Radiative cooling structure having a textile carrier substrate, a method for producing the radiative cooling structure and use thereof

Abstract

The invention relates to a radiative cooling structure having at least one radiative functional layer on a textile carrier substrate. The radiative cooling structure is characterised in that a radiative functional layer (A), made of a plastic matrix based on a crosslinked silicone rubber, is formed on the textile carrier substrate, wherein aluminium particles are embedded in the radiative functional layer (A) and a radiative functional layer (B), made of a plastic matrix which is also based on a crosslinked silicone rubber, is located on the radiative functional layer (A), wherein white pigments are embedded in the radiative functional layer (B). The textile carrier substrate is preferably a flat textile. The radiative cooling structure provides excellent reflectance and emission values and thus advantageous cooling capacities, this being independent of the substrate. The invention also relates to an advantageous method for producing the radiative cooling structure and to a use of the radiative cooling structure outdoors.

Description

[0001] Radiation cooling structure with a textile support substrate, a method for producing the radiation cooling structure and its use

[0002] Description

[0003] The invention relates to a radiation cooling structure with at least one radiation-functional layer on a textile carrier substrate, a method for producing the radiation cooling structure and its advantageous uses.

[0004] The technology of radiative cooling at night has been known for thousands of years (Persian ice houses "Yakchal"). Since 2014, cooling below ambient temperature can also be achieved during the day using radiative cooling. Since then, there has been an increasing number of publications investigating and proposing new material combinations and technologies in the field of radiative cooling. Daytime cooling is achieved when the heat radiated through the atmospheric window (8-13 pm) is greater than the heat absorbed by solar radiation and atmospheric counter-radiation. To achieve this, a radiative cooler must have spectrally selective emission between approximately 8 and 13 pm and high reflection of solar radiation to achieve maximum cooling performance. Radiative cooling is a ubiquitous process in which a surface loses heat through thermal radiation. The Earth's surface temperature is approximately 13 °C.300 Kelvin (K), while the cosmic microwave background of the universe has a thermal blackbody spectrum with a temperature of 2.7 K. This temperature difference can be exploited by deliberately releasing thermal infrared radiation into the universe through the atmosphere. Two basic requirements are necessary to achieve cooling during the day: First, a low emissivity close to zero (highly reflective) in the solar spectrum (approximately 0.3-2.5 pm) (visible light / VIS and near infrared / NIR) and, at the same time, a high emissivity in the mid-infrared (MIR) range for cooling during daylight in the atmospheric window between 8-13 pm. Daytime cooling is achieved when the heat radiated through the atmospheric window is greater than the heat absorbed by sunlight and atmospheric radiation (cooling below ambient temperature).

[0005] In radiation cooling structures, the materials used can be specifically selected based on the type and number of functional groups. Vibrational excitation of the functional groups by photons generates oscillations, resulting in emission peaks. If these peaks are between 8 and 13 pm, increased heat dissipation can be achieved.

[0006] In view of the above technological explanation of radiation cooling, various technical proposals have been made in the prior art: Among others, the use of PDMS (polydimethylsiloxane) as an emission material applied to a carrier has been suggested.

[0007] The following publications have already disclosed the use of PDMS as a matrix material to create hydrophobic and UV-resistant properties, for example, in Cheng et al., Surf. Interfaces 26, 101325, 2021. EP 3 760 678 A1 describes the use of silicone resin as a functional resin. A low-e layer (low emissivity or low-emissivity coatings) can also prevent the influence of the underlying substrate material on the spectral response. US 10386097 B2 describes a layered structure of a radiative cooler with, among other materials, PDMS as the emitting functional layer. Aluminum oxide is applied in the form of nanoparticles in a protective cover layer. The combination of a low-e material with a high-e material is also described in the literature.In this context, a two-layer textile for close-to-body application is disclosed, whereby, depending on the textile, the low-e layer has a warming function or the high-e layer has a cooling effect (Manara et al., Prog. Org. Coat. 70, 199-204, 2011).

[0008] The disadvantages associated with the state of the art can be summarized as follows: In state-of-the-art radiation cooling structures, the increase in emission is usually structure-dependent or material-dependent, i.e., it depends on the respective material of the carrier substrate. This requires, for example, high-precision manufacturing (e.g., laser lithography for nanostructuring). Precise layer structure formation is not possible on textile substrates and would be uneconomical for upscaling, as is necessary on textile surfaces. It is fundamentally disadvantageous if the increase in emission depends on the material of the carrier substrate used. This leads to a significant limitation of application, especially in outdoor areas. It should be noted that to date, no combination of low-e materials (reflection between 0.3 and 2.5 pm) and high-e material (emission in the MIR) orbetween 8 and 13 pm on textile substrates is proposed to achieve substrate-independent radiative cooling. Furthermore, state-of-the-art radiative cooling structures have shown unsatisfactory reflection (visual (VIS) / near IR (NIR)) and emission (MIR). Solutions must be found here that lead to a significant improvement.

[0009] The invention described below offers particular advantages in building cooling. Therefore, the relevant state of the art and its essential features will be presented below:

[0010] Passive cooling methods for building cooling include sun and heat protection. These include pure shading systems, the use of water basins for insulation and evaporative cooling on building roofs, and natural cooling pathways through vegetation on and around building surfaces. There are also developments using PCM (phase-change material) capsules, which are added to wall paint, for example, and provide temporary cooling, as well as systems based on natural ventilation. In membrane construction, solutions for cooling membrane roofs with increased solar reflectance values ​​(between 65% and a maximum of 85%) or so-called low-emissivity (low-e) coatings are being discussed. These approaches are not specifically designed for cooling below ambient temperature and offer only marginal advantages. Some require extensive renovation measures, making these approaches economically viable only for new buildings.In densely populated or urban regions, a comprehensive and cost-effective redesign to achieve an energy-sustainable building design for cooling purposes is not feasible. It is precisely here that alternative solutions for energy-free and sustainable cooling are being sought. Previous publications in the field of building cooling with textile materials focus on specific fiber structures and textile carrier materials, as well as complex multi-layer structures. This severely limits or even prevents the use of textiles for highly scaled, industrially manufactured outdoor applications. To achieve the greatest possible flexibility in application, a substrate-independent coating for self-cooling must be developed. Application areas include textile materials for membrane roofs, facade elements, awnings, sunshades, and tent construction. Other possible uses include glacier protection, which currently only provides shielding and does not provide passive cooling.

[0011] Accordingly, the present invention aims to advantageously overcome the disadvantages of the prior art, in particular to propose a radiation cooling structure in which the desired increase in emission and reflection is independent of the type of carrier substrate material, while maintaining satisfactory cooling performance. In particular, the present invention is intended to enable the following advantages: advantageous effects with the lowest possible coating thickness and thus conserve resources, increased reduction of dust attraction, and improved weather resistance, water resistance, and water repellency compared to known systems.

[0012] The invention accordingly provides a radiation cooling structure with at least one radiation-functional layer on a textile carrier substrate, characterized in that a radiation-functional layer (A) made of a plastic matrix based on a cross-linked silicone rubber is formed on the textile carrier substrate, wherein aluminum particles are embedded in the radiation-functional layer (A), and a radiation-functional layer (B) made of a plastic matrix, which is also based on a cross-linked silicone rubber, is located on the radiation-functional layer (A), wherein white pigments are embedded in the radiation-functional layer (B). The radiation-functional layer (B) is essentially chemically structurally identical to the radiation-functional layer (A), but wherein white pigments are embedded in the radiation-functional layer (B) instead of aluminum particles.These two specially designed layers, in their functional interaction, lead to a particularly advantageous solution to the task at hand, which is described in more detail below.

[0013] A central technical concept of the present invention is that aluminum particles with a low-e effect are additionally embedded in a radiation-functional layer (A), which is based on a plastic matrix with a high-e effect. These two materials with the described effect, in their functional interaction, lead to a particularly advantageous solution to the stated problem, which is described in more detail below, in conjunction with the radiation-functional layer (B).

[0014] The features "high-e effect" and "low-e effect" within the meaning of the invention will be described in more detail, taking into account the expert's understanding: For an explanation of the low-e effect of the aluminum particles used in the invention, reference is made to the standard DIN EN 15976:2011-07. For typical calibration standards for low-emission surfaces (low-e effect), taking into account the sL values ​​selected in the DIN standard, 0.01 < sL < 0.02 should apply, and for the calibration standards for high-emission surfaces (high-e effect), sh > 0.94 should apply. The materials can then be classified. If the average measured emission values ​​for the low-e effect, particularly between 0.3 and 2.5 pm, and for the high-e effect, particularly between 8 and 13 pm, are close to the respective calibration standards (0.01 < sL < 0.02; sh > 0.94), the materials can be defined as low-e or high-e materials.

[0015] The following can be stated regarding further advantageous embodiments of the inventive teaching presented above: Within the scope of the invention, a textile carrier substrate for the radiation-functional layer (A) is used for the radiation cooling structure. This is preferably a flat textile. The flat textile is, in particular, a woven fabric, a warp-knitted fabric, a nonwoven fabric, or a scrim. The flat textile is not subject to any critical restrictions with regard to its fibers or filaments. These are preferably natural fibers and / or chemical fibers, in particular fibers made of cellulose, cellulose derivatives, polyester, polyamide, and / or glass.

[0016] The basis weight of the flat textile used in the invention should be considered with a view to optimal implementation of the invention. This is preferably approximately 25 to 1800 g / m 2 , in particular about 30 to 1500 g / m 2and most preferably 80 to 1000 g / m 2 .

[0017] A key concept of the invention is that metallic particles in the form of aluminum particles, which are a low-e material, are embedded in the radiation-functional layer (A). The aluminum particles are expediently spherical and / or, in particular, plate-shaped. The aluminum particles could also be referred to as plate-shaped metal pigments (colloquially also called "flakes"). They consist of ductile aluminum, on which incident light is reflected analogously to a mirror. (Partial) absorption of the light radiation does not occur. It is advantageous if the spherical particles have a diameter of approximately 10 to 60 pm, in particular of approximately 20 to 40 pm, and very particularly of approximately 25 to 35 pm, and the platelets have an average particle size distribution d50 of approximately 24 to 50 pm, in particular of approximately 30 to 40 pm, particularly preferably of approximately 33 to 37 pm.

[0018] The radiation-functional layer (A) preferably contains about 5 to 30 wt.%, in particular about 10 to 25 wt.%, particularly preferably about 15 to 20 wt.%, of aluminum particles.

[0019] Regarding the plastic matrix with high-e effect: The plastic matrix is ​​generally based on a cross-linked silicone rubber. This is particularly a cross-linked polysiloxane, especially a cross-linked polydialkylsiloxane, and particularly preferably a cross-linked polydimethylsiloxane (PDMS). As a starting material, polydimethylsiloxane (PDMS), cross-linked in the radiation cooling structure, is of particular importance for its practical implementation and will be explained in more detail below:

[0020] Polydimethylsiloxane (PDMS) has a backbone consisting of a Si-O-Si unit. PDMS is a polymer in which two methyl groups are bonded to the siloxane backbone. This means that the original polydimethylsiloxane is not cross-linked. It preferably contains additional cross-linkable organic groups, such as a vinyl, phenyl, or other cross-linkable group, to accommodate the cross-linking concept of a cross-linkable silicone rubber.

[0021] To enable the crosslinkability of the silicone rubber, in particular polydimethylsiloxane (PDMS), during the production of the radiative cooling structure according to the invention, a crosslinkable polydimethylsiloxane is preferably used in which a small number of methyl groups are replaced by vinyl groups. Phenyl groups can also be used instead of the vinyl groups.

[0022] The silicone rubber used in the production of the radiant cooling structure according to the invention preferably utilizes a chemical crosslinker for the desired crosslinking. In principle, the type of crosslinker is not subject to any relevant restrictions, as long as it enables crosslinking, particularly via vinyl groups. For the polydimethylsiloxane (PDMS) mentioned, a hydrogen polysiloxane (Crosslinker 525 from Wacker AG) has proven particularly suitable. This will be discussed in more detail below in connection with the preferred production of the radiant cooling structure according to the invention. Ultimately, the choice of crosslinker for the particular silicone rubber selected, in particular for the polydimethylsiloxane, is a matter of expert judgment.

[0023] From the above, it follows that, within the scope of the invention, a two-component liquid silicone rubber (LSR) is used to produce the radiation-functional layer (A) and the radiation-functional layer (B). A commercially available liquid silicone rubber is particularly important here, which will be discussed later in the examples. The crosslinking carried out according to the invention leads to the desired crosslinking, particularly under the influence of a catalyst, in particular a platinum catalyst. In this case, crosslinking takes place in the form of an addition reaction.

[0024] Taking into account the above description of silicone rubbers, the following can be summarized: It is advantageous if the silicone rubbers or liquid silicones (here, in particular, the commercial product, as described in the following examples) are characterized by a short crosslinking time, in particular, optimal crosslinking occurs in a short time of 1 to 3 minutes, which preferably takes place at high temperatures (> 150°C). It is particularly preferred if crosslinking is carried out under heat exposure between 60°C and 180°C, particularly preferably between 90°C and 160°C.

[0025] It is also advantageous if the liquid silicones have a low viscosity, making them suitable for application with a doctor blade. In this case, it is preferred if the liquid crosslinkable silicone rubber has a viscosity of 10,000 to 150,000 mPa.s, especially 50,000 to 120,000 mPa.s (measured with a Brookfield rotational viscometer).

[0026] All liquid silicones have a similar structure with regard to their ingredients. Preferably, the silicone rubbers consist of long-chain polydialkylsiloxanes, especially polydimethylsiloxanes. In unvulcanized form, these materials are generally referred to as PDMS, which is the polymer chemical term for these chains, although this does not yet provide any information about the chain length. The liquid silicones advantageous within the scope of the invention are used in particular as terminally vinyl-functional polydialkylsiloxanes, especially polydimethylsiloxanes (these would be alpha-omega-divinylpolydimethylsiloxanes). In addition, a laterally SiH-functional siloxane is used as a crosslinker. The liquid silicone rubber is advantageously crosslinked under heating with the aid of platinum catalysts, in particular. Accordingly, the main component of all silicone rubbers within the scope of the invention is, in particular, PDMS.It is preferred that the radiation-functional layer (A) and the radiation-functional layer (B) have a total layer thickness of about 50 to 1500 μm, in particular about 70 to 1000 μm, and particularly preferably about 70 to 500 μm. The radiation-functional layer (A) is formed, as shown, on a textile carrier substrate.

[0027] Surprisingly, it has been shown that when white pigments are incorporated into the radiation-functional layer (A) according to the invention, significant efficiency improvements are achieved. This particularly applies to reflection, but also to emission. There is a technical and functional connection between the structure of the radiation-functional layer (A) and the radiation-functional layer (B), which incorporates white pigments. This results in a particularly favorable cooling performance.

[0028] The following should be noted regarding the amounts of white pigments preferably used in the radiation-functional layer (B) and optionally (A): It is preferred that the radiation-functional layer (B) contains white pigments in an amount of about 5 wt.% to 60 wt.%, preferably 10 wt.% to 50 wt.%, and particularly preferably from about 20 wt.% to 40 wt.%. The radiation-functional layer (A) can also additionally include white pigments. It is preferred that white pigments are embedded in particular in an amount of about 5 to 60 wt.%, particularly preferably from about 10 to 50 wt.%, and very particularly preferably from about 15 to 40 wt.%.

[0029] The invention is not subject to any significant restrictions with regard to the white pigments mentioned. It is preferred if the white pigments consist of titanium dioxide, zinc oxide, zinc sulfide, lead carbonate, and / or barium sulfate. The white pigments are preferably spherical and have a particle size of approximately 0.3 to 2.5 pm, in particular approximately 0.3 to 1 pm.

[0030] It is also advantageous if, to optimize the performance properties, a topcoat transparent across the entire wavelength range (in particular between 0.25 pm and 25 pm), in particular based on a crosslinked silicone rubber, is applied to the radiation-functional layer (B), wherein the transparency is preferably at least 70%, in particular at least 80%, and most preferably 90%. When reference is made here to improved performance properties, this means, in particular, effective dirt repellency, advantageous fungicidal action, reduced dust attraction, weather resistance, water resistance, water repellency, and the like.

[0031] The radiation cooling structure according to the invention is characterized by a special cooling performance, whereby the cooling performance of the structure is approximately 10 to 150 W / m 2 , in particular about 15 to 90 W / m 2 (at a solar irradiance of 700 W / m 2). The cooling capacity is determined according to the method described in Aili et al., "Atmosphere" 2021, 12, 1379, Methodology, pp. 2 to 10.

[0032] The radiant cooling structure according to the invention can be used in a variety of applications, with the textile carrier substrate being determinable by one of the following applications: in particular as a tent tarpaulin, as a shading element on building surfaces to be cooled, as a textile curtain, as a textile awning, as weather and sun protection for buildings, in membrane construction, and for outdoor clothing. Thus, it is possible to initially design a tent tarpaulin according to the invention and then later produce a tent from it. On the other hand, it is also possible to apply a fully formed radiant cooling structure according to the invention in a flat form to conventional objects, for example, to a car body and to building surfaces.

[0033] In principle, the radiation cooling structure according to the invention can be used for coating any objects if it achieves the advantages sought according to the invention, in particular satisfactory overall cooling due to advantageous reflection and emission values, regardless of the substrate material.

[0034] The invention also provides an advantageous process for producing the above-described radiation cooling structure according to the invention. This process is characterized in that a liquid crosslinkable silicone rubber is provided with a chemical crosslinker and aluminum particles, optionally additionally with white pigments, the resulting liquid dispersion (A) is applied to a textile carrier substrate, and the crosslinkable silicone rubber is crosslinked by the chemical crosslinker, in particular in the presence of a catalyst, particularly preferably a platinum catalyst, and a radiation-functional layer (A) is formed, and a radiation-functional layer (B) is formed on the radiation-functional layer (A) by providing a liquid crosslinkable silicone rubber with a chemical crosslinker and white pigments.the resulting liquid dispersion (B) is applied to the radiation-functional layer (A) and the crosslinkable silicone rubber is crosslinked by the chemical crosslinker, in particular in the presence of a catalyst, particularly preferably a platinum catalyst, and the radiation-functional layer (B) is formed.

[0035] The crosslinking mentioned is preferably carried out under the influence of heat, in particular in a temperature range of about 60°C to 180°C, with the range between 90°C and 160°C being particularly preferred.

[0036] The liquid crosslinkable silicone rubber crosslinked by the process according to the invention is preferably a crosslinkable polysiloxane, in particular a crosslinkable polydialkylsiloxane, particularly preferably a crosslinkable polydimethylsiloxane (PDMS). The polydimethylsiloxane (PDMS) preferably has a crosslinkable vinyl functionality with a crosslinking effect. Within the scope of the process according to the invention, crosslinking is initiated by a crosslinking agent, which is in particular a polymethylhydrogensiloxane (PMHS). For further information on the feature "liquid silicone rubber," reference is made to the above statements regarding the radiative cooling structure according to the invention.

[0037] When carrying out the process according to the invention, it is advantageous if 25 to 40 parts by weight of crosslinkable silicone rubber, particularly preferably 28 to 35 parts by weight of crosslinkable silicone rubber, in particular in the form of crosslinkable polydimethylsiloxane (PDMS), are used for 1 part by weight of crosslinker, in particular in the form of PMHS. It is considered advantageous if the liquid silicone rubber (dispersion A) containing the crosslinker and the aluminum particles is applied to the textile carrier substrate in a layer thickness of about 5 to 500 pm, in particular from about 40 to 280 pm and particularly preferably from about 70 to 200 pm, and / or the liquid dispersion B containing the white pigments is applied to the radiation-functional layer (A) in a layer thickness of about 5 to 500 pm, in particular from about 70 to 350 pm and particularly preferably 70 to 300 pm, wherein the application is carried out in particular by means of a doctor blade.

[0038] The advantages associated with the invention are manifold: The functional Si groups incorporated according to the invention (in the PDMS) are excited by photons in the fingerprint region between 8 and 13 pm, resulting in emission peaks in the important atmospheric window. The radiation cooling structure according to the invention is UV-resistant, water-repellent (hydrophobic), flexible, wash-resistant, and long-term stable. A particular advantage of the radiation cooling structure is that it is largely independent of the material of the textile carrier substrate. Emission is increased in the MIR to sh > 0.9. By utilizing the low-e effect, substrate independence, or rather, independence from the material of the carrier substrate, is achieved, thus achieving the emission power between 8 and 13 pm, regardless of the textile substrate used. The radiation cooling structure according to the invention has a wide range of applications.The coating, and thus the textile radiant cooler, can be used for various outdoor applications without constantly having to readjust the coating formulation. The combination of aluminum particles (low-e effect) and the plastic matrix material (high-e effect), with the further combination of white pigments in the radiation-functional layer (B) (plastic material with high-e effect), is being used for the first time in an outdoor textile application. The inventive radiant cooling structure enables cost-effective and large-scale outdoor application.

[0039] The particular advantages that arise from the practical implementation of the present invention are highlighted below: Equally good cooling performance is always achieved with different substrates, i.e., there is advantageous substrate independence. Finally, the invention enables cooling to be achieved to an exceptionally favorable extent below ambient temperature, while also providing long-term stability, so that the coating generally does not require an additional weather-stable and hydrophobic coating. It is particularly advantageous that the radiation cooling structure according to the invention still achieves the desired cooling with an exceptionally thin total coating thickness of less than 500 μm, in particular less than 300 μm. The coating thicknesses mentioned above are therefore lower than those of other coating systems described in the literature, especially for lightweight textile construction.A smaller coating thickness has the particular advantage that a folded material can be obtained and transported more efficiently before application. The possibility of achieving the desired effects with a small overall coating thickness in the formation of the sealing thickness of the radiative cooling structure according to the invention is also important from the perspective of resource conservation.

[0040] The radiant cooling structure according to the invention is of particular importance for the conversion of building surfaces in order to achieve cooling there. Here, the inventive concept can be directly implemented by using the product in the form of a tarpaulin or membrane, for example when applied to a building wall. In other words, the product according to the invention is attached as a shading element to the building surfaces to be cooled. For this purpose, metal structures are already known in the prior art with which flat shading elements are fixed to the building surfaces to be cooled. Measures for achieving a cooling effect on building surfaces are already known in the prior art. These include, for example, natural vegetation, ventilation, and additional forced cooling. However, the inventive concept, when implemented in practice, leads to a noticeable reduction in costs.

[0041] The invention will be explained in more detail below using examples. Example 1 (Production of a coating material based on a liquid silicone rubber in the form of a polydimethylsiloxane (PDMS) (commercial product ELASTOSIL LR 6250 F from Wacker AG))

[0042] The liquid silicone rubber (type ELASTOSIL LR 6250 F from Wacker AG) (here component a)) is more precisely polydimethylsiloxane (specifically, a vinylated PDMS). This polydimethylsiloxane (PDMS) has a small proportion of crosslinkable vinyl groups. A special crosslinker in the form of hydrogen polysiloxane (commercial product Crosslinker 525 from Wacker AG) with a high content of reactive SiH groups is used for this purpose. This crosslinker (here component b)) is particularly suitable for the thermal curing of solvent-free silicone rubbers.

[0043] Components a) and b) are precisely weighed and mixed in a weight ratio of 100:3. To ensure uniform and reproducible mixing, a fully automated stirring system with automatic lifting arm guidance (Unguator PRO) is used. This creates a dispersion. To reduce the formation of air bubbles, the following stirring parameters are set: stirring time: 3 min - stirring speed: 800 rpm. The stirring time and speed result in a gentle yet very thorough mixing of components a) and b).

[0044] Example 2 (comparison) (radiative cooling structure with textile support and with radiation-functional layer (High-e))

[0045] A textile carrier substrate is used (surface weight 65 g / m 2) (fabric type PES), which has a reflection (ViS / NIR) of 0.35 and an emission (MIR) of 0.77. The textile carrier substrate measuring 20 cm x 30 cm (total area 0.06 m 2 ) is fixed in a clamping frame. The doctor blade is adjusted to a defined height using a slide knife. The doctor blade height, or the distance between the doctor blade and the carrier substrate, determines the layer thickness, in this case approximately 100 μm. After applying the coating material produced according to Example 1 using a commercially available doctor blade applicator (Mathis Lab Coater), the clamping frame with the sample (with the coated carrier substrate) is moved into an oven (Mathis Lab Dryer). The material remains there for 3 minutes at 150°C. The material is then removed and can be measured. For the cooling performance, see Table 1.

[0046] Example 3 (Comparison of textile carrier substrate with transparent radiation-functional layer A (high-e effect) and incorporated aluminum particles (low-e effect))

[0047] The liquid silicone dispersion is combined as described in Example 2, but not yet mixed. Based on the total amount of matrix material (polysiloxane dispersion) and crosslinker, the required concentration of aluminum particles can be calculated in weight percent (wt%). Accordingly, the particle concentrations are weighed to four decimal places using a commercially available precision balance (Mettler AE200) and added to the silicone rubber dispersion. In this example, a particle concentration of 20 wt% is used. The dispersion with the aluminum particles is then automatically mixed using identical settings as described in Example 2. This gentle mixing leads to a uniform particle distribution in the silicone rubber system without damaging the aluminum particles due to strong shear forces.The resulting dispersion is then applied to the textile carrier material clamped in the laboratory coater and coated with a doctor blade at a thickness of approximately 100 μm. The procedure is the same as in Example 2. The drying / curing time depends on the polysiloxane matrix material, so no changes are made to the settings here. The textile carrier substrate used was that of Example 2. For the cooling performance, see Table 1.

[0048] Example 4 (Invention with radiation-functional layer (A) containing aluminum particles and with radiation-functional layer (B) containing white pigments) The paste-like coating material is produced as described in Example 1. The coating material is then applied to the textile carrier substrate (according to Example 3) to form the radiation-functional layer (A) and dried and crosslinked in an oven (Mathis Lab Dryer) at a temperature of 150°C for 3 minutes. The textile carrier substrate with coating is still on the tenter frame during removal, so that a second radiation-functional layer (B) can be applied directly onto the first radiation-functional layer (A) on top of the now crosslinked radiation-functional layer (A) containing the aluminum particles.The second radiation-functional layer (B) contains the white pigment titanium dioxide with a particle size distribution d50 of 0.4 pm in an amount of 20 wt.%. This layer, together with the already crosslinked transparent radiation-functional layer (A), is then dried and crosslinked under identical conditions. For the cooling performance, see Table 2.

[0049] Example 5 (Surveying)

[0050] The radiation cooling structures, manufactured in the manner described in the above examples, are spectrally analyzed as follows:

[0051] Using an integrating sphere or integrating sphere, the directed hemispherical spectral reflectance R g ,x and the directed-hemispheric spectral transmittance T g,x can be determined. The measurements are performed at room temperature. The sample is placed in front of the outlet opening of the integrating sphere for reflection measurement. The incident radiation is directed through the inlet opening of the sphere and strikes the sample at an angle of 8°, allowing the entire reflected radiation component to be detected.

[0052] A reflection standard is used for calibration. For transmission measurement, the outlet opening is closed with the reflection standard and the sample is attached in front of the inlet opening.

[0053] The visible and near-infrared spectrum from 250 nm to 2500 nm is measured using a LAMBDA™ 1050+ from Perkin Elmer. This is a dual-beam spectrometer with a double monochromator for the UV / Vis / NIR wavelength range. The measurement is performed according to EN 14500:2021. The data are evaluated using UVWinLab software. The spectral curve in the mid-infrared (2.5 to 25 pm) is measured using a Fourier transform infrared (FTIR) spectrometer, a Vertex 80 from Bruker. A gold-coated integrating sphere with a DLaTgs detector is used. The data are evaluated using OPUS software.

[0054] The maximum and average reflection values ​​can be read from the curves and the emission values ​​can be calculated taking Kirchhoff's radiation law into account.

[0055] The absorption and emissivity are always proportional to each other. This means that in thermal equilibrium and for the same frequencies and directions, the directional spectral absorption coefficient (o' v ) and the directional spectral emissivity (s' v ) are equal to:

[0056] Q v = E v

[0057] The emission curve can be calculated from the transmission and reflection spectrum:

[0058] Eg, A (A) = 1 - Rg,A (X) - Tg,A ( )

[0059] The measured values ​​obtained using the materials discussed in the previous examples can be found in Table 1 below.

[0060] Table 1: List of emission and reflection values

[0061]

[0062] Notes:

[0063] The maximum values ​​for reflection are given at 0.3 to 2.5 pm and the average emission power at 8 to 13 pm.

[0064] The cooling capacity is determined based on Aili et al. (2021): solar irradiance = 500 W / m 2 ; Ambient temperature: 25°C; relative humidity: 25%; wind: 1.0 m / s; water column: 10 5 Pa;

[0065] Surface temperature of the textile: 25°C, for comparability of the values, the transmission between 0.3 - 2.5 pm is set equal to 0, which corresponds to a maximum absorption of the transmitted light.

[0066] Example 3 (comparison) with radiation-functional layer A (without radiation-functional layer B) using the high-e and low-e effects has improved reflection and emission and also improved cooling performance compared to Example 2 (comparison).

[0067] Example 6 (measurement) (with different carrier substrates to demonstrate the substrate independence of the radiation cooling structure according to the invention)

[0068] Three different fabrics are used, namely based on PA6.6 (polyamide) (150 g / m 2 ), PES (polyester) (65 g / m 2 ) and glass (163 g / m 2 ).

[0069] The following basic structures are used:

[0070] In Table 2 below, the fabrics listed above are used as substrates. The following basic structures are used:

[0071] 1.) Textile without radiation-functional layers;

[0072] 2.) Textile + radiation-functional layer (B) without radiation-functional layer

[0073] (A); and 3.) Textile + radiation-functional layer (A) + radiation-functional layer (B) (invention).

[0074] Further details: Structure 3.) (invention) is produced according to the instructions of Example 4. For structure 2.) the procedure is as in Example 4, but the radiation-functional layer (B) is deposited on a layer of cross-linked silicone (ie without aluminum particles).

[0075] The measured values ​​of reflection, emission, cooling capacity and solar absorption are shown in Table 2 below:

[0076] Table 2

[0077]

[0078] Notes: * The maximum values ​​given are for reflection at 0.3 to 2.5 pm and the average emission power at 8 to 13 pm. Total layer thickness (200 pm)

[0079] * The cooling capacity is determined based on Aili et al. (2021): solar irradiance = 500 W / m 2 ; Ambient temperature: 25°C; relative humidity: 25%; wind: 1.0 m / s; water column: 10 5Pa; surface temperature of the textile: 25°C, for comparability of the values, the transmission between 0.3-2.5 pm is set equal to 0, which corresponds to a maximum absorption of the transmitted light.

[0080] Table 2 shows, based on the calculated cooling performance, that the coating of the radiation-functional layer (A) achieves consistent cooling performance regardless of the respective basis weight or fiber type, compared to the coating applied only with the radiation-functional layer (B). The advantage of the invention therefore lies in its clear substrate independence.

[0081] * * *

[0082] Notes on the above-mentioned product ELASTOSIL LR 6250 F (trade name of Wacker AG): This is a liquid silicone rubber (LSR). It is solvent-free, free-flowing, addition-curing, and particularly suitable for textile coatings. Properties of the uncured product: dynamic viscosity: 100,000 mPa.s (Brookfield rotational viscometer); cured product (recommended curing conditions: mixture of 100 parts LR 625 F + 3 parts Crosslinker 525, 5 min / 165°C; appearance: transparent); Shore A hardness: 36 (according to ISO 7619-1); density: 1.07 g / cm 3 (according to DIN EN ISO 1183-1A); tensile strength 5.0 N / mm 2 (according to ISO 37 Type 1); elongation at break 350% (according to ISO 37 Type 1); elongation at break 10 N / mm (according to ASTM D 624 B).

Claims

x AMENDED CLAIMS received by the International Bureau on 12 September 2024 (12.09.2024) 1. Radiation cooling structure with at least one radiation-functional layer on a textile carrier substrate, characterized in that a radiation-functional layer (A) made of a plastic matrix based on a cross-linked silicone rubber is formed on the textile carrier substrate, wherein metallic particles in the form of aluminum particles are embedded in the radiation-functional layer (A), and a radiation-functional layer (B) made of a plastic matrix, which is also based on a cross-linked silicone rubber, is located on the radiation-functional layer (A), wherein white pigments are embedded in the radiation-functional layer (B).

2. Structure according to claim 1, characterized in that the textile carrier substrate is a flat textile.

3. Structure according to claim 2, characterized in that the flat textile is a woven, knitted, knitted fabric, nonwoven or scrim.

4. Structure according to claim 2 or 3, characterized in that the flat textile is based on natural fibers and / or chemical fibers, in particular on fibers made of cellulose, regenerated cellulose, polyester, polyamide and / or glass.

5. Structure according to at least one of claims 2 to 4, characterized in that the flat textile has a basis weight of about 25 to 1800 g / m 2 , in particular from about 30 to 1500 g / m 2 and particularly preferably from about 80 to 1000 g / m 2 , has.

6. Structure according to at least one of the preceding claims, characterized in that the aluminum particles are spherical and / or in particular platelet-shaped.

7. Structure according to claim 6, characterized in that the spherical aluminum particles have a diameter of about 10 to 60 pm, in particular of about 20 to 40 pm, particularly preferably of about 25 to 35 pm, and the aluminum platelets have an average particle size distribution d50 of about 24 to 50 pm, in particular of about 30 to 40 pm and particularly preferably of about 33 to 37 pm.

8. Structure according to at least one of the preceding claims, characterized in that the radiation-functional layer (A) contains about 5 to 30 wt.%, in particular about 10 to 25 wt.% and particularly preferably about 15 to 20 wt.% of aluminum particles.

9. Structure according to at least one of the preceding claims, characterized in that the plastic matrix based on cross-linked silicone rubber is based on a cross-linked polysiloxane.

10. Structure according to claim 9, characterized in that the crosslinked polysiloxane is present as a crosslinked polydialkylsiloxane, in particular as a crosslinked polydimethylsiloxane (PDMS).

11. Structure according to at least one of the preceding claims, characterized in that the radiation-functional layer (A) and the radiation-functional layer (B) have a total layer thickness of about 50 to 1500 pm, in particular of about 70 to 1000 pm and particularly preferably of about 70 to 500 pm.

12. Structure according to one of the preceding claims, characterized in that the radiation-functional layer (B) contains white pigments in an amount of about 5 to 60 wt.%, in particular about 10 to 50 wt.% and particularly preferably about 20 to 40 wt.%.

13. Structure according to at least one of the preceding claims, characterized in that white pigments are additionally embedded in the radiation-functional layer (A), in particular in an amount of about 5 to 60 % by weight, more preferably from about 10 to 50 % by weight and most preferably from about 15 to 40 % by weight.

14. Structure according to at least one of the preceding claims, characterized in that the white pigments consist of titanium dioxide, zinc oxide, zinc sulfide, lead carbonate and / or barium sulfate.

15. Structure according to one of the preceding claims, characterized in that the white pigments are spherical and have a particle size of about 0.3 to 2.5 pm, in particular about 0.3 to 1 pm.

16. Structure according to at least one of the preceding claims, characterized in that the cooling capacity (determined according to "Atmosphere" 2021, 12, 1379, "Methodology", pp. 2 to 10) of the structure is approximately 10 to 150 W / m2 , in particular about 15 to 90 W / m 2 (at a solar irradiance of about 700 W / m 2 ) amounts.

17. Structure according to at least one of the preceding claims, characterized in that, in order to optimize the performance properties of the structure, there is a topcoat on the structure which is transparent over the entire wavelength range, in particular from about 0.25 pm to 25 pm, whereby reduced dust attraction, improved weather resistance as well as water resistance and water repellency are achieved.

18. Structure according to claim 17, characterized in that the topcoat is based on a cross-linked silicone rubber and has a high degree of transparency, preferably of at least 70%, in particular of at least 80% and most preferably of at least 90%.

19. Structure according to at least one of the preceding claims, characterized in that the material of the textile carrier substrate is determined by the intended use of the structure, in particular as a tarpaulin, as a textile curtain, as a textile awning or as weather and sun protection for buildings.

20. A method for producing a radiation cooling structure according to at least one of claims 1 to 19, characterized in that a liquid crosslinkable silicone rubber is provided with a chemical crosslinker and metallic particles in the form of aluminum particles, optionally additionally with white pigments, the resulting liquid dispersion (A) is applied to a textile carrier substrate and the crosslinkable silicone rubber is crosslinked by the chemical crosslinker, in particular in the presence of a catalyst, particularly preferably a platinum catalyst, and a radiation-functional layer (A) is formed, and a radiation-functional layer (B) is formed on the radiation-functional layer (A) by providing a liquid crosslinkable silicone rubber with a chemical crosslinker and white pigments,the resulting liquid dispersion (B) is applied to the radiation-functional layer (A) and the crosslinkable silicone rubber is crosslinked by the chemical crosslinker, in particular in the presence of a catalyst, particularly preferably a platinum catalyst, and the radiation-functional layer (B) is formed.

21. The method according to claim 20, characterized in that the crosslinking is carried out under the influence of heat, in particular between 60 °C and 180 °C, particularly preferably between 90 °C and 160 °C.

22. The method according to claim 20 or 21, characterized in that the liquid crosslinkable silicone rubber is a polydialkylsiloxane, in particular a polydimethylsiloxane (PDMS).

23. The method according to claim 22, characterized in that the polydimethylsiloxane (PDMS) has a vinyl functionality, in particular in terminal form, which causes crosslinking by the action of the chemical crosslinker.

24. Process according to one of claims 20 to 23, characterized in that the chemical crosslinker is polymethylhydrogensiloxane (PMHS).

25. The method according to claim 24, characterized in that about 25 to 40 parts by weight, in particular about 30 to 35 parts by weight of polydimethylsiloxane (PDMS) are used for 1 part by weight of polymethylhydrogensiloxane (PMHS).

26. The method according to at least one of claims 20 to 25, characterized in that the liquid dispersion A is applied to the textile carrier substrate in a layer thickness of about 5 to 500 pm, in particular from about 40 to 280 pm and particularly preferably from about 70 to 200 pm, and / or the liquid dispersion B, which contains the white pigments, is applied to the radiation-functional layer (A) in a layer thickness of about 5 to 500 pm, in particular from about 70 to 350 pm and particularly preferably 70 to 300 pm, wherein the application is carried out in particular by means of a doctor blade.

27. Use of the radiant cooling structure according to at least one of claims 1 to 19 as a covering of surfaces, in particular as a covering of motor vehicles, of buildings, in particular for weather and sun protection, in particular as a shading element on building surfaces, as a textile curtain, as a textile awning, as tarpaulins and as outdoor clothing. * * *

Images