tg) of less than 480 ° C., Young's modulus (E) of 75 to 95 GPa, Poisson's ratio (ν) of 0.3 or less, and coefficient of linear expansion α (30 to 200 ° C.).
Is 115 or less, and the tensile stress (σ) calculated from the following formula (1) is 20 × 10 ⁵ GPa or less, The glass composition according to claim 1 or 2. σ = 2 · E · α · (T _l −T _s ) / 3 (1−ν) (1) where T _{l is the} glass internal temperature and T _{s is the} glass surface temperature. 4. An optical element obtained by molding the glass composition according to claim 1. 5. The optical element according to claim 4, which is one of a reflection mirror, a lens, a prism, and a diffraction grating.