An improved high reflectivity mirror coating

Abstract

The present application relates to an improved high-reflective mirror coating, comprising a high-refractive layer, a low-refractive layer, an auxiliary layer and at least one composite layer arranged in sequence, the auxiliary layer is used for diffusion barrier and adhesion promotion of high-reflective metal material. The high-reflective mirror coating is coated on the plating surface of a metal substrate. The composite layer is located between the auxiliary layer and the metal substrate. The composite layer comprises a silver coating, an ultrathin coating, an intermediate layer and an aluminum coating arranged in sequence, the intermediate layer is made of zinc oxide or metal-doped zinc oxide, and the ultrathin coating is made of chromium, chromium alloy, nickel, nickel alloy and / or nickel-chromium alloy. When there are at least two composite layers, the composite layers are arranged in sequence. Through the above structure, the high-reflective mirror coating is more economical in cost, has the highest reflectivity, is stable at high temperatures up to 180 DEG C or even higher, and is stable in a humid environment.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of light reflecting coatings, and in particular to an improved high reflectance mirror coating. BACKGROUND

[0002] High reflectance mirror coatings, especially those with very high reflectance in the wavelength range from 400 nm to 2500 nm, are widely used in lighting engineering, equipment applications (such as: flashlights, projectors, solar energy collection and decorative applications), and emerging market requirements are applications in the field of concentrated solar power (CSP) and as back reflectors for LEDs in MC-COB modules.

[0003] The widely used high reflectance mirror coatings are prepared by depositing a high reflectance metal coating (such as aluminum or silver; among which the reflectance of silver is the highest among all metals in the wavelength range of interest) on a metal substrate, and then combining it with low refractive index layers, high refractive index layers, etc. However, the high reflectance mirror coating of this structure, especially the structure with silver as the high reflectance metal, often has difficulty in balancing product cost control and its high temperature resistance, corrosion resistance (such as in a humid environment), etc. For example, a coating system with high durability and its preparation method disclosed in patent US6078425, 2000, a thin nickel chromium nitride ((NiCr x )N y ) layer below the silver film layer makes the overall high temperature stability only general, especially if a substrate surface that is smooth enough and free of any defects cannot be achieved, which is foreseeable in a large-area coating system used for mass production; and in the improved scheme disclosed in patent US20060141272, 2006, a thick tungsten (W) film layer is used to avoid galvanic corrosion between the silver film layer and the aluminum substrate through pinhole defects, but the stability information in high temperature applications is still missing, and from the cost point of view, the additional tungsten layer greatly increases the cost of the coating. For example, the vacuum coating scheme disclosed in patent CN101379218B is also only suitable for good environmental conditions, and its durability is poor in high temperature (such as up to 180℃ or even 200℃) and more severe (such as humid) environments.

[0004] To maintain stability under high temperature conditions, both patents CN106796312B and CN108351442B suggest setting and implementing a diffusion barrier layer between the substrate and the adhesion layer below the silver film layer. The function of the proposed diffusion barrier layer is to provide additional inhibition of intermetallic diffusion between the aluminum-based substrate and the silver film layer. But as estimated from the information disclosed in their patent documents, they both require a low production rate or high investment cost for the plating equipment. The applicant has considered a feasible method to reduce operating costs and ensure productivity in patent application CN110908027A. However, further cost and material reduction is the expected direction, and lower costs can improve the market positioning of the product. SUMMARY

[0005] The present application provides an improved high-reflective mirror coating to solve the above problems.

[0006] The present application adopts the following technical solutions:

[0007] An improved high-reflective mirror coating, comprising a high refractive index layer, a low refractive index layer, an auxiliary layer, and at least one composite layer arranged in sequence, the auxiliary layer being used for diffusion barrier and adhesion promotion of high-reflective metal materials. The high-reflective mirror coating is coated on the plating surface of a metal substrate. The composite layer is located between the auxiliary layer and the metal substrate. The composite layer comprises a silver coating, an ultra-thin coating, an intermediate layer, and an aluminum coating arranged in sequence. The intermediate layer is made of zinc oxide or metal-doped zinc oxide. The ultra-thin coating is made of chromium, chromium alloy, nickel, nickel alloy, and / or nickel-chromium alloy. When there are at least two composite layers, the composite layers are arranged in sequence.

[0008] Further:

[0009] The silver coating is formed by magnetron sputtering deposition. When there is one composite layer, the thickness of the silver coating is ≤50 nm. When there are at least two composite layers, the thickness of the silver coating is <40 nm.

[0010] The aluminum coating is formed by magnetron sputtering deposition. When there is one composite layer, the thickness of the aluminum coating is ≤50 nm. When there are at least two composite layers, the thickness of the aluminum coating is <50 nm.

[0011] The intermediate layer is made of aluminum-doped zinc oxide.

[0012] The intermediate layer is formed by magnetron sputtering deposition, and the thickness of the intermediate layer is 3-30 nm. The thickness of the ultra-thin coating is 1-5 nm.

[0013] The thickness of the ultra-thin coating is 2.5 nm.

[0014] Further:

[0015] The metal substrate is provided with a surface treatment layer on the plating film surface, the composite layer is arranged on the surface treatment layer, the auxiliary layer is arranged on the composite layer, the low-refractive index layer is arranged on the auxiliary layer, and the high-refractive index layer is arranged on the low-refractive index layer. The surface treatment layer is an anodized layer, a varnish coating layer, or a highly polished layer.

[0016] The metal substrate is made of aluminum or aluminum alloy, and the surface treatment layer is an anodized aluminum film layer. The metal substrate is a metal strip or a metal sheet with a thickness of 0.1 mm to 1.5 mm and a width of 500 mm to 1500 mm.

[0017] The auxiliary layer is made of metal silicon nitride (Me:Si)N X The compound is made of metal or metal alloy, the ratio between Me and Si is represented by (Me:Si), the index X represents the reaction coefficient of nitrogen element N, and Me is Ti, Cr, NiCr, or NiV. The thickness of the auxiliary layer is 0.5 nm to 20 nm.

[0018] The thickness of the auxiliary layer is 2 nm to 5 nm.

[0019] The low-refractive index layer is made of silicon oxide or silicon aluminum oxide, the low-refractive index layer is formed by electron beam evaporation deposition, and the thickness of the low-refractive index layer is 40 nm to 100 nm. The high-refractive index layer is made of titanium oxide, the high-refractive index layer is formed by electron beam evaporation deposition, and the thickness of the high-refractive index layer is 30 nm to 90 nm.

[0020] As can be seen from the description of the present application, compared with the prior art, the present application has the following advantages:

[0021] The present application replaces the structure of the "first auxiliary film layer" and "high-reflection silver film layer" in the prior art CN110908027A document by the composite layer of the aluminum-silver composite film structure, that is, the aluminum-silver composite film structure is introduced instead of using a relatively thick pure silver layer, which helps to significantly reduce the cost.

[0022] Furthermore, in at least one composite layer structure, there is an aluminum bottom coating and a thin silver top coating, with a zinc oxide layer or a metal-doped zinc oxide layer (such as an aluminum-doped zinc oxide layer) in between. An ultrathin chromium or chromium alloy, nickel or nickel alloy, or nickel-chromium alloy layer is placed at the interface between the zinc oxide or metal-doped zinc oxide and the silver coating for isolation. This aluminum-silver composite film structure defines a substructure that can be used not only alone (i.e., with only one composite layer) but also repeatedly (i.e., with at least two composite layers), offering greater flexibility in performance adjustment and cost control. The zinc oxide or metal-doped zinc oxide isolation layer between the aluminum and silver inhibits intermetallic diffusion. Placing the ultrathin chromium or chromium alloy, nickel or nickel alloy, or nickel-chromium alloy layer at the interface between the zinc oxide or metal-doped zinc oxide and the silver coating improves durability, i.e., adhesion in humid environments.

[0023] When combined with auxiliary layers, low-refractive-index layers, and high-refractive-index layers on the composite layer, a high-reflectivity mirror coating structure is formed that is more economical in cost, has the highest reflectivity, is stable at high temperatures of up to 180°C or even higher, and is stable in humid environments. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of the high-reflectivity mirror coating of the present invention.

[0025] Figure 2 This is a schematic diagram of the structure of a single composite layer of the present invention.

[0026] Figure 3 This is a schematic diagram of the structure of the n composite layers of the present invention.

[0027] Figure 4 This is an example diagram illustrating the adjustment of silver coating thickness based on reflection output contrast in this invention. Detailed Implementation

[0028] The specific embodiments of the present invention will now be described with reference to the accompanying drawings.

[0029] refer to Figure 1 An improved high-reflectivity mirror coating is disclosed, wherein the improved high-reflectivity mirror coating is applied to the coating surface of a metal substrate S0. This specific embodiment is illustrated with a structure in which one side of the metal substrate S0 is the coating surface and the other side is the back surface. Figure 1The high reflectance mirror coating is deposited on one side of the metal substrate S0, which is the coated side. The other side, which is opposite to the coated side, is the back side. The metal substrate S0 is preferably made of aluminum or an aluminum alloy. The metal substrate S0 is preferably in the form of a metal strip or sheet having a thickness of 0.1 mm to 1.5 mm, a width of 500 mm to 1500 mm and a length of at least 10 cm for a sheet and up to several kilometers for a coiled metal strip.

[0030] With reference to the drawings Figure 1 The coated side of the metal substrate S0 comprises in order from the metal substrate S0 a surface treatment layer SF, at least one composite layer L10, an auxiliary layer L20, a low refractive index layer L30 and a high refractive index layer L40. The surface treatment layer SF serves to smooth the surface and / or to increase the hardness of the surface. For example, the metal substrate S0 is made of aluminum or an aluminum alloy and the surface treatment layer SF is an anodized aluminum layer. Of course, the surface treatment layer SF can also be prepared by applying a clear coat or a paint or even consist of a highly polished metal surface only. Above the surface treatment layer SF is the composite layer L10 of the aluminum-silver composite film structure.

[0031] With reference to the drawings Figure 1 , Figure 2 , Figure 3 The composite layer L10 comprises in order a silver coating L14, an ultra-thin coating L13, an intermediate layer L12 and an aluminum coating L11. The intermediate layer L12 is made of zinc oxide or metal-doped zinc oxide and the ultra-thin coating L13 is made of chromium, a chromium alloy, nickel, a nickel alloy and / or a nickel-chromium alloy. For the same composite layer L10 structure, the aluminum coating L11 is at the bottom and the silver coating L14 is at the top. When there are at least two composite layers L10, the composite layers L10 are arranged one on top of the other. Thus, the composite layer L10 of the aluminum-silver composite film structure defines a substructure which can be applied in multiple layers. Specifically, Figure 2 Fig. 1 shows a structure with a single composite layer L10, and Figure 3 Fig. 2 shows a structure with n composite layers L10, Figure 3 The -1, -2 and -n in the reference numerals in Figs. 1 and 2 indicate the repetition of the respective coatings of each composite layer L10, i.e. the repetition of the 1, 2 to n substructures. Specifically,

[0032] The aluminum coating L11 is deposited by magnetron sputtering and has a thickness of up to 50 nm if there is only one composite layer L10. If there are several composite layers L10, the skilled person knows how to adjust the thickness of the aluminum coating L11 to below 50 nm in order to achieve the maximum reflection output.

[0033] The zinc oxide (ZnO) layer or metal-doped zinc oxide barrier layer of the intermediate layer L12 has the effect of inhibiting intermetallic diffusion. The intermediate layer L12 is prepared by magnetron sputtering and can have a thickness of 3 nm to 30 nm, depending on the production efficiency of the coating and the number of composite layers L10. The preferred intermediate layer L12 is aluminum-doped zinc oxide (AZO). Studies have shown that the diffusion coefficient of aluminum-doped zinc oxide (AZO, 3 wt%) can be as low as 5.0E-21 or lower. For comparison, the diffusion coefficient of silicon nitride (SiNx) can be 5.5E-20 or lower. Silicon nitride is a commonly used diffusion barrier material.

[0034] The chromium (Cr) or chromium alloy, nickel (Ni) or nickel alloy, or nickel-chromium alloy (NiCr) layer of the ultra-thin coating L13 described above is placed at the interface between the intermediate layer L12 and the silver coating L14 to improve durability, i.e. adhesion in a humid environment. The coating is deposited using magnetron sputtering or other vacuum deposition techniques and has a thickness of 1 nm to 5 nm, with an optimum thickness of about 2.5 nm. A key problem with PVD coatings is that so-called pinholes can be present in the coating. These pinholes can still act as a conductive path for moisture. Depending on the size and density of the pinholes, these size defects can deteriorate over time when exposed to extreme humidity. This effect is widely explained as lateral migration of silver atoms. It is further understood that water, such as from a humid environment, can adhere to the surface of the zinc oxide, weakening the adhesion to the silver. By applying a metal interface between the zinc oxide and the silver coating L14, this effect can be inhibited. The metal interface layer between the zinc oxide and the silver must be thin enough not to inhibit the positive effect of the zinc oxide on the growth of the silver thin film, in particular the contribution to the spreading and crystallization growth properties of the silver thin film. Studies by the present applicant have shown that a thickness of about 2.5 nm is optimal. As for the material selection of the ultra-thin coating L13, metals with a high solubility for silver, such as aluminum or titanium, can help to inhibit the lateral migration of silver in a humid environment and promote adhesion, but can also have drawbacks, such as reducing the initial reflectivity of the silver by dissolving into the silver. The use of pure chromium or chromium alloys, pure nickel or nickel alloys, or nickel-chromium alloys by the present invention avoids this drawback. Although the addition of a pure metal layer between the zinc oxide and the silver coating L14 increases the complexity of the film system, it is beneficial for durability in a humid environment and can significantly reduce costs due to the possibility of significantly reducing the thickness of the silver coating L14.

[0035] The silver coating L14 is deposited by magnetron sputtering and can have a thickness of up to 50 nm, but if the composite layer L10 is provided with only one layer, the thickness should preferably not exceed 40 nm. If the composite layer L10 is provided with several layers, the skilled engineer knows how to adjust the thickness of the silver coating L14 below 40 nm to achieve the maximum reflection output. By adjusting the thickness of the silver coating L14, not only the reflection output can be optimized, but also the costs, or more specifically, the costs versus reflection output.

[0036] With reference to Figure 1 The composite layer L10 is provided with an auxiliary layer L20, which is used for diffusion barrier and adhesion promotion of the high reflective metal material and can also serve as an oxidation barrier to protect the silver coating L14 on top of the composite layer L10 from oxidation. The auxiliary layer L20 is composed of a metal: silicon nitride (Me:Si)N X compound, wherein Me represents a metal or metal alloy, (Me:Si) represents the ratio between Me and Si, the index X represents the reaction coefficient of the nitrogen element N, and Me is Ti, Cr, NiCr or NiV, i.e. preferably a compound comprising (Ti:Si)Nx, (Cr:Si)Nx, (NiCr:Si)Nx or (NiV:Si)Nx. A more preferred version of the auxiliary layer L20 can be sputtered with SiAl instead of pure Si to improve the efficiency, with a Si:Al content of 90:10. i.e. (Me:Si)N X Pure Si is not easy to sputter and has a low sputtering efficiency, so SiAl is used to improve the efficiency. The preferred coating technology for the auxiliary layer L20 is magnetron sputtering. The thickness of the auxiliary layer L20 is 0.5 nm to 20 nm, preferably 2 nm to 5 nm. On top of the auxiliary layer L20 is a low refractive index layer L30, followed by a high refractive index layer L40. Both the low refractive index layer L30 and the high refractive index layer L40 serve as reflectivity enhancement layers and have a protective effect on the composite layer L10. The low refractive index layer L30 is preferably composed of silicon oxide (SiOx) or silicon aluminum oxide (Si:Al)Ox, and the high refractive index layer L40 is preferably composed of titanium oxide (TiOx). The preferred coating method for the low refractive index layer L30 and the high refractive index layer L40 is electron beam evaporation, but other PVD coating methods such as magnetron sputtering can also be considered. The thickness of the low refractive index layer L30 is 10 nm to 200 nm, preferably 40 nm to 100 nm. The thickness of the high refractive index layer L40 is 10 nm to 200 nm, preferably 30 nm to 90 nm.

[0037] With reference to Figures 1-4 The skilled engineer can adjust the thickness of the aluminum and the thickness of the silver in the composite layer L10 and the number of composite layers L10 to optimize the costs versus reflection output and to optimize the durability, according to the embodiments described above. Different applications can require different adjustments.Figure 4 Several examples of the adjustment of the reflectance output versus the thickness of the silver coating L14 are given. The thinner the silver coating L14, the lower the cost. But the lower cost is compromised by the lower reflectance output. Among them Figure 4 R_vis in the above equation represents the visible light reflectance according to the standard CIE D65 daylight specification.

[0038] The following is further illustrated with a specific experimental data.

[0039] Example 1:

[0040] Composite layer L10:

[0041] L11 Al 25nm

[0042] L12 AZO (Aluminum-doped Zinc Oxide) 5nm

[0043] L13 NiCr 5nm

[0044] L14 Ag 30nm

[0045] High reflectance mirror coating:

[0046] L40 TiOx 30nm

[0047] L30 SiOx 60nm

[0048] L20 (NiCr:SiAl)Nx 2nm

[0049] L10 Al-Ag composite thin film structure 65nm

[0050] SF Anodized Aluminum 1000-1300nm

[0051] S0 Alumium 1085 alloy

[0052] The measurement of the total visible light reflectance R_vis is based on the ISO 6719:2010 standard and the joint ISO / CIE standard, ISO 10526:1999 / CIE S005 / E-1998 (CIE standard illuminant for quantitative analysis of colorimetry) and D65 light source 2° observer angle.

[0053] After coating (not tested) 97.6%

[0054] After high temperature baking at 180°C for 168 hours 97.6%

[0055] After exposure to 85°C, 85% r.H. environment for 168 hours 97.7%

[0056] *(moisture test)

[0057] Coating adhesion was measured according to the cross-hatch adhesion test described in ISO 2409:2013 and GB / T 9286-1998 standards.

[0058] Grade 0, no delamination after coating (not tested).

[0059] Grade 0, no delamination after 180°C, 168 hours high temperature baking.

[0060] Grade 0, no delamination after 85°C, 85% r.H. exposure for 168 hours.

[0061] * (moisture test)

[0062] The test data show that the structure of the application can obtain higher optical reflection performance and durability. The data particularly show high temperature stability.

[0063] The above is only a specific embodiment of the application, but the design concept of the application is not limited thereto, and any non-essential modification of the application using this concept shall be deemed to infringe the protection scope of the application.

Claims

1. An improved high-reflective mirror coating, comprising a high-refractive layer, a low-refractive layer, and an auxiliary layer arranged in sequence, the auxiliary layer being used for diffusion barrier and adhesion promotion of the high-reflective metal material; the high-reflective mirror coating is coated on the plated surface of a metal substrate; characterized in that: Further comprising at least one composite layer, the composite layer is located between the auxiliary layer and the metal substrate; the composite layer comprises silver coating, ultra-thin coating, intermediate layer and aluminum coating arranged in sequence, the intermediate layer is made of zinc oxide or metal-doped zinc oxide, the ultra-thin coating is made of chromium, chromium alloy, nickel, nickel alloy and / or nickel-chromium alloy; when the composite layer is provided with at least two, the composite layers are arranged in sequence one by one; the aluminum coating and the silver coating are formed by magnetron sputtering deposition; when the composite layer is provided with one, the thickness of the aluminum coating is ≤50nm, and the thickness of the silver coating is ≤50nm; when the composite layer is provided with at least two, the thickness of the aluminum coating is <50nm, and the thickness of the silver coating is <40nm; the intermediate layer is formed by magnetron sputtering deposition, and the thickness of the intermediate layer is 3nm-30nm; the thickness of the ultra-thin coating is 1nm-5nm; the auxiliary layer is made of metal: silicon nitride (Me:Si)N X The compound is composed of, wherein, Me represents metal or metal alloy, (Me:Si) represents the ratio between Me and Si, the index X represents the reaction coefficient of nitrogen element N, Me is Ti, Cr, NiCr or NiV; the thickness of the auxiliary layer is 0.5nm-20nm.

2. An improved high reflectivity mirror coating according to claim 1, wherein: The intermediate layer is made of aluminum-doped zinc oxide.

3. An improved high reflectivity mirror coating according to claim 1, wherein: The ultra-thin coating has a thickness of 2.5 nm.

4. An improved high reflectivity mirror coating as claimed in any one of claims 1 to 3, wherein: The metal substrate is provided with a surface treatment layer on the plating surface, the composite layer is arranged on the surface treatment layer, the auxiliary layer is arranged on the composite layer, the low-refractive layer is arranged on the auxiliary layer, and the high-refractive layer is arranged on the low-refractive layer; the surface treatment layer is an anodic oxidation layer, a varnish coating layer or a highly polished layer.

5. An improved high reflectivity mirror coating according to claim 4, wherein: The metal substrate is made of aluminum or aluminum alloy, and the surface treatment layer is an anodic aluminum oxide film layer; the metal substrate is a metal strip or a metal sheet with a thickness of 0.1 mm-1.5 mm and a width of 500 mm-1500 mm.

6. An improved high reflectivity mirror coating according to claim 1, wherein: The auxiliary layer has a thickness of 2 nm-5 nm.

7. An improved high reflectivity mirror coating according to claim 4, wherein: The low-refractive layer is made of silicon oxide or silicon aluminum oxide, is formed by electron beam evaporation deposition, and has a thickness of 40 nm-100 nm; the high-refractive layer is made of titanium oxide, is formed by electron beam evaporation deposition, and has a thickness of 30 nm-90 nm.

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