LU508167B1

LU508167B1 - NIR-blocking coating compositions and articles coated with said coating compositions

Info

Publication number: LU508167B1
Application number: LU508167A
Authority: LU
Inventors: Paiva Sa Jacinto De
Original assignee: Duck Tech Ab
Priority date: 2024-09-03
Filing date: 2024-09-03
Publication date: 2026-03-03

Abstract

The present invention relates to a coating composition for application on an article, comprising plasmonic silver nanoplates, a polymer for use as a binder; and an organic solvent, a method of obtaining thereof and a coated article with said coating composition

Description

NIR-blocking coating compositions and articles coated with said coating LU508167 compositions

Field of the Invention

The present invention relates to the field of energy-efficient coatings, specifically silver nanoplates/polymer coatings for use on windows to enhance energy savings by improving thermal insulation properties.

Background of the Invention

The use of windows in modern buildings has become ubiquitous, providing natural light and a connection to the outside environment. However, conventional windows contribute significantly to energy loss due to their poor thermal insulation properties. The high transmittance of near-infrared rays (NIR) from these windows leads to increased energy consumption for heating, ventilation, and air conditioning (HVAC) systems, as heat is easily lost through the glass during colder months and gained during warmer periods.

Existing solutions to this problem, such as low-emissivity (Low-E) glass, rely on complex and expensive vacuum sputtering coatings to improve the thermal insulation properties of windows. These coatings are designed to reflect infrared radiation while allowing visible light to pass through, reducing heat transfer and improving energy efficiency. However, the high cost and complexity of the vacuum sputtering process limit the widespread adoption of Low-E glass, particularly in retrofit applications and large-scale projects.

Furthermore, the visual qualities of the coatings used in Low-E glass can sometimes be compromised, leading to distorted colors or reduced natural light transmission. Maintaining a balance between energy efficiency and visual comfort is crucial for the occupants' well-being and productivity in the building.

Despite the advancements in Low-E glass technology, there remains a need for more cost-effective and scalable solutions that can be easily applied to both new and existing windows. These solutions should aim to provide excellent thermal insulation properties while maintaining high visible light transmittance and minimal color distortion. Additionally, the development of flexible and durable coatings that can be applied to various substrates, such as plastic films, would expand the potential applications beyond traditional architectural windows. As the demand for energy- efficient buildings continues to grow, further advancements in the field of window 1 coatings are necessary to address these challenges and promote sustainable LVS08167 construction practices.

As an alternative to traditional vacuum sputtering methods, a direct spray-coating process of silver nanowires (AgNWs) and polyvinyl butyral (PVB) onto glass is proposed inthe article S. Lin et al, Nano Energy 62 (2019) 111-116. The spray-coating process can be manual or automated and produces a coating with high visible light transmittance and significant mid-infrared reflectivity. However, this coating does not provide near-infrared reflectivity, which is essential for further enhancing energy efficiency.

Summary of the Invention

It is an object of the present invention to provide energy-efficient coated articles, such as coated windows, that are cost-effective, easy to produce, scalable, and highly efficient. It is a further object of the present invention to provide coated articles with high visible light transmittance and transparency, to ensure a high visual comfort for a user. It is also an object of the present invention to provide a stable coating composition that can be used to produce coated energy-efficient articles with high energy efficiency.

These objectives are achieved by a coating composition for application on an article, comprising at least: a. plasmonic silver nanoplates; b. a polymer for use as a binder; and

C. an organic solvent.

In a preferred coating composition, the silver nanoplates are capped with a capping agent. For example, the capping agent may be selected from

Polyvinylpyrrolidone (PVP), Polyvinylalkohol (PVA), citrate, oleylamine, more preferably Polyvinylpyrrolidone (PVP)

In another preferred example, freely combinable with the previous ones, the silver nanoplates have a triangular shape, having two larger triangular surface areas, which represent the bases of the nanoplate, and a thickness, which corresponds to the average distance in betwsen the two bases, wherein the nangular surface areas have triangle edges {or sides) ranging from about 20 nm to 200 nm, mors preferably from 20 to 150 nm, even more preferably from 30 to 100 nm and the thickness being of less than shout 20 nim, more preferably between 1 and 15 nm, even more preferably 2 from 1 to 10 nm and most preferred between 1 and 5 nm, as measured by DLg LUS08167 {Dynamic Light Scattering).

In another preferred example, the dimension of the silver nanoparticles is chosen such that they exhibit an absorption peak in the wavelength range of 700 to 1500 nm, by known methods known in the art. This is done, for example, by tunning the length and the thickness of the nanoplates.

In another preferred example, freely combinable with the previous ones, the silver nanoplates are present in an amount of at least 0.2wt% based on the total weight of the composition, more preferably at least 0.5wt% based on the total weight of the composition and even more preferably of at least 1wt% based on the total weight of the composition. Also, preferably, the amount of silver nanoplates is not more than 2 wt% based on the total weight of the composition

Preferably, the polymer in the coating composition is present in an amount of

O3wt% to 0.8wt% based on the total weight of the composition.

In another preferred example, freely combinable with the previous ones, the coating composition contains no water, or has a content of water of 0.01wt% to 0.1wt% or less based on the total weight of the composition.

In another preferred example, freely combinable with the previous ones, the polymer in the coating composition acts as a binder and is able to produce films that are noted for optical clarity, physical toughness and adhere well to a variety of surfaces. Preferably the polymer is selected from Polyvinylpyrrolidone (PVP),

Polyvinyl Alcohol (PVA), Poly(methyl methacrylate) (PMMA) and Polyvinyl Butyral (PVB).

Yet in another preferred example, freely combinable with the previous ones, the organic solvent used in the coating composition is a tertiary alcohol, preferably having a boiling point below 100°C. Also preferred, the solvent may have a vapour pressure of at least 4kPa at a temperature of 20°C. Preferably, the solvent is selected from tert- butanol, 2-methyl-2-butanol, 3-methyl-2-butanol or 4-methyl-2-pentanol. Even more preferably, the solvent is tert-butanol.

Preferably, the amount of organic solvent is 99.5 wt% or less, based on the total weight of the composition.

According to a second aspect, the invention relates to a coating film obtainable by applying the coating composition according to the present invention on a substrate and allowing the solvent to evaporate, to obtain a dry coating film on the substrate. 3

Preferably, the coating film has a thickness of 1000 nm or less, preferably 100 nm or LU508167 less, even more preferably 50 nm or more, as measured by AFM (Atomic Force

Microscopy). More preferably, the coating film is configured to block at least 60% of infrared radiation in the wavelength range of 700 to 1500 nanometers and/or to maintain a visible light transmittance of at least 80%.

In a third aspect, the invention relates to a method of obtaining a coating composition as described above, comprising the steps of: a) mixing silver nanoplate particles with an organic solvent and subsequently adding a polymer for use as a binder to the mixture; or b) mixing the polymer for use as a binder in the organic solvent and subsequently adding the silver nanoplate particles; or c) mixing silver nanoplate particles with the organic solvent, separately mixing the polymer for use as a binder with another amount of the organic solvent and mixing the two solutions together.

In a preferred embodiment, the silver nanoplates in step a are wet silver nanoplate particles taken from an aqueous solution and without post treatment, for example without drying them previous to the insertion in the organic solvent.

In a fourth aspect, the invention relates to a method of obtaining a coated article by: a) applying the coating composition as described above on the article; b) allowing the organic solvent to evaporate, to obtain a dry coating film on the article.

Preferably, the method of obtaining a coated article takes place at room temperature and ambient pressure. Also preferably, the coating composition is applied using a method selected from spray coating, dip coating, brush coating, and roll coating. For example, the coating composition may be applied by using a roll-to-roll (R2R) coating process.

Steps a) and b) may be repeated one or several times to obtain a multi-layer coating on the article.

In a fifth aspect, the invention relates to a coated article produced by the method described above, with the aim of reflecting solar radiation and reducing cooling costs. The article may be a transparent substrate, preferably a transparent glass substrate or a plastic substrate. For example, the substrate on which the coating 4 composition is applied may be a window or a door in buildings, vehicles, or aircraft. LVS08167

Detailed description of the Invention

The present invention will be described with respect to particular embodiments, but the invention is not limited thereto.

Coating composition

A coating composition according to a first aspect of the present invention comprises: a. plasmonic silver nanoplates; b. a polymer for use as a binder; and

C. an organic solvent.

Plasmonic silver nanoplates

The silver nanoplates (or nanoprisms) according to the present invention are dimensioned specifically to optimize a plasmonic effect and to exhibit desired absorption peaks in the near infrared wavelength range. This characteristic effectively minimizes the penetration of heat-bearing near-infrared (NIR) solar energy through articles coated with a composition comprising the plasmonic silver nanoplates. For instance, when windows of a building are treated with the coating of the present invention, the interior temperature is consequently reduced due to diminished solar heat ingress. This reduction in heat penetration leads to decreased dependence on air conditioning systems, thereby enhancing energy efficiency within the building.

The silver nanoparticles have a plate-ke morphology, with a high aspect ratio between the lateral dimensions of the plates larger surface areas, which represent the bases of the nanoplate, compared to its thickness, Thus, in the context of the present invention, "thickness" refers to the smallest dimension of the material, representing the average distance between the lwo bases. The “lateral dimensions” of a silver nanoplate, on the other hand, are the dimensions along its larger surface areas.

Preferably, the thickness of the nanoplales is less than 20nm, or less than 15nm, or less than 10nm. Also preferably, the thickness of the nanonlates Is more than Snm, as measured by DLS. The lateral dimensions may be of less than 200 nm, for example less than 150 nm, or less than 100nm and more than 30 nm, as measured by BLS. In another preferred example, the dimension of the silver nanoparticles is chosen such that they exhibit absorption peaks between 700 to 1500 nm.

The nanopiates can be, for example, trangular, rectanguiar, square, or hexagonal in shape. More preferably, the nanopiates are trianguier in shape. The tnangular surface areas may have triangie edges (or sides) ranging from about 30 nm to 200 nm, mors 5 preferably from 30 to 150 nm, and the thickness of the nanoplate may be of less than LUS08167 about 20 nm, more preferably between 5 and 15 nm, as measured by DLS (Dynamic

Light Scattering).

Capping agent

In a preferred coating composition, the silver nanoplates are capped with a capping agent. The capping agent provides stability and prevents agglomeration of the nanoparticles. For example, the capping agent may be selected from

Polymer

In the coating composition, a polymer is used as a binder. Thus, the polymer serves as a flexible, durable matrix that enhances the mechanical stability and integrity of the embedded silver nanoplates. In addition, the polymer should have adhesive qualities, which facilitate strong bonding between the substrate and the silver nanoparticles. The polymers of the present invention are available in a variety of molecular weights. Preferably, the polymer is selected such that the coating can be applied using a cost-effective, scalable spray-coating process suitable for both manual and automated roll-to-roll applications. Also preferably, the polymer can be engineered to offer high optical clarity, which ensures that the film maintains high visibility and light transmittance.

In a preferred embodiment, the polymer is selected from Polyvinylpyrrolidone (PVP),

Polyvinyl Alcohol (PVA), Poly(methyl methacrylate) (PMMA) and Polyvinyl Butyral (PVB). Even more preferred, the polymer is Polyvinyl Butyral (PVB).

Organic solvent

The organic solvent is chosen to ensure the stability of the nanoplates. Unlike spherical silver nanoparticles, nanoplates are particularly sensitive to environmental conditions due to the high surface energy associated with their sharp edges and corners at the atomic scale. This high surface energy makes silver ions more labile and susceptible to etching by surrounding species or atomic rearrangement. Additionally, organic solvents can remove the capping agent that protects the silver nanoplates, potentially reacting with and destabilizing the nanoplate shape.

Thus, the organic solvent should be carefully selected to ensure the desired stability of the nanoplates and to effectively dissolve the polymer used as a binder. Preferably, the solvent should have a boiling point below 100°C to allow quick evaporation during 6 film formation. Additionally, it is preferable for the solvent to have a vapor pressure of LU508167 at least 4 kPa at 20°C. Vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed liquid phase at a given temperature in a closed system.

Preferably, the solvent is a tertiary alcohol. It has been found by the present inventors that if a tertiary alcohol is used, the nanoplates keep their shape in a solution for a long time and during manipulation in a coating composition. Preferably, the solvent is selected from tert-butanol, 2-methyl-2-butanol, 3-methyl-2-butanol or 4-methyl-2- pentanol. Even more preferably, the solvent is tert-butanol.

Coating film

In the second aspect, the present invention relates to a coating film obtainable by applying the coating composition of any embodiments of the first aspect on a substrate and allowing the solvent to evaporate, to obtain a dry coating film on the substrate. As used herein, and unless otherwise specified, the term "dry coating film" refers to a coating formed after the solvent in the coating composition has evaporated, leaving behind a solid film containing the non-volatile components.

In embodiments, the coating has a thickness of 500 nm or less, preferably 100 nm or less. Also preferably, the coating has a thickness of 50 nm or more. This thickness may provide high flexibility to the film, as well as high transparency, in case it is desired. In embodiments, the thickness and composition of the film are chosen such that it can block at least 60% of infrared radiation in the wavelength range of 700 to 1500 nanometers and/or maintain a visible light transmittance of at least 80%. These optical properties enable energy savings.

Method of obtaining a coating composition

In the third aspect, the present invention relates to a method of obtaining a coating composition comprising the steps of: a) mixing silver nanoplate particles with an organic solvent and subsequently adding a polymer for use as a binder to the mixture; or b) mixing the polymer for use as a binder in the organic solvent and subsequently adding the silver nanoplate particles; or c) mixing silver nanoplate particles with the organic solvent, separately mixing the polymer for use as a binder with another amount of the organic solvent and mixing the two solutions together.

In a preferred embodiment, the method comprises the steps: 7 a) providing an aqueous solution of silver nanoplates; LU508167 b) adding a polymer for use as a binder in a liquid organic solvent; c) adding wet silver nanoplate particles from the aqueous solution to the liquid organic solvent.

Thus, in one approach, the silver nanoplates are first added to the organic solvent, followed by the addition of the polymer. In another embodiment, the silver nanoplates are initially dispersed in the organic solvent separately from the polymer solution. The two mixtures are then combined by adding the nanoplate dispersion to the polymer solution.

As used herein, and unless otherwise specified, the term "wet silver nanoplates" refers to silver nanoparticles that have been taken from an aqueous dispersion and have not been fully dried to remove all the water before being dispersed in a different solvent, such as an organic solvent. Thus, a water content of less than 0.1 wt% and more than 0.01 wt% based on the total weight of the composition may remain in the coating composition. When water is mixed with the organic solvent, it can lower the freezing point of the mixture compared to the pure solvent. This is particularly useful if the solvent is in a solid state at room temperature, like in the case of tert-butanol. Tert-butanol can form hydrogen bonds with water due to the presence of the hydroxyl (-OH) group in both molecules. These hydrogen bonds create a more stable liquid phase and lower the freezing point of the solution. Thus, tert-butanol can be used efficiently in a coating composition according to the present invention if the content of water is kept low. Nevertheless, especially for other solvents already in liquid form at room temperature, the water content may be zero.

Method of obtaining a coated article

In the fourth aspect, the present invention relates to a method of obtaining a coated article by: a) applying the coating composition of any of claims 1 to 11 on the article; b) allowing the organic solvent to evaporate, to obtain a dry coating film on the article.

The method involves applying the coating composition of the present invention on the article and allowing the solvent to evaporate completely, resulting in a dried coating on the article.

In embodiments, the applying step may take place at room temperature and ambient pressure. This simplifies the coating process. In embodiments, the coating 8 composition may be applied using methods selected from spray coating, dip coating, LVS08167 brush coating, and roll coating. These methods are suitable for various substrates. In embodiments, the coating composition may be applied using a roll-to-roll (R2R) coating process. This enables continuous production. In embodiments, steps a) and b) may be repeated to obtain a multi-layer coating.

Coated article

In the fifth aspect, the present invention relates to a coated article produced by the method of any embodiments of the fourth aspect.

The coating composition as described above in the present invention is applied to the article, and after the solvent evaporates, a dried coating is formed on the surface of the article. In embodiments, the article may be a transparent substrate, preferably a transparent glass substrate or a plastic substrate. It has been found by the present inventors that when a coating composition according to the present invention is applied on a transparent article, the penetration of heat-bearing near-infrared (NIR) solar energy is minimized, while the transparency is maintained, ensuring both high visual comfort and heat comfort with low energy consumption for the user.

In embodiments, the article may be a window or a door in buildings, vehicles, or aircraft. This enables energy savings in various applications.

Exemplary embodiments that demonstrate the advantages of the present invention are provided below.

Examples

Example 1. Synthesis of silver nanoplates stabilized with PVP

The silver nanoplates were synthesized using a seed-mediated process. The process was adapted from the protocol published by Aherne et al. (Adv. Funct. Mater. 2008, 18, 2005-2016). Silver seeds were produced by combining aqueous trisodium citrate (5mL, 2.5mM), aqueous poly(sodium styrenesulphonate) (PSSS; 0.25 mL, 500 mg/L, 1,000 kDa) and aqueous NaBH4 (0.3 mL, 10 mM, freshly prepared) followed by addition of aqueous AgNO3 (5 mL, 0.5 mM) at a rate of 2 mL/min while stirring continuously. The silver nanoplates were produced by combining 5 mL distilled water, aqueous ascorbic acid (75 mL, 10 mM) and various quantities of seed solution, followed by the addition of aqueous AgNO3 (3 mL, 0.5 mM) at a rate of 1 mL/min. By adjusting the amount of volume of seeds, different sizes can be obtained, with bigger sizes obtained when smaller volumes of seeds are used. 9

After synthesis, an aqueous solution of polyvinylpyrrolidone (PVP) (40'000 mol wt, 0.5 LU508167 mL, 25 mM) was added as a capping agent to stabilize the particles. The particle size was determined by dynamic light scattering. The obtained nanoplates were triangular in shape with triangle edges from 60-150nm +/- 30 nm and thicknesses between 5-15 nm.

Example 2. Coating composition

The PVP-stabilized silver nanoplates were centrifuged at 5000 rpm for 15 min. The aqueous supernatant was discarded and the silver nanoplates were redispersed in an equal volume of tert-butanol as the discarded supernatant. This process was repeated twice to reduce the water content to less than 0.1 wt% based on the total weight of the composition.

A final solution containing 0.2 g of silver nanoplates in 1 mL of tert-butanol was prepared. This solution was then added to a separate solution consisting of 0.4 g of polyvinyl butyral (PVB) dissolved in 100 mL of tert-butanol, resulting in the coating composition as a spraying solution.

Example 3. Coated article

The coating composition was sprayed onto microscope glass slides of 76 x 26 x 1.2 mm with an airbrush gun at 3 bar pressure.

The spraying process is carried out at room temperature and ambient pressure, ensuring an even application by maintaining a consistent distance and motion over the surface of ca. 10-15 cm from the glass. After spraying, the tert-butanol solvent evaporates naturally at room temperature within approximately five minutes, leaving behind a uniform, transparent Ag nanoplates/PVB film adhered to the glass substrate.

Example 4. Evaluation

The UV-VIS-NIR absorption spectroscopy was conducted to assess the optical properties of the coated article, specifically their ability to absorb light across the near- infrared (NIR) regions.

The following describes the methodology, results, and their implications for the performance of the samples. UV-VIS-NIR absorption was performed on an Agilent

Cary 5000 UV-VIS-NIR spectrometer in transmission mode, measuring the amount of light absorbed and reflected by the applied coating. The coating was applied to half of the glass slide, leaving the uncoated side as a reference for the glass's original light absorption and reflection. Coating the glass with only the polymer in the formulation led to a 10% increase in light scattering across the entire measurement range. When 10

0.1 wt% of Ag triangular nanoplates with a triangle length of 90 nm and thickness of LU508167 15 nm and a single layer of coating was applied to the glass, an additional absorption peak between 800-1300 nm with a maximum of 1000 nm appeared. The presence of the Ag nanoplates increases the absorption at the peak maximum by about 3%.

Itis to be understood that although preferred embodiments, specific constructions and configurations, as well as materials, have been discussed herein for devices according to the present invention, various changes or modifications in form and detail may be made without departing from the scope of this invention. 11

Claims

Claims LU508167

1. A coating composition for application on an article, comprising:

a. plasmonic silver nanoplates;

b. a polymer for use as a binder; and

C. an organic solvent

2. The coating composition of claim 1, wherein the silver nanoplates are capped with a capping agent, preferably selected from Polyvinylpyrrolidone (PVP), Polyvinylalkohol (PVA), citrate, oleylamine, more preferably Polyvinylpyrrolidone (PVP)

3. The coating composition of any preceding claim, wherein the silver nanoplates have a triangular shape, having two larger triangular surface areas, which represent the bases of the nanoplate, and a thickness, which corresponds io the average distance between the two bases, wherein the triangular surface areas have triangle edges ranging from about 20 nm to 200 nm, more preferably from 20 to 150 nm, even more preferably from 30 to 100nm: and the thickness being of less than about 20 nm, more preferably between 1 and 15nm even more preferably from 1 to Snm and most preferred between 1 and Srim.

4. The coating composition of any preceding claim, wherein the silver nanoplates are present in an amount of at least 0.2 wt% based on the total weight of the composition and/or the polymer is present in an amount of 0.3wt% to 0.8wt% based on the total weight of the composition.

5. The coating composition of any preceding claim, having a content of water of 0.01 wt% or more to 0.1 wt% or less based on the total weight of the composition.

6. The coating composition of any preceding claim, wherein the polymer is selected from Polyvinylpyrrolidone (PVP), Polyvinyl Alcohol (PVA), Poly(methyl methacrylate) (PMMA) and Polyvinyl Butyral (PVB). 12

7. The coating composition of any preceding claim, wherein the solvent is LU508167 a tertiary alcohol, preferably having a boiling point below 100°C and a vapour pressure of at least 4kPa at a temperature of 20°C.

8. The coating composition of any preceding claim, wherein the solvent is selected from tert-butanol, 2-methyl-2-butanol, 3-methyl-2-butanol or 4-methyl-2- pentanol.

9. A coating film obtainable by applying the coating composition of any of claims 1 to 8 on a substrate and allowing the solvent to evaporate, to obtain a dry coating film on the substrate.

10. A method of obtaining a coating composition according to any of claims 1 to 8, comprising the steps of: a) mixing silver nanoplate particles with an organic solvent and subsequently adding a polymer for use as a binder to the mixture; or b) mixing the polymer for use as a binder in the organic solvent and subsequently adding the silver nanoplate particles; or c) mixing silver nanoplate particles with the organic solvent, separately mixing the polymer for use as a binder with another amount of the organic solvent and mixing the two solutions together.

11. A method of obtaining a coated article by: a) applying the coating composition of any of claims 1 to 8 on an article; b) allowing the organic solvent to evaporate, to obtain a dry coating film on the article.

12. The method of claim 11, wherein the coating composition is applied using a method selected from spray coating, dip coating, brush coating, and roll coating.

13. A coated article produced by the method of any of claims 11 or 12. 13

14. The coated article of claim 13, wherein the article is a transparent LU508167 substrate, preferably a transparent glass substrate or a plastic substrate.

15. The coated article of claims 13 or 14, wherein the article is a window or a door in buildings, vehicles, or aircraft. 14