JPH11171586A - Lead-free optical barium flint glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To profitably produce a lead-free optical barium flint glass having good meltability and processability, very high chemical resistance, a refractive index nd of 1.55-1.66 and an Abbes's number ηd of 39-52. SOLUTION: The glass is a compsn. consisting of, by weight on the oxide basis, 40-60% SiO2 , 6.5-12% B2 O3 , 10-35% BaO, 0-1% CaO, 0-2% ZnO, 5-12% TiO2 , 0.5-3.5% Al2 O3 , 3-7.5% Na2 O and 3-8% K2 O (Na2 O+K2 O <=15%) and optionally contg. a usual amt. of a refining agent. The glass exhibits positive abnormal or normal partial dispersion in the blue region of its spectrum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION
It relates to a lead-free optical barium flint glass having a refractive index n _{d of} 6 and an Abbe number v _{d of} 39 to 52. In contrast to the customary classification of commercially available glass, which barium flint glass is said to have an Abbe number of 43 to 50, in the present application the term barium flint glass refers to glass having an Abbe number higher or lower than this range. Include.

[0002]

_2. Description of the Related Art In recent years, the glass components PbO and As ₂
Because of the open question of whether O ₃ is environmentally safe, some manufacturers of optical equipment have decided to use only glass that does not contain PbO and also does not contain As ₂ O _3. Some are trying to convert. Therefore, such types of glasses with their respective optical properties must be available on the market. It is also desirable to eliminate PbO in the production of lightweight glass members, that is, low-density glass. Simply replacing the lead oxide with one or more components is generally not enough to reproduce a glass having such desired properties because the optical and glass technical properties are affected by PbO. Can not. Therefore, it is necessary instead to develop new glass compositions or at least make extensive changes.

Various specifications have already been described in the patent literature, and lead-free glasses having optical values in or near the above range are described. However, these glasses have various disadvantages. For example, JP-A-60-2
No. 21338 also describes a glass having a relatively high refractive index, and Y ₂ O ₃ , L
It contains a ₂ O ₃ , B ₂ O ₃ and Li ₂ O, for example, SiO ₂ is merely an optional component. Glasses are expensive and uneconomical for continuous production processes because of their Y ₂ O ₃ content of up to 20% by weight and La ₂ O ₃ content of up to 52% by weight. In some cases very B ₂ O
₃ High content (up to 50% by weight) and the presence of Li ₂ O, which makes the chemical resistance of the glass inferior, which makes the further processing more difficult and their It also limits the use. Li ₂ O
Reduces the crystallization stability of the glass. Further, JP-A-3-5341 describes a glass having a remarkably high Abbe number. However, this glass also requires the addition of Li ₂ O, and further has a relatively high ratio of L ₂ O.
It contains a ₂ O ₃ .

Further, the glasses described in US Pat. Nos. 2,433,883 and 2,523,266 contain Li ₂ O as an essential component. These glasses are further contain ZrO ₂ (respectively 4 to 15 wt% and 2-15 wt%), which also easily crystallized glass. True for glass described in U.S. Patent No. 2,523,265 containing 6-8 wt% of ZrO ₂ in this regard.

A similar disadvantage (disadvantage) for La ₂ O ₃ and Y ₂ O _{3 is also} true for Nb ₂ O ₅ . This oxide increases the overall price and thus significantly increases the manufacturing costs. It is German patent DE 1 496 5
No. 24, JP-A-6-107425, JP-A-52-45
612 is an essential component of the glass. DE 14
The glass described in 96 524 has a fairly high refractive index (1.65 or higher). In the glasses described in JP-A-6-107425 and JP-A-52-45612, in some cases, they are affected by very high alkali metal oxide contents (up to 30% by weight and up to 40% by weight, respectively). Nb ₂ O ₅ is essential to improve the significant adverse effects on chemical resistance and crystallization stability.

[0006] Al ₂ described in US Pat. No. 975,617
O ₃ -free glass and the glass proposed in JP-A-5-17176 require SrO and contain this component in an amount of up to 20% by weight and up to 14% by weight, respectively. ZrO ₂ described in US Pat. No. 5,300,467.
The containing glass also contains SrO in an amount of up to 20% by weight. The effect on the optical properties of SrO is that BaO and C
Although it is almost equivalent to that of aO, BaO and CaO can be added to glass with a very inexpensive raw material.
Could be advantageous for economic production.

Japanese Patent Application Laid-Open No. 56-73646 discloses a high Ba
Glasses having an O content and optionally containing up to 3% by weight of TiO ₂ are described. At least when they do not contain PbO, these glasses do not achieve optical states with high refractive index and low Abbe number. further,
Their chemical resistance will not be good. JP-A-1-13
The glass shown in 3956 has a very high Al ₂ O ₃ content. This is particularly true for the optional B component
_{In the} absence of ₂ O ₃ , melting of the glass becomes difficult.

[0008] DE-B 191 835, German Patent Application Publication
The glasses shown in No. 0 do not contain alkali metal oxides or simply contain them in small amounts. The resulting poor meltability is compensated for by a fluorine content of 2 to 14.5% by weight. When the fluorine content is high as described above, it is difficult and expensive to purify exhaust gas containing HF and SiF ₄ during production on an industrial scale.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to provide good melting and processing characteristics and economical production. And very high chemical resistance, 1.55
Refractive index n _d of １1.66 and Abbe number ν _{d of} 39-52
To provide a lead-free optical barium flint glass having Chemical resistance is important for both the subsequent processing of the glasses and their possible applications.

[0010]

Means for Solving the Problems] To achieve the above object, according to the basic aspect of the present invention, the following composition SiO ₂ 40 to 60 wt% on an oxide basis, B ₂ O ₃ 6.5 to 12 wt%, BaO 10 to 35 wt%, CaO 0 to 1 wt%, ZnO 0 to 2 wt%, TiO ₂ 5 to 12 wt%, Al ₂ O ₃ 0.5~3.5 wt%, Na ₂ O 3 to 7.5 wt%, K ₂ O 3 to 8% by weight, provided that Na ₂ O + K ₂ have the O ≦ 15 wt%, 1, characterized in that it contains conventional amounts of fining agent, if necessary. Refractive index n _d of 55 to 1.66 and 39 to
Unleaded optical barium flint glass having a 52 Abbe number [nu _d is provided.

[0011]

Glass DETAILED DESCRIPTION OF THE INVENTION The present invention comprises a glass former SiO ₂ 40 to 60 wt%. When the SiO ₂ content is lower than the above range, the acid resistance of the glass decreases, and when it is high, the meltability of the glass is impaired. The glasses according to the invention contain at least 0.5% by weight of Al ₂ O ₃ and at least 5% by weight of TiO ₂ in order to improve the acid resistance. However, the maximum content of these oxides is
Al ₂ O ₃ is 3.5% by weight (preferably 3% by weight);
iO ₂ is 12% by weight and should not be exceeded if this upper limit is exceeded, since the meltability is again impaired. TiO ₂ is effective not only for improving the chemical resistance but also for achieving a high refractive index and finely adjusting the Abbe number, and has an effect of giving a particularly high refractive index. Due to a similar effect on acid resistance and meltability, in a preferred embodiment of the invention, the total amount of said oxides (SiO ₂ + Al ₂
O ₃ + TiO ₂ ) is limited to 47-72% by weight.

The glass contains 3 to 7.5% by weight of Na ₂ O and 3 to 8% by weight of K ₂ O. However, Na ₂ O and K
The total amount of ₂ O should not exceed 15% by weight. These alkali metal oxides are effective for improving the melting property of glass. If the amount is less than the above range, the melting point is not sufficiently lowered, so that economical production becomes more difficult.
On the other hand, if it is larger than the above range, the coefficient of thermal expansion increases, the transition temperature decreases, and the chemical resistance is impaired.

The glass further comprises 6.5 to 12% by weight of B ₂
Contains O ₃ . This component also improves the meltability, but in this case the adverse effect on the swelling need not be taken into account. However, when it exceeds the above range,
Chemical resistance, especially alkali resistance, is reduced. Maximum content is 1
Preferably it is limited to 1% by weight.

In a particularly preferred embodiment of the present invention, B ₂ O ₃
The weight ratio of / (SiO ₂ + TiO ₂ + Al ₂ O ₃ ) is limited to a maximum of 0.20, and the B ₂ O ₃ content is also limited according to the content of the oxide in the denominator. Glasses satisfying this condition exhibit very good alkali resistance. As the weight ratio increases, this alkali resistance decreases,
When the weight ratio exceeds the value of 0.2, the best alkali resistance, class 1, is no longer achieved.

In order to achieve the desired Abbe number range, the glass contains 10 to 35% by weight of BaO. If the content of BaO is less than the above range, the Abbe number in the barium flint glass range cannot be obtained, while if the content is higher than the above range, the tendency of devitrification increases. To improve the crystallization stability, the glass can contain up to 1% by weight of CaO and up to 2% by weight of ZnO. It is preferred that at least 0.1% by weight of CaO and / or ZnO, especially at least 0.1% by weight, of CaO is present. C
When the contents of aO and ZnO exceed the above upper limits, it becomes more difficult to achieve a high refractive index with a high Abbe number.

A prior German application (application number P19 703 39) of the applicant's application which has not been published on the filing date of the present invention.
The lead-free optical glass described in 1.1) partially overlaps with the glass shown in the present application in refractive index and Abbe number, and has a similar composition. Compared to these glasses, the glasses described herein differ in that no ZrO ₂ is used. Since the glass of the present invention does not contain ZrO ₂ , it can be melted at a low temperature and can be manufactured more economically. The glasses of the present invention also have better melting properties due to the higher Na ₂ O content.

Within the composition ranges specified in the basic aspect of the present invention for the glass having the above-mentioned refractive index and Abbe number, there are two preferred composition ranges as shown below, one of which is: Providing glass with a high refractive index,
The other provides a low refractive index glass. (1) A glass having a high BaO content and a relatively low SiO ₂ content, having the following composition on an oxide basis: 41 to 48% by weight of SiO ₂ , 6.5 to 8% by weight of B ₂ O ₃ , BaO 28 to 35 wt%, CaO 0.5 to 1 wt%, ZnO 1 to 2 wt%, TiO ₂ 5 to 12 wt%, Al ₂ O ₃ 0.5~1.5 wt%, Na ₂ O 3~5 wt%, K ₂ O 3 to 5 wt%, provided that Na ₂ O + K ₂ O 6.5~8 wt%. These glasses have a refractive index n _d of 1.60-1.66 and an Abbe number v _{d of} 39-52.

(2) Relatively rich in SiO ₂ and low Ba
A glass of O content has the following composition on an oxide basis: SiO ₂ forty-six to fifty-nine wt%, B ₂ O ₃ 6.5 to 8.5 wt%, BaO 10 to 28 wt% (preferably 10 to <28 wt%), CaO 0.1 to 1 wt%, ZnO 0 to 2 wt%, TiO ₂ from 6.5 to 12% by weight (preferably 7 to 12 wt%), Al ₂ O ₃ 0.5~2 % By weight, _{3 to} 7.5% by weight of Na ₂ O, 3 to 7.5% by weight of K ₂ O, provided that Na ₂ O + K ₂ O ≧ 6.5% by weight. These glasses have a refractive index n _d of 1.56-1.61 and an Abbe number v _{d of} 39-52.

Further, within the composition range specified in the basic embodiment of the present invention, the composition has a particularly balanced composition, and its optical data n _d and ν _d change in a narrow range, and are very good. There is a family of barium flint glasses that exhibit excellent chemical resistance and very good meltability and workability. The composition range of these oxide basis is as follows: SiO ₂ 43 to 57 wt%, B ₂ O ₃ 7~11 wt%, BaO 11 to 26 wt%, CaO 0.1 to 0.5 wt% , ZnO 0 to 1.5 wt%, TiO ₂ 7.5 to 11 wt%, Al ₂ O ₃ 0.8~3 wt%, Na ₂ O 3.5~7 wt%, K ₂ O 3.5~ 7.5% by weight, provided that Na ₂ O + K ₂ O ≦ 14% by weight. These glasses have a refractive index n _d of 1.57-1.61 and an Abbe number v _{d of} 43-48.

In order to improve the glass quality, one or more fining agents known per se can be added in customary amounts to the batch (mixture) in order to clarify the glass. This results in a glass having particularly good internal quality without bubbles and streaks. The fining agent used is As ₂
If instead of O ₃ , for example Sb ₂ O ₃ is used, which can be added without compromising the glass quality,
In that case, the novel lead-free glass according to the invention is also arsenic-free. In a further preferred embodiment of the present invention, the glass following fining agents: Sb ₂ O ₃ + F ^- at least 0.05 wt%, however, F in Sb ₂ O ₃ content _of 0 to 0.5 wt% ^- 0 ０．１0.1 weight, which results in excellent internal glass quality. F ^- is added, for example, as KF.

The glasses according to the invention have a positive anomaly or normal partial dispersion in the blue region of the spectrum. Description: The partial dispersion ability in the blue region of the spectrum, so-called relative partial dispersion, is represented by the following equation (1).

(Equation 1)

The "normal (normal) straight line" is defined by the following equation (2) by definition in the blue region of the spectrum.

P _{g, F} = 0.6438−0.001682 · ν _d (2) Glass whose partial dispersion is on the straight line is called “regular glass”.

For glasses having a dispersion behavior different from "normal glass", a coordinate difference △ P _{g, F} indicating the displacement of the corresponding P _{g, F} −ν _d point from the “normal line” is specified: P
_{g and F} are above the normal line (positive abnormal partial variance: △ P
_{g, F} = positive) or below (negative anomalous partial variance: △ P _{g, F}
= Negative), it is usual to roughly classify the glass into two groups. Glass exhibiting anomalous partial dispersion is important for correcting the residual coloring effect, so-called secondary spectrum.

[0024]

The novel glass composition range according to the present invention is as follows:
Thus, another group of lead-free optical glasses having the above-mentioned optical properties is provided. These glasses overcome the disadvantages of the prior art without introducing other disadvantages. The glasses according to the invention have very good chemical resistance (which is critical for subsequent processing such as grinding and polishing, and for potential uses of the glass), and very high crystallization stability . This high crystallization stability allows glass production in fairly large melting equipment, such as optical tanks. Thus, the glass can be easily melted and processed, and the glass can be produced at low cost, coupled with the elimination of the use of some expensive components. The fact that the glasses do not contain PbO is important not only for the aforementioned environmental protection reasons, but also in terms of the advantageous effects obtained by reducing the density of the glasses and raising their transition temperature. A further advantage is that the glasses according to the invention have a P
Not only does it contain no bO, but in a preferred embodiment A
s ₂ O ₃ is not contained.

[0025]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but it is needless to say that the present invention is not limited to the following examples.

EXAMPLES 1 TO 8 The novel glasses of the eight examples of the present invention within the preferred composition range were prepared from conventional raw materials. An example of the dissolution is shown in Table 1.

[Table 1] The properties of the glass obtained by this melting example are shown in Example 3 in Table 2 below.

The glass according to the present invention was produced as follows. That is, the raw materials for oxides, preferably carbonates and nitrates, were weighed, and a fining agent Sb ₂ O ₃ was added thereto, followed by sufficient stirring. The glass batch is placed in a continuous melting apparatus for about 1,
Melted at 340-1390C, then clarified and homogenized well. The glass was formed to the desired dimensions at a casting temperature of 1,180-1,230 ° C.

Table 2 shows the respective compositions (weight% on oxide basis) and the refractive index n
_d , Abbe number ν _d , partial dispersion P _gF in the blue region of the spectrum, anomalous ΔP _gF of this partial dispersion, density ρ [g /
cm ³ ], coefficient of thermal expansion α _20/300 [10 ⁻⁶ / K], and transition temperature [° C.].

[Table 2]

With respect to Examples 6 to 8, other glass properties were also measured. Table 3 shows the results. As shown in Table 3, each glass exhibited high crystallization stability (one measurement being the liquidus temperature of the crystal) and good chemical resistance. The glass of the present invention belongs to the class 1 of acid resistance, and particularly has an acid resistance of 1.0. These glasses also belong to class 1 in alkali resistance. In this case, the alkali resistance is expressed by the weight ratio B ₂ O ₃ / (SiO ₂ + TiO ₂ + Al ₂ O ₃ ).
Is reduced, and the alkali resistance of 1.3 at a weight ratio of 0.19 becomes 1.0 at a weight ratio of 0.12.

[Table 3]

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Magdalena, Winkler-Trudewig, Germany, 55126 Mainz, Am Kirchborn 20 b. 231

Claims (8)

[Claims] 1. The following composition, based on oxides: 40 to 60% by weight of SiO _2, 6.5 to 12% by weight of B ₂ O ₃ , 10 to 35% by weight of BaO, 0 to 1% by weight of CaO, 0 to 2 of ZnO wt%, TiO ₂ 5 to 12 wt%, Al ₂ O ₃ 0.5 to 3.5 wt%, Na ₂ O 3 to 7.5 wt%, K ₂ O 3 to 8% by weight, provided that Na ₂ O + K ₂ A refractive index n _d of 1.55-1.66 and 39-35, characterized by having O 2 ≦ 15% by weight and, if necessary, containing customary amounts of fining agents.
52 unleaded optical barium flint glass having an Abbe number [nu _d of. 2. The following composition based on oxides: 41 to 48% by weight of SiO _2, 6.5 to 8% by weight of B ₂ O _3, 28 to 35% by weight of BaO, 0.5 to 1% by weight of CaO, ZnO 1 ２2 wt%, TiO ₂ 5-12 wt%, Al ₂ O ₃ 0.5-1.5 wt%, Na ₂ O 3-5 wt%, K ₂ O 3-5 wt%, provided that Na ₂ O + K ₂ 2. Barium according to claim 1, having an index of refraction n _{d of} 1.60 to 1.66, characterized in that it comprises O 6.5 to 8% by weight and, if necessary, contains a customary amount of fining agent. Flint glass. 3. The following composition based on oxides: 46 to 59% by weight of SiO _2, 6.5 to 8.5% by weight of B ₂ O _3, 10 to 28% by weight of BaO, 0.1 to 1% by weight of CaO, ZnO 0 to 2 wt%, TiO ₂ 6.5 to 12 wt%, Al ₂ O ₃ 0.5~2 wt%, Na ₂ O 3 to 7.5 wt%, K ₂ O 3 to 7.5 wt% , however claim with _{Na 2 O + K 2 O ≧} 6.5 has a weight%, refractive index of 1.56 to 1.61, characterized in that it contains conventional amounts of refining agents optionally n _d 2. The barium flint glass according to 1. 4. The following composition based on oxides: 43 to 57% by weight of SiO _2, 7 to 11% by weight of B ₂ O _3, 11 to 26% by weight of BaO, 0.1 to 0.5% by weight of CaO, ZnO 0 1.5 wt%, TiO ₂ 7.5~11 wt%, Al ₂ O ₃ 0.8~3 wt%, Na ₂ O 3.5~7 wt%, K ₂ O 3.5~7.5 A refractive index n _d of 1.57 to 1.61, characterized in that it has a Na ₂ O + K ₂ O ≦ 14 wt%, and optionally contains a conventional amount of a fining agent.
Barium flint glass according to claim 1 having an Abbe number [nu _d 48. 5. The barium flint glass according to claim 1, wherein the total amount of SiO ₂ , TiO ₂ and Al ₂ O ₃ is 47 to 72% by weight. 6. The weight ratio B ₂ O ₃ / (SiO ₂ + TiO ₂₎
+ Al ₂ O ₃ ) is at most 0.20, barium flint glass according to any one of claims 1, 4 and 5. 7. The Sb ₂ O ₃ 0 to 0.5 wt% as a fining agent, F ^- a 0 to 0.1 _{^{wt%, F - + Sb 2 O}} 3 ≧
The barium flint glass according to any one of claims 1 to 6, which is contained in a total amount of 0.05% by weight. 8. The barium flint glass according to claim 1, which contains no arsenic oxide except for inevitable impurities.