EP3551706A1

EP3551706A1 - Composite product

Info

Publication number: EP3551706A1
Application number: EP17825380.3A
Authority: EP
Inventors: Anica Lacau; Mattijs G.J. TEN CATE; Hans BJERKAAS; Tore KOLÅS; Bente Gilbu Tilset; Mathieu Grandcolas
Original assignee: Norsk Hydro ASA
Current assignee: Speira GmbH
Priority date: 2016-12-12
Filing date: 2017-11-29
Publication date: 2019-10-16
Also published as: WO2018108529A1

Abstract

The invention provides a composite product (1) having a first side (2) and an opposite second side (3), the product (1) comprising: an aluminium substrate (10) having a first side (11) corresponding to the first side (2) of the product (1) and an opposite second side (12) corresponding to the second side (3) of the product (1), wherein the aluminium substrate (10) comprises an aluminium sheet metal, a first coating (20) directly provided on the first side (11) of the aluminum substrate (10) and in physical contact therewith, wherein the first coating (20) forms the outermost layer of the first side (2) of the composite product (1), wherein the first coating (20) comprises at least one a pigment embedded in a matrix material, and wherein the first coating (20) is a single-layer coating, and a second coating (30) provided on the second side (12) of the aluminium substrate (10), wherein the second coating (30) forms the outermost layer of the second side (3) of the composite product (1), wherein the composite product (1) is configured such that a spectral portion of solar radiation having a wavelength of 700 nm to 2500 nm is or can be incident on the first side of the aluminium substrate (10) and is or can be reflected by the first side (11) of the aluminum substrate (10), and wherein the first side (2) of the composite product (1) has a reflectance for a spectral portion of solar radiation having a wavelength of 700 nm to 2500 nm of 50% or more, optionally of 60% or more, optionally of 70%, or more.

Description

Composite Product

Technical Field

The present document relates to a composite product having an aluminium substrate or core and a first coating that is transparent to NIR (near-infrared) radiation and is directly provided on the aluminium substrate such that NIR radiation is reflected on a surface of the aluminium substrate, and a second coating that is provided on the substrate on a side opposite to the first coating. The present document also relates to a method for

continuously producing a composite product.

Background

It is known to provide a sheet metal with a coating on a surface of the sheet metal in order to obtain desired properties of the sheet metal. In this respect, document

US2005/0129964A1 discloses a flat metal structural element made from galvanized steel, characterized in that a) its first, outer surface is provided with a first coating that protects the metal from corrosion and reflects on average 60% of sunlight in the wavelength region of 320 to 1200 nm b) its first, outer surface is provided with a second coating that has on average a reflection of less than 60% in the visible light wavelength spectrum of 400 to 700 nm and has on average a reflection of more than 60% in the near infrared wavelength region of 700 to 1200 nm. According to said document, the flat metal structure element is further characterized in that its second, inner surface is provided with a first coating that protects the metal from corrosion, and b) its second, inner surface is provided with a second coating that has low emissivity and an emissivity of less than 0.75 in the thermal infrared wavelength region of 5 to 25 μιτι. It is described in said document that said flat metal structural element is used because the lower solar absorption of the outer coating and the low emissivity of the inner coating cause less heat to be transported from the outside into the interior of a building so that a better internal climate in a building with a roof comprising said flat metal structural element is achieved.

However, the flat metal structural element requires at least two coatings on each side of the flat metal structural element and is therefore inefficient and expensive to produce. Further, the flat metal sheet is made from steel and therefore heavy, cumbersome to handle and prone to corrosion. In addition, there is a demand by designers, architects and builders for composite products having a pleasing visual appearance.

Accordingly, it is the object of the present invention to provide a more efficient and visually pleasing composite product, as well as a more effective method for producing a composite product.

Brief Description

To solve the above and other objects, the present invention provides a composite product and a method for producing a composite product.

According to the invention, a composite product may have a first side and an opposite second side and may comprise: an aluminium substrate or aluminium core, in the following referred to as "aluminium substrate" or "substrate", having a first side corresponding to the first side of the product and an opposite second side corresponding to the second side of the product, wherein the aluminium substrate may be formed by (e.g. consist of) an aluminium sheet metal, a first coating that may be directly provided on the first side of the aluminum substrate and may be in direct physical contact therewith, wherein the first coating may form the outermost layer of the first side of the composite product, wherein the first coating may comprise at least one pigment (e.g. pigment particles/molecules that may be of the same type or of different types) embedded (e.g. distributed) in a (e.g. first) matrix material, and wherein the first coating may be a single-layer coating, and a second coating which may be provided on the second side of the aluminium substrate, wherein the second coating may form the outermost layer of the second side of the composite product, wherein optionally the second coating may be a single-layer coating and/or may be provided in direct physical contact with the second side of the aluminium substrate, wherein the composite product may be configured such that, when a spectral portion of solar radiation (e.g. solar light) having a wavelength of 700 nm to 2500 nm (near infrared solar radiation) is incident on the first side of the aluminium substrate, the spectral portion of solar radiation having the wavelength of 700 nm to 2500 nm is reflected by the first side of the aluminium substrate after transmission through the first coating, and wherein the first side of the composite product may have a total reflectance for a spectral portion of solar radiation having a wavelength of 700 nm to 2500 nm of 50% or more, optionally of 55% or more, optionally of 60% or more, optionally of 70% or more. The matrix material may be an organic matrix material. The second coating may be configured such that the second side of the composite product has a thermal emissivity of 0.5 or less, optionally of 0.34 or less, optionally of 0.15 or less. The first coating may be a polyester-type coating.

A composite product as described herein may have a defined color (visible to humans) and improved corrosion and abrasion resistances but at the same time may have excellent thermal properties, as spectral components of solar radiation may be reflected by the composite product without imparting excessive energy (that would result in a temperature increase) on the composite product. Further, the composite product according to the invention is more efficient as it uses the reflective properties of the aluminium substrate, so that it is not necessary to provide an additional primer layer between the substrate and the first coating. In this respect, the composite product according to the invention may be characterized in that the aluminium substrate is exposed to NIR radiation which is incident via and through the first coating. Accordingly, the composite product may be configured such that the first side thereof has a solar reflectance of at least 50%, e.g. at least 55%, e.g at least 60%, e.g. at least 70%, for electromagnetic radiation with a wavelength between 700 nm and 2500 nm, as said radiation may pass through the first coating and may be reflected by the first side of the aluminium substrate. In addition, the second coating may, according to embodiments in combination with the second side of the substrate, prevent or reduce emission of thermal energy from the second side of the composite product. The second coating, according to embodiments, may also protect the second side of the substrate from degradation (e.g. by corrosion or mechanical wear). Such a degradation could influence the thermal and/or optical properties of the composite product during the lifetime of the composite product. Accordingly, the invention provides a more efficient composite product that has excellent insulation properties, especially against heat from incident solar radiation. That is, the composite product according to the present invention may be used as a building material that keeps the temperature on the inside of a building, that is exposed to solar radiation on the outside thereof, low.

The invention further provides a method for continuously producing a composite product having a first side and an opposite second side, wherein the method may comprise providing a first coil of an aluminium substrate having a first side and a second side opposite to the first side (at least in the uncoiled/unwound condition), wherein the aluminium substrate is produced using cold rolling (the aluminium substrate may for example be produced from an ingot by hot rolling followed by cold rolling or may be produced by cold rolling a sheet metal produced by continuous casting), unwinding the first coil of aluminium substrate, pretreating said substrate by moving the substrate through a pretreatment bath while applying alternating electric current (AC) while unwinding the first coil, coating the first side of the substrate with a first coating by bringing the substrate into contact with a first coating composition such that the first coating composition comes in direct contact with the first side of the aluminium substrate after pretreating the aluminium substrate and while unwinding the first coil, coating the second side of the substrate with a second coating by applying a second coating composition on the second side of the substrate, wherein the second coating composition comes into direct contact with the second side of the substrate or into indirect contact with the second side of the substrate (e.g. when there is a further layer between the second side of the substrate and the second coating composition), after pretreating the aluminium substrate and while unwinding the first coil, posttreating the first and the second side of the substrate after coating the first side and the second side of the substrate by exposing the first and the second side of the substrate with the first and second, respectively, coating composition thereon to air having a temperature between 200°C and 600°C such that the aluminium substrate reaches a peak metal temperature (PMT) between 220°C and 255°C such as to produce the composite product having a reflectance for a spectral portion of solar radiation having a wavelength of 700 nm to 2500 nm of 50% or more, optionally of 55% or more, optionally of 60% or more, optionally of 70% or more, while unwinding the first coil, and optionally winding the composite product in a second coil to produce the second coil of the composite product while performing the above-mentioned steps. The described method may be used to produce the composite product according to the invention.

Further embodiments of the invention are described in the dependent claims.

Brief Description of the Drawing

The above and other features of the present invention will now be described in detail with reference to embodiments thereof illustrated in the accompanying drawings which are given by way of illustration only.

Fig. 1 shows the spectral solar energy distribution.

Fig. 2 schematically shows a composite product according to an embodiment of the invention.

Fig. 3 schematically shows a method according to an embodiment of the invention that can be used to produce a composite product according to embodiments of the invention. Figs. 4 to 7 show reflection spectra of embodiments of the invention.

It should be understood that the appended drawings are not necessarily to scale and may present a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes, will be determined in part by the particular intended application and use

environment.

In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing.

Detailed Description

Reference will now be made in detail to various embodiments of the present invention, examples of which are illustrated in the accompanying drawings and described below. While the invention will be described in conjunction with exemplary embodiments, it will be understood that the present description is not intended to limit the invention to those exemplary embodiments. On the contrary, the invention is intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included in the scope of the invention as defined by the appended claims. All embodiments described herein are compatible with each other and may be combined with each other unless it is indicated otherwise.

Unless indicated otherwise, SI units and definitions are used herein. Unless indicated otherwise, terms used herein have the same meaning as generally understood in the fields of optics and solar science. Unless indicated otherwise, the terms "visible" or "visual" means perceptible for a human eye. The solar reflectance or solar reflectance value is a weighted average reflectance, weighted according to the intensity of solar radiation in that wavelength region (as observed at the surface of the earth). Herein, unless indicated otherwise, solar reflectance is measured according to ASTM E903. Unless indicated otherwise, all standards referred to herein refer to the latest version of the standard on November 1 , 2016.

In this respect and with reference Fig. 1 , "near-infrared" (NIR) radiation may comprise electromagnetic radiation having a wavelength between 700 nm and 2500 nm. Solar radiation in the NIR spectral portion comprises about 52% of the total solar power that is transmitted from the sun through the earth's atmosphere to the ground. According to the invention, "NIR transparent" may mean that an object transmits NIR radiation. This may for example mean that an object that is described herein as "NIR transparent" transmits at least 50% of all NIR radiation that is incident on that object.

According to the invention, the terms "transmissivity" and "transmittance" and similar terms used herein may describe the relative amount of radiation that is transmitted through an object, e.g. a first coating as described herein. For example, a transmissivity or

transmittance of 50% may mean that 50% of radiation (e.g. of the energy of the radiation) that is incident on an object may pass through that object and exit said object on a side generally opposite to the side on which the radiation has entered the object (refraction may occur).

Herein, the reflection spectra are measured and the solar reflection is calculated according to standards ASTM E903 and ASTM G173. Further to calculation of the total solar reflection (TSR), as described in the standards, solar reflection values in the UV region (300 - 400 nm), visible region (400-700 nm) and the near infrared region (700-2500 nm) were calculated separately from the respective dataset. In this respect, as visible color of the composite product is determined by the reflectance in the visible region, it has been found that the solar reflectance in the near infrared region is of interest because it allows characterizing improvements in solar reflectance independent from the visible color of the composite product.

According to the invention, thermal emittance is measured and defined according to ASTM standard E 408.

Herein, a reference to the composite product is to be understood as a reference to the ready-for-use composite product (e.g. after posttreatment including drying/curing).

Composite Product

With further reference to Fig. 2 and Fig. 3, a composite product 1 according to an embodiment of the invention may comprise a substrate 10 having a first side 1 1 (e.g. first surface) and a second side 12 (e.g. second surface). The first side 1 1 and the second side 12 may be (at least locally) opposing outer surfaces of the substrate 10. The first side 1 1 and the second side 12 may be (at least substantially) parallel to each other.

The substrate 10 may be an aluminium substrate. For example, the substrate 10 may be aluminium sheet metal. The substrate 10 may for example be made of pure, e.g. 99% pure or purer, aluminium or may be an aluminium alloy. For example, the substrate 10 may be made from AA3003, AA3105 (such as EN AW3105, AIMn0.5Mg0.5), AA3005 (such as EN AW3005, AIMn1 Mg0.5(A)) or AA5005 series aluminium.

Unless it is indicated otherwise, a reference to the substrate 10 or the aluminium substrate 10 is to be understood as a reference to a substrate comprising (and/or consisting) of pure aluminium or comprising (and/or consisting of) an aluminium alloy as described above. According to the invention, the substrate 10 may be characterized by not being iron-based and/or not being steel-based.

The substrate 10 may, according to embodiments, have an oxide layer (e.g. naturally grown alumina) on the first 1 1 and/or second 12 side thereof. According to embodiments of the invention, such a layer that is grown on the substrate 10 by oxidizing the substrate (e.g. naturally or purposefully grown oxide) is not considered to be a separate layer but is considered to be part of the substrate 10.

The substrate 10 may be produced by a process including cold rolling. For example, the substrate 10 may be produced by hot rolling followed by cold rolling of an ingot that has been produced by non-continuous casting. Further, for example, the substrate 10 may be produced by cold rolling a product obtained from a continuous casting process. It has been found that using aluminium substrates 10 that underwent cold rolling during their production results in a more efficient composite product 1 having desirable optical properties compared to using aluminium substrates 10 that do not comprise a cold rolling step in their production. Further, it is thought that cold rolling gives the aluminium substrate 10 according to embodiments of the invention a favorable metallographic texture resulting in better macroscopic properties.

The substrate 10 may according to embodiments have a thickness between 0.2 mm and 2.00 mm. Depending on the intended use of the composite product 1 , the substrate (e.g. core) 10 may have a thickness lower than 0.2 mm or may have a thickness of more than 2.00 mm. The thickness of the substrate 10 may correspond to the minimum distance between a point of the first side 1 1 and a point on the second side 12 thereof.

First Coating

A first coating 20 may be provided on the first side 1 1 of the substrate 10. The first coating may fixedly adhere to the first side 1 1 of the substrate 10. A coating as described herein may refer to a layer or film applied on the substrate that is ready for final use, e.g. after posttreatment. A coating according to the invention may consist of one film/layer only, unless it is specified otherwise.

The first coating 20 may comprise a matrix material 25 and a pigment 26. A pigment 26 may comprise a plurality of separate pigment particles/molecules. In addition to the pigment 26, the first coating 20 may optionally also comprise a dye giving a color effect to the first coating 20 and consequently the first side 2 of the composite product 1 . The matrix material 25 and/or the pigment 26 (e.g. pigment particles/molecules thereof) may be in direct contact with atoms of the aluminium substrate 10. In other words, according to the invention, there may be no additional layer provided between the first coating 20 and the first side 1 1 of the substrate 10. The first coating 20 may be the outermost layer of the composite product 1 according to the invention. The first coating 20 of the composite product 1 may be directly exposed to the atmosphere when the composite product 1 is used, e.g. is used as a building material for buildings.

The pigment 26 may be dispersed in the matrix material 25. The pigment 26 may comprise particles/molecules of the same type (e.g. all particles/molecules of the pigment may have a substantially similar chemical composition) or may be of two or more different types (e.g. the particles/molecules may have different chemical compositions). The pigment may have a (visible) color, such as black, yellow, red, blue, green, cyan, white etc.

The pigment 26 may be a organic pigment or inorganic pigment or a mixture thereof. It has been found that organic pigments show better dispersion ability than inorganic pigments due to the higher chemical compatibility of organic pigments with the matrix material 25. The use of a micro-sized or nano-sized inorganic pigment in the first coating 20 of the composite product 1 according to the invention may therefore comprise optimizing dispersion and modifying opacity. This may for example include a surface functionalization of the pigment 26 to improve the dispersion of pigment particles/molecules. To obtain high material dispersion of the pigment 26 in coating compositions according to the invention, various techniques are applied, including mechanical stirring, high shear dispersion (Ultraturrax type), pre-suspension in an organic solvent and ball milling.

According to the invention, the first coating 10 may comprise a pigment 26 with

particles/molecules of the same color or pigments 26 of different colors. For example, the first coating 20 may comprise yellow and red pigments 26 at the same time or the first coating 20 may comprise only a pigment 26 having particles/molecules of the same color and type, e.g. red or yellow pigment particles of a specific type.

The pigment 26 may be transparent (or at least substantially transparent) for NIR electromagnetic radiation. A Pigment 26 that are transparent for NIR radiation allow that solar NIR radiation can efficiently propagate through the first coating 20 to be reflected on the first side 1 1 of the substrate 10 without imparting excessive energy on the composite product 1 .

In order to reduce surface temperature of the first coating 20 even more when solar radiation is incident, the first coating 20 may comprise a fluorescent substance. The fluorescent substance may e.g. be provided as a pigment 26 or a dye in the first coating 20, e.g. in addition to other, non-fluorescent pigment(s) 26 and/or other non-fluorescent dyes.

In particular a pigment 26 or a dye that absorbs light in the visible (and optionally UV) region and reemits light in the near infrared region (NIR) may be used as a fluorescent substance. By this approach, the absorbed energy in the visible region is not transformed to heat, but is emitted in a region that is not visible to the human eye. Accordingly, it is possible to obtain a very low surface temperature (comparable to that of a white surface), even for a black or dark colored first coating 20. The reemitted radiation (light) of the first coating 20 comprising a fluorescent substance in the near infrared region is emitted in all directions, including the direction towards the substrate 10. However, the high NIR reflectance of the aluminium substrate 10 according to the invention prevents an excessive temperature increase of the substrate 10. Examples of fluorescent substances that can be used as dye or pigment 26 with the first coating 20 include:

Ruby (AI2O3:Cr),

Nd-dopedYAG (yttrium aluminum garnet),

Cadmium pigments CdS, CdSe and their alloys,

Alkali earth copper silicates such as Egyptian blue (CaCuSi4O10) and Han blue (BaCuSi4O10) or a mixture of the mentioned compounds.

The first coating 20 may be produced by posttreating a first coating solution provided on the first side 1 1 of the substrate 10 comprising a resin (e.g. polymer resin), optionally a dye, pigment 26, solvents and optionally additives as described further below in order to achieve the optical properties of the composite product 1 according to the invention.

According to the invention, a "solution" may also comprise matter that is not in solution but is dispersed. In this respect, according to embodiments of the invention, the pigment 26 (e.g. the particles/molecules thereof) may for example be dispersed in the first coating solution.

In this respect, the first coating solution may for example comprise (by weight percent based on the total weight of the first coating solution):

4-15% organic solvent,

0- 2% dispersant

1 - 20% pigment

balance (e.g 65-85%) resin, e.g. solution of organic polymer.

The first coating solution may also comprise de-foaming and de-aerating agents, such as e.g. Evonik Tego Airex 990.

The resin, e,g, a solution of organic polymer, may be for example be produced by mixing of 60% to 85% by weight of pure polymer of type polyester in an organic solvent added to balance (e.g. 40 to 15% by weight). The organic solvent may also be a mixture of organic solvents, e.g a mixture of 10-15% solvent naphtha heavy aromatic, 5-7% 2- buthoxyethanol, 5-10% solvent naphtha light aromatic, and other organic solvents to balance.

The matrix material 25 may refer to the material that is obtained by posttreating (e.g.

curing) the first coating solution and is not a pigment 26 (i.e. not a pigment

particle/molecule).

The organic solvent may for example be one or more selected from the group comprising (e.g. consisting of): naphta, 2-buthoxyethanol, naphta heavy aromatic, naptha light aromatic, DBE (dibasic ester).

The organic polymer that may be used for the resin may for example be one or more selected from the group comprising (e.g. consisting of): og type high durable polyester, standard polyester (PE), polyvinyliden difluoride (PVDF), polyurethane, polyester- polyamide, polyurethane-polyamide.

The dispergent may for example be Evonik Tego Dispers 675 or a different dispergent. The pigment 26 may be one or more selected from the group comprising (e.g. consisting of): Ferro 10550 Brown, Ferro 10202 Eclipse Black, Ferro 13810 Red, Ferro 10406 Yellow, Heubach IR Blue 550, Heubach IR Black 940, Heubach IR Yellow 259, Heubach IR Brown 869, Heubach Blue 5-100, BASF S0084 Black, BASF L0086 Black, BASF Irgazin Red L 3660 HD, BASF Irgazin Yellow L 2060, BASF Paliotol Yellow L 0962 HD, BASF Irgazin Orange L3250 HD, BASF Irgazin Red L3670 HD, Shepherd 30C342 Orange, etc.

Other types of pigment 26 may be used as well. The first coating 20 of the composite product 1 may, according to embodiments, have a thickness of 15 to 35 μιτι. A thickness in said range offers an efficient balance between the optical and reflective properties of the composite product 1 and the protection effect (e.g. against corrosion and wear) of the first coating 20. While a thinner coating may result in better reflective properties of the composite product 1 , the (visible) color induced by the pigment of a first coating 20 that is too thin may not have the desired properties and the too thin first coating 20 may not protect the aluminium substrate 10 sufficiently from corrosion and degradation by exposure to the atmosphere. On the other hand, if the first coating 20 of the composite product 1 is thicker than about 35 μιτι, the reflective properties of the composite product 1 may deteriorate as less NIR radiation propagates through the first coating 20 and is reflected by the first side 1 1 of the aluminium substrate 10 resulting in increased heat absorption (and a corresponding increase of the temperature) of the composite product 1 .

However, there may be applications of the composite product 1 according to the invention that require a different balance of the properties of the composite product 1 , so that the first coating 20 according to the invention may also have a thickness of less than 15 μιτι and/or more than 35 μιτι.

The following Table 1 shows matrix materials 25 of first coatings 20 according to the invention and the measured properties thereof. All examples were prepared from

respective first coating compositions having a solid content of 56-60 % by weight based on the total weight of the first coating composition. The wet density of the first coatings 20 before posttreatment was between 1 .02 and 1 .25 g/cm². The peak metal temperature (PMT) used for posttreatment/curing the first coatings 20 according to the examples in Table 1 was between 232°C and 241 °C (see also the description of the method according to the invention below).

The flexibility has been evaluated according to EN 13523-7 by bending a coated test specimen parallel to the direction of rolling through 135° to 180°, wherein the specimen has the first coating 20 on the outside of the bend. The degree of resistance to cracking of the first coating 20 is determined, as well as the degree of delamination in the bending zone.

The abrasion and wear resistance was evaluated according to EN 13523-4 via the relative hardness of the first coating 20 after application and posttreatment. The first coating 20 is intentionally damaged by pushing across the surface different pencils of decreasing and known hardness, until the lead of a pencil does not remove the first coating 20.

The adhesion of the first coating 20 to the substrate 10 was measured using the tape-test on cross-cuts using a multiblade cutting tool in accordance with EN 13523-6 to produce a cross-hatched zone in the coating film, followed by an indentation from the other side. Thereafter a tape is applied over the lattice and removed, and the percentage of cross- hatched squares removed is measured. In deviation from the norm, higher stress conditions were applied by placement of the samples, as described above, in boiling water for 5 and 60 minutes, respectively, before carrying out the tape-test. The UV performance was evaluated using both an accelerated weathering tester from Q-Lab equipped with UV- B (313) lamps in accordance with EN ISO 1 157 and a SUNTEST XXL+ from Atlas Material Testing Technology GmbH equipped with Xenon arc lamps in accordance with ISO 16474- 2.

Filliform corrosion was measured in accordance with DIN EN 3665 / EN 4623-2.

As can be seen, substrates 10 with the matrix materials 25 of the first coatings 20 according to examples of the invention thereon have a very high reflection for solar radiation in the near-infrared spectral portion of the solar radiation with a wavelength from 700 to 2500 nm of 0.602 (that is 60.2%) or more. All examples show an at least good flexibility and in general show a wear resistance that is at least good. Further, all examples exhibit a good adhesion to the substrate 10 together with good long-term UV stability and good corrosion performance. Table 1

Further, experiments 1 to 4 as described in the following have been carried out to gain insights about the composite product 1 according to the invention and to assess the respective influences of the substrate 10 and the first coating 20 on the optical properties of the composite product 1 .

As mentioned above, the targeted colors of the first coating 20 according to the present invention are obtained by dispersing one or more NIR-transparent and/or NIR-reflective pigment 26 in a matrix material 25. The matrix material 25 may be obtained by posttreating a coating solution comprising a resin, such as a polymer resin, suitable organic solvents and additives that has been mixed in a steel ball mill. Coating compositions are applied onto electrochemically pre-treated (using alternating current and an inorganic electrolyte at an elevated temperature as described below) aluminium substrates 10 using coating bars and subsequently posttreated (cured) by hot air inducing peak metal temperatures (PMTs) of 220-255°C in the substrate 10. The pigment concentration was kept between 1 % and 20% by weight. The thickness of the posttreated first coating 20 was kept constant around 19-20 μιτι for the examples.

As mentioned above, the reflection spectra are measured and the solar reflection calculated according to ASTM E903 and ASTM G173. Beside calculation of the total solar reflection (TSR), as described in the norms, reflection values in the UV region (300 - 400 nm), visible region (400-700 nm) and the near infrared region (700-2500 nm) were calculated separately from the same dataset.

As mentioned, total solar reflection values (300-2500 nm), and solar reflectance values within the visible (400-700 nm) and the near infrared (700-2500 nm) region were calculated and compared. Since the visible color of the composite product 1 is determined by the reflectance in the visible region, the solar reflectance in the near infrared region is particularly interesting because these values allow observing improvements in solar reflectance of the composite product 1 according to the invention independent of the visible color.

Example no.1

The first coating 20 was prepared as solution on a laboratory scale, using a clear transparent polymer of type polyester resin with isocyanate-based crosslinkers, with high outdoor performance, dissolved partially in organic solvents such as solvent naphtha (petroleum) and 2-butoxyethanol, by adding a mixture of defoaming and deaerating substances (Evonik Tego Airex 990), a high molecular weight dispersant additive (Evonik Tego Dispers 675) and BASF Paliogen Black S0084 pigment as pigment 26, as shown in Table 2.

Table 2

The mixture was dispersed using a steel ball mill at >200 RPM, resulting in a homogenous fluid formulation for the first coating solution. This coating solution was applied by bar coating on aluminium substrates 10 (alloy AA3105) that were pretreated using alternating current and a hot electrolyte as described below, and were posttreated (cured) in a laboratory oven with warm air circulation, at a PMT of 220°- 255°C, giving a dry film thickness of the first coating 20 in the range of 19-20 μιτι.

It has been found that first coatings 20 may give the composite product 1 higher solar reflectance (SR) values when they are applied directly onto a reflective aluminium substrate 10 without use of a primer layer, basecoat or the like between the substrate 1 and the first coating 20.

In this respect, a surface with high SR is characterized by a high reflectance in the NIR region. The reflectance in the visible region is also important for the heat absorption, but this reflectance is determined by the desired color of the surface, and generally cannot be changed without altering the color.

As is apparent from Table 3, the solar reflection in the NIR region (700-2500 nm) is 0.6576, and the TSR values for the whole spectrum (UV, VIS and NIR) are as shown in the Table 3 below and as shown in Fig. 4 that shows the reflectance of the example according to the invention designated as H056.

The SR values of the uncoated aluminium substrate 10 are also given in the table for comparison. For further comparison, also the reflection values for substrates having only an opaque white basecoat ("white substrate") and an opaque black basecoat ("black substrate") but no first coating are shown. In the white substrate and the black substrate, the basecoat has a thickness of approximately 20 μιτι.

For most examples below, the first coating 20 was applied in the same thickness also on the aluminium substrate 10 coated before with the opaque black coating ("black substrate") as a base coating to compare the reflection values of the composite product 1 according to the invention with comparative examples having a black base coating ("black substrate") between the first coating 20 and the substrate 10. The comparative examples do not use the aluminium substrate 10 to reflect solar radiation, but the solar radiation is reflected by the base coating. As is apparent, application of a base coating according to the comparative examples results in an ineffective and very expensive composite product.

Table 3 - Solar reflectance values (Total, UV, VIS and NIR)

Example no. 2

Coating prepared on laboratory scale as described above and according to Table 2 but with a different pigment 26, i.e. the orange pigment Orange 30C342 from Shepherd. The concentration of the pigment was increased to 10% by weight and the concentration of the organic polyester based polymer was reduced accordingly.

The solar reflection in the NIR region (700-2500 nm) is 0.6493, and the TSR values for the whole spectrum are as given in the Table 4 below and as shown in Fig. 5 that shows the reflectance of the example according to the invention designated as H068.

Table 4 - Solar reflectance values (Total, UV, VIS and NIR)

H068 - Shepherd

Orange - 10 % - Al

substrate (invention) 0.4690 0.0526 0.3008 0.6493

Al substrate 0.7406 0.6421 0.7405 0.7501

White substrate 0.7356 0.1329 0.8163 0.7257

Black substrate 0.0513 0.0531 0.0505 0.0519

Shepherd Orange

- 10 % - on Black

substrate 0.2526 0.0509 0.1977 0.3176

Example no.3

The Coating was prepared on laboratory scale as described above and according to Table 2, but using the blue pigment IR Blue 550 from Heubach as pigment 26. The concentration of the pigment was 5% by weight.

The solar reflection in the NIR region (700-2500 nm) is 0.5967, and the TSR values for the whole spectrum are presented in Table 5 below and in Fig. 6 that shows the reflectance of the example according to the invention designated as H044-2.

Table 5 - Solar reflectance values (Total, UV, VIS and NIR)

Example no .4

The coating was prepared on Laboratory scale as described above and according to Table 2 but using the yellow pigment 10406 Yellow from Ferro as pigment 26. The concentration of the pigment was increased to 20% by weight and the concentration of the organic polyester based polymer was reduced accordingly. The solar reflection in the NIR region (700-2500 nm) is 0.5496, and the TSR values for the whole spectrum are as presented in the Table 6 below and as shown in Fig. 7 that shows the reflectance of the example according to the invention designated as H075-1 .

Table 6 - Solar reflectance values (Total, UV, VIS and NIR)

As is apparent from the examples shown in Tables 3 to 6, the composite product 1 according to the invention has favorable reflective properties. Further, according to the present invention, a more efficient composite product 1 can be achieved, as there is no additional basecoat necessary between the substrate 10 and the first coating 20.

Second Coating

The composite product 1 may in addition have a second coating 30 on the second side 12 of the aluminium substrate 10 and opposite to the first coating 10.

The second coating 30 may be provided to improve the thermal properties of the composite product 1 . Further, the second coating 30 according to the invention may enable continuous production of the composite product 1 by a coil coating process.

Accordingly, the second coating 30 may be configured to have at least substantially the same friction coefficient as the first coating 10 in order to facilitate winding the composite product 1 onto a coil and unwinding the composite product 1 from a coil, as it has been found that different friction coefficients of the first side 2 and the second side 3 of the composite product 1 may result in a degradation of the first side 2 of the composite product 1 during winding/unwinding a coil. In addition, the second coating 30 may be configured to give the composite product 1 a low thermal emissivity on the second side 3 thereof to improve the thermal insulation property of the composite product 1 . Accordingly, less heat will be radiated from the second side 3 of the composite product 1 , e.g. towards the interior of a building when the composite product 1 forms an outside of the building. The second coating 30 may be transparent or substantially transparent for thermal radiation, e.g. corresponding to wavelengths between 3.5 μιτι and 20 μιτι. A second coating 30 that is transparent for thermal radiation allows to at least partially use the favorable thermal emission properties of the second side 12 of the aluminium substrate 10 to obtain a more efficient composite product 1 .

In this respect, the second coating 30 may be characterized by being a low-thermal- emissivity coating that is

-coil-coatable,

-transparent in the thermal region (e.g. wavelengths of 3.5 - 20 μιτι), and/or

-is thin, e.g. has a thickness from approximately 0.5 μιτι to 3.00 μιτι, e.g. from 0.5 μιτι to 1 .5 μιτι.

Such a coating allows it to utilize the favorable properties of the aluminium substrate 10 with respect to low thermal emissivity in the composite product 1 , in order to reduce or prevent emission of thermal energy (e.g. radiation) from the second side 3 of the composite product. In this respect, according to embodiments of the invention, the second coating 30 may be configured such that the thermal emissivity of the second side 3 of the composite product 1 corresponding to the second coating 30 may be lower than 0.5, e.g. lower than 0.34, e.g. lower than 0.17, e.g. lower than 0.1 .

As mentioned, according to embodiments of the invention, the second coating 30, after posttreatment (e.g. drying), may have a thickness of less than 3.0 μιτι, e.g. equal to or less than 2 μιτι, e.g. equal to or less than 1 μιτι. In order to have sufficient properties with respect to friction, wear-resistance etc. as also described below, the second coating 30 may have a thickness of equal to or more than 0.5 μιτι.

It has been found that the properties as described above offer favorable properties of the composite product 1 . However, depending on the use environment, the second coating 30 may also be thinner than 0.5 μιτι and/or thicker than 3 μιτι. It has further been found that the application of the second coating 30 by using a coil coating process results in an efficient composite product 1 . Accordingly, according to embodiments, the second coating 30 may be characterized by being a coating that has been produced by a coil coating process or is obtainable by a coil coating process.

As mentioned, the second coating 30 may also prevent unwanted oxidation of the second side 12 of the substrate 10 during the lifetime of the composite product 10 by forming a barrier between atmospheric oxygen and the second side 12 of the substrate 10. In this respect, it has been found that the growth of unwanted alumina may change the emissivity of the second side 3 of the composite product 1 during the lifetime of the composite product 1 resulting in a less efficient composite product 1 .

According to embodiments of the invention, the second coating 30 is configured such that it has a friction coefficient that is within a window of 40%, e.g. 20%, based on the friction coefficient of the first side 2 of the composite product 1 . That is, the friction coefficient of the second coating 30 forming the second side 3 of the composite product 1 may be from 40% smaller to 40% larger (e.g. from 20% smaller to 20% larger) than the friction coefficient of the first side 2 of the composite product 1 . If for example the first side 2 of the composite product 1 has a friction coefficient of 0.5, the second coating 30 may be configured so that it has a friction coefficient from 0.3 to 0.7 (40% smaller or larger than 0.5). It has been found that friction coefficients outside of that window may result in problems, such as surface degradation of the first surface 2 of the composite product 1 , during winding and unwinding of coils.

The second coatings 30 described in the following fulfill the above-mentioned criteria and result in an efficient composite product 1 .

For example, the second coating 30 may be a (at least in the thermal region) transparent organic coating, e.g. coating of polyester-type or epoxy-type. In this respect, second coatings 30 according to the invention are compared in Table 7 with an uncoated substrate 10 to show that the emissivity of the second side 3 of the composite product 1 is dependent on the thickness of the second coating 30 and to show that the second side 12 of the substrate 10 generally has desirable properties with respect to thermal emissivity. However, as mentioned, in order to obtain a more efficient composite product 1 , the second coating 30 is provided as described herein. Table 7

According to embodiments of the invention, the second coating 30 may also be an inorganic coating based on a metal oxide sol, such as CeO2 based sol. It has been found that CeO2 is transparent in large parts of the thermal IR region (3.5 - 20 μιτι). For this reason, a CeO2 coating on an aluminium substrate 10 may provide the desired property of low emissivity. Experiments showed that CeO2 coatings performed well with respect to adhesion and scratch resistance and also have a friction coefficient similar to the first coating 20 according to embodiments of the invention.

Optionally, the second coating 30 may comprise a pigment (e.g. to achieve a visible color) or may be substantially free of pigment, e.g. when there is no color requirement for the second side 3 of the composite product 1 .

The following starting materials were used to produce the second coating 30 according to the examples of the invention given in Table 8:

- Ceria nitrate sol, with 10-30 wt% CeO2, particle size 10-20 nm and pH = 1 .5

- black pigment , Manganese ferrite black spinell with average particle size 0.5 μιτι and pH = 6.0 when dispersed in water, and

- balance water and organic acrylic polymer.

The pigment has a very low reflectance in the UV-VIS-NIR range (the spectral range corresponding to ultraviolet, visible and near-infrared light). The composition of the black pigment was shown to be Mn3Cu2FeO8 by SEM (EDS). While this example uses a black pigment for the second coating 30, the use of pigment in the second coating 30 is optional according to the invention. The second coating 30 may for example comprise pigment when a specific color is desired for the second side 3 of the composite product 1 . Optionally, the second coating 30 may further comprise an organic additive, e.g. for improving adhesion to the substrate 10 after heat treatment (280°C) during posttreatment.

The organic additive in the second coating 30 may be one or more selected from the group comprising: acrylate- and styrocopolymer, a mixure of polyvinyl acetate polymer and - copolymer, polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyurethane and/or polymetacrylathomo and -copolymer, acrylat dispersions, polyester.

Further, the second coating 30 may be based on a mixture of two sols, wherein the second sol may e.g. be a (e.g. nano-sized) AI2O3, SnO2, Y2O3, ZnO or S1O2 sol.

According to embodiments, preferably a particle size≤ 0.5 μηη for the black pigment of the second coating 30 should be achieved to enable good dispersion of the pigment in the sol. IR and UV-VIS-NIR spectra were obtained to characterize optical properties of the second side 3 of the composite product 1 .

The IR spectrum was weighted, using black body radiation at 300 K, to obtain the emissivity (ε).

The results from experiments as described above are shown in the Table 8 below.

Table 8

Sol+10%Black

6 pigment+5% Additive 0.17

10% Black pigment +

7 1 % Additive 0.07

Sol+8% Black

8 pigment+7%Additive 0.13

It has also been found that the adhesion of the second coating 30 on the aluminium substrate 10 can be improved by preparing the second side 12 of the aluminium substrate 10 with an interlayer between the sol-gel coating and the aluminium substrate 10. This interlayer can for example be a conversion coating or an inorganic silicate based primer.

The second coating compositions according to the examples in Table 9 have been produced as follows:

- Ce02(N03) sol, with 20 wt% CeO2, particle size 10-20 nm and pH = 1 .5

- Black Pigment , Manganese ferrite black spinel with average particle size 0.5 μιτι and pH = 6.0 when dispersed in water, and

-balance acrylic polymer and water.

After posttreatment (curing) of the second coating compositions, the following

measurements as shown in Table 9 were obtained. For comparison, Table 9 also contains uncoated substrates as reference.

Table 9

Sol +10% 1050 ECC 0,06

black pigment

Sol+15%Black 801 1 A Cr free Si 0,1 1 -0,17

pigment

Sol +10% 3005 Cr VI NR 0,06

Black pigment uncoated 3005 Cr 3+ 0,09 uncoated 1050 ECC 0,03 uncoated 3005 Cr free Si 0,03

In the table, ECC refers to electro chemical cleaning using a pretreatment step in an inorganic electrolyte at an elevated temperature while applying alternating current as described below, Cr VI NR refers to a chemical pre-treatment by chromating with

hexavalent chromium without rinsing (no rinse), Cr free Si refers to chromium free chemical pre-treatment in the presence of silicon (Si), and Cr 3+ refers to chemical pretreatment with trivalent chromium. While pretreatments using chrome/chromating do not necessarily have a negative influence on the emission properties of the second side 3 of the composite product 1 , according to embodiments of the present invention, chromating is avoided for the first side 1 1 of the substrate or for the first 1 1 and second 12 sides of the substrate, as it is thought that it has a negative influence on the properties of the first side 2 of the composite product 1 , because the chromating may cause formation of a chromate conversion layer based on chromium (III or IV) oxide having a thickness of up to 2 μιτι, which can affect the reflection properties of the substrate 10 and can be colored

(yellowish-greenish), which also may affect the optical properties of the composite product 1 in an undesired way.

According to embodiments of the invention and as mentioned above, the second coating 30 may be implemented as an organic coating. Said organic coating forming the second coating 30 may optionally be at least substantially transparent (e.g. transparent) in the thermal region. Such a second coating 30 formed by an organic coating may have a thickness of less than 5 μιτι, e.g. less than 3.5 μιτι, e.g. less than 2 μιτι, e.g. less than 1 μιτι. According to embodiments, the thickness of the second coating 30 may be between 1 μιτι and 2 μιτι. If the thickness is too low (e.g. lower than 0.5 μιτι), the second side 12 of the substrate 10 may form oxides during the lifetime of the composite product 1 which might be undesirable for some applications. On the other hand, when the second coating 30 formed by an organic coating is too thick, the thermal properties (e.g. a desirable low emissivity) of the second side 3 of the product 1 may deteriorate. The organic coating may comprise (e.g. consist of) one or more from the group consisting of: polyester, acrylic, epoxy, epoxy phenol, polyurethane (c.f. Table 7).

While it has been mentioned that the second coating 30 may optionally be an organic or inorganic coating having a thickness of 0.5 μιτι to 3 μιτι, according to embodiments, the second coating 30 may also be implemented by a silane surface modification layer provided on alumina grown on the substrate 10. The silane surface modification layer may have a thickness of up to 10 nm, e.g. up to 5 nm, e.g. up to 1 nm. It is thought that the higher the thickness of the silane layer, the better the resistance against corrosion.

Further, according to embodiments of the invention, the minimum thickness of the silane layer is configured such that the second side 3 of the composite product has a friction coefficient similar (e.g. within a 40% window as indicated above) to the one of the first side 2 of the composite product 1 . Before application of the silane layer, the second side 12 of the substrate 10 may be anodized to form the alumina layer on the second side 12 on which the silane surface modification layer is applied. The alumina layer may for example have a thickness between 30 nm and 3.5 μιτι. A second coating 30 formed by a silane surface modification layer as described herein is hydrophobic, offers corrosion resistance and enables a low thermal emissivity by utilizing the favorable emission properties of the aluminium substrate 10.

According to embodiments, the second coating 30 may also be a polysilazane coating. Polysilazanes are inorganic polymers comprising silicon, nitrogen and hydrogen.

According to the invention, the polysilazanes forming the second coating 30 may be modified by organic substituents. Second coatings 30 using perhydropolysilazanes were tested, amongst others second coatings 30 comprising NL 120A and NP 1 10 from

Clariant. The lowest emissivity value for the polysilazane coatings was found to be 0.1 for a second coating 30 comprising Clariant NL120A and having a thickness of 0.8 μιτι.

According to the invention,the substrate 10 may comprise an artificially grown alumina layer on the first 1 1 and/or second side thereof. The substrate 10 may also be treated to remove naturally occurring alumina (i.e. alumina that has not be purposefully grown) from the first 1 1 and/or second 12 side of the substrate 10 so that there is no unintended alumina layer between the substrate 10 and the first 20 and/or second 30, respectively, coating.

Production method

In the following and with reference to Fig. 3, a method for producing a composite product 1 according to embodiments of the invention is described.

The method may be a method for continuously producing a composite product 1 suitable for an efficient large scale production. It has been found that traditional non-continuous methods including dip coating and the like are not efficient enough to satisfy customer demand with respect to product quality, product quantity and price.

It has further been found that a cold rolling process results in optical properties of the aluminium substrate 10 that have to been taken into account when producing the composite product 1 in order to produce an efficient composite product 1 .

Accordingly, the present invention is also directed to providing an efficient method for producing a composite product 1 according to the invention.

The method according to the invention may comprise providing a first coil 50 of an aluminium substrate 10, the substrate 10 having a first side 1 1 and a second side 12. The aluminium substrate 10 according to the invention may for example be produced by a hot rolling and cold rolling process or by continuous casting followed by cold rolling. After the cold rolling step common to both production routes, the aluminium substrate 10 may be wound on a first coil 50. However, the first coil 50 may also be produced using other methods.

The method according to the invention may further comprise unwinding the first coil 50. The unwinding may be carried out continuously during carrying out the method according to the invention in order to obtain the aluminium substrate 10 in a continuous manner and to produce the composite product 1 in a continuous manner as is schematically shown in Fig. 3.

The method may further comprise cleaning (e.g. degreasing) the aluminium substrate 10 as an optional step while unwinding the first coil 50. The cleaning may serve to remove residues from the cold rolling process used to produce the aluminium substrate 10 such as cold rolling oil or the like. For example, if the first coil 50 has been previously cleaned or has been produced in a way that leaves no or only a little residue such as cold rolling oil on the sides of the aluminium substrate 10, the cleaning step may be omitted. The cleaning (e.g. degreasing) may for example be carried out by moving the aluminium substrate 10 through an optional cleaning bath 70 while unwinding the first coil 50. The cleaning bath may for example comprise a lipophilic substance, e.g. an alkaline substance, that dissolves cold rolling oil and thereby cleans the aluminium substrate 10.

The method according to the invention may further comprise pretreating the aluminium substrate 10 by moving the substrate through a pretreatment bath 80 while applying alternating current after (optionally) cleaning the aluminium substrate and while unwinding the first coil 50. The pretreatment bath 80 may for example contain an inorganic

electrolyte, e.g. an inorganic acid such as sulphuric acid, or a mixture of inorganic electrolytes. The pretreatment bath 80 may for example have an elevated temperature, e.g. 45° to 95°C.

During the pretreatment, the aluminium substrate 10 may be exposed to alternating current (AC). The pretreatment according to the invention may simultaneously comprise cleaning of the substrate 10, removal of a natural oxide layer from the first 1 1 and second 12 side of the substrate 10 by etching, and build-up/growth of a new alumina layer 10 having well-defined optical properties by exposing the substrate 10 to a pretreatment bath 80 with an inorganic electrolyte and alternating electric current. As the pretreatment has also a cleaning effect on the substrate 10 and may remove residues such as cold rolling oil, the previously described separate cleaning step using the optional cleaning bath 70 is an optional step of the method according to the invention. During the AC treatment, the substrate 10 may act as an electrode.

Good results have been achieved by using sulphuric acid having a concentration of 100 to 200 g/liter (gram per liter), for example 135 to 165 g/liter, and having a temperature of 50 to 90 °C (degree Celsius), e.g. 60 to 90 °C, as inorganic electrolyte and using a current density of up to 800 A/dm² (Ampere per square-decimeter), e.g. up to 200 A/dm² (Ampere per square-decimeter) for the alternating current when the substrate is exposed for 1 to 20 s (seconds), preferably 3 to 10 s, to the pretreatment in the pretreatment bath 80. It has been found that good results can be achieved when the temperature of the inorganic electrolyte in the pretreatment bath 80 is lower than the boiling point of the inorganic electrolyte. As mentioned, according to the invention, cleaning and pretreating can be carried out simultaneously during pretreatment, e.g. using only one bath, e.g. the pretreatment bath 80.

It has been found that chromating the aluminium substrate 10 may result in undesirable properties of the first side 1 1 of the aluminium substrate 10 as described above. Therefore, according to embodiments, optionally the method according to the invention may not comprise any chromating step, i.e. the method according to the invention may be free of any chromating, e.g. of any chromating of the substrate 10.

The method according to the invention may further comprise coating the first side 1 1 of the substrate 10 with a first coating 20 by applying a first coating solution on the first side 1 1 of the substrate 10, such that the first coating composition is in direct contact with the first side 1 1 of the aluminium substrate 10 after pretreating the aluminium substrate 10 while unwinding the first coil 50. The first coating composition may be applied e.g. by using coating rollers transferring the first coating solution from a reservoir to the first side 1 1 or by moving the first side 1 1 of the substrate 10 through a first coating bath 90 holding a first coating composition as exemplarily shown in Fig. 3. The first coating bath 90 and the reservoir may contain any of the first coating compositions mentioned above. The first coating composition may comprise at least one pigment 26. The coating of the first side 1 1 of the substrate 10 may for example be implemented by coil coating, e.g. by using a two- roll-configuration or by using a three-roll-configuration for the coating rollers. Particularly good surface properties may be achieved by using a three-rollers-double-reverse coil coating technique, although also other coil coating techniques may be applied according to the invention.

The method according to the invention may further comprise coating the second side 12 of the substrate 10 with a second coating 30 by applying a second coating solution to the second side 12 of the substrate 10 after pretreating the aluminium substrate 10 and while unwinding the first coil 50. The second coating composition may for example be applied by coating rollers transferring the second coating solution from a (second) reservoir or by moving the substrate 10 through a second coating bath 100 holding the second coating composition. In this respect, the coating of the second side 12 of the substrate 10 may be carried out before or after the coating of the first side 1 1 of the substrate 10. The second coating bath 100 and the (second) reservoir may hold any second coating composition described above. The coating of the second side 12 of the substrate 10 may for example be implemented by coil coating, e.g. by using a two-roll-configuration or by using a three- roll-configuration. Particularly good surface properties may be achieved by using a three- rollers-double-reverse coil coating technique, although also other coil coating techniques may be applied for coating the second side 12 of the substrate 10 according to the invention. While the first coating composition is directly applied on the first side 1 1 of the substrate 10, the second coating composition may optionally also be applied on one or more intermediate layers that, according to embodiments, may be provided between the second side 12 of the substrate 10 and the surface on which the second coating composition is applied. However, omission of any intermediate coating between the substrate 10 and the second coating 30 results in an efficient composite product 1 having excellent properties as described herein. The first and second coating compositions may be applied such that they, at least after posttreating, form the outermost layer of the composite product 1 on the first side 2 and second side 3, respectively, thereof.

The method according to the invention may further comprise posttreating the first 1 1 and the second 12 side of the substrate 10 after coating the first side 1 1 and the second side 12 of the substrate 10 by exposing the first 1 1 and second 12 side of the substrate 10 with the first and second, respectively, coating compositions thereon to air 1 10 having a temperature between 200°C and 600°C such that the aluminium substrate 10 reaches a peak metal temperature (PMT) between 220°C and 255°C, such as to produce the composite product 1 having a reflectance for a spectral portion of solar radiation having a wavelength of 700 nm to 2500 nm of 50% or more, optionally of 55% or more, optionally of 60% or more, optionally of 70% or more, while unwinding the first coil 50. According to the invention, the posttreatment is carried out so that the aluminium substrate 10 reaches a peak metal temperature (PMT) of between 220°C and 255°C. A PMT within that range results in durable first 20 and second coatings 30 that have good thermal and optical properties as outlined above. It has been found that lower or higher PMTs during posttreatment may lead to composite products 1 with undesirable properties. The posttreating may impart energy to the composite product 1 resulting in a curing reaction of the constituents of the first coating 20 and the second coating 30. Said posttreating may also involve a drying of the first 20 and second 30 coating.

The method according to the invention may optionally further comprise winding the composite product 1 on a second coil 60 after posttreatment to produce a second coil 60 of composite product 1 . However, this step is optional and may be omitted, e.g. when the composite product 1 is desired in a different form (e.g. as substantially planar sheet material) other than a second coil 60.

The method according to embodiments of the invention allows an efficient production of the composite product 1 according to embodiments of the invention. Any method step described herein may also describe a property of the composite product 1 and any property of the composite product 1 may be reflected in a method step. Further, any first coating described herein may be combined with any second coating described herein.

Claims

1 . Composite product (1 ) having a first side (2) and an opposite second side (3), the product (1 ) comprising:

an aluminium substrate (10) having a first side (1 1 ) corresponding to the first side

(2) of the product (1 ) and an opposite second side (12) corresponding to the second side

(3) of the product (1 ), wherein the aluminium substrate (10) comprises an, optionally cold rolled, aluminium sheet metal,

a first coating (20) directly provided on the first side (1 1 ) of the aluminum substrate (10) and in physical contact therewith, wherein the first coating (20) forms the outermost layer of the first side (2) of the composite product (1 ), wherein the first coating (20) comprises at least one pigment (26) embedded in a matrix material (25), and wherein the first coating (20) is a single-layer coating, and

a second coating (30) provided on the second side (12) of the aluminium substrate (10), wherein the second coating (30) forms the outermost layer of the second side (3) of the composite product (1 ),

wherein the composite product (1 ) is configured such that a spectral portion of solar radiation having a wavelength of 700 nm to 2500 nm is or can be incident on the first side of the aluminium substrate (10) and is or can be reflected by the first side (1 1 ) of the aluminum substrate (10), and

wherein the first side (2) of the composite product (1 ) has a reflectance for a spectral portion of solar radiation having a wavelength of 700 nm to 2500 nm of 50% or more, optionally of 60% or more, optionally of 70% or more.

2. Composite product (1 ) according to claim 1 , wherein the aluminium substrate (10) comprises AA3xxx and/or AA5xxx aluminium, in particular AA3003, AA3105, AA3005 and/or AA5005 series aluminium.

3. Composite product (1 ) according to claim 1 or 2, wherein the second side (3) of the composite product (1 ) has a thermal emissivity of 0.5 or less, optionally of 0.34 or less, optionally of 0.15 or less and wherein the second coating (30) has a thickness of 3.5 μηι or less, e.g. of 3.0 μηι or less.

4. Composite product (1 ) according to any preceding claim, wherein the first coating (20) is at least substantially free of dye.

5. Composite product (1 ) according to any preceding claim, wherein the pigment (26) is an organic pigment and the matrix material (25) comprises an organic polymer.

6. Composite product (1 ) according to any preceding claim, wherein the second coating (30) comprises a polymer, is at least substantially free of dye, free of pigment and has a thickness of equal to or more than 0.5 μηι and of less than 3.5 μηπ, optionally of less than 1 .50 μπι.

7. Composite product (1 ) according to any preceding claim, wherein the substrate (10) comprises an oxide layer directly grown on the second side (12) of the substrate (10) by anodizing the substrate in an organic acid such as tartaric acid or glutamic acid.

8. Composite product (1 ) according to any preceding claim, wherein the second coating (30) comprises a layer of silanes provided on alumina, the layer of silanes having a thickness of less than 5 nm, optionally less than 1 nm, the alumina optionally having a thickness between 30 nm and 3.5 μηι.

9. Composite product according to any of claims 1 to 7, wherein the second coating (30) comprises polysilazane in a layer having a thickness of less than 2 μηι, optionally less than 1 μηι.

10. Composite product according to any of claims 1 to 7, wherein the second coating (30) comprises a sol-gel coating comprising one or more types of nanoparticles selected from the group consisting of: ceria, zirconia, silica, alumina, tin oxide, yttria, zinc oxide.

1 1 . Composite product according to any preceding claim, wherein the first coating (10) has a thickness of equal to or more than 15 μηι and equal to or less than 35 μηι.

12. Composite product (1 ) according to any preceding claim, wherein the composite product (1 ) is configured such that, in the described order, solar radiation incident on the first side (2) of the composite product (1 ) can propagate through the first coating (20), can be incident on the first side (1 1 ) of the aluminium substrate (10), can be reflected by the first side (1 1 ) of the aluminium substrate (10) towards the first side (2) of the composite product (1 ), and can propagate through the first coating (20) towards the first side (2) of the composite product (1 ), and can exit the composite product (1 ) via the first side (2) of the composite product (1 ).

13. A building comprising the composite product (1 ) according to any preceding claim fixedly provided with the building, wherein the first side (2) of the composite product (1 ) is arranged such as to be exposed to direct sunlight and the second side (3) is arranged so as to be facing towards an interior of the building.

14. Method for continuously producing a composite product (1 ) having a first side (2) and an opposite second side (3), the method comprising

providing a first coil (50) of an aluminium substrate (10) having a first side (1 1 ) and a second side (12), wherein the aluminium substrate (10) is produced using cold rolling, unwinding the first coil of aluminium substrate (10),

optionally cleaning the aluminium substrate (10) while unwinding the first coil (50), pretreating the substrate (10) by moving the substrate (10) through a pretreatment bath (80) while applying an alternating electric current after optionally cleaning the aluminium substrate and while unwinding the first coil (50),

coating the first side (1 1 ) of the substrate (10) with a first coating (20) by applying a first coating composition to the first side (1 1 ) of the substrate (10) such that the first coating composition is in direct contact with the first side (1 1 ) of the aluminium substrate (10) after pretreating the aluminium substrate (10) and while unwinding the first coil (50), applying a second coating composition after pretreating the aluminium substrate (10) and while unwinding the first coil (50) directly or indirectly on the second side (12) of the aluminium substrate (10) such that the second coating composition is or is not, respectively, in direct contact with the second side (12) of the aluminum substrate (10), posttreating the first and the second (12) side of the substrate (10) after coating the first side (1 1 ) and the second side (12) of the substrate (10) by exposing the first (1 1 ) and second (12) side of the substrate (10) to air (1 10) having a temperature between 200°C and 600°C such that the aluminium substrate (10) reaches a peak metal temperature (PMT) between 220°C and 255 C such as to produce the composite product (1 ) having a reflectance for a spectral portion of solar radiation having a wavelength of 700 nm to 2500 nm of 50% or more, optionally of 60% or more, optionally of 70% or more while unwinding the first coil (50), and

optionally winding the composite product (1 ) into a second coil (60) to produce a second coil (60) of the composite product (1 ).

15. Method according to claim 14, wherein the pretreating comprises anodizing the first (1 1 ) and/or the second side (12) of the substrate (10) by moving the substrate (10) through an inorganic electrolyte in the pretreatment bath (80) while exposing the substrate (10) to the alternating electric current (AC) having a current density of up to 800 A/dm² , optionally of up to 200 A/dm², and wherein optionally the inorganic electrolyte has a temperature of 60°C to 90°C.

1 6. Method according to claim 14 or 15, wherein the composite product (1 ) is the composite product (1 ) according to any of claim 1 to 1 1 .