JPS5814378B2 - fluorophosphate optical glass - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a composition of a fluorophosphate optical glass having a particularly small dispersion, the optical constant of which is a refractive index nd=1.
．． 42 to 1.47, Atsbe number vd=90 to 97.

Using low-dispersion glass in optical equipment reduces chromatic aberration, resulting in better quality images.

In particular, fluorophosphate optical glass exhibits a relatively large anomalous partial dispersion and allows modification of the secondary spectrum, so the effect is even greater.

So-called fluoride glass, which uses beryllium fluoride as a glass forming material, has been known as a glass with a high fluorine content.
Its optical constants are nd=1.33~l. 42, νd=9
Ranges from 0 to 105.

However, since BeJJ is highly toxic, fluorophosphate glass is known which does not contain it and has a stabilized glass structure by adding phosphate as a glass former.

For example, in Special Publication No. 32-7430, P-A7-RI-
Rl-F-0 (Rn is an alkaline earth metal, R■ is an alkali metal), and its optical constant is nd-1.45 to 1.
55, νd=80 to 90 has been disclosed, but this could not be applied to fluoride glasses in which beryllium fluoride is used as a glass forming material.

On the other hand, in JP-A-50-43112, the refractive index is 1.45.
Although fairly low refractive indexes of 8 or less have been disclosed, this is not always sufficient to keep dispersion as low as possible while maintaining stability against devitrification.

An object of the present invention is to provide a fluorophosphate optical glass which does not contain hydrogen and has a lower dispersion and can be produced stably and easily.

The fluorophosphate optical glass according to the present invention is essentially the same as the above-mentioned fluorophosphate optical glass <P-A7-R...-Rl-F-
0 (RI is an alkali metal, R1 is an alkali metal), but by using these components in proportions different from conventional ones, a low dispersion glass (with Atsube number This makes it possible to obtain νd=90 to 97).

P-Al-Rl-RI-F-0 (R
In systems where l is an alkaline earth metal and R1 is an alkali metal, stability against devitrification can be improved by adding a certain amount of alkali metal R1, but on the other hand, the softening point becomes extremely low and This made it difficult to control the amount of tanuki, so care had to be taken in deciding how much to contain.

However, in the present invention, if lithium fluoride LiF, which is a fluoride of lithium Li having the smallest atomic number among alkali metals, is added, it is possible to achieve lower dispersion and at the same time stabilize against devitrification with a relatively small amount. Furthermore, it was found that this tendency was remarkable in a region where phosphorus P and oxygen O were low and calcium fluoride CaF2 was relatively high.

Based on the above findings, the present invention determined the optimal content range of lithium fluoride LiF added as an essential component, reduced the content of phosphorus and oxygen, and introduced a relatively large amount of calcium fluoride. It is something.

The composition range of the fluorophosphate optical glass according to the present invention is shown below in mole percent.

PF5 5-20 AlF3 18-42 CaF2 17-35 SrF2 0-25 BaF2 0-22 SrF2+BaF2 8-33 LiF 0.8-7 MPF2 0.8-22 ZnF2 0-5 PbF2 0-2 YF3 0-7 LaF3 0-7 ZrF4 0-3 NdF3 0-5 Of these, the substitution ratio of fluorine ions and oxygen ions F-/02-
is 2.5 to 15.

The content range of each component was determined for the following reasons.

Fluoride glass that does not contain lagoonium Be will not vitrify unless it is extremely rapidly cooled, making it unsuitable for industrialization. However, in the presence of phosphorus pentoxide, P20, acts as a glass-forming oxide. , increasing the stability of the structure, ie stability against devitrification.

P20 is also an essential component for improving chemical durability.

If it is less than 5%, it is unstable against devitrification and the chemical durability is also significantly reduced.

If it exceeds 20%, dispersion increases and the desired optical constants cannot be obtained.

Aluminum fluoride AlF3 is important as a component that imparts low dispersion properties to glass, and further contributes to stabilizing the glass structure and improving chemical durability together with P20.

If it is less than 18%, the desired low dispersion cannot be obtained,
If it exceeds 42%, it will not vitrify.

Fluorides of alkaline earth metals with low atomic numbers reduce dispersion, and especially calcium fluoride, CaF2, gives glass the property of low dispersion and widens the range of stable vitrification against devitrification. It is effective for

Among alkaline earth metals, fluorides of relatively large atomic numbers such as strontium Sr and barium Ba are magnesium fluoride M? Although it has the disadvantage of increasing dispersion compared to F,A calcium fluoride, CaF2, it is essential for the purpose of maintaining stability against devitrification.

CaF2 is unstable to devitrification below 17%;
Furthermore, the desired low dispersion cannot be obtained.

On the other hand, when it exceeds 35%, the tendency to devitrify increases significantly.

The content of SrF2 and BaF2 must be at least 8% in order to maintain stability against devitrification of the glass.

However, as these components increase, the dispersion increases, so the upper limits for SrF2 and BaF2 are 25% and 22%, respectively.
and the content shall not exceed 33%.

In addition, as the alkali metal fluoride, the above-mentioned lithium fluoride LiF is the most effective for suppressing devitrification and maintaining the softening point, but if it is less than 0.8%, it does not have sufficient stability against devitrification. On the other hand, if it exceeds 7%, the softening point becomes extremely low, making manufacturing difficult.

Furthermore, the substitution ratio of fluorine ions and oxygen ions (F-/0
2-) has a great influence on the stability against glass dispersion and devitrification.

If the value of this ratio is less than 2.5, the dispersion becomes too large, and if it exceeds 15, the tendency to devitrify increases.

P-A7-Ca-Sr-Ba-Li-F- as above
Although it is possible to obtain the desired optical glass with 0 series, by adding appropriate amounts of other components, the range of optical constants can be further expanded and the stability against devitrification can be further improved.

Similar to CaF2, MSF2 imparts low dispersion properties to glass, and when used in combination with other alkali metal fluorides, increases the stability of glass against devitrification.

In particular, by increasing CaF2 relative to MgF2,
The value of the ratio of MSF2 to F2, that is, the Mgf2 value.

．． If it is 63 or less, it will be lost. Stability will be better.

However, if M1F2 exceeds 22%, the tendency to devitrify increases significantly.

On the other hand, when ZnF2 and PbF2 are added, the refractive index of the glass can be increased.

However, in order to maintain the property of low dispersion, the amount added must not exceed 5% for ZnF2 and 2% for PbF2.

YF3, ZrF4 and rare earth fluorides, especially LaF
By adding a small amount of s, chemical durability and stability against devitrification can be improved.

If added in excess of an appropriate amount, the tendency to devitrify increases, so it is desirable to use YF3 at 7%, ZrF4 at 3%, and LaF3 at 7% or less.

In addition, fluorophosphate glass with NdF3 added within 5% is
It can be used as a laser glass with a small nonlinear refractive index coefficient.

Furthermore, M? Glasses of the second composition containing F2 in the range of 0.8 to 22 mole percent are stable to devitrification and can yield glasses with lower dispersion.

Among the above first composition ranges, the glass having the following second composition (expressed in mole percent) has better chemical durability.

PF, 5.5~20 A7F3 25~42 PbF2 0 Among these, some of the fluorine ions are replaced with oxygen ions, and at that time, F-/02- (ratio of the number of fluorine ions to the number of oxygen ions) in the glass is , 2.6 to 13.2 In the following third composition (expressed in mole percent) of the second composition range, a glass that is particularly stable against devitrification can be obtained.

PF5 7.5-17.5 MfF2 0.8-18 CaF2 20-32 SrF2 0.8-23 BaF2 0.8-18 SrF2+BaF2 8-27 LiF 1.3-7 Of these, some of the fluorine ions are replaced with oxygen ions F-/02 (ratio of the number of fluorine ions to the number of oxygen ions) in the glass is 3.0 to 10.0.

As the phosphorus and oxygen raw materials in the present invention, for example, metal phosphates containing component cations are used.

Usually, it is preferable to use metaphosphates of alkali metals, alkali metals, or aluminum.

For the other components, the fluorides described in the examples are used as raw materials, and the desired proportions are weighed and mixed to give 800 to 100%
It can be manufactured by placing it in a platinum crucible in an electric furnace at 00°C, melting it, clarifying it, stirring it, homogenizing it, casting it, and slowly cooling it.

Table 1 shows the composition (expressed in mole percent), refractive index nd, and Atsube number νd of the optical glass according to the present invention.
Shown below.

In Table 1, the composition examples in the upper row use the fluoride display method, and the lower row shows the mixing ratios (expressed in mole percent) of raw materials corresponding to the compositions in the upper row.

According to the present invention as described above, a fluorophosphate optical glass that has small dispersion and is stable against devitrification is provided.

Furthermore, since the softening point is not so low, it can be manufactured industrially more easily.

Claims (1)

[Claims] 1 Fluorine ion F- and oxygen ion 02 as anions
- and when the cations in the glass are expressed as fluorides, PF5 5-20 AnoF3 18-42 CaF2 17-35 SrF2 0-25 BaF2 0-22 SrF20 BaF2 8-33 LiF 0.8-7 MgF2 0.8-22 ZnF2 0-5 PbF2 0-2 YF3 0-7 LaF3 0-7 ZrF, O-3 NdF3 0-5 and further CaF by mole percent
The value of the ratio of MgF2 to 2 is 0.63 or less, and some of the fluorine ions are replaced with oxygen ions, at which time F-/02- (ratio of the number of fluorine ions to the number of oxygen ions) in the glass. is in the range of 2.5 to 15, and the refractive index nd
= 1.42 to 1.47, and an Abpe number νd = 90 to 97. 2% allowance The fluorophosphate optical glass according to claim 1 has a composition range of PF5 5.5 to 20 A7F3 25 to 42 PbF2 0 in mole percent, and has a composition range of F-702- (fluorine ion A fluorophosphate optical glass having a ratio of the number of oxygen ions to the number of oxygen ions in the range of 2.6 to 13.2. 3. In the fluorophosphate optical glass according to claim 2, PF in mole percent, 7.5-17.5 MgF2 0.8-18 CaF2 20-32 SrF2 0.8-23 BaF2 0.8- 18 SrF2+BaF2 8 to 27 LiF 1.3 to 7, and F-/02- (ratio of the number of fluorine ions to the number of oxygen ions) in the glass is in the range of 3.0 to 10.0. Phosphate optical glass.