JP7361326B2 - Metal nanorod-containing resin, near-infrared shielding lens, near-infrared shielding glasses, protective gear, near-infrared shielding window material, near-infrared shielding device, near-infrared shielding film, near-infrared shielding glass, and method for producing metal nanorod aggregate - Google Patents

Description

The present invention relates to the production of metal nanorod-containing resins, near-infrared shielding lenses, near-infrared shielding glasses, protective gear, near-infrared shielding window materials, near-infrared shielding devices, near-infrared shielding films, near-infrared shielding glasses, and metal nanorod aggregates. Regarding the method.

Biological tissues are affected in various ways by light (electromagnetic waves) with wavelengths ranging from ultraviolet light to visible light to near-infrared light. The effects vary depending on the part of the living tissue, but visible light and infrared rays reach the retina, especially in the eye tissue, and when they act for a long time or with strong intensity, they can cause severe and lasting damage to the iris, retina, etc. Are known. Furthermore, ultraviolet rays are strongly absorbed by the cornea and crystalline lens, and are known to cause disorders such as ophthalmitis and cataracts when they act for a long time or at high intensity.

For example, sunlight contains a lot of light in the wavelength range of ultraviolet light, visible light, and near-infrared light. may cause. For this reason, people who are likely to have their eyes exposed to strong sunlight for long periods of time, such as car drivers, athletes, and aircraft pilots, should use ultraviolet to visible light to near-infrared light to protect their eyes from the sun's rays. Eyeglasses (eyewear) having layers that reduce light having wavelengths of external light may be worn.

For example, lasers with wavelengths from ultraviolet light to visible light to near-infrared light (hereinafter sometimes simply referred to as "lasers") have high intensity, so if your eyes are exposed to that light, it may be compared to sunlight. May cause similar or more serious eye damage.

In addition, for example, in gas welding work, gas cutting work, work using arc lamps or mercury lamps, work using infrared lamps or germicidal lamps, work in blast furnaces, billet heating furnaces, ingot making, etc. Intense eye exposure to may cause eye damage.

Persons involved in work that involves exposure to strong light such as lasers should also wear glasses (eyewear) that have layers that reduce light with wavelengths from ultraviolet to visible light to near-infrared light, or A protective surface or the like having a window (a work viewing window) may be used.

In this way, there is a need to protect the eyes from light of various wavelengths, and various materials have been proposed so far as layers, glasses, and windows to protect the eyes from near-infrared light. Ta. For example, JIS T 8141 (2016) stipulates the light-shielding protective gear that each worker should wear to protect the eyes of workers in places where ultraviolet and infrared radiation and intense visible light that are harmful to the eyes are generated. stipulated. Furthermore, JIS T 8143 (1994) stipulates laser protection filters and laser protection glasses used to protect the eyes of workers regarding laser radiation with a wavelength of 180 nm to 1 mm.

Furthermore, for example, in Patent Document 1, a multilayer film in which a dielectric film with a high refractive index and a dielectric film with a low refractive index are alternately laminated on both sides of a transparent resin substrate is formed, and the wavelength range is 420 nm or more and 740 nm or less. A near-infrared filter that transmits 90% or more of visible light and cuts near-infrared rays in a wavelength range of 770 nm or more and 1800 nm or less, and the first multilayer film formed on one surface of the transparent resin substrate has short wavelengths. The second multilayer film formed on the other side blocks near infrared rays in the long wavelength range other than the short wavelength range, so that the wavelength range is 770 nm or more on both sides of the transparent resin substrate. A near-infrared cut filter is disclosed that cuts the near-infrared rays so that the average transmittance of near-infrared rays relative to the cumulative irradiation amount of sunlight of 1800 nm or less is 15% or less.

Patent Document 2 discloses an adapter that can be attached to the outer circumferential surface of the objective lens side barrel of binoculars, and the adapter has a rotatably attached yellow glass and a polarizing filter laminated, and further includes a yellow glass and a polarizing filter. A binocular adapter is disclosed in which a polarizing and ultraviolet cut filter is detachably attached, which is selected from at least one of glass, heat ray absorbing glass, and soda lime glass, and the selected glass is laminated and bonded to the polarizing filter side. . An example is also disclosed in which yellow glass is further provided with a dielectric vapor-deposited multilayer film as an IR coat.

Patent Document 3 discloses a lens for safety glasses in which a first lens element for shielding laser light and a second lens element for anti-glare are superimposed. In particular, the first lens element for blocking laser light contains an absorbent that selectively absorbs laser light having a specific wavelength in the ultraviolet wavelength region, visible light wavelength region, or infrared wavelength region, and also contains an absorbent in the visible light wavelength region. It is disclosed that the substrate is transparent. Various organic compounds are listed as absorbers that selectively absorb laser beams.

Further, Patent Document 4 describes (a) methyl methacrylate, (b) at least one hydrophilic monomer selected from (meth)acrylic acid and hydroxyl group-containing (meth)acrylic ester, (c) the above (a) After cast-polymerizing a monomer mixture mainly consisting of component (a) and a polyfunctional monomer copolymerizable with component (b), and (d) an oil-soluble dye and/or a near-infrared absorber, Lenses for laser safety glasses have been disclosed that have been subjected to plasma treatment or have a cured film formed thereon.

Japanese Patent Application Publication No. 2015-161731 International Publication No. 1998/058290 Japanese Patent Application Publication No. 2006-184596 Japanese Patent Application Publication No. 4-353819

The inventors of the present invention have studied these prior art techniques.

Then, the prior art utilizes the principles of either (1) reflection of light by a multilayer film, or (2) absorption by an organic dye with respect to blocking near-infrared light, each of which has its own problems. there were.

The principles and issues of each will be explained below.
(1) Reflection of light by multilayer film In this case, the multilayer film has a structure in which two types of layers with different refractive indexes, that is, high refractive index layers and low refractive index layers are alternately laminated. By setting the thickness of each layer to [wavelength of reflected light]÷4, only light of a specific wavelength is selectively reflected due to the light interference effect. For example, among the prior art documents mentioned above, Patent Documents 1 and 2 disclose shielding of near-infrared light based on the principle of light reflection by such a multilayer film.

However, light reflection by a multilayer film has a problem in that a laminated structure with one type of layer thickness can only reflect light in a narrow region centered on a specific wavelength. For this reason, even if it has a high shielding performance for near-infrared light of a certain wavelength, it sometimes has almost no shielding performance for light of a different wavelength. Although it is possible to widen the reflected wavelength range by increasing the number of laminated layers, the process becomes complicated and costs increase.

Furthermore, when the principle is that light is reflected by a multilayer film, the optical path length at which interference occurs changes when the incident angle differs, so the wavelength of the reflected light due to interference shifts to a wavelength different from that originally designed. There was also a problem. For example, when this principle is used in laser safety glasses, it is assumed that the scattered light of the laser will enter the glasses not only from the front of the glasses but also from unintended angles, which may pose a problem.
(2) Absorption by organic dye In this case, the base material contains a high concentration of an organic dye that has the property of absorbing near-infrared light, thereby selectively absorbing only light of a specific wavelength. For example, among the prior art documents mentioned above, Patent Documents 3 and 4 disclose shielding of near-infrared light based on absorption by such an organic dye.

However, the problem with absorption by organic dyes is that they can only absorb light in a narrow range centered around a specific wavelength, as the organic dyes generally have absorption only in a very narrow wavelength range. there were. For this reason, even if it has a high shielding performance for near-infrared light of a certain wavelength, it sometimes has almost no shielding performance for light of a different wavelength. A configuration has been considered to widen the wavelength range by simultaneously containing multiple organic dyes corresponding to various wavelengths, but this would complicate the process and increase costs. Furthermore, since the organic dye absorbs visible light at the same time, there is a problem in that the visible light transmittance decreases. Furthermore, organic dyes generally have low weather resistance, and depending on the environment and time in which they are used, organic dyes may deteriorate and their near-infrared light shielding performance may deteriorate.

In view of the above problems of the prior art, one aspect of the present invention aims to provide a metal nanorod-containing resin that can shield near-infrared rays over a wide wavelength range while maintaining high visible light transmittance. .

In one aspect of the present invention to solve the above problems,
A metal nanorod-containing resin in which metal nanorods are dispersed in the resin,
It has a maximum value of optical density at a light wavelength of 800 nm or more and 1400 nm or less,
The ratio of the optical density for a light wavelength of 550 nm and the maximum value of optical density, [maximum value of optical density]/[optical density for a light wavelength of 550 nm], is 6.0 or more,
The plurality of metal nanorods contained in the resin have an average short axis length of 17.5 nm or less, and have a gold core and a silver shell arranged around the core,
The present invention provides a metal nanorod-containing resin in which the average ratio of the long axis length to the short axis length of the metal nanorods is 6.0 or more and 12.0 or less .

According to one aspect of the present invention, it is possible to provide a metal nanorod-containing resin that can block near-infrared rays over a wide wavelength range while maintaining high visible light transmittance.

Transmission electron microscope image of metal nanorods obtained in Example 1.

Metal nanorod-containing resin, near-infrared shielding lens, near-infrared shielding glasses, protective equipment, near-infrared shielding window material, near-infrared shielding device, near-infrared shielding according to an embodiment of the present disclosure (hereinafter referred to as "this embodiment") Specific examples of the method for producing the film, near-infrared shielding glass, and metal nanorod aggregate will be described below. Note that the present invention is not limited to these examples, but is indicated by the scope of the claims, and is intended to include all changes within the meaning and scope equivalent to the scope of the claims.
[Resin containing metal nanorods]
In the metal nanorod-containing resin of this embodiment, metal nanorods are dispersed in the resin.

The metal nanorod-containing resin of the present embodiment has a maximum value of optical density at a light wavelength of 800 nm or more and 1400 nm or less, and the ratio of the optical density to the light wavelength of 550 nm and the maximum value of optical density is [optical Maximum value of concentration]/[optical density for a light wavelength of 550 nm] is 6.0 or more. Further, the plurality of metal nanorods contained in the resin have an average short axis length of 17.5 nm or less.

The metal nanorod-containing resin of this embodiment contains metal nanorods and resin. Note that the metal nanorod-containing resin of the present embodiment can be composed of metal nanorods and resin, but can also contain metal nanorods and other components other than the resin if desired.

The metal nanorod-containing resin according to the present embodiment will be described below in the following order: (1) metal nanorod-containing resin, (2) metal nanorods, (3) resin, (4) other components, and (5) summary.

Conventionally, metal nanorod-containing resins using metal nanorods can achieve low optical density while maintaining transparency to visible light, but they cannot achieve the high optical density used in the laser shielding field. It was common sense. However, after intensive study by the inventors of the present invention, it was found that when metal nanorods have a sufficiently small short axis length and have predetermined optical properties, they can be used for laser irradiation while maintaining transparency to visible light. The present invention was completed by discovering that a metal nanorod-containing resin can have a high optical density in the near-infrared region, which is required in the field of shielding.
(1) Metal nanorod-containing resin The metal nanorod-containing resin according to this embodiment contains metal nanorods and resin as described above.

The metal nanorods contained in the metal nanorod-containing resin of the present embodiment are the short axis length of an aggregate of a plurality of metal nanorods (hereinafter, the plurality of metal nanorods may be referred to as "metal nanorod aggregate"). It is preferable that the average value when statistically calculated is 17.5 nm or less. By dispersing metal nanorod aggregates with such an average minor axis length in a resin, it is possible to realize a resin containing metal nanorods that has high optical density in the near-infrared region and has low absorption and scattering in the visible light region. It is from.

More specifically, as described above, when the average minor axis length of the metal nanorods is 17.5 nm or less, scattering by particles can be suppressed and visible light transmittance can be increased. When the particle diameter is 15.0 nm or less, scattering due to particles can be further suppressed, which is more preferable.

Furthermore, for example, when the average short axis length of metal nanorods exceeds 17.5 nm, in addition to the main peak of localized surface plasmon resonance, absorption due to higher-order vibrational modes of plasmons may appear in the visible light region. . However, by setting the average minor axis length within the above range, it is possible to suppress such absorption from occurring in the visible light region, and it is possible to increase the visible light transmittance.

Although the lower limit of the average minor axis length of the metal nanorods is not particularly limited, it is preferably, for example, 3 nm or more.

The method for evaluating the average short axis length of a metal nanorod aggregate is not particularly limited, but for example, when observed with a transmission electron microscope, 100 particles are selected from a single field of view or multiple fields of view, and the short axis length of the metal nanorod aggregate is evaluated. The average value can be taken as the average minor axis length of the metal nanorod aggregate.

The metal nanorod-containing resin of the present embodiment has a maximum optical density at a light wavelength of 800 nm or more and 1400 nm or less (light wavelength region). Further, the ratio of the optical density for a light wavelength of 550 nm to the maximum value of optical density, ie, [maximum value of optical density]/[optical density for a light wavelength of 550 nm], is 6.0 or more.

Here, the optical density represents the property of blocking light at a specific wavelength by reflection or absorption, and the optical density can be calculated using the following equation (1).

なお、上記式（１）中ＯＤ（λ）は波長λでの光学濃度、Ｔ（λ）は波長λでの透過率（０～１００％）を意味する。

Note that in the above formula (1), OD (λ) means the optical density at the wavelength λ, and T (λ) means the transmittance (0 to 100%) at the wavelength λ.

The higher the optical density, the lower the transmittance of light of the corresponding wavelength, meaning that it is blocked.

Therefore, as described above, the metal nanorod-containing resin of the present embodiment has a maximum value of optical density in the near-infrared light wavelength region of 800 nm or more and 1400 nm or less, so that the near-infrared region including the maximum value can be It becomes possible to block near-infrared rays over a wide wavelength range.

In addition, by setting the ratio of the optical density for a light wavelength of 550 nm to the maximum value of optical density [maximum value of optical density]/[optical density for a light wavelength of 550 nm] to be 6.0 or more, it is possible to This is because even when high-intensity light is incident, the intensity of the light can be significantly reduced and, for example, the effect on the eyes can be suppressed.

The visible light transmittance of the metal nanorod-containing resin of this embodiment is not particularly limited, but the visible light transmittance calculated according to JIS R 3106 (1998) is preferably 2% or more and 70% or less, and 10% or more and 60% or less. % or less is more preferable.

This is because by setting the visible light transmittance to 2% or more, it will have a sufficiently high visible light transmittance even when used, for example, in protective equipment. On the other hand, if the visible light transmittance is attempted to be higher than 70%, it will be necessary to significantly suppress the content of metal nanorods, and there is a possibility that light in the near-infrared region may not be sufficiently suppressed.

The amount (content) of metal nanorods contained in the metal nanorod-containing resin of the present embodiment is not particularly limited, and is determined by the required visible light transmittance, the degree to which transmission of light in the near-infrared region is suppressed, etc. It can be arbitrarily selected depending on the situation. The content of metal nanorods can be evaluated using, for example, the weight per projected area as an index, and the weight per projected area can be measured and calculated by the following method. First, the amount of metal present in a certain volume of metal nanorod-containing resin is measured using a technique such as ICP (Inductively Coupled Plasma) mass spectrometry. The weight of the metal nanorods per measured volume (g/m ³ ) can be converted into the weight per projected area (g/m ² ) using the thickness of the metal nanorod-containing resin. The content of metal nanorods in the metal nanorod-containing resin of the present embodiment is preferably 0.01 g/m ² or more and 1.00 g/m 2 or less, and 0.10 g/m ^{2 or} more and 0.50 g/m 2 or less per projected area. It is more preferable that it is less than ^m2 .

By setting the content of metal nanorods per projected area (unit area in projected area) of the resin layer of the metal nanorod-containing resin to 0.01 g/m2 or ^more , high optical density for light with wavelengths in the near-infrared region can be achieved. This is because it can be realized. Further, by setting the thickness to 1.00 g/m ² or less, it is possible to prevent visible light transmittance from being lost due to absorption or scattering of light in the visible light region possessed by metal nanorods.
(2) Metal Nanorods It is preferable that the plurality of metal nanorods, that is, the metal nanorod aggregates contained in the metal nanorod-containing resin according to the present embodiment, have an average minor axis length of 17.5 nm or less as described above.

Further, it is preferable that the plurality of metal nanorods contained in the metal nanorod-containing resin of the present embodiment have an average value of the ratio of the long axis length to the short axis length of 4.0 or more and 12.0 or less, and 4.0 More preferably, it is 10.0 or less.

By setting the average value of the ratio of major axis length to minor axis length, that is, the average value of major axis length/minor axis length, to 4.0 or more and 12.0 or less, the main optical absorption peak of metal nanorods can be achieved. This is because most of the wavelength can be in the near-infrared region, specifically in the range from 800 nm to 1400 nm. In other words, when the average value of the long axis length/short axis length of multiple metal nanorods is less than 4.0, the visible light transmittance decreases due to the presence of an absorption peak in the visible light region, and the absorption peak in the near infrared region decreases. may become weak. On the other hand, by setting the average value of the long axis length/short axis length of multiple metal nanorods to 4.0 or more and 12.0 or less, the absorption peak in the visible light region can be removed and the visible light transmittance can be improved. , the absorption of light in the near-infrared region can be significantly increased. Furthermore, the handling properties of the metal nanorods can be improved.

The method for evaluating the average value of the ratio of the long axis length to the short axis length of multiple metal nanorods is not particularly limited, but for example, when observed with a transmission electron microscope, 100 particles are selected from within a single field of view or within multiple fields of view. However, the average value of the ratio of the long axis length to the short axis length can be set as the average value of the ratio of the long axis length to the short axis length of the plurality of metal nanorods.

Although the material of the metal nanorods contained in the metal nanorod-containing resin of this embodiment is not particularly limited, it is preferable that the metal nanorods have a gold core and a silver shell disposed around the gold core. That is, it is preferable that the metal nanorods contain silver.

This is because many metals other than silver have absorption in the visible light region, but silver does not have absorption in the visible light region. For this reason, when used as a near-infrared shielding material, for example, it becomes possible to shield only light in the near-infrared region without reducing visible light transmittance. Also, by containing silver, it is preferable in that the cost can be suppressed compared to, for example, when metal nanorods are formed only with gold.

It is preferable that the metal nanorods contained in the metal nanorod-containing resin of this embodiment contain silver in a mass proportion of 30% or more. As described above, since silver does not absorb in the visible light region, the visible light transmittance can be increased by containing silver in the metal nanorods of this embodiment. Further, it is preferable to set the content ratio of silver to 30% or more in terms of mass ratio, since this effect can be exhibited particularly markedly.

However, if the silver content is too high, it may not be possible to form the desired shape, so the silver content is preferably 95% or less in terms of mass percentage.

According to studies by the inventors of the present invention, the use of a gold core makes it easier to form metal nanorods with short minor axis lengths within a desired range. For this reason, the metal nanorods contained in the metal nanorod-containing resin of the present embodiment preferably have a gold core and a silver shell disposed around the gold core as described above.

When the metal nanorods contained in the metal nanorod-containing resin of this embodiment have a structure having a gold core and a silver shell as described above, the ends in the long axis direction have a {111} plane, The side surface is preferably a {100} plane. This is because when such crystal planes are present at each position, a silver shell tends to be stably formed on a gold core, and in particular, metal nanorods having a desired shape can be obtained.
(3) Resin The resin contained in the metal nanorod-containing resin of this embodiment is not particularly limited, and any resin can be used. However, considering the use of the metal nanorod-containing resin according to the present embodiment, it is desirable that the resin has sufficient transparency for light in the visible light range. Furthermore, in consideration of processability, thermoplastic resins are preferred.

Examples of resins contained in the metal nanorod-containing resin of this embodiment include polyethylene terephthalate resin, polycarbonate resin, acrylic resin, styrene resin, polyamide resin, polyethylene resin, vinyl chloride resin, olefin resin, epoxy resin, polyimide resin, and fluororesin. , a mixture of two or more resins selected from the resin group, or a copolymer of two or more resins selected from the resin group. There can be one or more types.

Among them, the metal nanorod-containing resin of this embodiment has high transmittance of light in the visible light region, and considering aspects such as rigidity, lightness, long-term durability, and cost, the resin contained in the metal nanorod-containing resin of this embodiment is polycarbonate resin, acrylic resin, and vinyl chloride resin, a mixture of two or more resins selected from the resin group, or a copolymer of two or more resins selected from the resin group. It is preferable.

When a polycarbonate resin is used as the metal nanorod-containing resin of this embodiment, a polycarbonate resin obtained by reacting dihydric phenols and a carbonate precursor by a solution method or a melt method is preferably used. be able to. Examples of dihydric phenols include 2,2-bis(4-hydroxyphenyl)propane [bisphenol A], 1,1-bis(4-hydroxyphenyl)ethane, 1,1-bis(4-hydroxyphenyl)cyclohexane, 2 ,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, 2,2-bis(4-hydroxy-3,5-dibromophenyl)propane, 2,2-bis(4-hydroxy-3-methyl) Representative examples include phenyl)propane, bis(4-hydroxyphenyl)sulfide, and bis(4-hydroxyphenyl)sulfone.

Preferred dihydric phenols include bis(4-hydroxyphenyl) alkanes, and those containing bisphenol A as a main component are particularly preferred.
(4) Other components In addition to the metal nanorods and resin described above, the metal nanorod-containing resin of the present embodiment may further contain arbitrary components. Examples of optional components include dispersants, ultraviolet absorbers, hindered amine light stabilizers, and antioxidants.

Components that can be optionally added will be explained below.
(dispersant)
The metal nanorod-containing resin of this embodiment can also contain a dispersant in order to uniformly disperse the metal nanorods described above in the resin.

The dispersant is not particularly limited and can be arbitrarily selected depending on the manufacturing conditions of the metal nanorod-containing resin.

Examples of dispersants include those that have a thermal decomposition temperature of 250°C or higher as measured using a differential thermal/thermogravimetric simultaneous analyzer (hereinafter sometimes referred to as TG-DTA), and that have a urethane main chain or acrylic main chain. The dispersant preferably has a main chain selected from a chain, a styrene main chain, or a main chain copolymerized with two or more types of unit structures selected from urethane, acrylic, and styrene. It is more preferable that the above-mentioned thermal decomposition temperature is 300°C or higher. Here, the thermal decomposition temperature is the temperature at which the weight of the dispersant starts to decrease due to thermal decomposition when measured using TG-DTA in accordance with JIS K 7120 (1987).

When the thermal decomposition temperature of the dispersant is 250°C or higher, it is possible to suppress decomposition of the dispersant during kneading with the resin component, and suppress browning of the resin and decrease in visible light transmittance caused by decomposition of the dispersant. This is because the situation in which the original optical characteristics cannot be obtained can be more reliably avoided.

Moreover, it is preferable that the dispersant has one or more types selected from an amine-containing group, a hydroxyl group, a carboxyl group, or an epoxy group as a functional group. A dispersant having any of the above-mentioned functional groups can be preferably used because it can adsorb onto the surface of metal nanorods, prevent aggregation of metal nanorods, and disperse metal nanorods more uniformly in the resin. .

Specific examples of the dispersant having any of the above-mentioned functional groups include an acrylic-styrene copolymer dispersant having a carboxyl group as a functional group, an acrylic dispersant having an amine-containing group as a functional group, etc. can be mentioned. The dispersant having an amine-containing functional group preferably has a molecular weight Mw of 2,000 to 200,000 and an amine value of 5 to 100 mgKOH/g. Further, the dispersant having a carboxyl group preferably has a molecular weight Mw of 2000 or more and 200000 or less and an acid value of 1 mgKOH/g or more and 50 mgKOH/g or less.

The amount of the dispersant added is not particularly limited, but for example, it is preferably added in an amount of 10 parts by mass or more and 1000 parts by mass or less, and 30 parts by mass or more and 400 parts by mass or less, per 100 parts by mass of metal nanorods. It is more preferable to add it so that

This is because if the amount of the dispersant added is within the above range, the metal nanorods can be more reliably and uniformly dispersed in the resin, and the physical properties of the resulting metal nanorod-containing resin will not be adversely affected.
(Ultraviolet absorber)
Moreover, the metal nanorod-containing resin of this embodiment can also further contain an ultraviolet absorber.

As mentioned above, since the metal nanorod-containing resin of this embodiment contains metal nanorods, it mainly suppresses the transmission of light in the near-infrared region, and when used as a material for, for example, eye protection equipment. , the eyes can be protected from such harmful light.

When the metal nanorod-containing resin of this embodiment further contains an ultraviolet absorber, it becomes possible to further cut out light in the ultraviolet region, and the effect of suppressing harmful light can be particularly enhanced. Additionally, visible light transmittance of a dispersion of metal nanorods dispersed in a resin may decrease due to long-term exposure to strong ultraviolet rays, but by adding an ultraviolet absorber to the metal nanorod-containing resin of this embodiment, , such a decrease in visible light transmittance can be suppressed. Furthermore, the polymer (resin) itself, which is the dispersion medium for metal nanorods, may suffer deterioration such as yellowing due to long-term exposure to ultraviolet rays. It is possible to suppress deterioration such as

The ultraviolet absorber is not particularly limited, and can be arbitrarily selected depending on the influence on the visible light transmittance of the metal nanorod-containing resin, ultraviolet absorption ability, durability, etc. Examples of UV absorbers include organic UV absorbers such as benzophenone compounds, salicylic acid compounds, benzotriazole compounds, triazine compounds, benzotriazolyl compounds, and benzoyl compounds, and inorganic UV absorbers such as zinc oxide, titanium oxide, and cerium oxide. etc. In particular, the ultraviolet absorber preferably contains one or more selected from benzotriazole compounds and benzophenone compounds. This is because benzotriazole compounds and benzophenone compounds can make the visible light transmittance of metal nanorod-containing resins extremely high even when added at concentrations sufficient to absorb ultraviolet rays, and they can also be used for long-term exposure to strong ultraviolet rays. This is because it has high durability against.

The content of the ultraviolet absorber in the metal nanorod-containing resin is not particularly limited, and can be arbitrarily selected depending on the visible light transmittance, ultraviolet shielding ability, etc. required of the metal nanorod-containing resin. It is preferable that the content of the ultraviolet absorber in the metal nanorod-containing resin is, for example, 0.02% by mass or more and 5.0% by mass or less. This is because if the content of the ultraviolet absorber is 0.02% by mass or more, ultraviolet light that cannot be absorbed by the metal nanorods can be sufficiently absorbed. In addition, if the content is 5.0% by mass or less, the ultraviolet absorber will not precipitate in the metal nanorod-containing resin and will not have a large effect on the strength and penetration resistance of the metal nanorod-containing resin. .
(Hindered amine light stabilizer)
Moreover, the metal nanorod-containing resin of this embodiment can also further contain HALS (hindered amine light stabilizer).

As described above, the metal nanorod-containing resin of this embodiment can increase its ultraviolet absorption ability by containing an ultraviolet absorber. However, depending on the environment in which the metal nanorod-containing resin of this embodiment is used or the type of ultraviolet absorber, the ultraviolet absorber may deteriorate with long-term use and the ultraviolet absorption ability may decrease. . On the other hand, by adding HALS, it is possible to prevent deterioration of the ultraviolet absorber and contribute to maintaining the ultraviolet absorption ability of the metal nanorod-containing resin of this embodiment.

Furthermore, as mentioned above, visible light transmittance of a dispersion of metal nanorods dispersed in a resin may decrease due to long-term exposure to strong ultraviolet rays. However, by adding HALS to the metal nanorod-containing resin of this embodiment, it is possible to suppress such a decrease in visible light transmittance, similarly to the case where an ultraviolet absorber is added.

Furthermore, among HALS, there are compounds that themselves have the ability to absorb ultraviolet rays. In this case, by adding the compound, it is possible to have both the effect of adding the ultraviolet absorber and the effect of adding HALS.

HALS is not particularly limited, and can be arbitrarily selected depending on the influence on the visible light transmittance of the metal nanorod-containing resin, compatibility with the ultraviolet absorber, durability, etc. For example, bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, 1-[2-[3-( 3,5-t-butyl-4-hydroxyphenyl)propionyloxy]ethyl]-4-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy]-2,2,6, 6-tetramethylpiperidine, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine, 8-acetyl-3-dodecyl-7,7,9,9-tetramethyl-1,3,8-triazaspiro[ 4,5]decane-2,4-dione, bis-(1,2,2,6,6-pentamethyl-4-piperidyl)-2-(3,5-di-t-butyl-4-hydroxybenzyl) -2-n-butylmalonate, tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate, tetrakis(2,2,6,6 -tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate, (Mixed 1,2,2,6,6-pentamethyl-4-piperidyl/tridecyl)-1,2,3,4 -Butanetetracarboxylate, Mixed {1,2,2,6,6-pentamethyl-4-piperidyl/β,β,β',β'-tetramethyl-3,9-[2,4,8,10- Tetraoxaspiro(5,5)undecane]diethyl}-1,2,3,4-butanetetracarboxylate, (Mixed 2,2,6,6-tetramethyl-4-piperidyl/tridecyl)-1,2, 3,4-Butanetetracarboxylate, Mixed {2,2,6,6-tetramethyl-4-piperidyl/β,β,β',β'-tetramethyl-3,9-[2,4,8, 10-tetraoxaspiro(5,5)undecane]diethyl}-1,2,3,4-butanetetracarboxylate, 2,2,6,6-tetramethyl-4-piperidyl methacrylate, 1,2,2, 6,6-pentamethyl-4-piperidyl methacrylate, poly[(6-(1,1,3,3-tetramethylbutyl)imino-1,3,5-triazine-2,4-diyl)][(2, 2,6,6-tetramethyl-4-piperidyl)imino]hexamethylene [(2,2,6,6-tetramethyl-4-piperidyl)iminol], dimethylsacinate polymer with-4-hydroxy-2, 2,6,6-tetramethyl-1-piperidineethanol, N,N',N'',N'''-tetrakis-(4,6-bis-(butyl-(N-methyl-2,2,6 ,6-tetramethylpiperidin-4-yl)amino)-triazin-2-yl)-4,7-diazadecane-1,10-diamine, dibutylamine-1,3,5-triazine-N,N'-bis (Polycondensate of 2,2,6,6-tetramethyl-4-piperidyl-1,6-hexamethylenediamine and N-(2,2,6,6-tetramethylpiperidyl)butylamine, decanedioic acid bis( One or more selected from 2,2,6,6-tetramethyl-1-(octyloxy)-4-piperidinyl) ester and the like can be suitably used.

The content of HALS in the metal nanorod-containing resin is not particularly limited, and can be arbitrarily selected depending on the visible light transmittance, weather resistance, etc. required of the metal nanorod-containing resin. It is preferable that the content of HALS in the metal nanorod-containing resin is, for example, 0.05% by mass or more and 5.0% by mass or less. This is because if the content of HALS is 0.05% by mass or more, the effect of adding HALS can be fully exhibited in the metal nanorod-containing resin. Further, if the content is 5.0% by mass or less, HALS will not precipitate in the metal nanorod-containing resin and will not have a large effect on the strength and penetration resistance of the metal nanorod-containing resin.
(Antioxidant)
The metal nanorod-containing resin of this embodiment can also further contain an antioxidant.

By adding an antioxidant to the metal nanorod-containing resin, it is possible to suppress oxidative deterioration of the resin contained in the metal nanorod-containing resin and further improve weather resistance. In addition, other additives other than the resin contained in the metal nanorod-containing resin, such as metal nanorods, ultraviolet absorbers, HALS, dye compounds, pigment compounds, coupling agents, surfactants, antistatic agents, etc., which will be described later. It is possible to suppress oxidative deterioration of and improve weather resistance.

The antioxidant is not particularly limited, and can be arbitrarily selected depending on the influence on the visible light transmittance of the metal nanorod-containing resin, the desired durability, and the like. For example, one or more selected from phenolic antioxidants, sulfur-based antioxidants, phosphorus-based antioxidants, etc. can be suitably used, and more specifically, 2,6-di-t-butyl -p-cresol, butylated hydroxyanisole, 2,6-di-t-butyl-4-ethylphenol, stearyl-β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2,2 '-Methylenebis-(4-methyl-6-butylphenol), 2,2'-methylenebis-(4-ethyl-6-t-butylphenol), 4,4'-butylidene-bis-(3-methyl-6-t -butylphenol), 1,1,3-tris-(2-methyl-hydroxy-5-t-butylphenyl)butane, tetrakis[methylene-3-(3',5'-butyl-4-hydroxyphenyl)propionate] Methane, 1,3,3-tris-(2-methyl-4-hydroxy-5-t-butylphenol)butane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butane) -butyl-4-hydroxybenzyl)benzene, bis(3,3'-t-butylphenol)butyric acid glycol ester, triphenylphosphine, bis-(diphenylphosphinoethane), trinaphthylphosphine, tris(2,4 -di-tert-butylphenyl) phosphite and the like can be suitably used.

The content of the antioxidant in the metal nanorod-containing resin is not particularly limited, and can be arbitrarily selected depending on the visible light transmittance, weather resistance, etc. required of the metal nanorod-containing resin. The content of the antioxidant in the metal nanorod-containing resin is preferably, for example, 0.05% by mass or more and 5.0% by mass or less. This is because when the content of the antioxidant is 0.05% by mass or more, the effect of adding the antioxidant can be fully exhibited in the metal nanorod-containing resin. Furthermore, if the content is 5.0% by mass or less, the antioxidant will not precipitate in the metal nanorod-containing resin, and will not have a large effect on the strength, adhesive strength, and penetration resistance of the metal nanorod-containing resin. It's for a reason.
(Other additive ingredients)
Up to this point, dispersants, ultraviolet absorbers, HALS, and antioxidants have been described as optional additive components to the metal nanorod-containing resin of this embodiment, but it is also possible to incorporate various other additives. .

For example, one or more dye compounds selected from azo dyes, cyanine dyes, quinoline dyes, perylene dyes, carbon black, etc., which can be used to color the resin, to give any color tone as desired. Alternatively, a pigment compound may be added.

As other additives, for example, a coupling agent, a surfactant, an antistatic agent, an infrared absorbing organic compound, etc. can also be added to the metal nanorod-containing resin of this embodiment.
(5) Summary According to the metal nanorod-containing resin of this embodiment described above, by containing predetermined metal nanorods, near-infrared rays can be blocked over a wide wavelength range while maintaining high visible light transmittance. be able to.

The metal nanorod-containing resin of the present embodiment preferably has particularly high light transmittance (transparency) in the visible light region and particularly high light shielding property in the near-infrared region. The light transmittance in the visible light region and the light shielding property in the near-infrared region of the metal nanorod-containing resin can be evaluated by visible light transmittance and optical density, respectively.

The degree of light transmittance in the visible light region and light shielding property in the near-infrared region required of the metal nanorod-containing resin of this embodiment is not particularly limited, and depends on the use of the metal nanorod-containing resin. It is preferable that the performance is as high as possible.

When used for applications such as window materials, it is preferable to have a high visible light transmittance from the viewpoint of maintaining the transparency of light in the visible light range to the human eye. From the viewpoint of reducing the incidence of light in the near-infrared region, it is preferable that the optical density is high.
[Method for manufacturing metal nanorod-containing resin]
Next, a configuration example of the method for manufacturing a metal nanorod-containing resin according to the present embodiment will be described. Note that the metal nanorod-containing resin described above can be manufactured by the method for manufacturing a metal nanorod-containing resin of this embodiment. Therefore, except for the points described below, the structure can be the same as in the case of the metal nanorod-containing resin described above, so the explanation will be partially omitted.

Although the method for producing the metal nanorod-containing resin of this embodiment is not particularly limited, two methods, (1) resin kneading method and (2) coating method, will be described below as examples.
(1) Resin kneading method The resin kneading method can include, for example, the following steps.

A dispersion liquid manufacturing process that manufactures a dispersion liquid in which metal nanorods and a dispersant are dispersed in a dispersion medium.
A dispersion production process in which a dispersion medium in the dispersion produced in the dispersion production process is removed to produce a metal nanorod dispersion in which metal nanorods are dispersed in a solid dispersant.
A kneading step of kneading the metal nanorod dispersion obtained in the dispersion manufacturing step and a resin.
A molding process in which a kneaded product of metal nanorod dispersion and resin is molded.

In addition, the dispersion liquid manufactured in the dispersion liquid manufacturing process can be subjected to a kneading process without implementing the dispersion manufacturing process, and the dispersion liquid and the resin can be kneaded in the kneading process. In this case, the kneading process allows the metal nanorods to be uniformly dispersed in the resin and at the same time, the dispersion medium can be removed. When the dispersion production process is not performed in this manner, a dispersion liquid may be prepared in which the metal nanorods are dispersed in a solvent such as a dispersion medium without adding a dispersant to the dispersion liquid in the dispersion production process.

However, from the viewpoint of reliably preventing a large amount of dispersion medium and air bubbles from remaining in the metal nanorod-containing resin, and from the safety point of view of preventing a large amount of dispersion medium from being exposed to the high temperature of resin kneading exceeding 200 ° C. It is preferable to carry out a dispersion manufacturing step before the kneading step.

Further, for example, after kneading the metal nanorods or the dispersion of the metal nanorods and the resin, the molding step can be performed directly. However, from the viewpoint of uniformly dispersing the metal nanorods in the resin, it is preferable to carry out the above-mentioned dispersion manufacturing process.

Each process will be explained.
(Dispersion manufacturing process)
In the dispersion manufacturing process, metal nanorods and a dispersant are added to and mixed with a dispersion medium, and a dispersion of metal nanorods can be obtained using a general dispersion method. The dispersion method is not particularly limited, and for example, a bead mill, ball mill, sand mill, ultrasonic dispersion, paint shaker, or other dispersion method can be used.

The metal nanorods, dispersant, etc. that can be suitably used in the dispersion liquid manufacturing process have already been described in the metal nanorod-containing resin, so their explanation will be omitted.

Further, the type of dispersion medium used in the dispersion manufacturing process is not particularly limited, but one or more types selected from various organic solvents, water, etc. can be used. For example, as a dispersion medium, one having a boiling point of 120° C. or lower can be preferably used. This is because if the boiling point is 120° C. or lower, the dispersion medium can be easily removed in the subsequent dispersion manufacturing process. By rapidly removing the dispersion medium in the dispersion manufacturing process, etc., productivity of the metal nanorod dispersion can be improved. Furthermore, since the dispersion manufacturing process proceeds easily and satisfactorily, it is possible to avoid excessive dispersion medium remaining in the metal nanorod dispersion. As a result, it is possible to more reliably avoid problems such as the generation of air bubbles in the resin layer during the molding process.

The lower limit of the boiling point of the dispersion medium used is not particularly limited, but it is preferably 30°C or higher, for example, 40°C or higher, since it is preferable to maintain a liquid state during the dispersion manufacturing process. It is more preferable that it is above.

When using an organic solvent as a dispersion medium, specifically, one or more types selected from toluene, methyl ethyl ketone, methyl isobutyl ketone, butyl acetate, isopropyl alcohol, ethanol, etc. can be preferably used as the organic solvent. However, it is not limited to these. Any material having a boiling point of 120° C. or lower and capable of uniformly dispersing metal nanorods can be suitably used.

The amount of the dispersion medium to be added is not particularly limited, and can be arbitrarily selected so that a dispersion can be formed depending on the amounts of the metal nanorods and the dispersant.

Note that when a dispersant is added, the amount added is not particularly limited as described above. For example, it is preferably added in an amount of 10 parts by mass or more and 1000 parts by mass or less, more preferably 30 parts by mass or more and 400 parts by mass or less, per 100 parts by mass of metal nanorods. When a dispersant is added, it is not necessary to add the entire amount of the dispersant when producing a dispersion in the dispersion production process. For example, taking into consideration the viscosity of the dispersion liquid, a part of the total amount of the dispersant added, the metal nanorods, and the dispersion medium are formed into a dispersion liquid by the above-mentioned dispersion method, and then the remaining part is further dispersed. Agents may also be added.
(Dispersion manufacturing process)
In the dispersion manufacturing process, a metal nanorod dispersion is manufactured by adding an appropriate amount of a dispersant, if desired, to a dispersion liquid in which metal nanorods and a dispersant are dispersed in a dispersion medium, and then removing the dispersion medium. I can do it. Although the method for removing the dispersion medium from a dispersion liquid in which metal nanorods and a dispersant are dispersed in a dispersion medium is not particularly limited, for example, drying under reduced pressure can be preferably used. Specifically, a dispersion in which metal nanorods and a dispersant are dispersed in a dispersion medium is dried under reduced pressure while stirring to separate the metal nanorod dispersion and the dispersion medium components. The device used for vacuum drying includes, for example, a vacuum stirring type dryer, but is not particularly limited as long as it has the above-mentioned functions. Further, the specific pressure of the reduced pressure when removing the dispersion medium is not limited and can be selected as appropriate.

In the dispersion manufacturing process, the removal efficiency of the dispersion medium is improved by using the vacuum drying method, and since the metal nanorod dispersion is not exposed to high temperatures for a long time, aggregation of the dispersed metal nanorods does not occur. It's very preferable. Furthermore, productivity is increased, and the evaporated dispersion medium can be easily recovered, which is preferable from environmental considerations.
(kneading process)
In the kneading step, the metal nanorod dispersion obtained in the dispersion manufacturing step and the resin can be kneaded. At this time, other additives such as ultraviolet absorbers, HALS, antioxidants, and infrared absorbing organic compounds may be added to the metal nanorod-containing resin as needed, and kneaded together. Note that the timing of adding these additives and the like is not particularly limited, and they can also be added in other processes, such as the dispersion manufacturing process. The kneading method is not particularly limited, and any known resin kneading method can be selected and used.
(molding process)
The molding process is a process of molding the kneaded product obtained in the kneading process, and the molding method is not particularly limited. It can be arbitrarily selected depending on the viscosity and the like. For example, various molding methods such as extrusion molding and calendar molding can be employed.

Further, the shape of the molded body is not particularly limited, and can be selected depending on the shape required of the metal nanorod-containing resin, and can be formed into, for example, a sheet shape, a board shape, or a film shape. When the molded product is used as a lens for eyeglasses, for example, it can be processed into a desired lens shape and laminated with other lens elements by a known method to produce a multilayer lens.
(2) Coating method The coating method can include, for example, the following steps.

A dispersion manufacturing process that produces a dispersion liquid in which metal nanorods are dispersed in a dispersion medium.
A coating liquid production process in which a binder resin (medium resin) is added to the dispersion liquid produced in the dispersion production process to produce a coating liquid.

A resin that forms a resin layer (resin coating) in which metal nanorods are dispersed on a transparent substrate by coating the surface of a transparent substrate with a coating liquid, then evaporating the dispersion medium and curing the binder resin using a predetermined method. Layer manufacturing process.

Each process will be explained.
(Dispersion manufacturing process)
In the dispersion manufacturing process, a dispersion can be prepared by dispersing metal nanorods in a dispersion medium, and at this time, a dispersant or the like can be added as necessary. (1) Since it can be carried out in the same manner as the dispersion manufacturing step of the resin kneading method, the explanation will be omitted.
(Coating liquid manufacturing process)
In the coating liquid manufacturing process, an appropriate amount of dispersant is added as desired to the dispersion liquid in which metal nanorods are dispersed in a dispersion medium, and then a binder resin is added in an appropriate ratio to be used in the subsequent resin layer manufacturing process. It is possible to produce a coating liquid that can be used.

The binder resin for the coating layer can be selected from UV curable resins, thermosetting resins, electron beam curable resins, room temperature curable resins, thermoplastic resins, etc. depending on the purpose. Specifically, polyethylene resin, polyvinyl chloride resin (vinyl chloride resin), polyvinylidene chloride resin, polyvinyl alcohol resin, polystyrene resin, polypropylene resin, ethylene vinyl acetate copolymer, polyester resin, polyethylene terephthalate resin, fluororesin, One or more types selected from polycarbonate resin, acrylic resin, polyvinyl butyral resin, etc. can be mentioned.

As the binder resin, for example, only one type selected from the above-mentioned resin group may be used alone, or two or more types selected from the above-mentioned resin group may be used in combination. However, among the binder resins for the resin layer, it is particularly preferable to use UV curable resins or thermosetting resins from the viewpoint of productivity, equipment cost, and the like.

Furthermore, instead of the binder resin described above, a binder using a metal alkoxide can also be used. Typical examples of the metal alkoxide include alkoxides of Si, Ti, Al, Zr, and the like. A binder using these metal alkoxides can be hydrolyzed and polycondensed by heating or the like to form a coating layer using an oxide film.
(Resin layer manufacturing process)
After coating the surface of a transparent substrate with the coating liquid created in the coating liquid manufacturing process, the dispersion medium is evaporated and the binder resin is cured using a predetermined method to form a resin layer in which metal nanorods are dispersed on the transparent substrate. can be formed.

The transparent base material will be described later in the section of [Near-infrared shielding base material], but for example, a film base material or a glass base material can be used.

The method of providing a coating layer on a transparent substrate is not particularly limited, and any method that can uniformly apply a coating liquid containing a binder resin to the surface of the substrate is not particularly limited. For example, one or more methods selected from a bar coating method, a gravure coating method, a spray coating method, a dip coating method, a flow coating method, etc. can be used.

For example, when a UV curable resin or a thermosetting resin is used as the binder resin and a resin layer (coating layer) is formed by a bar coating method, the resin layer can be formed by the following procedure.

First, a wire bar with a bar number that can appropriately satisfy the thickness of the resin layer and the content of metal nanorods is coated with a coating solution whose concentration and additives have been appropriately adjusted so as to have appropriate leveling properties. Alternatively, it is applied onto a transparent substrate using an applicator or by a suitable method such as a known flow coating method to form a coating film.

Next, after removing the dispersion medium (liquid medium) contained in the coating solution of the formed coating film by drying, the binder is removed by ultraviolet irradiation (in the case of UV curable resin) or heat treatment (in the case of thermosetting resin). Cure the resin.

A resin layer can be formed on a transparent base material by the above procedure. At this time, the drying conditions for the coating film vary depending on the components contained in the coating liquid constituting the coating film, the type of dispersion medium, and the proportion used, but usually at a temperature of 60°C or higher and 140°C or lower for 20 seconds or more. The time can be about 10 minutes or less. When irradiating UV curable resin with ultraviolet rays, there are no particular restrictions on the irradiation of ultraviolet rays, and for example, a UV exposure machine such as an ultra-high pressure mercury lamp can be suitably used. When heat-treating a thermosetting resin, an appropriate heat treatment can be carried out using an oven, a dryer, etc., depending on the usage conditions of the thermosetting resin.

In addition, the adhesion between the transparent substrate and the resin layer, the smoothness of the coating film during coating, the drying properties of the dispersion medium, etc. can also be controlled by the pre-process and post-process of forming the resin layer. Such pre- and post-processes include, for example, a surface treatment process for the transparent base material, a pre-bake (pre-heating of the transparent base material) process, a post-bake (post-heating of the transparent base material) process, etc., which may be selected as appropriate. , can be implemented.

The heating conditions in the pre-bake step and the post-bake step are not particularly limited, but, for example, the heating temperature is preferably 80° C. or more and 200° C. or less, and the heating time is preferably 30 seconds or more and 240 seconds or less.

The metal nanorod-containing resin of this embodiment described so far can be used in various applications where it is required to block near-infrared rays while transmitting visible light. For example, it can be used in the following near-infrared shielding lenses, near-infrared shielding glasses, protective gear, near-infrared shielding window materials, near-infrared shielding instruments, near-infrared shielding base materials, and the like.
[Near-infrared shielding lenses, near-infrared shielding glasses]
The near-infrared shielding lens of this embodiment can have the resin layer of the metal nanorod-containing resin described above.

The near-infrared shielding lens of this embodiment can have a near-infrared shielding base material in which, for example, a resin layer of the metal nanorod-containing resin described above is formed on a transparent base material. Moreover, the near-infrared shielding lens of this embodiment can also be constructed from the metal nanorod-containing resin described above. The near-infrared shielding lens of this embodiment has the resin layer of the metal nanorod-containing resin described above, so that it can suppress the transmission of near-infrared rays while transmitting visible light.

Moreover, near-infrared shielding glasses can also be made using such near-infrared shielding lenses. Specifically, the near-infrared shielding glasses of this embodiment can include, for example, the above-mentioned near-infrared shielding lenses in the lens portion.

Therefore, the near-infrared shielding glasses of this embodiment can have the resin layer of the metal nanorod-containing resin described above.

By providing near-infrared shielding glasses having a resin layer of the metal nanorod-containing resin described above, transmission of near-infrared rays can be suppressed while allowing visible light to pass through.
[Protective equipment]
The protective equipment of this embodiment can have the resin layer of the metal nanorod-containing resin described above.

By providing a protective device having a resin layer of the metal nanorod-containing resin described above, transmission of near-infrared rays can be suppressed while allowing visible light to pass through.

The protective equipment of this embodiment can be, for example, safety glasses, and for example, the above-mentioned near-infrared shielding lens can be used for the lens portion.
[Near-infrared shielding window materials, near-infrared shielding equipment]
The near-infrared shielding window material of this embodiment can have the resin layer of the metal nanorod-containing resin described above.

The near-infrared shielding window material of this embodiment can have a near-infrared shielding base material in which a resin layer of the metal nanorod-containing resin described above is formed on a transparent base material described below, for example. By having such a near-infrared shielding base material, transmission of near-infrared rays can be suppressed while allowing visible light to pass through. Note that the near-infrared shielding window material of this embodiment can also be made of the metal nanorod-containing resin described above.

Moreover, the near-infrared shielding device of this embodiment can have the above-mentioned near-infrared shielding window material. The near-infrared shielding device can include, for example, a near-infrared shielding window material and its mounting device.

The near-infrared shielding window material and the near-infrared shielding device of this embodiment can be used, for example, as a window material for an observation window of a device that internally emits near-infrared light. With this configuration, it is possible to protect the eyes of an observer observing the inside of the apparatus.
[Near infrared shielding base material]
The near-infrared shielding base material of this embodiment can have, for example, a resin layer of the metal nanorod-containing resin described above on a transparent base material. Although the transparent substrate is not particularly limited, for example, a film substrate or a glass substrate can be used.

When a film base material, that is, a resin base material is used as the transparent base material, a near-infrared shielding film in which a resin layer of the metal nanorod-containing resin described above is provided on the film base material can be used. That is, it can be a near-infrared shielding film that has a film base material and a resin layer of metal nanorod-containing resin disposed on the film base material.

Furthermore, when a glass substrate is used as the transparent substrate, the resin layer of the metal nanorod-containing resin described above can be used as a near-infrared shielding glass provided on the glass substrate. That is, it can be a near-infrared shielding film that has a glass base material and a resin layer of metal nanorod-containing resin disposed on the glass base material.

The film base material is not particularly limited, but for example, the thickness is preferably 10 μm or more and 200 μm or less, more preferably 30 μm or more and 120 μm or less.

This is because by setting the thickness of the film base material to 10 μm or more and 200 μm or less, the near-infrared shielding film as a whole can be made deformable while maintaining sufficient strength.

The glass substrate is also not particularly limited, but for example, the thickness is preferably 0.1 mm or more and 6 mm or less, and more preferably 1 mm or more and 4 mm or less.

This is because by setting the thickness of the glass base material to 0.1 mm or more and 6 mm or less, sufficient strength can be achieved while suppressing the overall weight of the near-infrared shielding glass from becoming excessively heavy. be.

The film base material is not limited to a film shape, and may be, for example, a board shape or a sheet shape. The material for the film base material is not particularly limited, but may be selected from, for example, polyester resin, acrylic resin, urethane resin, polycarbonate resin, polyethylene resin, ethylene vinyl acetate copolymer, vinyl chloride resin, fluororesin, etc. One or more types can be used. The film base material is preferably a polyester film, and more preferably a polyethylene terephthalate (PET) film.

Furthermore, the glass substrate is not particularly limited, and glass substrates such as silica glass and soda glass can be used.

Further, the surface of the transparent substrate is preferably subjected to surface treatment in order to improve the adhesion with the resin layer of the metal nanorod-containing resin. Furthermore, in order to improve the adhesiveness between the transparent base material and the resin layer, an intermediate layer may be formed on the transparent base material, and a resin layer may be formed on the intermediate layer. The structure of the intermediate layer is not particularly limited, and can be composed of, for example, a polymer film, a metal layer, an inorganic layer (for example, an inorganic oxide layer such as silica, titania, or zirconia), an organic/inorganic composite layer, etc. .

The thickness of the resin layer on the transparent substrate in the near-infrared shielding substrate is not particularly limited, but is preferably 20 μm or less, more preferably 6 μm or less. This means that if the thickness of the resin layer is 20 μm or less, it will not only exhibit sufficient pencil hardness and scratch resistance, but also avoid abnormalities such as warping of transparent substrates such as film substrates. It is from.

Note that the lower limit of the thickness of the resin layer is not particularly limited, but is preferably, for example, 10 nm or more, and more preferably 50 nm or more.
[Method for manufacturing metal nanorod aggregate]
Next, a method for manufacturing the metal nanorod aggregate of this embodiment will be described. Note that the metal nanorod aggregate means an aggregate of a plurality of metal nanorods. According to the method for manufacturing a metal nanorod aggregate of the present embodiment, metal nanorods and aggregates thereof that can be suitably used in the metal nanorod-containing resin described above can be manufactured. For this reason, some of the matters already explained will be omitted.

The method for manufacturing a metal nanorod aggregate according to the present embodiment can include, for example, the following steps.

The first step is to produce seed particles with a multi-twin structure.
The second step is to manufacture particles having a nanobipyramid structure based on seed particles.
The third step is to grow particles into nanorods based on particles having a nanobipyramid structure.

Then, the average value of the short axis length of each metal nanorod included in the metal nanorod aggregate obtained after the third step can be 17.5 nm or less.

Electrochemical methods, chemical methods, and photochemical methods are conventionally known as methods for synthesizing metal nanorods.

The metal nanorods contained in the metal nanorod-containing resin described above preferably have a core mainly made of gold and a shell mainly made of silver. The method for producing metal nanorods having a core-shell structure is not particularly limited, and any known method may be used.

Hereinafter, the method for producing a metal nanorod aggregate according to the present embodiment will be explained step by step, taking as an example a metal nanorod aggregate having a gold core and a silver shell around the core. However, the metal nanorod aggregate according to the present embodiment is not limited to the case where a metal nanorod aggregate having a gold core and a silver shell is manufactured, and the metal nanorod aggregate according to the present embodiment is manufactured using various metals. Can be applied to manufacturing. Therefore, a desired metal nanorod aggregate can be manufactured by reading the following explanations according to the configuration of the metal of the metal nanorod aggregate intended for gold or silver.
(First step)
In the first step, seed particles having a multi-twin structure can be produced. Therefore, the first step can also be called a seed particle manufacturing step.

In the first step, metal nanoparticles that become seed particles of metal nanorods can be manufactured. Commercially available products may be used as the metal nanoparticles, or they may be synthesized according to known methods. As mentioned above, when manufacturing metal nanorods having a gold core and a silver shell around the core, it is preferable that the seed particles contain at least gold.

In the first step, for example, metal ions can be reduced in an aqueous solution containing metal ions that are raw materials for seed particles and a protective agent (dispersant) to precipitate metal nanoparticles that will become seed particles. Note that the protective agent has a function of dispersing metal nanoparticles.

When producing metal nanorods having a gold core as described above, the seed particles that are the raw material for the gold core are reduced to gold ions in an aqueous solution containing gold ions and a protective agent (dispersant). It can be synthesized by

As the gold ion, it is preferable to use, for example, a halogenated auric acid such as chloroauric acid, or a salt of a halogenated auric acid such as sodium chloroauric acid.

The protective agent is not particularly limited as long as it can disperse the precipitated gold nanoparticles in an aqueous solution. One or more types selected from water-soluble salts of acids or bases can be used. As the protective agent, it is preferable to use one or more selected from, for example, citric acid and its salts, amine surfactants, and the like.

The synthesized gold nanoparticles are stably dispersed in water due to the protective effect of the protective agent. It is also commonly called gold colloid.

The protective agent has the effect of suppressing the aggregation of nanoparticles with high surface energy in order to lower that energy. It is known that some types of protective agents can also function as reducing agents. For example, sodium citrate and citric acid have both the functions of a protecting agent and a reducing agent. However, sodium citrate and citric acid have a weak reducing power compared to the types of reducing agents described below, so they cannot sufficiently reduce the target metal ions such as gold ions, and they do not remain in the seed particle dispersion after reduction. , there are cases in which there are almost no multiple twin grains, which will be described later. Therefore, when sodium citrate or citric acid is used as a protective agent in the first step, it is preferable to use a reducing agent separately.

The reducing agent is not particularly limited as long as it can reduce the target metal ion, but if the metal ion to be reduced is a gold ion, it may be selected from, for example, sodium borohydride, hydrazine, alcohol, ascorbic acid, etc. One or more types can be used.

The seed particle dispersion obtained in the first step usually contains single crystal particles and multiple twin crystal particles as seed particles. Note that the term "multiple twinned grain" refers to a grain having two or more twin planes, which are bonding surfaces between single crystal regions, per grain.

In order to obtain a nanobipyramid structure in the second step described below, it is preferable that the seed particles are multiple twins. For this reason, it is preferable that the ratio (number ratio) of multiple twin crystal particles is high among the single crystal particles and the multiple twin crystal particles contained as seed particles in the seed particle dispersion produced in the first step. Therefore, in the first step, it is preferable to select the conditions and the like so that the ratio of multi-twinned particles in the seed particles contained in the seed particle dispersion is high.

When synthesizing gold nanoparticles as described above, for example, in the first step, a reducing agent such as a sodium borohydride aqueous solution is quickly injected into a vigorously stirred aqueous solution containing gold ions and a protective agent. , the reduction reaction can occur very quickly. In this case, it is possible to obtain a seed particle dispersion in which the ratio of single crystal particles to multi-twin particles contained in the seed particles in the seed particle dispersion is high.

In addition, when citric acid and an amine surfactant are used together as a protective agent in the first step, and heat treatment is performed after adding a reducing agent, some of the single crystal grains are converted into multi-twinned particles, The yield of twinned grains can be improved.

As the amine surfactant, one or more selected from hexadecyltrimethylammonium bromide (CTAB), hexadecyltrimethylammonium chloride (CTAC), and dodecyltrimethylammonium chloride (DTAC) can be preferably used.

The temperature of the above heat treatment is not particularly limited, but is preferably 50°C or higher and 100°C or lower, more preferably 60°C or higher and 95°C or lower.

This is because by setting the temperature of the heat treatment to 50° C. or higher, conversion from single crystal grains to multi-twin grains can be promoted. However, if the temperature is higher than 100°C, the boiling point of the seed particle dispersion will be reached, and the conversion reaction from single crystal particles to multi-twin particles will become unstable, resulting in unintended reactions such as excessive particle growth reactions. This is because it may progress.

Although the heat treatment time depends on the treatment temperature, for example, when the reaction temperature is 85° C., it is preferably 30 minutes or more and 180 minutes or less, and more preferably 60 minutes or more and 150 minutes or less.
(Second process)
In the second step, particles having a nanobipyramid structure can be produced based on the seed particles contained in the seed particle dispersion obtained in the first step. That is, the seed particles can be grown into a nanobipyramid structure.

Therefore, the second step can also be called a step of synthesizing nano-bipyramid structured particles.

In the second step, the seed particle dispersion prepared in the first step is added to the initial aqueous solution containing, for example, a surfactant, metal ions, anisotropic growth aid, reducing agent, and if necessary a pH adjuster. By making a mixed aqueous solution and allowing it to stand, particles with a nanobipyramid structure can be produced.

As mentioned above, when producing a metal nanorod aggregate having a gold core and a silver shell around the core, the particles having a nanobipyramid structure may also contain at least gold. preferable.

When producing the metal nanorod aggregate, in the second step, an initial aqueous solution containing, for example, an amine surfactant, gold ions, an anisotropic growth aid, a reducing agent, and, if necessary, a pH adjuster, etc. The seed particle dispersion (gold nanoparticle dispersion) prepared in the first step can be added and allowed to stand. As a result, a dispersion containing gold nano bipyramid structure particles is obtained.

Any compound can be used as the gold ion source, and for example, as in the first step, halogenated auric acid such as chloroauric acid, or a salt of halogenated auric acid such as sodium chloroauric acid can be used. .

The anisotropic growth aid is not particularly limited, but includes, for example, a material whose crystal growth direction can be controlled by the oxidation-reduction potential of the metal.

According to studies by the inventors of the present invention, when silver ions are used and added as an anisotropic growth aid, the redox potential of gold changes, the crystal growth direction changes, and two pentagonal pyramids Particles with a bipyramid structure, which is a decahedral structure in which the bases of the two are combined, are obtained. For this reason, it is preferable to use silver ions as the anisotropic growth aid, and examples thereof include inorganic silver salts such as silver nitrate, silver cyanide, and silver acetate. From the viewpoints of availability, chemical stability, and toxicity, silver nitrate can be preferably used as a silver ion source for the anisotropic growth aid.

When using silver ions as an anisotropic growth aid, the amount of silver ions added to the aqueous solution is not particularly limited. However, in the second step, the ratio of the amount of silver ions to, for example, gold ions in the mixed aqueous solution obtained by adding and mixing the seed particle dispersion to the initial aqueous solution [the amount of silver ions in the mixed aqueous solution]/ [Amount of gold ions in the mixed aqueous solution] is preferably 0.05 or more and 0.5 or less, more preferably 0.1 or more and 0.5 or less.

If the mass ratio of silver ions to gold ions in the mixed aqueous solution is 0.05 or more and 0.5 or less, many of the multiple twinned particles contained in the seed particle dispersion will appropriately grow into a nanobipyramid structure, This is because the rate of growth of particles into unintended shapes such as spheres can be reduced.

As the amine surfactant, one or more selected from hexadecyltrimethylammonium bromide (CTAB), hexadecyltrimethylammonium chloride (CTAC), dodecyltrimethylammonium chloride (DTAC), etc. can be suitably used. In particular, CTAB can be suitably used as the amine surfactant in view of reaction stability and easy availability.

The amine surfactant dissolved in water forms a complex with metal ions and has the effect of suppressing rapid reduction, so it also functions as an anisotropic growth aid. Furthermore, after the seed particles grow and form nanobipyramid structure particles, the amine surfactant also functions as a protective agent and can suppress particle aggregation.

Examples of the reducing agent include ascorbic acid, citric acid, and sodium thiocyanate. Among these, ascorbic acid is preferred from the viewpoint of sufficiently promoting the reduction reaction of gold ions and the like in the mixed aqueous solution and appropriately controlling the rate of silver nucleation on the surface of gold nanoparticles.

Further, if necessary, a pH adjuster can be added to the initial aqueous solution to adjust the pH of the initial aqueous solution or mixed aqueous solution. The growth reaction of seed particles, that is, the reduction reaction that precipitates metal ions, such as gold ions and silver ions, on the seed particles is a redox reaction, and the reduction rate can be appropriately controlled by appropriately adjusting the pH, and the seed particles can be grown. Many of the multiple twinned particles contained in the particle dispersion can be grown into a nanobipyramid structure.

The pH of the mixed aqueous solution is preferably adjusted to be more acidic than neutral (pH=7). Therefore, it is preferable to use any acid or acidic compound as the pH adjuster. As a specific pH adjuster, for example, hydrochloric acid, hydrobromic acid, etc. can be suitably used, and it is particularly preferable to use hydrochloric acid. This is because hydrochloric acid is superior in terms of availability, and according to studies by the inventors of the present invention, the presence of multiple molecules in the seed particle dispersion is higher than when other acids or acidic compounds are used. This is because the yield of crystal particles growing into nanobipyramids is improved. The reason for this is not clear, but it is possible that chloride ions liberated from hydrochloric acid adsorb to specific crystal planes on the surface of nanobipyramid structure particles, promoting anisotropic growth into nanobipyramids. There is.

[ The molar concentration of gold in the seed particles in the mixed aqueous solution]/[molar concentration of gold ions in the mixed aqueous solution].

Conventionally, it has been thought that even if the above-mentioned ratio is changed, the short axis length of nanobipyramid structure particles does not fall below 19 nm. For example, when the value of [molar concentration of gold in seed particles in mixed aqueous solution]/[molar concentration of gold ions in mixed aqueous solution] is 1.25/100, the short axis length of nanobipyramid structure particles obtained is approximately It becomes 19 nm. However, if the [molar concentration of gold in the seed particles in the mixed aqueous solution]/[molar concentration of gold ions in the mixed aqueous solution] is set to a higher value, smaller particles with a nanobipyramid structure cannot be synthesized. It was thought that impurity particles having a structure other than the nanobipyramid structure would be mixed in.

However, according to studies by the inventors of the present invention, [molar concentration of gold in seed particles in mixed aqueous solution]/[molar concentration of gold ions in mixed aqueous solution] was set to a value much higher than the known conditions. By doing so, we confirmed that particles with a finer nanobipyramid structure could actually be synthesized. Specifically, by setting [molar concentration of gold in seed particles in mixed aqueous solution]/[molar concentration of gold ions in mixed aqueous solution] from 2.5/100 to 300/100, the average minor axis It has been found that gold particles having a length of 17.0 nm or less and having a nanobipyramid structure can be synthesized. Then, by growing metal nanorods using the nanobipyramid structure gold particles with an average short axis length of 17.0 nm or less in the third step described below, the average short axis length is 17.5 nm or less. We discovered that it is possible to synthesize certain metal nanorods.

The temperature of the mixed aqueous solution when the seed particle dispersion is added to the initial aqueous solution to form a mixed aqueous solution, that is, the reaction temperature, is not particularly limited, and can be around room temperature. For example, the reaction temperature is preferably 15°C or higher and 50°C or lower, more preferably 25°C or higher and 35°C or lower. This is because if the reaction temperature is 15° C. or more and 50° C. or less, the amine surfactant does not precipitate and most of the multiple twinned particles grow into a nanobipyramid structure.

The reaction time, which is the time for leaving the mixed aqueous solution to stand after preparing it, is not particularly limited, and can be selected depending on the reaction temperature and the like. For example, if 25°C is selected as the reaction temperature, by adding the seed particle dispersion to the initial aqueous solution and allowing it to stand for 30 minutes or more, the reactions in the aqueous solution, including the growth reaction to nanobipyramids, will be sufficiently carried out. This is preferable because it progresses and the liquid reaches a nearly equilibrium state. The upper limit of the reaction time in this case is not particularly limited, but from the viewpoint of increasing productivity, it can be set to, for example, 72 hours or less.

Note that the multi-twinned particles contained in the seed particle dispersion can grow into a nanobipyramid structure, but the single crystal particles contained in the seed particle dispersion do not grow into a nanobipyramid structure, but instead grow into spherical particles. grow up. Therefore, if the seed particle dispersion contains not only multitwinned particles but also single crystal particles, the dispersion containing gold particles with nanobipyramid structure obtained in the second step (hereinafter referred to as "gold nanobipyramid dispersion") ) may also contain spherical gold particles.
(Third step)
In the third step, particles can be grown into nanorod shapes based on the particles having a nanobipyramid structure contained in the dispersion of nanobipyramid structure particles obtained in the second step. Therefore, the third step can also be called a nanorod growth step.

Specifically, in the third step, for example, silver can be reduced onto particles having a gold nanobipyramid structure to cause anisotropic growth.

In the third step, particles can be grown into nanorod shapes based on particles having a nanobipyramid structure, for example, by the following procedure.

First, the gold nanobipyramid dispersion obtained in the second step is separated into a supernatant and a precipitate by centrifugation. The precipitate contains gold particles with a nanobipyramid structure.

Next, the precipitate containing gold particles having a nanobipyramid structure is collected and redispersed in an aqueous solution containing an amine surfactant.

As the amine surfactant, one or more selected from hexadecyltrimethylammonium bromide (CTAB), hexadecyltrimethylammonium chloride (CTAC), dodecyltrimethylammonium chloride (DTAC), etc. can be suitably used. Particularly from the viewpoint of reaction stability, CTAC can be suitably used as the amine surfactant.

Silver ions and a reducing agent are added to an aqueous solution containing the amine surfactant and gold particles having a nanobipyramid structure to obtain a mixed aqueous solution for nanorod growth. At this time, by adjusting the ratio of the concentration of silver ions to the concentration of gold particles in the nanobipyramid structure, the ratio of the short axis to the long axis of the metal nanorods after growth can be controlled.

Any compound can be used as the silver ion source, and examples thereof include inorganic silver salts such as silver nitrate, silver cyanide, and silver acetate. From the viewpoints of availability, chemical stability, and toxicity, silver nitrate is preferred as the silver ion source.

As the reducing agent, for example, ascorbic acid is preferable from the viewpoint of stability of the growth reaction and availability. The amount of the reducing agent added is preferably 1 times or more and 10 times or less, more preferably 2 times or more and 10 times or less, relative to the amount (molar amount) of silver ions added. preferable.

In a mixed aqueous solution for nanorod growth containing a silver ion source, an amine surfactant obtained by adding a reducing agent, gold particles with a nanobipyramid structure, silver ions, and a reducing agent, the nanobipyramid structure was Reduced silver ions can be precipitated onto gold particles, allowing the particles to grow. At this time, by anisotropic growth, metal nanorods having nanobipyramid structure gold particles as cores can be produced.

When performing the growth reaction, it is preferable that the temperature of the mixed aqueous solution for nanorod growth is 20° C. or higher and 80° C. or lower. This is because if the temperature of the mixed aqueous solution for nanorod growth is 20°C or more and 80°C or less, the reduction reaction of silver ions will proceed appropriately, and the unintentional growth of nanobipyramid-structured gold particles into shapes other than nanorods will be prevented. This is because the occurrence can be suppressed. From the viewpoint of promoting such a growth reaction, the reaction temperature is preferably higher than room temperature, for example, 40°C or more and 80°C or less.

The reaction time, which is the time for leaving the mixed aqueous solution for nanorod growth to stand after preparing it, can be selected depending on the reaction temperature and the like, and is not particularly limited. For example, if 65°C is selected as the reaction temperature, the reaction in the aqueous solution, including the growth reaction to nanorods, will sufficiently proceed by allowing it to stand for 30 minutes or more and 10 hours or less after preparing the mixed aqueous solution for nanorod growth. , which is preferable because the liquid reaches an almost equilibrium state. It is not preferable to leave the reaction mixture at a reaction temperature higher than room temperature for a longer period of time than 10 hours, as this may lead to unintended side reactions such as dissolution of the nanorods.

Note that the short axis length of the metal nanorods obtained in the third step depends on the short axis length of the nanobipyramid structure gold particles that are the basis of growth. That is, by performing the third step based on gold particles having a nanobipyramid structure having a shorter minor axis length, metal nanorods having a shorter minor axis length can be obtained. Then, as mentioned above in the second step, by performing the third step based on the dispersion of gold particles having a nano-bipyramid structure in which the average value of the short axis length is 17.0 nm or less, the average value of the short axis length is A metal nanorod dispersion containing metal nanorods having a diameter of 17.5 nm or less can be obtained.

Further, as described above, the gold nanobipyramid dispersion obtained in the second step may contain spherical gold particles as impurities. In the third step, particles having a gold nanobipyramid structure contained in the gold nanobipyramid dispersion grow into a nanorod structure. However, the spherical gold particles grow into spherical gold-silver core-shell particles with the spherical gold nanoparticles as the core and the spherical silver as the shell. Therefore, the dispersion of particles having a metal nanorod structure obtained in the third step (hereinafter referred to as "metal nanorod dispersion") may also contain spherical gold-silver core-shell particles.
(Fourth step)
The metal nanorod dispersion obtained in the third step contains particles having a metal nanorod structure, and can be used as near-infrared shielding particles as is. However, as described above, the metal nanorod dispersion obtained in the third step may contain core-shell spherical particles such as gold-silver core-shell particles.

Therefore, the method for manufacturing metal nanorods according to the present embodiment may further include, after the third step, a fourth step of removing impurities other than the metal nanorods, such as core-shell particles. By carrying out the fourth step, it is possible to form a metal nanorod-containing resin that further enhances the absorption contrast of light in the near-infrared region with respect to visible light.

In the fourth step, the method for removing impurities is not particularly limited, and various known methods may be used, for example. For example, separation by filtration, separation by centrifugation, separation using particle aggregation, etc. can be suitably used. Among these, separation using particle aggregation can be particularly preferably used. This is because the particle size and volume of the metal nanorods and the core-shell spherical particles contained in the metal nanorod dispersion are similar, and separation by filtration or centrifugation may be difficult.

Separation by particle aggregation means that one of the metal nanorods and core-shell spherical particles is kept dispersed while the other is aggregated, creating a difference in the dispersed particle size between the metal nanorod group and the core-shell spherical particle group, and then filtered. separation by centrifugation. Any method can be used to aggregate only one particle, but according to studies by the inventors of the present invention, a separation method using depletion interaction is effective.

Specifically, the metal nanorod dispersion liquid is separated into a supernatant liquid and a precipitate by centrifugation. An aqueous solution containing a surfactant at an appropriate concentration is added to the precipitate to redisperse it. Thereafter, by allowing the dispersion to stand at room temperature, only the metal nanorods can be aggregated while the core-shell spherical particles contained in the metal nanorod dispersion remain dispersed. Since the aggregation greatly increases the dispersed particle size of the metal nanorods, they can be separated into a supernatant liquid and a precipitate by performing filtration or centrifugation.

For example, when separation is performed by centrifugation, core-shell spherical particles as impurities are separated in the supernatant, and metal nanorods are included in the precipitate. By redispersing the precipitate in water or an aqueous surfactant solution, it is possible to obtain a metal nanorod dispersion in which the proportion of impurities is reduced compared to before the separation operation.

After centrifuging the metal nanorod dispersion liquid, any surfactant can be used as the surfactant contained in the surfactant aqueous solution added to the precipitate, and is not particularly limited. However, from the viewpoints of critical micelle concentration, solubility in water, availability, etc., hexadecyltrimethylammonium bromide (CTAB) can be preferably used as the surfactant.

After centrifuging the metal nanorod dispersion liquid, the concentration of the surfactant in the surfactant aqueous solution added to the precipitate depends on the short axis length of the metal nanorods, the long axis length of the metal nanorods, and the particle size of the core-shell spherical particles. There are no particular limitations. However, the surfactant concentration of the surfactant aqueous solution is, for example, preferably 100 mM or more and 450 mM or less, more preferably 200 mM or more and 350 mM or less. This is because if the concentration is 100 mM or more and 450 mM or less, the metal nanorods will aggregate, but the core-shell spherical particles will not aggregate, and the surfactant will not precipitate due to the solubility limit. In addition, in this specification, M means mol/L.

The temperature of the surfactant aqueous solution is preferably 20°C or higher and 40°C or lower, more preferably 25°C or higher and 40°C or lower. This is because when the temperature is 20° C. or higher and 40° C. or lower, the surfactant does not precipitate due to a decrease in solubility, and re-dispersion of the aggregated metal nanorods into the liquid is suppressed.

The metal nanorod aggregate obtained in the above steps is not particularly limited, but each metal nanorod contained in the metal nanorod aggregate preferably contains 30% or more of silver in mass proportion. As described above, since silver does not absorb in the visible light region, the visible light transmittance can be increased by containing silver in the metal nanorod aggregate of this embodiment. Further, it is preferable to set the content ratio of silver to 30% or more in terms of mass ratio, since this effect can be particularly markedly exhibited.

However, if the silver content is too high, it may not be possible to form the desired shape, so the mass percentage of the silver content is preferably 95% or less.

Further, the average value of the ratio of the long axis length to the short axis length of each metal nanorod included in the metal nanorod aggregate obtained by the method for producing a metal nanorod aggregate of the present embodiment is 4.0 or more and 12.0 or less. It is preferable that there be.

This can be done by setting the average value of the ratio of major axis length to minor axis length, that is, the average value of major axis length/short axis length, to be 4.0 or more, so that the major axis length is sufficient compared to the minor axis length. It can be made longer. This is because the visible light transmittance of the metal nanorod-containing resin of the present embodiment can be increased, and the absorption of light in the near-infrared region can be significantly increased. Further, by setting the average value of the ratio of the long axis length to the short axis length to be 12.0 or less, the handling property can be improved.

The metal nanorod aggregate obtained by the method for producing a metal nanorod aggregate of the present embodiment preferably has a maximum value of optical density in the wavelength range of light from 800 nm to 1400 nm. Further, the ratio of the optical density for a light wavelength of 550 nm to the maximum value of optical density [maximum value of optical density]/[optical density for a light wavelength of 550 nm] is preferably 6.0 or more, and 9.0 The above is more preferable.

The higher the optical density, the lower the transmittance of light at the corresponding wavelength, meaning that it is blocked. Therefore, as described above, the metal nanorod aggregate produced by the method for producing a metal nanorod aggregate of the present embodiment has a maximum value of optical density in the near-infrared wavelength region of 800 nm or more and 1400 nm or less. This makes it possible to block light in a wide wavelength range in the near-infrared region, including the maximum value.

In addition, by setting the ratio of the optical density for a light wavelength of 550 nm and the maximum value of optical density, [maximum value of optical density]/[optical density for a light wavelength of 550 nm] to 6.0 or more, lasers, etc. This is because even when high-intensity light is incident, the intensity of the light can be significantly reduced and, for example, the effect on the eyes can be suppressed.

Note that the optical density of the metal nanorod aggregate changes depending on the degree of dispersion of each metal nanorod included in the metal nanorod aggregate. Therefore, the maximum value of the optical density and the ratio of the optical density with respect to a light wavelength of 550 nm and the maximum value of the optical density are the same as those of the metal nanorod aggregate obtained by the method of manufacturing the metal nanorod aggregate of this embodiment. It is preferable that the metal nanorod-containing resin produced using the metal nanorod-containing resin satisfies the above range.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the following examples.

First, a method for evaluating samples in the following Examples and Comparative Examples will be described.
(Average value of short axis length, average value of ratio of long axis length to short axis length)
The obtained metal nanorods were observed with a transmission electron microscope (manufactured by JEOL, model: JEM-1011), and the short axis length and long axis length were determined for a total of 100 metal nanorods observed in 2 to 5 fields of view. was measured. Then, the average value of the short axis lengths of 100 metal nanorods was defined as the average short axis length of the metal nanorods. Further, the ratio of the long axis length to the short axis length, ie, the long axis length/short axis length, was calculated for each metal nanorod, and the average value of the ratio of the long axis length to the short axis length of 100 metal nanorods was calculated.
(Visible light transmittance, optical density)
The visible light transmittance of the metal nanorod-containing resin is determined from the transmittance of light in the wavelength range of 380 nm or more and 780 nm or less, measured using a spectrophotometer (Model: U-4100, manufactured by Hitachi, Ltd.), according to JIS R 3106 (1998). ).

The optical density of the metal nanorod-containing resin was calculated based on the following formula (1) from the transmittance of 550 nm or more and 1300 nm or less, which was similarly measured using a spectrophotometer.

ここでＯＤ（λ）は波長λでの光学濃度、Ｔ（λ）は波長λでの透過率（０～１００％）である。

Here, OD(λ) is the optical density at the wavelength λ, and T(λ) is the transmittance (0 to 100%) at the wavelength λ.

In addition, the wavelength of the maximum value of optical density at a light wavelength of 800 nm or more and 1400 nm or less, and [maximum value of optical density]/[optical density for a light wavelength of 550 nm] are also measured using the optical density calculated by the above procedure. I asked for it.
(Content of metal nanorods per projected area)
The obtained metal nanorod-containing resin was separated from the transparent soda-lime glass substrate, and the amount of metal in the resin was evaluated by ICP mass spectrometry (model: ICPE9000, manufactured by Shimadzu Corporation).

Then, the weight of the metal nanorods per volume (g/m ³ ) subjected to evaluation was converted into the weight per projected area (g/m ² ) using the thickness of the metal nanorod-containing resin, and the projected area The content of metal nanorods per unit was calculated.

The preparation conditions and evaluation results of samples of each example and comparative example will be explained below.
[Example 1]
(First step)
To 9.625 mL of pure water, 0.125 mL of an aqueous solution of tetrachloroauric acid (HAuCl ₄ ) with a concentration of 10 mM and 0.25 mL of an aqueous solution of sodium citrate with a concentration of 10 mM were added to create a solution. The solution was placed in a 25 mL round bottom beaker and stirred vigorously using a magnetic stirrer. 0.15 mL of an aqueous solution of sodium borohydride (NaBH ₄ ) having a concentration of 10 mM was quickly added to the stirring solution using a dropper to prepare a solution containing gold nanoparticles.

When the gold nanoparticles were observed using a transmission electron microscope, it was observed that they contained multiple twinned particles.
(Second process)
For 40 mL of an aqueous solution of hexadecyltrimethylammonium bromide (CTAB) with a concentration of 100 mM, 2 mL of an aqueous solution of HAuCl ₄ with a concentration of 10 mM, 0.4 mL of an aqueous solution of silver nitrate (AgNO ₃ ) with a concentration of 10 mM, and hydrochloric acid (HCl with a concentration of 1 M). A solution was prepared by adding 0.8 mL of aqueous solution) and 0.32 mL of an aqueous solution of ascorbic acid having a concentration of 100 mL.

Further, the pH of the solution was measured with a pH meter and was found to be 1.9.

The solution was put into a test tube with a capacity of 100 mL, and 6 mL of the solution containing gold nanoparticles prepared in the first step was added to form a mixed aqueous solution.

In addition, [the amount of silver ions in the mixed aqueous solution]/[the amount of gold ions in the mixed aqueous solution] is 0.2.

Further, in the mixed aqueous solution, [molar concentration of gold in the seed particles in the mixed aqueous solution]/[molar concentration of gold ions in the mixed aqueous solution] is 3.7/100.

After shaking this for 10 seconds, it was left standing in a constant temperature bath set at 25° C. for 12 hours to prepare a solution containing gold nanoparticles.

When the gold nanoparticles were observed using a transmission electron microscope, it was observed that they contained particles with a nanobipyramid structure. EDS analysis also confirmed that the particles contained gold.
(Third step)
10 mL of the solution containing the nano-bipyramid-structured gold particles produced in the second step was centrifuged to sediment the nano-bipyramid-structured gold particles. Note that centrifugation was performed at a rotation speed of 9000 rpm for 20 minutes. After removing the supernatant with a dropper, 7.5 mL of an aqueous solution of hexadecyltrimethylammonium chloride (CTAC) with a concentration of 80 mM was added to the precipitate, and the particles were redispersed by ultrasonication. Furthermore, 1.5 mL of AgNO ₃ aqueous solution with a concentration of 10 mM and 0.75 mL of an ascorbic acid aqueous solution with a concentration of 100 mM were added to prepare a mixed aqueous solution for nanorod growth. After shaking the mixed aqueous solution for nanorod growth for 10 seconds, it was left standing in a constant temperature bath set at 65° C. for 4 hours to prepare a solution containing metal nanorods.

When the nanoparticles were observed and analyzed using a transmission electron microscope and EDS, it was observed that they contained metal nanorods with silver arranged at least on the surface and a gold particle having a nanobipyramid structure in the center.
(Fourth step)
In the fourth step, impurities other than metal nanorods were removed by particle aggregation.

Specifically, 1.8 mL of the solution containing the metal nanorods prepared in the third step was centrifuged to precipitate the metal nanorods. Note that centrifugation was performed at a rotation speed of 10,000 rpm for 20 minutes. After removing the supernatant with a dropper, 1.5 mL of an aqueous solution of hexadecyltrimethylammonium bromide (CTAB) with a concentration of 300 mM was added to the precipitate, and the particles were redispersed by ultrasonication.

This was left to stand in a constant temperature bath set at 25°C for 10 hours, and then centrifuged to remove the supernatant. Note that centrifugation was performed at a rotation speed of 2000 rpm for 3 minutes. Then, 1.5 mL of pure water was added to the obtained precipitate and redispersed to prepare an aqueous dispersion of metal nanorods.

When the metal nanorods were observed and analyzed using a transmission electron microscope and EDS, it was observed that they contained at least metal nanorods with silver arranged on their surfaces, and that the spherical nanoparticles as impurities were almost completely removed. Ta. FIG. 1 shows an image of the particles obtained by transmission electron microscopy. As shown in FIG. 1, it was confirmed that the nanoparticles were composed of rod-shaped nanoparticles.

Based on transmission electron microscopy, size statistics of the metal nanorods contained in the metal nanorod aggregate were taken, and the average value of the major axis length was 97.5 nm, and the average value of the minor axis length was 13.0 nm. Ta. Moreover, the average value of the ratio of the long axis length to the short axis length was 7.5, and the standard deviation was 0.8. Furthermore, when the mass ratio of metal contained in the metal nanorods was measured by ICP mass spectrometry, it was confirmed that the metal nanorods contained 65.0% by mass of silver, with the remainder being gold.

Furthermore, when the spectral curve of the aqueous dispersion of the metal nanorods was measured, it was found that it had a strong absorption peak, that is, a maximum value, in the near-infrared region of 1015 nm. Table 1 shows the evaluation results for metal nanorods.
(Preparation and evaluation of metal nanorod-containing resin layer)
The above first to fourth steps were repeated multiple times to obtain respective aqueous dispersions containing metal nanorods. In addition, it was confirmed that metal nanorods having the same physical properties were obtained in both cases.

All aqueous dispersions of metal nanorods were then mixed in the same container and concentrated by centrifugation and decantation. ICP mass spectrometry was performed on the aqueous dispersion containing metal nanorods after concentration, and the mass percentage of metal nanorods contained in the dispersion was measured, and was found to be 0.28% by mass.

Next, Watersol S-701 (manufactured by DIC Corporation), which is an acrylic thermosetting resin, was added to the dispersion to prepare a near-infrared shielding ink as a coating liquid.

The near-infrared shielding ink was flow-coated onto a 3-mm-thick transparent blue plate glass, and then dried in an oven set at 100° C. to produce a resin layer made of a metal nanorod-containing resin.

When the optical properties of the obtained metal nanorod-containing resin were measured, the visible light transmittance was 52%. The optical density was 0.3 at a wavelength of 550 nm, 4.3 at a wavelength of 975 nm, 5.6 at a wavelength of 1015 nm, 4.0 at a wavelength of 1065 nm, and 0.6 at a wavelength of 1195 nm. The maximum value of absorption wavelength was 1015 nm, and the maximum value of optical density was at a light wavelength of 800 nm or more and 1400 nm or less.

Furthermore, the ratio between the optical density (0.3) for a light wavelength of 550 nm and the maximum value of optical density (5.6), [maximum value of optical density]/[optical density for a light wavelength of 550 nm], is 18 It was .7.

Table 2 shows the evaluation results for the metal nanorod-containing resin.
[Examples 2 to 4]
Watersol S-701 (manufactured by DIC), an acrylic thermosetting resin, was added to the aqueous dispersion of metal nanorods prepared in Example 1 to prepare a near-infrared shielding ink as a coating liquid. When adding the thermosetting resin to the aqueous dispersion of metal nanorods, the thermosetting resin was added so that the content of metal nanorods per projected area for each example was the value shown in Table 2. The amount was adjusted.

The near-infrared shielding ink was flow-coated onto a 3 mm thick transparent blue plate glass, and then dried in an oven set at 100° C. to produce a resin layer made of a metal nanorod-containing resin.

Table 2 shows the evaluation results of the obtained metal nanorod-containing resin.
[Example 5]
(First step)
For 4.45 mL of pure water, add 0.05 mL of an aqueous solution of tetrachloroauric acid (HAuCl ₄ ) with a concentration of 50 mM, 0.5 mL of an aqueous solution of citric acid with a concentration of 100 mM, and hexadecyltrimethylammonium chloride (CTAC) with a concentration of 100 mM. 5.0 mL of aqueous solution was added to create a solution. The solution was placed in a 25 mL round bottom beaker and stirred vigorously using a magnetic stirrer. 0.25 mL of an aqueous solution of sodium borohydride (NaBH ₄ ) having a concentration of 25 mM was quickly added to the stirring solution using a dropper to prepare a solution containing gold nanoparticles.

After stirring the solution vigorously for 5 minutes with a magnetic stirrer, the mouth of the round-bottomed beaker was sealed with a lid and heated in an oil bath at 85°C for 90 minutes to transform the single crystal particles into multi-twin particles. Conversion was performed.

When the gold nanoparticles were observed using a transmission electron microscope, it was observed that they contained multiple twinned particles.
(Second process)
For 40 mL of an aqueous solution of hexadecyltrimethylammonium bromide (CTAB) with a concentration of 100 mM, 2 mL of an aqueous solution of HAuCl ₄ with a concentration of 10 mM, 0.4 mL of an aqueous solution of silver nitrate (AgNO ₃ ) with a concentration of 10 mM, and hydrochloric acid (HCl with a concentration of 1 M). A solution was prepared by adding 0.8 mL of aqueous solution) and 0.32 mL of an aqueous solution of ascorbic acid having a concentration of 100 mL.

Further, the pH of the solution was measured with a pH meter and was found to be 1.9.

The solution was put into a test tube with a capacity of 100 mL, and 6 mL of the solution containing gold nanoparticles prepared in the first step was added to form a mixed aqueous solution.

In addition, [the amount of silver ions in the mixed aqueous solution]/[the amount of gold ions in the mixed aqueous solution] is 0.2.

Further, in the mixed aqueous solution, [molar concentration of gold in the seed particles in the mixed aqueous solution]/[molar concentration of gold ions in the mixed aqueous solution] is 7.3/100.

After shaking this for 10 seconds, it was left standing in a constant temperature bath set at 25° C. for 12 hours to prepare a solution containing gold nanoparticles.

When the gold nanoparticles were observed and analyzed using a transmission electron microscope and EDS, it was observed that they contained gold particles with a nanobipyramid structure.
(Third step)
10 mL of the solution containing the nano-bipyramid-structured gold particles produced in the second step was centrifuged to sediment the nano-bipyramid-structured gold particles. Note that centrifugation was performed at a rotation speed of 9000 rpm for 20 minutes. After removing the supernatant with a dropper, 7.5 mL of an aqueous solution of hexadecyltrimethylammonium chloride (CTAC) with a concentration of 80 mM was added to the precipitate, and the particles were redispersed by ultrasonication. Furthermore, 1.4 mL of AgNO ₃ aqueous solution with a concentration of 10 mM and 0.70 mL of an ascorbic acid aqueous solution with a concentration of 100 mM were added to prepare a mixed aqueous solution for nanorod growth. After shaking the mixed aqueous solution for nanorod growth for 10 seconds, it was left standing in a constant temperature bath set at 65° C. for 4 hours to prepare a solution containing metal nanorods.

When the nanoparticles were observed and analyzed using a transmission electron microscope and EDS, it was observed that they contained metal nanorods with silver arranged at least on the surface and a gold particle having a nanobipyramid structure in the center.
(Fourth step)
In the fourth step, impurities other than metal nanorods were removed by particle aggregation.

Specifically, 1.8 mL of the solution containing the metal nanorods prepared in the third step was centrifuged to precipitate the metal nanorods. Note that centrifugation was performed at a rotation speed of 10,000 rpm for 20 minutes. After removing the supernatant with a dropper, 1.5 mL of an aqueous solution of hexadecyltrimethylammonium bromide (CTAB) with a concentration of 300 mM was added to the precipitate, and the particles were redispersed by ultrasonication.

This was left to stand in a constant temperature bath set at 25°C for 10 hours, and then centrifuged to remove the supernatant. Note that centrifugation was performed at a rotation speed of 2000 rpm for 3 minutes. Then, 1.5 mL of pure water was added to the obtained precipitate and redispersed to prepare an aqueous dispersion of metal nanorods.

When the metal nanorods were observed and analyzed using a transmission electron microscope and EDS, it was observed that they contained at least metal nanorods with silver arranged on their surfaces, and that spherical nanoparticles as impurities had been removed.

Based on transmission electron microscopy, size statistics of the metal nanorods contained in the metal nanorod aggregate were taken, and the average value of the major axis length was 92.0 nm, and the average value of the minor axis length was 15.4 nm. Ta. The average value of the ratio of major axis length to minor axis length was 6.0, and the standard deviation was 0.8. Furthermore, when the mass ratio of metal contained in the metal nanorods was measured by ICP mass spectrometry, it was confirmed that the metal nanorods contained 63.0% by mass of silver, with the remainder being gold.

Furthermore, when the spectral curve of the aqueous dispersion of the metal nanorods was measured, it was found that it had a strong absorption peak, that is, a maximum value, in the near-infrared region of 1005 nm. Table 1 shows the evaluation results for metal nanorods.
(Preparation and evaluation of resin containing metal nanorods)
The above first to fourth steps were repeated multiple times to obtain respective aqueous dispersions containing metal nanorods. In addition, it was confirmed that metal nanorods having the same physical properties were obtained in both cases.

All aqueous dispersions of metal nanorods were then mixed in the same container and concentrated by centrifugation and decantation. ICP mass spectrometry was performed on the aqueous dispersion containing metal nanorods after concentration, and the mass percentage of metal nanorods contained in the dispersion was measured, and it was found to be 0.55% by mass.

Next, Watersol S-701 (manufactured by DIC Corporation), which is an acrylic thermosetting resin, was added to the dispersion to prepare a near-infrared shielding ink as a coating liquid.

The near-infrared shielding ink was flow-coated onto a 3 mm thick transparent blue plate glass, and then dried in an oven set at 100° C. to produce a resin layer made of a metal nanorod-containing resin.

When the optical properties of the obtained metal nanorod-containing resin were measured, the visible light transmittance was 60%. The optical density was 0.2 at a wavelength of 550 nm, 2.6 at a wavelength of 975 nm, 2.9 at a wavelength of 1015 nm, 1.9 at a wavelength of 1065 nm, and 0.4 at a wavelength of 1195 nm. The maximum value of absorption wavelength was 1005 nm, and the maximum value of optical density was at a light wavelength of 800 nm or more and 1400 nm or less.

Furthermore, the ratio between the optical density (0.2) for a light wavelength of 550 nm and the maximum value of optical density (3.0), [maximum value of optical density]/[optical density for a light wavelength of 550 nm], is 15 It was .0.

Table 2 shows the evaluation results for the metal nanorod-containing resin.
[Examples 6-7]
Watersol S-701 (manufactured by DIC Corporation), which is an acrylic thermosetting resin, was added to the aqueous dispersion of metal nanorods prepared in Example 5 to prepare a near-infrared shielding ink as a coating liquid. When adding the thermosetting resin to the aqueous dispersion of metal nanorods, the thermosetting resin was added so that the content of metal nanorods per projected area for each example was the value shown in Table 2. The amount was adjusted.

The near-infrared shielding ink was flow-coated onto a 3 mm thick transparent blue plate glass, and then dried in an oven set at 100° C. to produce a resin layer made of a metal nanorod-containing resin.

Table 2 shows the evaluation results of the optical properties of the obtained metal nanorod-containing resin.
[Comparative example 1]
Watersol S-701, which does not contain an aqueous dispersion of metal nanorods, was flow coated onto a 3 mm thick transparent soda-lime glass, and then dried in an oven set at 100°C to produce a resin layer according to Comparative Example 1. .

When the optical properties of the resin layer according to the comparative example were measured, the visible light transmittance was 88%. Further, the optical density in the near-infrared region was 0.0 at a wavelength of 950 nm, 0.0 at a wavelength of 1015 nm, 0.0 at a wavelength of 1065 nm, and 0.0 at a wavelength of 1195 nm.

Table 2 shows the evaluation results for the resin layer.

（実施例１～７および比較例１の評価）
表１および表２に示した実施例、比較例の結果によると、実施例１～７で作製した金属ナノロッド含有樹脂による樹脂層は、十分な可視光透過率を有することを確認できた。また、これらの実施例では、８００ｎｍ以上１４００ｎｍ以下の近赤外線領域の光の波長領域に光学濃度の極大値を有しており、極大値を含む、近赤外線領域の幅広い波長領域に渡って近赤外線を遮蔽できることを確認できた。すなわち、これらの実施例で得られた金属ナノロッド含有樹脂は、高い可視光透過率を保ちながら、広い波長領域に渡って近赤外線を遮蔽することができることを確認できた。このため、レーザーなどの強力な近赤外線領域の光の眼に対する影響を大幅に軽減することができる、優れた光学特性を発揮することが示された。

(Evaluation of Examples 1 to 7 and Comparative Example 1)
According to the results of Examples and Comparative Examples shown in Tables 1 and 2, it was confirmed that the resin layers made of metal nanorod-containing resins produced in Examples 1 to 7 had sufficient visible light transmittance. In addition, in these Examples, the maximum value of optical density is in the near-infrared light wavelength region of 800 nm or more and 1400 nm or less, and the near-infrared We confirmed that it was possible to shield the That is, it was confirmed that the metal nanorod-containing resins obtained in these Examples were able to block near-infrared rays over a wide wavelength range while maintaining high visible light transmittance. For this reason, it has been shown that it exhibits excellent optical properties that can significantly reduce the effects of powerful near-infrared light such as lasers on the eyes.

On the other hand, the resin layer prepared in Comparative Example 1 does not contain metal nanorods, so although it has a high visible light transmittance, its optical density for near-infrared rays is almost 0, and the strong near-infrared light is not sensitive to the eyes. It was confirmed that there is almost no function to reduce the impact.

Claims (21)

A metal nanorod-containing resin in which metal nanorods are dispersed in the resin,
It has a maximum value of optical density at a light wavelength of 800 nm or more and 1400 nm or less,
The ratio of the optical density for a light wavelength of 550 nm and the maximum value of optical density, [maximum value of optical density]/[optical density for a light wavelength of 550 nm], is 6.0 or more,
The plurality of metal nanorods contained in the resin have an average short axis length of 17.5 nm or less, and have a gold core and a silver shell arranged around the core,
A resin containing metal nanorods, wherein the average value of the ratio of the long axis length to the short axis length of the metal nanorods is 6.0 or more and 12.0 or less . The metal nanorod-containing resin according to claim 1, having a visible light transmittance calculated according to JIS R 3106 (1998) of 2% or more and 70% or less. The resin is one resin selected from the resin group of polycarbonate resin, acrylic resin, and vinyl chloride resin, a mixture of two or more resins selected from the resin group, or two selected from the resin group. The metal nanorod-containing resin according to claim 1 or 2, which is a copolymer of more than one type of resin. The metal nanorod-containing resin according to any one of claims 1 to 3, wherein the content of the metal nanorods is 0.01 g/m ² or more and 1.00 g/m ² or less per projected area. The metal nanorod-containing resin according to any one of claims 1 to 4, wherein the metal nanorods contain silver. The metal nanorod-containing resin according to any one of claims 1 to 5 , further comprising an ultraviolet absorber. The metal nanorod-containing resin according to any one of claims 1 to 6 , further comprising an antioxidant. A near-infrared shielding lens comprising a resin layer of the metal nanorod-containing resin according to any one of claims 1 to 7 . Near-infrared shielding glasses comprising a resin layer of the metal nanorod-containing resin according to any one of claims 1 to 7 . A protective device comprising a resin layer of the metal nanorod-containing resin according to any one of claims 1 to 7 . A near-infrared shielding window material comprising a resin layer of the metal nanorod-containing resin according to any one of claims 1 to 7 . A near-infrared shielding device comprising the near-infrared shielding window material according to claim 11 . A near-infrared shielding film, wherein a resin layer of the metal nanorod-containing resin according to any one of claims 1 to 7 is provided on a film base material. Near-infrared shielding glass, wherein a resin layer of the metal nanorod-containing resin according to any one of claims 1 to 7 is provided on a glass substrate. A method for producing a metal nanorod aggregate, the method comprising:
a first step of producing seed particles having a multi-twin structure;
a second step of producing particles having a nanobipyramid structure based on the seed particles;
a third step of growing particles into a nanorod shape based on the particles having the nanobipyramidal structure;
A method for producing a metal nanorod aggregate, wherein the average short axis length of each metal nanorod contained in the metal nanorod aggregate obtained after the third step is 17.5 nm or less. The method for producing a metal nanorod aggregate according to claim 15 , further comprising a fourth step of removing impurities other than the metal nanorods after the third step. The method for producing a metal nanorod aggregate according to claim 15 or 16 , wherein the seed particles contain at least gold. The method for producing a metal nanorod aggregate according to any one of claims 15 to 17 , wherein the particles having the nanobipyramid structure contain at least gold. The method for producing a metal nanorod aggregate according to any one of claims 15 to 18 , wherein each metal nanorod contained in the metal nanorod aggregate contains silver in a mass proportion of 30% or more. Any one of claims 15 to 19 , wherein the average value of the ratio of the long axis length to the short axis length of each metal nanorod included in the metal nanorod aggregate is 4.0 or more and 12.0 or less. The method for producing the metal nanorod aggregate described above. The optical density of the metal nanorod aggregate with respect to the optical wavelength is
It has a maximum value of optical density at a light wavelength of 800 nm or more and 1400 nm or less,
is the ratio of the optical density for a light wavelength of 550 nm and the maximum value of the optical density,
The method for producing a metal nanorod aggregate according to any one of claims 15 to 20 , wherein [maximum value of optical density]/[optical density at a light wavelength of 550 nm] is 6.0 or more.