Search

EP-4741889-A1 - OPTICAL FILTER AND INFRARED SENSOR AND OPTICAL FILTER MANUFACTURING METHOD

EP4741889A1EP 4741889 A1EP4741889 A1EP 4741889A1EP-4741889-A1

Abstract

An optical filter (1) includes a base material (10) containing a continuous phase (11) of a polycrystalline fluoride and an absorbent (20) dispersed in the base material (10); the optical filter (1) contains 0.1 to 10% by mass of the absorbent that absorbs light in an infrared region of more than 7.5 µm, and 9 µm or less; a wavelength bandwidth of the optical filter (1) having a linear transmittance of 30% or more per 1 mm thickness in a target wavelength band of 3 µm or more, and 7 µm or less, is 50 nm or more; a maximum linear transmittance of the optical filter (1) per 1 mm thickness in a target wavelength band of more than 7.5 µm, and 25 µm or less, is 10% or less; the optical filter (1) contains 80% by mass or more of an inorganic substance; the optical filter (1) contains 50% by mass or more of a polycrystalline fluoride; a porosity of the optical filter (1) is 30% or less; and a median pore diameter of the optical filter (1) is 500 nm or less.

Inventors

  • SATO NATSUKI
  • YOSHIOKA TATSURO
  • KURIZOE NAOKI
  • SAWA RYOSUKE
  • SEKINO TOHRU
  • GOTO TOMOYO
  • CHO SUNGHUN
  • SEO YEONGJUN

Assignees

  • Panasonic Intellectual Property Management Co., Ltd.

Dates

Publication Date
20260513
Application Date
20240702

Claims (7)

  1. An optical filter comprising: a base material containing a continuous phase of a polycrystalline fluoride; and an absorbent dispersed in the base material, wherein the optical filter contains 0.1 to 10% by mass of the absorbent that absorbs light in an infrared region of more than 7.5 µm, and 9 µm or less, a wavelength bandwidth of the optical filter having a linear transmittance of 30% or more per 1 mm thickness in a target wavelength band of 3 µm or more, and 7 µm or less, is 50 nm or more, a maximum linear transmittance of the optical filter per 1 mm thickness in a target wavelength band of more than 7.5 µm, and 25 µm or less, is 10% or less, the optical filter contains 80% by mass or more of an inorganic substance, the optical filter contains 50% by mass or more of a polycrystalline fluoride, a porosity of the optical filter is 30% or less, and a median pore diameter of the optical filter is 500 nm or less.
  2. The optical filter according to claim 1, wherein the fluoride includes a complex fluoride containing an alkali metal.
  3. The optical filter according to claim 2, wherein the complex fluoride includes a compound having a cryolite crystal structure.
  4. The optical filter according to any one of claims 1 to 3, wherein the absorbent contains a fluororesin.
  5. The optical filter according to claim 4, wherein the fluororesin contains a resin including a perfluoroalkyl group.
  6. An infrared sensor comprising an optical filter according to any one of claims 1 to 5.
  7. A method of manufacturing an optical filter comprising a step of pressurizing a mixture containing a polycrystalline fluoride and an absorbent at a temperature of 250°C or lower, wherein the optical filter contains 0.1 to 10% by mass of the absorbent that absorbs light in an infrared region of more than 7.5 µm, and 9 µm or less, a wavelength bandwidth of the optical filter having a linear transmittance of 30% or more per 1 mm thickness in a target wavelength band of 3 µm or more, and 7 µm or less, is 50 nm or more, a maximum linear transmittance of the optical filter per 1 mm thickness in a target wavelength band of more than 7.5 µm, and 25 µm or less, is 10% or less, the optical filter contains 80% by mass or more of an inorganic substance, the optical filter contains 50% by mass or more of a polycrystalline fluoride, a porosity of the optical filter is 30% or less, and a median pore diameter of the optical filter is 500 nm or less.

Description

TECHNICAL FIELD The present invention relates to an optical filter, an infrared sensor, and a method of manufacturing an optical filter. BACKGROUND ART Conventionally, infrared transmissive windows using inorganic fluoride as a base material have been used for special applications in fields such as academic research and industry, such as window materials for physical and chemical equipment. Patent Literature 1 discloses a Fourier transform infrared spectrophotometer for measuring fluorinated gases in a sample containing corrosive gases, which includes a measuring cell with a cell window composed of one selected from the group consisting of CaF2, BaF2, MgF2, LiF, and ZnSe. CITATION LIST PATENT LITERATURE Patent Literature 1: WO 2019/176624 SUMMARY OF INVENTION There is known a technology for sensing various gases and flames using an infrared detection element and an optical filter for infrared transmission. However, there is a possibility that the materials mentioned above may transmit even an undesired wavelength, for example, and may not be suitable as an optical filter for an infrared sensor. The present invention has been made in view of such problems of the prior art. An object of the present invention is to provide an optical filter suitable for an infrared sensor for detecting flames, for example, an infrared sensor using the optical filter, and a method of manufacturing an optical filter. In order to solve the problem mentioned above, an optical filter according to a first aspect of the present invention includes a base material containing a continuous phase of a polycrystalline fluoride, and an absorbent dispersed in the base material. The optical filter contains 0.1 to 10% by mass of an absorbent that absorbs light in an infrared region of more than 7.5 µm, and 9 µm or less. A wavelength bandwidth of the optical filter having a linear transmittance of 30% or more per 1 mm thickness in a target wavelength band of 3 µm or more, and 7 µm or less, is 50 nm or more. A maximum linear transmittance of the optical filter per 1 mm thickness in a target wavelength band of more than 7.5 µm, and 25 µm or less, is 10% or less. The optical filter contains 80% by mass or more of an inorganic substance. The optical filter contains 50% by mass or more of a polycrystalline fluoride. A porosity of the optical filter is 30% or less. A median pore diameter of the optical filter is 500 nm or less. An infrared sensor according to a second aspect of the present invention includes an optical filter. A method of manufacturing an optical filter according to a third aspect of the present invention includes a step of pressurizing a mixture containing a polycrystalline fluoride and an absorbent at a temperature of 250°C or lower. The optical filter contains 0.1 to 10% by mass of the absorbent that absorbs light in an infrared region of more than 7.5 µm, and 9 µm or less. A wavelength bandwidth of the optical filter having a linear transmittance of 30% or more per 1 mm thickness in a target wavelength band of 3 µm or more, and 7 µm or less, is 50 nm or more. A maximum linear transmittance of the optical filter per 1 mm thickness in a target wavelength band of more than 7.5 µm, and 25 µm or less, is 10% or less. The optical filter contains 80% by mass or more of an inorganic substance. The optical filter contains 50% by mass or more of a polycrystalline fluoride. A porosity of the optical filter is 30% or less. A median pore diameter of the optical filter is 500 nm or less. BRIEF DESCRIPTION OF DRAWINGS [FIG. 1] FIG. 1 is a cross-sectional view schematically illustrating an example of an optical filter according to the present embodiment.[FIG. 2] FIG. 2 is an enlarged schematic cross-sectional view of a part of the optical filter illustrated in FIG. 1.[FIG. 3] FIG. 3 is a cross-sectional view schematically showing another example of an optical filter according to the present embodiment.[FIG. 4] FIG. 4 is an enlarged schematic cross-sectional view of a part of the optical filter shown in FIG. 3.[FIG. 5] FIG. 5 is a cross-sectional view schematically showing an example of an infrared sensor according to the present embodiment.[FIG. 6] FIG. 6 is an infrared absorption spectrum of the fluororesin used in an example.[FIG. 7] FIG. 7 is an infrared absorption spectrum of PVDF used in an example.[FIG. 8] FIG. 8 is a linear transmittance of a test sample according to Example 1.[FIG. 9] FIG. 9 is a linear transmittance of a test sample according to Example 2.[FIG. 10] FIG. 10 illustrates the linear transmittance of a test sample according to Example 3.[FIG. 11] FIG. 11 illustrates the linear transmittance of a test sample according to Example 4.[FIG. 12] FIG. 12 is secondary electron images of a cross section of a test sample according to Example 1.[FIG. 13] FIG. 13 is reflected electron images of a cross section of a test sample according to Example 1.[FIG. 14] FIG. 14 is binarized images of the reflected electron images of FIG. 13.[FIG.