Thermally stable silver layer for a viewing pane
Patent Information
- Application Number
- PCT/EP2026/060612
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2025-04-15
- Filing Date
- 2026-04-13
- Publication Date
- 2026-10-22
Smart Images
Figure EP2026060612_22102026_PF_FP_ABST
Abstract
Description
[0001] Thermally stable silver layer for a viewing window
[0002] Description
[0003] The invention relates generally to a viewing window with an infrared-reflective coating. In particular, the invention relates to a viewing window with an infrared-reflective coating for a fireplace or an oven.
[0004] Thermally resistant glass or glass-ceramic panes are generally used to thermally insulate a heated room from its surroundings while simultaneously providing a viewing window into the room. Such panes are particularly common in fireplaces, ovens, and as fire-resistant glazing. The thermal insulation is achieved through (partial) reflection of the infrared radiation emitted by the heat source. For the purposes of this disclosure, the terms "infrared" and "infrared radiation" are abbreviated as "IR".
[0005] For example, DE 102017102377 A1 discloses a thermal protective glazing for a fireplace or oven. This discloses a glass or glass-ceramic pane with an IR-reflective coating, the coating comprising a first and a second layer. The first layer consists of a doped transparent conductive zinc oxide, and the second layer is an X-ray amorphous aluminum-containing oxide layer. Since the thermal and chemical properties of zinc and aluminum are insufficient, these layers are further provided with an inner (i.e., facing the glass pane) and an outer (i.e., facing the atmosphere) barrier coating.
[0006] Furthermore, IR-reflective systems based on thin silver or gold coatings are known, so-called "low-E glass" (low-E for "low emissivity"). A glass with such a coating is known, for example, from DE 102006 050 113 A1. However, to withstand the environmental stresses that occur, for example, during continuous use as window glazing, low-E glass must be protected by a complex laminated glass system. This laminated glass system typically includes an inert gas (e.g., argon). Laminated glass systems are used, among other things, in architecture.
[0007] The invention is based on the objective of providing a viewing window for a fireplace or stove environment which has a thermally and chemically resistant IR-reflecting coating, wherein the coating is to be realized via the simplest possible layer structure.
[0008] The invention is specified in detail by the independent claims. Advantageous embodiments and further developments of the invention are the subject of the dependent claims.
[0009] To solve the problem, a viewing window for a fireplace or oven environment is provided, wherein the viewing window comprises a substrate and a coating arranged at least partially on the substrate. The coating consists of at least two embedding layers and at least one IR reflective layer, wherein the IR reflective layer borders at least one embedding layer, such that an interface region between the IR reflective layer and the embedding layer, as well as an interior region of the IR reflective layer, is formed, the interior region adjoining the interface region. The IR reflective layer comprises silver and at least one dopant, wherein the dopant contains silicon, aluminum, titanium, and / or zinc. For the purposes of this disclosure, the aforementioned material names also include the respective stoichiometric and non-stoichiometric oxide compounds of the materials.Furthermore, the aforementioned substances can also be present in compounds with one another (e.g., SiAl). The viewing window is characterized by the fact that the concentration of the dopant is higher in at least one interface region than in the interior of the IR reflection layer.
[0010] A disc designed in this way is particularly well-suited for use as a viewing window for fireplaces or ovens, as it exhibits high reflectivity, especially in the wavelength ranges of the predominant radiation (IR radiation). The silver present in the IR reflective layer is stabilized by one or more dopants. The silver is preferably part of a silver-based alloy that is applied to the substrate and then doped with the at least one dopant. The metals or semimetals silicon, aluminum, titanium, and zinc, as well as their oxides, have proven to be particularly suitable dopants. The stabilization of the silver in the IR reflective layer is achieved by embedding it in thin protective layers formed by the dopants, resulting in a core-shell effect at the molecular level.The dopant acts as a trap for diffusing substances (so-called "getters"), such as oxygen, thus preventing a reaction between the silver and the diffusing substance. This prevents corrosion of the silver.
[0011] With the described coating, reflections of over 80% or even over 90% can be achieved, particularly in the short-wavelength IR range (wavelengths between 2.5 pm and 10 pm), despite doping. Simultaneously, a plasma wavelength range between 750 nm and 3,000 nm is achieved, with the plasma wavelength preferably being between 800 nm and 2,500 nm, and particularly preferably between 800 nm and 2,000 nm. The plasma wavelength is defined as the inflection point of the reflection slope in the near-infrared range, i.e., the maximum slope of the edge of the reflection curve.
[0012] According to a further embodiment, the doping amount of the at least one additional dopant should be at least 0.1% (mass percent) and at most 50%, based on the total amount of the metallic and semiconducting components. The total amount of the metallic and semiconducting components is understood to be the sum of the silver and the additional dopant. Preferably, the doping amount should be at least 0.2% and at most 10%. According to a particularly preferred embodiment, the doping amount should be at least 0.5% and at most 2%. It has been found that the IR-reflective properties of the silver can be ensured with such low doping amounts of the at least one additional dopant. Doping amounts above the particularly preferred range can negatively affect the IR-reflective properties of the silver.
[0013] According to a further embodiment, the substrate can be a glass and / or glass-ceramic substrate, wherein the substrate is particularly transparent in the visible spectral range. Such a substrate is especially well suited for protective glazing of heated rooms such as fireplaces, chimneys, or ovens. Possible glass substrates include, for example, borosilicate glass, soda-lime glass, aluminosilicate glass, LAS glass (glass consisting of lithium oxide, aluminum oxide, and silicon dioxide), glass-ceramic, blue glass, phosphate glass, or filter glass.
[0014] The substrate has two opposing surfaces, with the coating applied to at least one of these surfaces. The coating is applied at least partially, but preferably over the entire surface of the respective surface of the substrate. It is also conceivable that both surfaces of the substrate are coated, either partially or over the entire surface.
[0015] According to a further embodiment, the dopant may comprise silicon, wherein the dopant is in particular Si or SiO. x (Silicon oxide). SiO xIn this disclosure, the term "silicon oxide" is used as a collective term for stoichiometric and non-stoichiometric silicon oxide, unless otherwise indicated by the context. The same applies to the oxides of the other substances disclosed. The use of silicon as a dopant has proven to be particularly stabilizing for the silver present in the IR reflection layer.
[0016] According to a further embodiment, the embedding layers may comprise at least one material selected from the group consisting of silicon, aluminum, zinc, boron, titanium, hafnium, zirconium, copper, and yttrium, as well as their oxides, nitrides, and oxynitrides. For example, the embedding layers may be aluminum-doped zinc oxide. The at least one embedding layer preferably has a crystalline structure. Such an embedding layer prevents alkali diffusion from the substrate into the IR reflector layer, even under extreme thermal conditions. Furthermore, the aforementioned materials protect against atmospheric oxidation of the IR reflector layer. In addition, the embedding layers may comprise nickel and / or chromium, or nickel oxides and / or chromium oxides. Nickel and chromium oxidize at high temperatures earlier than silver.This allows the embedding layers to act as a kind of sacrificial layer and protect the IR reflection layer from unwanted corrosion.
[0017] According to a further embodiment, the IR reflection layer can be arranged between a first embedding layer and a second embedding layer, wherein a first interface region is formed between the IR reflection layer and the first embedding layer, and wherein a second interface region is formed between the IR reflection layer and the second embedding layer. Advantageously, the first embedding layer is the layer that is deposited directly onto the substrate. The first embedding layer should, in particular, consist of Al₂O₃ (aluminum oxide), SiN₂ (silicon nitride), or SiO₂. x and / or ZrO xThese materials are particularly well-suited for application to glass or glass-ceramics. Furthermore, it may be possible for at least one of the embedding layers to act as an electrical insulator – which would also indicate that the respective layer was deposited stoichiometrically and has tightly bound the oxygen.
[0018] According to a further embodiment, the maximum concentration of the dopant in at least one of the interface regions can be twice as high as the maximum concentration of the dopant in the interior region of the IR reflection layer. This ratio is achieved with the preferred parameters.
[0019] According to a further embodiment, the coating may also include a top layer, wherein the top layer has a thickness of at most 20 nm, preferably at most 10 nm. The thickness of the top layer is specifically designed to achieve planarization of the coating by filling depressions that may occur due to island growth, insufficient compaction, or other defects in the individual layers of the coating. A further functional aspect is the formation of a lubricating film when the top layer comes into contact with moisture (for example, at room temperature, high humidity, or in aqueous environments). The top layer should be a metal oxide (M) capable of forming a non-adhesive hydrated film consisting of M-OH. The metal oxide may, in particular, comprise titanium, zirconium, hafnium, or niobium.The top layer can also comprise two or more of the aforementioned metal oxides. Alternatively, the top layer can comprise fluorine and / or chlorine and be based on organic silicon.
[0020] According to a further embodiment, the ratio of the dopant to silver in the interface area is 0.002 to 1 atomic % and in the interior area is 0.001 to 0.5 atomic %.
[0021] According to a further embodiment, the coefficient of thermal expansion (CTE) of the IR reflective layer can be lower in at least one interface region than in the interior region of the IR reflective layer. This is because silver has a higher CTE than the dopants used in this invention. Since the concentration of the dopant is higher in the interface region than in the interior region of the IR reflective layer – in other words, there is less silver relative to the dopant in the interface region – the interface region exhibits a lower CTE than the interior region of the IR reflective layer, where a higher silver concentration is present.According to a further embodiment, it can be provided that the GTE of the embedding layer adjacent to the IR reflection layer is smaller than the GTE of the at least one interface region of the IR reflection layer, and that the GTE of the interior region of the IR reflection layer is larger than the GTE of the at least one interface region of the IR reflection layer.
[0022] According to another embodiment, it can be provided that the GTE of the embedding layer adjacent to the substrate is smaller than the GTE of the substrate.
[0023] According to another embodiment, it can be provided that the GTE of any two adjacent embedding layers differ from each other by a maximum of 300%.
[0024] According to a further embodiment, the embedding layers can each have a thickness of 5 nm to 300 nm and / or the IR-reflecting layer can have a thickness of 5 nm to 30 nm. Layers of such thickness ensure optimal IR reflection without leading to an unwanted transmission loss of the viewing window. The transmission of the viewing window for visible light should preferably be above 50%.
[0025] According to a further embodiment, at least one embedding layer can be located between the glass or glass-ceramic substrate and the IR-reflecting layer, preferably exactly one embedding layer being located between the substrate and the IR-reflecting layer. The embedding layer advantageously prevents alkali diffusion from the substrate into the IR-reflecting layer. Furthermore, it can act as an adhesion promoter between the substrate and the IR-reflecting layer, or as an optical matching layer. An optical matching layer ensures that not too much light in the visible spectrum is reflected – it is thus a kind of anti-reflective layer. The Ag layer alone already reflects relatively strongly in the visible range. This reflection is reduced by the layer system according to the invention and, in particular, by an additional matching layer.
[0026] According to a further embodiment, the viewing window can be provided with an IR reflectance of more than 20%, preferably more than 30%, from a wavelength of 900 nm. The advantageous reflectance results from the material properties of the silver.
[0027] According to a further embodiment, the viewing window can have an average transmittance of more than 40%, preferably more than 50%, and particularly preferably more than 70% in the visible light range. The transmittance can be adjusted, for example, by the thickness of the IR reflection layer, i.e., the silver-containing layer.
[0028] According to a further embodiment, the IR-reflecting layer can be designed for a continuous operating temperature of more than 300°C, preferably more than 400°C, particularly preferably more than 500°C for more than 1 h.
[0029] According to a further embodiment, the IR reflective layer can have a reflection maximum in the range of 1,500 to 3,000 nm, preferably in the range of 2,000 to 2,500 nm, which differs by a maximum of 20% from the reflection maximum of the range of 1,000 to 20,000 nm. The high temperature stability of the coating according to the invention makes it possible to carry out subsequent treatment steps at high temperatures during the production of the glazing after the application of the IR-reflective coating. Thus, according to a further embodiment, a thermally or chemically tempered glass pane can be used. Thermal tempering can also be carried out after the deposition of the IR-reflective coating without impairing the coating.
[0030] According to a further embodiment, the surface resistance of the IR reflective layer can be in the range of 1 to 100 ohms / sqr (ohms per unit area), with the surface resistance of the IR reflective layer preferably being in the range of 2 to 20 ohms / sqr and particularly preferably in the range of 3 to 8 ohms / sqr. Furthermore, the surface resistance of the entire coating, i.e., the at least one IR reflective layer and the at least two embedding layers, can be in the range of 1 to 100 ohms / sqr, with the surface resistance of the entire coating preferably being in the range of 3 to 8 ohms / sqr. The surface resistance can be measured, for example, using an inductive surface resistance meter. Surface resistance and IR reflection are essentially inversely proportional to each other; that is, the lower the surface resistance, the higher the reflection in the IR range.Consequently, the coating should have the lowest possible surface resistance - after all, a disc coated according to the invention should be characterized by high IR reflection.
[0031] The invention is described in more detail below with reference to the figures and examples.
[0032] Table 1 below provides an overview of various embodiments, each differing in terms of the dopant used and the doping angle applied. The doping angle is defined as the angle at which the dopant is oriented towards the substrate in a co-sputtering setup, specifically in the form of the magnetron. The higher the angle, the more dopant is deposited into the layer. The experimental coatings comprised a first embedding layer (ZnO:Al 40 nm), a second embedding layer (ZnO:Al 40 nm), and an IR reflectance layer (Ag:X 12.5 nm, where X is the dopant under investigation) positioned between the embedding layers.
[0033] Table 1:
[0034] Dopant Surface resistivity FW after FW after Transmission Haze X angle [°] (FW) [R / sqr] 300°C / 100h 400°C / 100h [%]
[0035] undoped - 3.91 4.18 48.54 73.9 0.45 Si:Al (90:10 30 6.15 3.68 4.02 83.2 0.14 wt-%)
[0036] Si:Al (50:50 60 29.12 15.06 50 65.9 0.12 wt%)
[0037] Ti 20 5.2 4.59 5.82 86.1 0.12 Si 30 7.8 5.3 5.06 86.3 0.09 AI 70 22.21 9.23 10 75.4 0.12
[0038]
[0039] Fig. 1 shows a schematic cross-section through a viewing window according to a first embodiment.
[0040] Fig. 2 shows a schematic cross-section through a viewing window according to a further embodiment.
[0041] Fig. 3 shows a schematic cross-section through a viewing window according to a further embodiment. Fig. 4 shows a reflectivity diagram for two different coatings in the infrared spectral range.
[0042] Fig. 1 shows a schematic cross-section through a viewing window 1 according to one possible embodiment. The viewing window 1 shown by way of example comprises a glass or glass-ceramic substrate 2 with a coating 3 applied to the substrate 2. The coating 3 consists of an IR-reflective layer 5 and two embedding layers 4, 4', wherein the IR-reflective layer 5 is arranged between the two embedding layers 4, 4'. Consequently, one of the embedding layers 4' is applied directly to one of the surfaces of the substrate 2, while the other embedding layer 4 encloses the coating 3 on the outside and is therefore in contact with the atmosphere.The IR reflection layer 5 arranged between the embedding layers 4, 4' can be divided into three regions: two interface regions 6, 6', each of which borders one of the embedding layers 4, 4', and an inner region 7 arranged between the interface regions 6, 6'. The transitions from the inner region 7 to the interface regions 6, 6' are shown as a clear boundary in Fig. 1; however, the individual regions preferably merge gradually into one another.
[0043] According to the invention, the IR reflection layer 5 comprises silver (not shown) and at least one dopant (also not shown) containing silicon, aluminum, titanium and / or zinc, or an oxide or nitride of the aforementioned metals or metalloids. The coating 3 of the viewing window 1 is characterized in particular by the fact that the concentration of the dopant is higher in the interface regions 6, 6' than in the inner region 7 of the IR reflection layer 5.
[0044] The disc 1 shown in Fig. 1 is particularly well suited for use as a fireplace or oven viewing window, as it primarily reflects radiation from the IR spectral range, while at the same time having a high transmission for radiation from the visible spectral range.
[0045] Fig. 2 shows a schematic cross-section through a viewing window 1 according to a further embodiment. The example shown in Fig. 2 differs primarily from the example in Fig. 1 in that the coating 3 of the embodiment in Fig. 2 has a third embedding layer 4" arranged on the surface of the substrate 2. Consequently, according to the example in Fig. 2, two embedding layers 4' and 4" are arranged between the substrate 2 and the IR reflective layer 5. Towards the ambient atmosphere 8, the coating 3 terminates with only one embedding layer 4, as in the example in Fig. 1. Providing a third embedding layer 4" has the advantage that the third embedding layer 4" can act as an adhesion promoter between the substrate 2 and the IR reflective layer 5 or the second embedding layer 4'.The second embedding layer 4', however, can additionally serve as a seed layer for the IR reflection layer 5 or as an optical matching layer. Silver layers do not grow equally well on every substrate. The less exchange with other layers is allowed, the better and more stable the resulting system. Against this background, it is advantageous to provide an additional embedding layer 4".
[0046] Fig. 3 shows a schematic cross-section through a viewing window 1 according to a further embodiment. The example shown in Fig. 3 differs primarily from the examples in Fig. 1 and Fig. 2 in that the coating 3 of the embodiment shown in Fig. 3 has a fourth embedding layer 4'', which is applied as the outermost layer facing the ambient atmosphere 8. Thus, the IR reflection layer 5 is enclosed on both sides, i.e., towards the substrate 2 and towards the atmosphere 8, by two embedding layers 4, 4', 4", 4''' each. The provision of a fourth embedding layer 4''' serves as an additional barrier to the atmosphere 8. Finally, due to the properties of the silver in the IR reflection layer 5, it can be advantageous to first apply the first embedding layer 4 to the IR reflection layer 5 so that it can directly influence the silver.Following this, the fourth embedding layer 4'" can be applied as the actual barrier to the atmosphere 8. Furthermore, another embedding layer can also be used as an optical matching layer.
[0047] Fig. 4 shows a reflectivity diagram for two different coatings in the IR spectral range, one of which is a coating 3 of the viewing window 1 according to the invention. The diagram plots the reflectance (y-axis) as a function of the radiation wavelength (x-axis). Curve A shows the values of coating 3 of a viewing window 1 according to the invention, and curve B shows those of a TCO-based coating (TCO stands for "transparent conductive oxide"). The TCO-based layer can, for example, comprise ITO or SnÜ2:F. Additionally, TCO coatings must be protected from the external environment by at least one barrier, which is why interferences such as those shown can occur. The diagram impressively demonstrates that the coating 3 according to the invention already reflects over 60% of the IR radiation from wavelengths of approximately 800 nm (see curve A). Thus, high reflectance values of approximately 90% are already achieved from about 2,000 nm (i.e., approximately 90% of the IR radiation is reflected).90% of the IR radiation is reflected by coating 3). This high value is still achieved even at wavelengths above 9,300 nm. In contrast, the IR-reflective effect of the TCO-based coating only begins at approximately 1,300 nm, and in the example shown, it initially decreases at wavelengths around 2,500 nm before slowly increasing again from 2,200 nm onwards. The increase or decrease in the IR reflection of the TCO layer can result, for example, from the thickness of the barrier coating. However, the IR reflection of the TCO-based coating does not exceed 85% in any wavelength range. TCO layers are generally suitable for use in hot environments and are still used for this purpose today, but with the disadvantage of reduced reflectivity. Reference numeral list.
[0048] 1 viewing window
[0049] 2 Substrat
[0050] 3 coating
[0051] 4 Embedding layer
[0052] 5 IR reflection layer
[0053] 6 Interface area
[0054] 7 Indoor area
[0055] 8 Atmosphere
[0056] A Doped Ag coating
[0057] B TCO-based coating
Claims
Claims 1. Viewing screen (1) comprising a substrate (2) and a coating (3) arranged at least partially on the substrate (2), the coating comprising at least two embedding layers (4) and an IR reflection layer (5), wherein the IR reflection layer (5) borders at least one of the embedding layers (4), such that an interface region (6) exists between the IR reflection layer (5) and the embedding layer (4), as well as an interior region (7) of the IR reflection layer (5), wherein the IR reflection layer (5) comprises silver and at least one further dopant, and wherein the dopant comprises silicon, aluminum, titanium, and / or zinc, characterized in that the concentration of the dopant in the at least one interface region (6) is higher than in the interior region (7) of the IR reflection layer (5).
2. Viewing screen (1) according to claim 1, characterized in that the substrate (2) is a glass and / or glass-ceramic substrate (2).
3. Viewing window (1) according to one of claims 1 or 2, characterized in that the dopant is silicon oxide or silicon monoxide.
4. Viewing screen (1) according to one of the preceding claims, characterized in that the IR reflection layer (5) is arranged between a first embedding layer (4) and a second embedding layer (4), wherein a first interface region (6) is formed between the IR reflection layer (5) and the first embedding layer (4) and wherein a second interface region (6) is formed between the IR reflection layer (5) and the second embedding layer (4).
5. Viewing screen (1) according to claim 4, characterized in that the maximum concentration of the dopant in at least one of the interface regions (6) is twice as large as the maximum concentration of the dopant in the interior region (7) of the IR reflection layer (5).
6. Viewing window (1) according to one of claims 4 or 5, characterized in that the ratio of the dopant to silver in the interface region (6) is 1 to 0.002 atomic % and in the inner region (7) is 0.5 to 0.001 atomic %.
7. Viewing window (1) according to one of claims 4 to 6, characterized in that the GTE of the IR reflection layer (5) in the at least one interface region (6) is lower than in the inner region (7) of the IR reflection layer (5).
8. Viewing screen (1) according to one of claims 4 to 7, characterized in that the GTE of the embedding layer (4) adjacent to the IR reflection layer (5) is smaller than the GTE of the at least one interface region (6) of the IR reflection layer (5).
9. Viewing screen (1) according to one of claims 4 to 8, characterized in that the GTE of the embedding layer (4) adjacent to the substrate (2) is smaller than the GTE of the substrate (2).
10. Viewing screen (1) according to one of claims 4 to 9, characterized in that the GTE of each two adjacent embedding layers (4) differ from each other by a maximum of 300%.
11. Viewing window (1) according to one of the preceding claims, characterized in that the at least one embedding layer (4) comprises at least one material selected from the group comprising silicon, aluminium, zinc, boron, titanium, hafnium, zirconium and yttrium as well as their oxides, nitrides and oxynitrides.
72. Viewing screen (1) according to one of the preceding claims, characterized in that the at least one embedding layer (4) has a thickness of 5 nm to 300 nm and / or that the IR-reflecting layer has a thickness of 5 nm to 30 nm.
13. Viewing screen (1) according to one of the preceding claims, characterized in that at least one embedding layer (4) is located between the substrate (2) and the IR reflection layer (3), wherein exactly one embedding layer (4) is located between the substrate (2) and the IR reflection layer (5).
14. Viewing screen (1) according to one of the preceding claims, characterized in that the viewing screen (1) has an IR reflectance of at least 20%, preferably at least 30%, at a wavelength of 900 to 1,200 nm.
15. Viewing window (1) according to one of the preceding claims, characterized in that the viewing window (1) has an average transmittance of at least 40%, preferably more than 50% and particularly preferably at least 70% in the visible light range.
16. Viewing screen (1) according to one of the preceding claims, characterized in that the IR-reflecting layer already has a reflection maximum in the range of 1,500 to 3,000 nm, preferably already in the range of 2,000 to 2,500 nm, which deviates by a maximum of 20% from the reflection maximum of the range 1,000 to 20,000 nm.
17. Use of the viewing window (1) according to one of the preceding claims as a fireplace viewing window or as an oven viewing window. 15