JPH08253341A - Near infrared cutting filter glass - Google Patents

Abstract

PURPOSE: To improve the transmittance in visible sight range, sharp cutting properties in near infrared region, long-term retention of initial transmittance and hardness of a near infrared cutting filter glass by adding CuO to a base glass comprising fluorophosphate-based glass. CONSTITUTION: CuO in an amount of 0.5-6wt.% is added to 100wt.% of base glass comprising a fluorophosphate-based glass having a composition of 10-45wt.% of P2 O5 , 10-25wt.% of MgF2 , 0-20wt.% of CaF2 O, 0-30wt.% of SrF2 , 0-30wt.% of BaF2 , 10-45wt.% of MgF2 +CaF2 , 10-45wt.% of SrF2 +BaF2 , 0.5-12wt.% of LiF+NaF+KF and <1wt.% of AlF3 (<=60wt.% of the total of the fluorides can be replaced with oxides) to give a blend. The blend is melted, stirred, cleaned, cast, annealed, cut and polished to give the objective filter glass having 430kg/mm<2> Vickers hardness, excellent transmittance in 400-600nm visible range and excellent sharp cutting properties in the vicinity of 700nm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a near-infrared cut filter glass which is used as a color correction filter for a color VTR camera and which efficiently transmits a visible region of 400 to 600 nm and has an excellent sharp cut characteristic near 700 nm.

[0002]

C used in a color VTR camera
An image pickup device such as a CD has a spectral sensitivity ranging from the visible region to the near infrared region around 1100 nm. Therefore, good color reproducibility cannot be obtained as it is,
It is necessary to correct the normal luminosity by using a filter that absorbs the infrared region.

Conventionally, in this type of filter, glass in which CuO is added to phosphate glass so as to selectively absorb near infrared rays has been used. This glass contains a large amount of P ₂ O
₅ and CuO as an essential component, it has a blue-green color by forming Cu ²⁺ ions coordinated with a large number of oxygen ions in an oxidizing molten atmosphere, and has near-infrared cut characteristics. is there.

Recently, in order to improve the low weather resistance of phosphate glass, fluorophosphate glass is used as the basic glass, and CuO is added to the glass, for example, JP-A 1-219037, Glass and the like described in JP-A-3-73041 have been developed.

[0005]

When the content of CuO is increased in order to promote the near-infrared ray cutting effect, the above-mentioned phosphate-based glass generally lowers the spectral transmittance in the wavelength range of 400 to 500 nm and thus becomes green. However, there is a problem that the sharp cut property deteriorates in the wavelength range of 600 to 700 nm. In particular, since such a filter glass is used in the form of a thin plate, a high CuO content is required, but it is difficult to obtain a filter glass having a desired spectral transmission characteristic due to the above problems. Further, since the phosphate glass, which is the basic glass, has insufficient weather resistance, it causes weathering on the polished surface of the glass, and thus has a problem in long-term use as an optical filter.

Further, although the above fluorophosphate type glass has excellent weather resistance, it easily devitrifies, and if the P ₂ O ₅ content is kept low in order to improve the weather resistance, the coefficient of thermal expansion becomes large and it is weak against thermal shock. There is a drawback that. In order to use the glass which is solidified after melting as a filter, steps such as grinding and polishing are performed. However, the fluorophosphate glass described in JP-A 1-219037 is heated by a heat shock at a temperature difference of 50 to 100 ° C. The yield in the molding process is low because cracks occur. On the other hand, in the glass described in JP-A-3-17304, the heat expansion resistance was improved by increasing the P ₂ O ₅ content within a range not impairing the weather resistance to suppress the thermal expansion coefficient of the glass to a low level. .

However, in the color VTR camera, which is the main application of such a glass filter, the solid-state image pickup device such as CCD is miniaturized and densified along with the rapid development of semiconductor technology, and at the same time, the tendency toward high image quality is strengthened. There is. In order to meet the demand for higher resolution, the solid-state image sensor is required to have a smaller size and a higher density. In addition, the size of the element is reduced from 1/2 inch system to 1/3 inch system in order to respond to the downsizing of the optical system. It has been promoted by reducing to / 4 inch system. As a result, the area per pixel becomes extremely small, and even in the glass filter placed on the front surface of the solid-state image sensor, minute defects that have not been a problem in the past have come to be regarded as a problem.

From such a background, since the glass hardness of each of the above fluorophosphate-based glasses is lower than that of the phosphate-based glass, when optical polishing is carried out, minute scratches remain on the polished surface or end portions It has come to be pointed out that there is a high rate of occurrence of minute chippings in the. In addition, if a minute chip generated during polishing adheres to the glass substrate,
This also causes damage to the polished surface in the subsequent steps and during transportation, and the substrate itself to which the defective pieces are attached also becomes a defective product, resulting in a significant decrease in yield. In particular, the filter for the solid-state image pickup device built in the apparatus is reduced in size as the solid-state image pickup device is miniaturized as described above, and the thickness must be polished to about 2 to 1 mm. There is a limit to the measures that can be taken only by handling the board.

The present invention has been made in consideration of such circumstances, and has excellent chemical durability while maintaining desired spectral transmission characteristics, and has high hardness of glass, and the above-mentioned minute defects occur during polishing. An object is to provide a near-infrared cut filter glass that is difficult to do.

[0010]

The present invention achieves the above object by setting the hardness of glass to a predetermined value or more. That is, the present invention is a near-infrared cut filter glass which is a fluorophosphate glass containing 0.5 to 6 mass% of CuO and has a Vickers hardness of 430 kg / mm ² or more.

Further, the glass of the present invention has a mass percentage of
_{P 2 O 5 10~45%, MgF} 2 10~25%, CaF
_{2 0~20%, SrF 2 0~30%} , BaF 2 0~30
%, But MgF ₂ + CaF ₂ 10-45%, SrF ₂
+ BaF ₂ 10 to 45%, LiF + NaF + KF 0.
0.5 to 6% by mass of CuO is added to 100 parts by mass of basic glass consisting of 5 to 12% and AlF ₃ less than 1% (however, up to 60% of the total amount of fluoride can be replaced with oxide). It is characterized by that.

[0012]

The present inventor carried out gradual cooling treatment on various kinds of glass in the same manner as in the case of producing varieties to polish the glass plate from which distortion was completely removed, and confirmed the occurrence of chips and scratches. Vickers hardness of 43 even with salt-based glass
Those that are 0 kg / mm ² or more have a significant difference in the occurrence rate of chips and scratches compared to those that are less than that, and especially those that are 450 kg / mm ² or more have a very low occurrence rate of scratches and scratches. Was confirmed.

Next, the reason why the glass composition of the present invention is limited to the above range will be described.

P ₂ O ₅ is a main component forming a glass network structure, but if it is less than 10%, vitrification is difficult,
If it exceeds 45%, the weather resistance becomes poor.

MgF ₂ is a component that has the effect of increasing the hardness of the glass, but if it is less than 10%, its effect is not sufficiently obtained, and if it exceeds 25%, the devitrification tendency becomes strong, which is not preferable. It is preferably 20 to 24%, and in this range, the above effect becomes more remarkable.

CaF ₂ has the effect of stabilizing the glass without lowering the hardness of the glass, but if it exceeds 20%, the melting temperature becomes high and devitrification tends to occur. However, if the total amount of MgF ₂ and CaF ₂ is less than 10%, the effect of increasing the hardness of the glass is insufficient, and it is more effective if it is 20% or more. Further, if the total amount exceeds 45%, the melting temperature becomes high and the glass tends to devitrify, which is not preferable.

SrF ₂ and BaF ₂ have the effect of stabilizing the glass and improving the weather resistance, but if each exceeds 30%, the devitrification tendency becomes strong, which is not preferable. However, Sr
If the total amount of F ₂ and BaF ₂ is less than 10%, the above effect cannot be sufficiently obtained, and if it exceeds 45%, the devitrification tendency becomes remarkable and the desired glass cannot be obtained.

LiF, NaF and KF are effective components for lowering the melting temperature, but if less than 0.5%, the effect cannot be expected, and if more than 12%, the weather resistance is deteriorated.

AlF ₃ is a component effective for improving weather resistance, but since it has a large viscosity difference with other components in a molten state, if it exceeds 1%, homogenization of the glass becomes difficult, and it becomes difficult to homogenize the glass. Heterogeneous layers are likely to occur. Also Al
When F ₃ is less than 1%, the melting temperature can be suppressed to a low level, volatilization of each component is prevented, and the glass composition is stabilized. In particular, the effect becomes remarkable in the range of 0.2 to 0.7%.

It is possible to replace up to 60% of the total amount of fluoride in the above components with oxides.
If the substitution amount exceeds 60%, the desired spectral transmittance, weather resistance and hardness cannot be obtained.

CuO is an essential component for near-infrared ray cutting, but if it is less than 0.5%, sufficient near-infrared ray cutting property cannot be obtained, and if it exceeds 6%, the transmittance in the visible region decreases, and The glass becomes unstable.

In the glass of the present invention, Pb, Zn, L
Since the addition of a fluoride or oxide of a, Y, Yb tends to significantly reduce the hardness of the glass, it may be contained as an impurity, but it is preferably less than 1%.

[0023]

Embodiments of the present invention will be described below. Examples of the present invention are shown in Table 1. The glass composition in Table 1 is shown by mass percentage, and the weather resistance is obtained by polishing the glass at a temperature of 60 ° C.
It was kept under the condition of relative humidity of 95%, and it was shown by the time until the deterioration of the glass surface was observed.

The glass shown in Table 1 was prepared by mixing the raw materials so that each of them had a predetermined composition, accommodating it in a platinum crucible, covering it with a lid, melting it at a temperature of 650 to 850 ° C., stirring and refining it.
After being cast in a mold and gradually cooled, it was cut and mechanically polished into a flat plate having a thickness of 1.6 mm. In Table 1, No.
The glass Nos. 21 to 26 show comparative examples, and No. 21-23
Is an example of phosphate glass, No. 24 to 26 are examples of conventional fluorophosphate glass. In the same manner for these comparative examples, a flat plate-like sample having a thickness of 1.6 mm was prepared.

[0025]

[Table 1]

[Table 1]

[Table 1]

[Table 1]

The spectral transmittance of the flat glass thus prepared was measured. Of these, the example Nos. 2, 9, 11, 15, 20 and Comparative Example N
o. The spectral transmittance curves of 21, 22, and 23 are shown in FIG. As is apparent from FIG. 1, the glass of the example according to the present invention has a higher transmittance at 400 to 500 nm than the glass of the comparative example and is excellent in the sharp cut property from 600 to 700 nm.

As a result of the weather resistance test, the phosphate glass of the comparative example showed surface deterioration after 250 hours, whereas the glass of the example showed surface deterioration after 1000 hours. I couldn't do it.

In the preparation of the flat plate-shaped sample, each glass was sliced from a glass block cast in a mold and gradually cooled to a thickness of about 2.2 mm, and 11 × 11 mm
300 pieces each of which was cut to the size of the above were fixed to the surface plate of the polishing apparatus, cerium oxide was used as the polishing material, the load was 100 g / cm ² , the rotation speed was about 50 rpm, and the wall thickness was 1.6.
It was mechanically polished until it became mm.

After washing and drying, the rate of occurrence of scratches and chips, including minute ones of about 5 μm, was examined for the obtained flat plate-like samples. The results are also shown in Table 1. No. showing the conventional fluorophosphate glass. Although the glass Nos. 24 to 26 have almost the same performance as the present example in weather resistance, the hardness of the glass is low and the occurrence rate of scratches and chips in the working process is high. On the other hand, in the glass of this example, the higher the Vickers hardness (kg / mm ² ) shown as “hardness” in the table, the lower the occurrence rate of scratches and chips in the working process. Two
20% or more lower than the comparative examples of 4 to 26.

From the above, the glasses of the examples according to the present invention are
The processing quality for mechanical processing can be improved while maintaining the excellent weather resistance and near-infrared sharp cut property of the fluorophosphate glass. As a result, it is possible to reduce secondary defects caused by minute scratches and defective pieces that occur in conventional glass,
It is possible to provide a high-quality glass filter that meets the demand for higher resolution with a high yield.

[0031]

As described above, the glass filter of the present invention is made of fluorophosphate-based glass having excellent weather resistance, has a high transmittance in the visible region, and has an excellent initial cut property in the near infrared region. Rate characteristics can be maintained for a long period of time.
Further, by increasing the hardness of the glass, minute defects are less likely to occur even during mechanical processing, and it is particularly ideal as a small optical filter.

[Brief description of drawings]

FIG. 1 is a curve diagram showing a spectral transmittance of a glass of an example of the present invention and a glass of a comparative example.

[Explanation of symbols]

Example No. 1 of the present invention. Spectral transmittance curve 2 of glass Nos. 2, 9 and 15 Spectral transmittance curves of glasses 11 and 20 3 Comparative example No. Spectral transmittance curves of 21, 22 and 23 glass

Claims (2)

[Claims] 1. A basic glass 1 made of fluorophosphate glass.
A glass containing 0.5 to 6 parts by mass of CuO with respect to 00 parts by mass, and having a Vickers hardness of 430 kg / mm ^2.
The above is the near-infrared cut filter glass characterized by the above. 2. The base glass is P _{2 in} mass percentage.
O ₅ 10-45%, MgF ₂ 10-25%, CaF ₂ 0
-20%, SrF ₂ 0-30%, BaF ₂ 0-30%,
However, MgF ₂ + CaF ₂ 10-45%, SrF ₂ + B
aF ₂ 10-45%, LiF + NaF + KF 0.5-
The near-infrared cut filter glass according to claim 1, which has a composition of 12% and AlF ₃ less than 1% (however, up to 60% of the total amount of fluoride can be replaced with an oxide).