Formulation for producing an ir radiation-reflecting coating

Abstract

The invention relates to a formulation for preparing an IR radiation-reflecting coating. The formulation comprises at least one electrically conductive metallic nanomaterial, at least one binder and at least one solvent, the weight ratio of electrically conductive metallic nanomaterial to binder being greater than 0.005.

Description

[0001] Formulation for producing an IR radiation reflecting coating

[0002] Technical area

[0003] The invention relates to a formulation for producing an IR radiation reflecting coating, a composite material comprising such an IR radiation reflecting coating arranged on a substrate and a method for producing such a composite material.

[0004] State of the art

[0005] Materials with a sufficiently high transmittance are considered transparent in the visible wavelength range. The transmittance is defined as the quotient of the light intensity behind an obstacle divided by the light intensity in front of the obstacle. The transmittance therefore ranges between 0 and 1, or between 0% and 100%. The visible range of the electromagnetic spectrum encompasses the wavelengths between 400 nm and 850 nm.

[0006] An example of a material with a very high light transmittance is Plexiglas, which has a transmittance of 92%. Other types of glass have lower transmittances, such as thermal insulation glass with a transmittance of 73% to 80%. In comparison, heavily tinted sunglasses have a transmittance of around 18%.

[0007] Infrared radiation is divided into three wavelength ranges: near IR from 690 nm to 3.0 pm, mid IR from 3.0 pm to 50 pm, and far IR in the wavelength range from 50 pm to 1 mm. Electromagnetic radiation in the mid IR is referred to as thermal radiation.

[0008] Coatings that reflect thermal radiation are well-known and used in many applications. Such coatings are often referred to as "cool coatings" or low-emissivity ("low E") coatings.

[0009] Cool coatings can improve the energy efficiency of buildings and other objects by reducing the absorption of solar heat energy. To achieve this, these coatings must have high near-IR reflectivity and high thermal emissivity to release the absorbed solar heat energy back into the environment.

[0010] For example, WO 2020 / 069183 A1 discloses compositions and methods for the use of anhydrous tricalcium phosphate as a multifunctional additive for coatings, such as paint systems, for improved solar reflection and heat emission properties. WO 2022 / 212376 A1 describes a coating solution that can be sprayed onto substrates and is reflective in the UV, visible, and near-infrared range. The spray coating not only offers high reflectivity across all visible wavelengths but also high emissivity in the mid-infrared range for effective surface cooling.

[0011] Due to their high emissivity, cool coatings are unsuitable for so-called low-E applications. In low-E applications, IR radiation is reflected to reduce heat loss and minimize heat penetration into the building through low thermal emissivity. At the same time, these coatings are intended to be transparent to visible light. For this reason, low-E coatings are typically applied to glass surfaces to reduce heat transfer and improve the energy efficiency of buildings.

[0012] In addition to special dyes, coatings made of metal or metal oxide layers, i.e., conductive materials, offer a way to reflect electromagnetic radiation. Low-E applications therefore typically use metal or metal oxide layers vapor-deposited onto glass panes.

[0013] In modern thermal insulation glazing (e.g., double and triple glazing), the space between the glass panes is filled with gas. Previously, air was used, but now argon is predominantly used. The side of the pane of effective thermal insulation glazing facing the gas side is / are coated with a thin, transparent, heat-reflecting layer(s). This layer(s) is typically sputtered on and exhibits very good heat-reflecting properties. Furthermore, the pane can be cleaned and polished without losing these properties because the layer is protected from mechanical influences due to its positioning on the gas-facing side. The very thin sputtered layers are fragile to mechanical influences and cleaning.

[0014] Retrofitting such thermal insulation in existing buildings is only possible by completely replacing the windows, since subsequent sputtering of an installed window can only be carried out on its surfaces facing away from the gas, which means that the sputtered layer is subsequently not protected against external influences.

[0015] In addition, the use of pigments such as graphite, silver, or gold flakes to create heat-reflecting layers is known. Such layers are used, for example, as insulation or rescue foils to reflect heat radiation emitted by the body and thus keep a person warm or minimize heat loss. However, this type of foil is not transparent.

[0016] Packaging materials are also made from such films. Furthermore, plastics coated with metal foil are used to reflect heat radiated by radiators into the room. These composite materials (plastic with a metal coating) are opaque, seal the walls, and have low permeability to water vapor, which can lead to mold growth.

[0017] DE 699 21 053 T2 describes a coated glass that can be used in windows for homes and vehicles. This type of coated glass offers effective solar protection with minimal emissions from the glass. The coatings contain tin oxide with various dopants, but the coating application method described in DE 699 21 053 T2 is not suitable for retrofitting existing glazing.

[0018] EP 1 025 057 B1 describes a thermal insulation coating that is almost completely transparent in the visible range of the electromagnetic spectrum and exhibits only low absorption in the near-IR range. The coating comprises several crosslinked or polymerized cholesteric IR-reflecting layers.

[0019] If a binder is added to such a transparent conductive layer in a typical concentration to improve the stability of the layer, this leads to a loss of the heat-reflecting effect, especially if the transparency of the layer in the visible wavelength range is to be maintained at the same time.

[0020] Conductive layers containing silver nanowires are transparent in the visible wavelength range and reflect thermal radiation, particularly in the range from 3 pm to 50 pm. The proportion of reflected IR radiation depends on the silver content of the surface coating (Graubmann J. et al., "Silver nanowires: a new nanomaterial with advances for electrical, optical and IR systems" Proc. SPIE 11159, Electro-Optical and Infrared Systems: Technology and Applications XVI, 1115903 (9 October 2019); doi: 10.1117 / 12.2532245). By increasing the silver nanowire content in the coating, an increase in electrical conductivity and increased IR reflection can be achieved. Therefore, a percolating network is required to achieve reflection properties in the wavelength range from 3 pm to 50 pm.A percolating network is formed when electrically conductive particles cluster together densely enough to transport electrical current over long distances.

[0021] However, these coatings are not resistant to external influences such as mechanical impacts or scratching, and can also be easily washed off by cleaning agents or water. Even with these systems, it has been shown that the addition of a binder in typical concentrations to improve the stability of the coating leads to a loss of conductivity and IR reflection, especially if transparency is to be maintained. Applying a protective coating with common, commercially available binder systems for transparent surfaces therefore leads to a loss of the heat-reflecting effect on the surface.

[0022] There is therefore still a need for formulations suitable for coating substrates, whereby the coating has a high optical transparency in the visible range and ensures good thermal insulation in the IR range by reflecting infrared radiation, in particular by reflecting radiation in the mid-IR range.

[0023] Description of the invention

[0024] The object of the present invention is therefore to provide a formulation suitable for coating substrates, wherein the coating should exhibit transparent properties in the visible range and thermal radiation-reflecting properties in the IR range. At the same time, the coating should be easy to apply, cure at low temperatures, and exhibit mechanical stability.

[0025] This object is achieved according to the invention by the formulation according to independent claim 1. Further advantageous aspects, details and embodiments of the invention emerge from the dependent claims, the description and the drawing.

[0026] The present invention provides a formulation for producing an IR-reflecting coating. The formulation comprises at least one electrically conductive metal nanomaterial, at least one binder, and at least one solvent, wherein the weight ratio of electrically conductive metal nanomaterial to binder is greater than 0.005. Surprisingly, it has been found that when an electrically conductive metal nanomaterial is used in combination with a defined proportion of binder in a formulation used to produce an IR-reflecting coating, the resulting coating exhibits heat-reflecting properties, even if no surface conductivity can be measured. At the same time, optical transparency is also present in the visual range of the electromagnetic spectrum.The formulation according to the invention can also be cured at low temperatures down to room temperature. Furthermore, no conventional protective layer needs to be subsequently applied to the coating, thus avoiding the reduced IR-reflective properties associated with such a protective layer.

[0027] In the context of the present invention, the term "electrically conductive metal nanomaterial" refers to electrically conductive metal nanoparticles, electrically conductive metal nanowires and electrically conductive metal nanotubes.

[0028] According to a general definition, "nanoparticles" refers to particles with a size in the range of less than 100 nm. The use of the prefix "nano" thus represents a distinction from particles in the sub-micrometer range (> 100 nm), according to the official definition of ISO TC 229.

[0029] In this text, the term "metal nanowire" and in particular "silver nanowire" refers to all materials that

[0030] - consist predominantly of particles with a metal content and in particular metallic silver content of > 90 wt.%,

[0031] - have a "one-dimensional" geometry like a rod or a hair with a long axis (length) and a short axis (diameter),

[0032] - have an aspect ratio (length / diameter) of at least 5 and

[0033] - whose diameter is in the range between 1 nm and 1000 nm.

[0034] The term "nanotubes" (NT), as used here, describes structures that have similar dimensions in the range of 1 nm to 1000 nm in at least two spatial directions and have an extension in the third spatial direction of at least 5 times the other two extensions and are at least predominantly hollow.

[0035] The term "IR radiation-reflecting coating" is understood in the context of the present invention to mean that the coating reflects at least 10% of the IR radiation averaged over the wavelength range in the wavelength range from 3 pm to 50 pm. To determine the reflected IR radiation, the IR reflection of the coating in the wavelength range from 3 m to 50 m is determined in wavelength steps of, for example, 5 nm, the measured reflection values ​​are added together, and the sum of the reflection values ​​is divided by the number of measured values.

[0036] According to a preferred embodiment of the present invention, the weight ratio of electrically conductive metal nanomaterial to binder is greater than 0.01, preferably greater than 0.02, and particularly preferably 0.05. It has been shown that with increasing binder content, the IR-reflecting properties decrease.

[0037] Sufficient IR reflection has been demonstrated up to the inventive weight ratio of electrically conductive metal nanomaterial to binder of at least more than 0.005.

[0038] According to a further preferred embodiment of the present invention, the weight ratio of electrically conductive metal nanomaterial to binder is less than 2, preferably less than 1, particularly preferably less than 0.5.

[0039] Particularly preferably, the weight ratio of electrically conductive metal nanomaterial to binder is between 0.01 and 0.5, preferably between 0.02 and 0.2, and particularly preferably between 0.05 and 0.1. It has been shown that, with a weight ratio of electrically conductive metal nanomaterial to binder in the above-mentioned ranges, formulations are available from which coatings with excellent IR-reflecting properties can be produced.

[0040] The electrically conductive metal nanomaterial is preferably electrically conductive metal nanoparticles, in particular electrically conductive silver nanoparticles, electrically conductive metal nanowires, in particular electrically conductive silver nanowires, electrically conductive metal nanotubes, in particular electrically conductive silver nanotubes.

[0041] The binder is preferably an IR-active binder, which absorbs IR radiation in the wavelength range from 3 pm to 50 pm. An "IR-active binder" within the meaning of the present invention is present if the binder, at concentrations familiar to the person skilled in the art, absorbs more than 70% of the IR radiation averaged over the wavelength range from 3 pm to 50 pm.

[0042] According to a preferred embodiment, the electrically conductive metal nanomaterial contained in the formulation is, in particular, electrically conductive silver nanoparticles, electrically conductive silver nanowires, or mixtures thereof. These electrically conductive materials achieve particularly good properties of the coating produced using the formulation with regard to its IR reflectivity.

[0043] Particularly good properties with regard to the desired IR reflection are achieved when the formulation additionally contains electrically conductive carbon, electrically conductive carbon nanotubes, graphene, electrically conductive polymers or mixtures thereof.

[0044] The production of the metal nanoparticles, in particular silver nanoparticles, and metal nanowires, in particular silver nanowires, used as electrically conductive metal nanomaterial in the formulation for producing an IR radiation-reflecting coating is described in detail in WO 2016 / 166074 A1, to which reference is hereby made and the content of which with regard to the production of metal nanoparticles, in particular silver nanoparticles, and metal nanowires, in particular silver nanowires, is made part of the present text.

[0045] The formulation particularly preferably comprises one or more additives, preferably thickeners, adsorptives, wetting aids, flame retardants, polyvinylpyrrolidone, defoamers, film formers, chemical stabilizers, and color pigments, wherein the color pigments absorb predetermined portions of the electromagnetic radiation in the wavelength range from 400 nm to 800 nm. By using additives, the mechanical properties of the coating produced using the formulation can be specifically adjusted and improved.

[0046] In contrast to the prior art, in which formulations with metallic nanowires mixed with commercially available weight proportions of binder are described, coatings produced using a formulation according to the invention have IR-reflecting properties after drying.

[0047] Since the color pigments absorb predetermined portions of electromagnetic radiation in the wavelength range from 400 nm to 800 nm, only those wavelengths are specifically transmitted that can be used, for example, for applications in interior decoration or plant growth. By adding color pigments, in addition to the IR-reflecting properties of the coating, its color can be customized as desired. The coating produced using a formulation according to the invention can therefore be transparent, semi-transparent, or opaque in the visible wavelength range. UV-absorbing additives serve to protect against UV radiation and absorb predetermined portions of electromagnetic radiation in the wavelength range from 100 nm to 400 nm.

[0048] In principle, any type of binder system known to those skilled in the art can be used. Particularly preferably, the binder is a binder based on acrylates, epoxides, polyurethanes, silicones, siloxanes, polyolefins, cellulose derivatives, polythiophenes, polyanilines, perfluorinated polymers, and copolymers of the aforementioned polymers, and mixtures thereof. Binder systems are formulations containing polymers used to fix the produced metal structures. Thus, in preferred embodiments, binder systems based on acrylates, epoxides, polyurethanes, silicones, siloxanes, polyolefins, cellulose derivatives, polythiophenes, polyanilines, perfluorinated polymers, and copolymers of the aforementioned polymers, and mixtures thereof, are used. The aforementioned binder systems exhibit particularly good properties with regard to processability and IR-reflecting properties.

[0049] According to a particularly preferred embodiment, the electrically conductive metal nanomaterial comprises electrically conductive metal nanowires, in particular electrically conductive silver nanowires, wherein the quotient of the length and diameter of the metal nanowires is greater than 5. The quotient of the length and diameter of the metallic structure is also referred to as the aspect ratio. It has been shown that when using particles with a smaller aspect ratio, these particles must either have a comparatively larger diameter, or a higher concentration of metal nanoparticles must be selected in the formulation to achieve the desired effectiveness with regard to IR-reflecting properties.

[0050] The present invention also encompasses a composite material comprising a substrate and an IR radiation-reflecting coating arranged on the substrate, wherein the coating is made from a formulation specified above. The coating produced using a formulation according to the invention improves the thermal insulation properties by reflecting electromagnetic radiation in the wavelength range from 3 pm to 50 pm and reduces the thermal emission of the substrate.

[0051] The IR-reflective properties of the coating are evident even though no electrical conductivity can be detected. One explanation for this is that discrete aggregates of conductive particles, such as a multitude of individual nanowires not directly connected, are sufficient to generate IR-reflective properties, rather than a percolating network. However, IR reflection is only achieved when the proportion of electrically conductive metal nanomaterial to binder is present in the ratio specified in the invention. In these cases, IR reflection is still observed even though no electrical conductivity can be detected.

[0052] Particularly preferably, the IR-reflecting coating of the composite material has an average spectral transmission of less than 30% in the wavelength range from 3 μm to 50 μm. The coating of the composite material therefore has a high reflectivity in the wavelength range from 3 μm to 50 μm. Preferably, the IR-reflecting coating of the composite material has a reflection of more than 20%, preferably more than 30%, particularly preferably more than 40% in the wavelength range from 3 μm to 50 μm.

[0053] The composite material according to the invention can be used for the reflection of IR radiation in the wavelength range from 3 pm to 50 pm in interior spaces (buildings, greenhouses, automotive, public transportation), in aerospace products (aircraft), mobility (passenger cars), and clothing (camouflage, signature management).

[0054] Despite the use of a binder to create a coating with good mechanical stability, good surface resistance and reflection properties can be achieved with metallic nanowires without compromising the mechanical stability of the coating and its stability against other external influences (e.g., waterlogging).

[0055] The substrate is preferably a polymer film, a woven fabric, a knitted fabric, a textile material, glass, paper, concrete, cement, wood, gypsum, plasterboard, a metal, or a plastic. The coating produced using a formulation according to the invention can therefore be applied to synthetic or natural substrates, which may have varying degrees of flexibility.

[0056] According to preferred embodiments of the invention, the IR-reflecting coating of the composite material has a layer thickness after drying of a maximum of 60 μm, preferably a maximum of 30 μm, and particularly preferably a maximum of 15 μm. It has been shown that the stated layer thicknesses achieve the desired IR-reflecting properties to a sufficient degree while minimizing material consumption. According to a further preferred embodiment, the coating has an average spectral transmission of at least 30% in the wavelength range from 400 nm to 800 nm. In the context of the present text, a coating that has an average transmission of at least 30% in the wavelength range from 400 nm to 800 nm is referred to as "transparent."

[0057] According to further embodiments, the coating can also be translucent or opaque. Generally, materials that allow light to pass through but through which objects behind the material cannot be seen, such as frosted glass, are referred to as translucent or translucent. However, a translucent coating can certainly meet the average transmission of at least 30% in the wavelength range from 400 nm to 800 nm required for an optically transparent coating.

[0058] Particularly preferably, the IR-reflecting coating has no measurable electrical conductivity. Using measurement methods known to the person skilled in the art (e.g.

[0059] In such cases, no conductivity can be measured using a four-point measuring device. By combining the binder with conductive metallic structures, a coating is formed in which no electrical conductivity can be measured, but an IR reflection effect still occurs.

[0060] Contrary to the prevailing opinion in the prior art, it has been shown that when metallic nanowires are used in a formulation for producing an IR-reflecting coating, no conductive network is necessary to produce IR-reflecting properties.

[0061] The present invention also encompasses a process for producing one of the composite materials described above, the process comprising the following steps: a) providing a substrate, b) providing one of the formulations described above, c) applying the formulation provided in step b) to the substrate provided in step a), d) drying the article obtained in step c) to form a composite material consisting of a substrate and an IR radiation-reflecting coating arranged on the substrate.

[0062] After drying, a layer with IR-reflecting properties forms on the substrate. Drying in step d) preferably takes place at a temperature T < 200°C, preferably T < 100°C, particularly preferably T < 50°C, and especially preferably T < 30°C. The coating can be dried at room temperature or at temperatures up to 200°C. For energy efficiency reasons, the skilled person will choose the lowest possible temperature at which the binder develops its binding properties and at which the layer dries within an acceptable time period.

[0063] According to a further preferred embodiment, after step a) and before step c) the step

[0064] Pretreatment of the substrate surface is carried out by plasma pretreatment, corona pretreatment, cleaning, chemical pretreatment, or by applying a primer. In step c), the formulation prepared in step b) is applied to the thus pretreated substrate.

[0065] In some specific embodiments, pretreatment of the substrate is necessary, for example, by plasma pretreatment or corona pretreatment, by cleaning to remove foreign substances, by chemical pretreatment, or by applying a primer. Pretreatment achieves improved wetting and also better adhesion of the formulation to the substrate. The most suitable type of pretreatment in each individual case can be selected by the person skilled in the art based on their specialist knowledge.

[0066] In step c), the formulation prepared in step b) is preferably applied by spiral coating, screen printing, transfer printing, flow coating, spraying, or brushing. The preferred method of application in each individual case depends on the type of substrate. For example, screen printing is not possible for application to a wall, and the use of a brush to brush the substrate is unusual for application to fabrics.

[0067] Short description of the drawings

[0068] The invention will be explained in more detail below using exemplary embodiments in conjunction with Fig. 1. Fig. 1 shows a comparison of the heat reflection of an uncoated and a coated concrete specimen. Ways of implementing the invention

[0069] Example 1: Coating a PET film

[0070] Silver nanowires were produced in a polyol process according to the method described in DE 10 2010 017 706 B4. Aqueous and alcoholic formulations with a silver nanowire content of 0.3 wt.% were prepared from the resulting silver nanowire concentrate containing 4.0 wt.% silver. For this purpose, 7.5 g of silver nanowire concentrate were mixed with 74.5 g of water or alcohol in a plastic screw-cap container and homogeneously dispersed by shaking. Subsequently, 13 g of SURFLINK and 5 g of acrylate binder were added to the dispersion. The weight ratio of silver nanowires to acrylate binder was 0.06.

[0071] SURFLINK is an additive commercially available from HeiQ RAS for the activation of Ag nanowire networks. It is a mixture of 1 wt% to 10 wt% ethanolamine and up to 2.0 wt% hydroxypropylmethylcellulose in water.

[0072] The resulting formulation was applied to approximately 10 x 10 cm PET films using stainless steel doctor blades to achieve wet film thicknesses of 12 μm, 24 μm, or 40 μm. The coated substrates were oven-dried for 3 minutes at 150 °C or for 24 hours at room temperature. The electrical conductivity of the coating was measured using a four-point meter (RCHEK 4 Point Meter, manufacturer EDTM, model #RC2175). No electrical conductivity could be detected within the device's measuring range (1-19990 ohms / sq.). Measurements with a commercially available infrared camera (model: Für One Pro from Für) indicate a significant reflection of IR radiation in the wavelength range from 3 μm to 50 μm.

[0073] Example 2 (comparative example): Coating of a PET film

[0074] Silver nanowires were produced in a polyol process according to the method described in DE 10 2010 017 706 B4. Aqueous and alcoholic formulations containing 0.3 wt.% silver were prepared from the resulting silver nanowire concentrate containing 4.0 wt.% silver. For this purpose, 7.5 g of silver nanowire concentrate were mixed with 14.5 g of water or alcohol in a plastic screw-cap container and homogeneously dispersed by shaking. Subsequently, 13 g of SURFLINK and 60 g of acrylate binder were added to the dispersion. The weight ratio of silver nanowires to acrylate binder is 0.005. Using stainless steel doctor blades, the resulting formulation was applied to approximately 10 x 10 cm PET films to form wet films with thicknesses of 12 μm, 24 μm, and 40 μm, respectively. The coated substrates were dried for 3 min at 150 °C in an oven or for 24 h at room temperature.The electrical conductivity of the coating was measured using a four-point meter (RCHEK 4-Point Meter, manufacturer EDTM, model #RC2175). No electrical conductivity was detected within the device's measuring range (1-19990 ohms / sq.). Measurements using a commercially available infrared camera (model: Für One Pro from Für) showed no increased reflection of IR radiation in the wavelength range from 3 pm to 50 pm.

[0075] Example 3 (comparative example): Coating on fabrics, woven fabrics, knitted fabrics

[0076] A formulation according to Example 2 with an acrylate binder was prepared and qualitatively tested for homogeneity. The formulation was applied directly to fabric, woven plastics, and knitted plastics. The coated substrates were dried for 3 minutes at 150 °C in an oven or for 24 hours at room temperature.

[0077] The electrical conductivity of the coating was measured using a four-point meter (RCHEK 4-Point Meter, manufacturer EDTM, model #RC2175). No electrical conductivity was detected within the device's measuring range (1-19990 ohms / sq.). Measurements using a commercially available infrared camera (model: Für One Pro from Für) showed no increased reflection of IR radiation in the wavelength range from 3 pm to 50 pm.

[0078] Example 4: Coating on fabrics, woven fabrics, knitted fabrics

[0079] A formulation according to Example 1 with an acrylate binder was prepared and qualitatively tested for homogeneity. The formulation was applied directly to fabric, woven plastics, and knitted plastics. The coated substrates were dried for 3 minutes at 150 °C in an oven or for 24 hours at room temperature.

[0080] The electrical conductivity of the coating was measured using a four-point meter (RCHEK 4-Point Meter, manufacturer EDTM, model #RC2175). No electrical conductivity was detected within the device's measuring range (1-19990 ohms / sq.). Measurements with a commercially available infrared camera (model: Für One Pro from Für) indicate a clear reflection of IR radiation in the wavelength range from 3 pm to 50 pm. Example 5: Coating of a whitewashed or colored wall specimen

[0081] A formulation according to Example 1 with an acrylate binder was prepared and qualitatively tested for homogeneity. Both whitewashed and colored wall specimens were coated with the formulation using a brush or paint roller. Drying took place for approximately 24 hours at room temperature.

[0082] The color of the colored wall specimens remained unchanged even after drying. Measurements with a commercially available infrared camera (model: Flir One Pro) indicate a clear reflection of IR radiation in the wavelength range from 3 pm to 50 pm.

[0083] Example 6: Coating of a concrete specimen

[0084] A formulation according to Example 1 was prepared with an acrylate binder and qualitatively tested for homogeneity. Concrete test specimens were coated with the formulation using a brush or paint roller. Drying took place for approximately 24 hours at room temperature.

[0085] Measurements taken with a commercially available infrared camera (model: Flir One Pro from Flir) indicate a significant reflection of IR radiation in the wavelength range from 3 pm to 50 pm. Figure 1 shows a corresponding measurement of heat reflection comparing an uncoated and a coated concrete specimen. The significantly increased reflection of IR radiation in the case of the coated specimen is clearly visible. Using a heat source with a temperature of 33 °C, the measurement shows a temperature of 25.2 °C for the uncoated concrete specimen, while the temperature of the coated concrete specimen is 29.8 °C.

[0086] Example 7: Coating of a gypsum specimen

[0087] A formulation according to Example 1 was prepared with an acrylate binder and qualitatively tested for homogeneity. Gypsum test specimens were coated with the formulation using a brush or paint roller. Drying took place for approximately 24 hours at room temperature. Measurements with a commercially available infrared camera (model: Für One Pro from Für) indicate a clear reflection of IR radiation in the wavelength range from 3 μm to 50 μm. The electrical conductivity of the coating was measured using a four-point meter (RCHEK 4-Point Meter, manufacturer EDTM, model #RC2175). No electrical conductivity could be detected within the device's measuring range (1-19990 ohms / sq.).

[0088] Example 8: Coating of a wooden specimen

[0089] A formulation according to Example 1 was prepared with an acrylate binder and qualitatively tested for homogeneity. Wooden test specimens were coated with the formulation using a brush or paint roller. Drying took place for approximately 24 hours at room temperature.

[0090] Measurements with a commercially available infrared camera (model: Für One Pro from Für) show a clear reflection of IR radiation in the wavelength range from 3 pm to 50 pm.

[0091] Example 9: Coating a wallpaper

[0092] A formulation according to Example 1 with an acrylate binder was prepared and qualitatively tested for homogeneity. Both plain and patterned wallpaper pieces were coated with the formulation using a brush and roller or a transfer printing method. Drying took place at room temperature for approximately 24 hours or in an oven at 150 °C for 10 minutes.

[0093] Measurements with a commercially available infrared camera (model: Für One Pro from Für) indicate significant reflection of IR radiation in the wavelength range from 3 pm to 50 pm. The electrical conductivity of the coating was measured using a four-point meter (RCHEK 4 Point Meter, manufacturer EDTM, model #RC2175). No electrical conductivity could be detected within the device's measuring range (1-19990 ohms / sq.).

[0094] Example 10: Coating of paper

[0095] A formulation according to Example 1 with an acrylate binder was prepared and qualitatively tested for homogeneity. White paper sheets were coated with the formulation using a brush. Drying was carried out at room temperature for approximately 24 hours or in an oven at 120 °C for 5 minutes.

[0096] Measurements with a commercially available infrared camera (model: Flir One Pro from Für) show a clear reflection of IR radiation in the wavelength range from 3 pm to 50 pm.

Claims

A formulation for producing an IR-reflecting coating, the formulation comprising at least one electrically conductive metal nanomaterial, at least one binder, and at least one solvent, the weight ratio of electrically conductive metal nanomaterial to binder being greater than 0.

005. Formulation according to claim 1, characterized in that the weight ratio of electrically conductive metal nanomaterial to binder is greater than 0.01, preferably greater than 0.02, particularly preferably greater than 0.

05. Formulation according to claim 1 or 2, characterized in that the weight ratio of electrically conductive metal nanomaterial to binder is less than 2, preferably less than 1, particularly preferably less than 0.5.Formulation according to one of claims 1 to 3, characterized in that the electrically conductive metal nanomaterial comprises electrically conductive metal nanoparticles, in particular electrically conductive silver nanoparticles, electrically conductive metal nanowires, in particular electrically conductive silver nanowires, electrically conductive metal nanotubes, in particular electrically conductive silver nanotubes. Formulation according to one of claims 1 to 4, characterized in that the formulation additionally contains electrically conductive carbon, electrically conductive carbon nanotubes, graphene, electrically conductive polymers, or mixtures thereof.Formulation according to one of claims 1 to 5, characterized in that the formulation comprises one or more additives, the additives preferably being thickeners, adsorptives, wetting aids, flame retardants, polyvinylpyrrolidone, defoamers, film formers, chemical stabilizers, and color pigments, the color pigments absorbing predetermined portions of the electromagnetic radiation in the wavelength range from 400 nm to 800 nm. Formulation according to one of claims 1 to 6, characterized in that the binder is a binder based on acrylates, epoxies, polyurethanes, silicones, siloxanes, polyolefins, cellulose derivatives, polythiophenes, perfluorinated polymers, and copolymers of said polymers, and mixtures thereof.

8. Formulation according to one of claims 1 to 7, characterized in that the electrically conductive metal nanomaterial is electrically conductive metal nanowires, in particular electrically conductive silver nanowires, wherein the quotient of length and diameter of the metal nanowires is preferably greater than 5.

9. A composite material comprising a substrate and an IR radiation-reflecting coating arranged on the substrate, wherein the coating is made from a formulation according to any one of claims 1 to 8.

10. Composite material according to claim 9, characterized in that the substrate is a polymer film, a woven fabric, a knitted fabric, a textile material, glass, paper, concrete, cement, wood, gypsum, plasterboard, a metal or a plastic.

11. Composite material according to claim 9 or 10, characterized in that the coating has a dry layer thickness of at most 60 pm, preferably of at most 30 pm, particularly preferably of at most 15 pm.

12. Composite material according to one of claims 9 to 11, characterized in that the coating has an average spectral transmission of at least 30% in the wavelength range from 400 nm to 800 nm.

13. Composite material according to one of claims 9 to 12, characterized in that the coating has a reflection of more than 20%, preferably more than 30%, particularly preferably more than 40% in the wavelength range from 3 pm to 50 pm.

14. Composite material according to one of claims 9 to 13, characterized in that the coating has no measurable electrical conductivity.

15. A process for producing a composite material according to any one of claims 9 to 14, comprising the steps of a) providing a substrate, b) providing a formulation according to any one of claims 1 to 8, c) applying the formulation provided in step b) to the substrate provided in step a), d) drying the article obtained in step c) to form a composite material consisting of a substrate and an IR radiation-reflecting coating arranged on the substrate.

16. The method according to claim 15, characterized in that the drying in step d) takes place at a temperature T < 200°C, preferably T < 100°C, particularly preferably T < 50°C, especially preferably T < 30°C.

17. Method according to claim 15 or 16, characterized in that after step a) and before step c) the step Pretreating the surface of the substrate by plasma pretreatment, corona pretreatment, cleaning, chemical pretreatment, or by applying a primer, and in step c) applying the formulation provided in step b) to the pretreated substrate.

18. The method according to any one of claims 15 to 17, characterized in that in step c) the formulation provided in step b) is applied by spiral doctor blade, screen printing, transfer printing, flood coating, spraying or brushing.

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