EP-4741890-A1 - VISIBLE/INFRARED SEPARATION FILM AND METHOD FOR MANUFACTURING SAME

Abstract

A visible/infrared separation film includes aggregates in each of which metal nanoparticles each having a major axis of 25 nm or less are aggregated, wherein a distance between surfaces of the metal nanoparticles in the aggregate is 2 nm or less, wherein a size of the aggregate is 50 nm or less, wherein the aggregates are spaced apart from each other at intervals of 5 nm or more, and wherein a film thickness is 120 nm or less.

Inventors

• MATSUMOTO Nagisa
• KUWAHARA TAKESHI
• TSUCHIDA Nami

Assignees

• Minebea AccessSolutions Inc.

Dates

Publication Date

20260513

Application Date

20240701

Claims (11)

1. A visible/infrared separation film comprising aggregates in each of which metal nanoparticles each having a major axis of 25 nm or less are aggregated, wherein a distance between surfaces of the metal nanoparticles in the aggregate is 2 nm or less, wherein a size of the aggregate is 50 nm or less, wherein the aggregates are spaced apart from each other at intervals of 5 nm or more, and wherein a film thickness is 120 nm or less.
2. The visible/infrared separation film according to claim 1, wherein a resin is included between the metal nanoparticles and between the aggregates.
3. The visible/infrared separation film according to claim 1 or 2, wherein, in the aggregates included in the visible/infrared separation film, aggregates having an aspect ratio (major axis/minor axis), which is a ratio of a major axis to a minor axis, in a range of 1 to 2 are 70% or more in a proportion by number.
4. The visible/infrared separation film according to claim 1 or 2, wherein the metal nanoparticles are composed of silver.
5. The visible/infrared separation film according to claim 1 or 2, wherein the metal nanoparticles are composed of indium.
6. A method for manufacturing a visible/infrared separation film, comprising: a preparation step of dispersing at least one silver compound selected from silver oxide and silver carbonate and a polymer dispersant in an alcohol solvent, irradiating the alcohol solvent with ultrasonic waves to disperse the silver compound, and then leaving the alcohol solvent in a dark place to prepare a coating liquid; and a coating film formation step of coating a surface of a substrate with the coating liquid obtained in the preparation step.
7. The method for manufacturing a visible/infrared separation film according to claim 6, wherein a concentration of the silver compound in the alcohol solvent is 5% to 40% by mass.
8. The method for manufacturing a visible/infrared separation film according to claim 6, wherein the alcohol solvent is at least one selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, and 1-methoxy-2-propanol.
9. The method for manufacturing a visible/infrared separation film according to claim 6, wherein the polymer dispersant has an acid value of 150 or less.
10. The method for manufacturing a visible/infrared separation film according to claim 9, wherein the polymer dispersant has a styrene-maleic anhydride resin structure, and some of the maleic anhydride is modified with a polyalkylene glycol having a terminal hydroxyl group or a polyalkylene glycol having a terminal amino group.
11. The method for manufacturing a visible/infrared separation film according to claim 6, wherein an amount of the polymer dispersant added to the silver compound is 2% to 25% in term of mass percentage of a nonvolatile content.

Description

TECHNICAL FIELD The present invention relates to a visible/infrared separation film that reflects visible light and transmits infrared light and a method for manufacturing the same. Priority is claimed on Japanese Patent Application No. 2023-110183, filed July 4, 2023 and Japanese Patent Application No. 2023-110185, filed July 4, 2023, the contents of which are incorporated herein by reference. BACKGROUND ART In the related art, in a case in which visible light and infrared light are separated from each other, a dielectric multilayer film that reflects the visible light out of incident light while transmitting infrared light out of the incident light has sometimes been used. The dielectric multilayer film is formed by alternately stacking two types of dielectrics with different refractive indices. Such a dielectric multilayer film specifically reflects only the visible light by exhibiting an ideal multilayer thin film interference phenomenon seen in the skin of fish such as a hairtail in nature while allowing the rest to be transmitted due to the dielectric properties, thereby performing visible/infrared separation. A commonly known example is a so-called cold mirror, as described in Patent Document 1, which is made by precisely stacking generally 20 or more thin film layers on a substrate by sputtering or the like. The cold mirror is used in an optical filter, particularly, a projector or the like, to remove infrared rays from a light source. In addition, as shown in Patent Document 2, the cold mirror is used as a reflector mirror in a head-up display (HUD) to cut out infrared rays from sunlight entering from the outside and prevent heating. Furthermore, the cold mirror separates the sunlight into visible light and infrared light and is used as the core of a system that uses the visible light to generate electricity and the infrared light as a heat source, thereby making it possible to utilize sunlight with high efficiency. In addition, recently, a film that is composed of a multilayer film in which approximately 1000 layers of resins with slightly different refractive indices are alternately stacked and that exhibits a metallic appearance has also become known. Such a film is used in automobile emblems that are transmissive to millimeter-wave radar, taking advantage of the appearance and radio wave transmitting properties thereof and is used in decorative materials that cover the infrared ray receiving portions of remote controls for home appliances, taking advantage of the infrared ray transmitting properties thereof. Citation List Patent Document Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2006-259124Patent Document 2: Japanese Patent No. 6577342 SUMMARY OF INVENTION Technical Problem In the cold mirror of the related art, the exhibition principle of the appearance is structural color, and thus the cold mirror is made by determining the film thickness of each layer in nanometer units using an optical calculation simulation to specifically reflect only the visible light with a smaller number of layers and precisely reproducing the determined film thickness by sputtering or the like. However, since a thin film having a total of 20 or more layers is formed by precisely sputtering while changing the components thereof, ultimately to have a film thickness of 1 micrometer, there is a problem that the manufacturing process takes a long time and is very costly. In addition, due to limitations in film-forming equipment, it is difficult to make a film large in area, and there is also a problem that the degree of freedom in the shape of the substrate is low. An aspect of the present invention has been made in view of the above circumstances, and one of objects of the present invention is to provide a visible/infrared separation film that can be made large in area and that allows for a high degree of freedom in a shape of a substrate. Another aspect of the present invention have been made in view of the above circumstances, and one of objects of the present invention is to provide a method for manufacturing a visible/infrared separation film that enables easy manufacturing without using a thin film manufacturing technology such as a sputtering method. Solution to Problem To solve the above problems, the present invention employs the following configuration. According to an aspect of the present invention, there is provided a visible/infrared separation film including aggregates in each of which metal nanoparticles each having a major axis of 25 nm or less are aggregated, wherein a distance between surfaces of the metal nanoparticles in the aggregate is 2 nm or less,wherein a size of the aggregate is 50 nm or less,wherein the aggregates are spaced apart from each other at intervals of 5 nm or more, andwherein a film thickness is 120 nm or less. According to another aspect of the present invention, there is provided a method for manufacturing a visible/infrared separation film, in