Technical Field

[0001] The present invention relates to improved anti-reflective glazing, characterized through a visible light transmittance of at least 90% and a visible light reflectance of at most 1.0%. The glazing of the invention is heat treatable and chemically and mechanically durable. Thanks to its properties, the glazing of the invention is suitable for applications involving monolithic glass substrates, laminated glass substrates and multiple glazing units. Applications are in automotive, building and house appliances.

Background Art

[0002] There is a demand from the market to have glass articles with a very low reflectance, also allowing a very high light transmission and a good vision through the glass article. For example, such articles may fulfil demand of the market for commercial fridge door, to allow the customer to have a better seeing inside the fridge through its window. It may also be helpful for commercial window or for protecting glass in museum, and so on... These are of course only few examples of what purposes may be for such articles.

[0003] The glass article of the invention is separating external and internal part of a building or of a closed system such a fridge. Each glass surface is responsible for a light reflection. It is well known that a special coating is capable of decreasing this reflection at the surface between air and glass. For example, prior art disclose anti-reflective coating and by anti-reflective coating, we hereby mean a stack comprising a succession of high and low refractive index layers. A lot of solutions describes such successions of alternative high and low refractive index layers. Such coatings may be deposited by any known method on the glass surface. For example, WO2016066994A1 discloses a glass substrate and a coating formed over the glass substrate which comprises a first oxide layer with a refractive index of at least 1.8 and a second oxide layer with a refractive index of at most 1.6, resulting in a visible light reflectance of at most 6.5%. The two oxide layers are preferably deposited by CVD during the float glass process. US20070236798A1 discloses a four layers reflecting stack (alternating high and low refractive index) deposited by Magnetron sputtering which allow an increase of at least 3 % of the light transmission thanks to a lower reflection.

[0004] Still a lower light reflection is possible by adding a second anti reflective coating on the other side of the glass substrate. AGC has develop a highly transparent product (EP3385236A1) with the same anti-reflective coating deposited on both main surfaces of the glass substrate, allowing a maximum of 2% visible light reflectance. Both coatings are deposited following a sputtering method. As can be seen very good results may be obtained in term of anti-reflective glass substrates.

[0005] Despite, having an anti-reflective coating on each main side of the glass substrate, is a good way to get very good result, this solution still proves to face other problems. Most often, sputtering installations are equipped with rolls that support the glass substrate and allow it to progress under sputtering targets. This means that after a first passage into the installation, the substrate is reversed and the second side is allowed to pass under the same targets. This two steps process render the entire operation complicate and expensive. But above all, because a sputtered coating is a soft coating, it is known that, when the PVD coated surface is transported in that way, there is a risk, that marks appear on the final product, this risk being still greater when the coated glass needs to be heat treated.

[0006] As can be understood there still remains interest to find a better solution to obtain a better anti-reflective article with a high visible light transmission at lower cost and with good durability. Summary of invention

[0007] This invention concerns anti-reflective coated article with enhanced anti- reflective effect. The present invention is the result of an investigation concerning the possibility of combining CVD air side anti-reflective coating with PVD tin side anti-reflective coating and show how it is possible to improve the visible light transmission and decrease the visible light reflection. Oxide layers of high and low refractive index material have been deposited on both side of a glass substrate. To optimize the thicknesses of the oxide layers, some simulations have been made and were indicating promising results. On a very surprising and still not understood way, it appears that the real optical parameters were far better than the simulated ones. It thus appears that by combining a PVD anti-reflective coating with a CVD anti-reflective coating, an unexpected synergy results in a higher decrease of the visible reflection. Up to now, no one can explain this surprising effect but the man skilled in the art knows that a layer made from the same material and having the same thickness may be different if the deposition process is CVD or PVD. Indeed in the first case deposition is made at a very high temperature under atmospheric pressure while the PVD process implies a vacuum process at lower temperature. We can assume that the resulting layer has at least a different crystallinity and a different density.

[0008] Moreover we have observed that the anti-reflective coated article of the invention is far less impacted through a heating process. Namely, the difference between the reflected colour after tempering is less affected by the heating than the reflected colour of the double sides anti-reflected coating when both sides are PVD-coated. In other words, the coated article of the invention has a better matchability between heat treated and non-heat treated article. More particularly the colour variation in reflection expressed as AE* Rc is lower than 4.0, preferably lower than 3.5 and more preferably lower than 3.0.

Our invention will now be described in more details. The anti-reflective coated article of the invention comprises a glass substrate having two major surfaces, hereby called the air-side and the tin-side surfaces, those names referring to the float manufacturing process of the glass article. The air-side is coated with a CVD coating and the tin-side is coated with a PVD coating. Both coatings are designed to have anti-reflective properties and both coating are a succession of oxide layers with high refractive index and low refractive index. Preferably, for both coatings, the low refractive index layers comprise silicon oxide. Advantageously the CVD high refractive index layers comprise tin oxide or titanium oxide. The specifications of the coated article of the invention are given in the

[0009] Table 1. The coated article of the invention is a class A product, as defined in the norm EN 1096-2, being as a consequence a durable coated article and also meaning that the PVD coating does not contain silver layer. This is true for the article before and after heat treatment. This means that it is possible to perform a heat treatment on the coated article of the invention when necessary.

[0010] Table 1

[0011] By anti-reflective coating, we mean a coating such that the measurement of visible light reflection made on the coated article is at least 1 % lower, preferably at least 1.5% lower and more preferably at least 2% lower than the reflection measured on the uncoated same glass article. This effect is verified on both sides.

[0012] With a double sides anti-reflective coated article, the measurement of the visible light reflection is at least 2% lower, preferably at least 2.5% lower and more preferably at least 3% lower than the measurement of the visible light reflection of the corresponding single side anti-reflective coated article. [0013] By CVD coating, we mean a coating deposited during the float glass process involving gaseous, powder or sprayed precursors that are chemically transformed during deposition on glass at temperature greater than 400°C. By CVD oxide layer, we mean an oxide layer deposited by a CVD process. Any CVD process known in the art is convenient for manufacturing the CVD-coating of the invention, such as an online or an offline process. For example WO2010107998 gives good non limiting examples for the CVD online process and is incorporated here in its entirety by reference. The CVD offline process is also possible, though more expensive.

[0014] By PVD coating, we refer to the well-known deposition process involving plasma sputtering of a target in high vacuum atmosphere. By PVD oxide layer, we mean an oxide layer deposited by a PVD process. Any sputtering process is suitable to build the anti-reflective coating of the invention. Alternatively, part or all of the PVD coating may also be made through a process known in the art as a PECVD process.

[0015] By temperable coated article, we mean that the coated article after having been heat treated at a temperature greater than 600°C for more than 2 minutes and less than 10 minutes, has not been altered. Namely, no marks, scratches or cracks, nor corrosion traces should be observed on the coated product after tempering. Time and duration for the heat treatment are adjusted in a known way depending the glass thickness.

[0016] The optical properties of the samples are measured with a spectrophotometer Perkin Elmer Lamdba 950 with an integrating sphere of 150 mm diameter. The visible transmittance and visible reflectance performances are expressed according to the standard EN 410 (2011). The integrated values visible transmittance (Tv) and reflectance (R) are determined with a D65 illuminant defined by the CIE standard and at a solid observer angle of 2°. The other properties (L*, a*, b*) are also measured with a D65 illuminant but at a solid observer angle of 10°. The external reflectance (measured from a point outside the building or outside the enclosed system) is represented by R _ou t and the internal reflectance (measured from a point inside the building or the enclosed system) is represent by Rin. Speaking of reflection or reflectance without any precision means that figures are almost same for one side and the other side.

[0017] Colour variations before and after heat treatment are evaluated from the optical properties L*, a*, b* defined above and may be expressed as AE*, corresponding to the formula:

AE* = (AL* ² +Aa* ² +Ab* ² ) ^1/2 where

AL* is the difference in colour coordinates L* before and after heat treatment,

Aa* is the difference in colour coordinates a* before and after heat treatment,

Ab* is the difference in colour coordinates b* before and after heat treatment.

The AE* value may be calculated for the colour in transmission or reflection.

[0018] The refractive index n is calculated from the light spectrum wavelength at 550 nm. By low refractive index oxide layer, we mean an oxide layer which refractive index is not greater than 1 .8, preferably not greater than 1 .7 and more preferably not greater than 1 .6. By high refractive index oxide layer, we mean an oxide layer which refractive index is not smaller than 1.7, more preferably not smaller than 1.8 and more preferably not smaller than 1.9.

[0019] Durability of the coating has been assessed following the tests described in the norm EN 1096-2 2012E and the articles of the invention pass the tests to be qualified as being class A.

[0020] Formula of the oxide layers are described using “x” as a subscript. This means that this subscript may take any possible value that fits on a chemical point of view. Brief description of drawings

[0021] The figures illustrate combination of the different embodiments of the invention. They are by no way to be considered at scale and they are by no way to be consider as limitation of this invention.

Fig 1a. shows the first embodiment of the invention

Fig 1b shows the first embodiment of the invention in combination with the fourth embodiment.

Fig 2a shows the second embodiment of the invention

Fig 2b shows the second embodiment of the invention in combination with the fourth embodiment.

Fig 3a. shows the third embodiment of the invention

Fig 3b shows the third embodiment of the invention in combination with the fourth embodiment.

Fig 4a. shows a combination of the second and the third embodiments of the invention

Fig 4b shows a combination of the second, the third and the fourth embodiments of the invention.

Description

[0022] The substrate is an inorganic soda-lime glass from a float process.

Advantageously, the substrate is a clear glass or an extra clear glass. The clear glass has a composition characterized by an iron content expressed in weight percent of Fe O3 which is at most 0.1 %. This value drops to at most 0.015% for the extra clear glass. The glass substrate of the invention has a thickness that is greater than 1 mm, preferably greater than 1.5 mm and more preferably greater than 2 mm. The thickness of the glass substrate of the invention is at most 20 mm, preferably at most 15 mm and more preferably at most 10 mm. Advantageously the thickness of the glass substrate is comprised between 3 and 6 mm. A 4 mm clear glass substrate has a light transmittance of about 90.5%. A 4 mm glass substrate with the extra clear composition has a light transmittance of about 91.7% and a reflectance value of about 8% [0023] The anti-reflective coated article with enhanced anti-reflective effect of the invention comprises a substrate with two main surfaces, each of the main surface being coated with an anti-reflective coating. The so-called air-side of the substrate which is the upward main surface during the float process, is coated through a CVD on-line process with at least 3 CVD oxides layers, those at least 3 CVD oxide layers being characterized by a succession of low and high refractive index (first embodiment). The first and third CVD oxide layers have both a low refractive index and the second CVD oxide layer is characterized by a high refractive index, said high refractive index being higher than the refractive index of both first and third CVD oxide layers. The said first CVD oxide layer is the layer which is the nearest layer of the substrate, the second CVD oxide layer is deposited between first and third oxide layers.

[0024] Alternatively the at least 3 CVD oxide layers may be deposited through an offline process and speaking of CVD oxide layer means equally a layer deposited by an online process or an offline process.

[0025] Alternatively, at least one of the CVD oxide layer may be replaced by at least one PVD or at least one PECVD oxide layer. Advantageously when at least one of the CVD oxide layer is replaced by at least one PVD or at least one PECVD layer, it is the third (or last) CVD oxide layer.

[0026] The resulting CVD coated substrate is characterized by a lower reflectance than the uncoated corresponding glass substrate. Typically the reflectance of the CVD coated substrate is at least 1 % lower, preferably at least 1 .5% lower and more preferably at least 2% lower than the uncoated substrate.

[0027] Advantageously, the CVD low refractive index oxide layers are based on silica and they may contain other elements such as carbon, hydrogen, nitrogen, tin, boron and phosphorus.

[0028] Advantageously the CVD high refractive index oxide layers is chosen from a titanium based oxide, a tin based oxide layer or mixture of both. In order to attain the requested low reflectance, not only the nature but also the thickness of each layer must be adjusted. [0029] The Table 2 illustrate the composition of the CVD coating of the invention. Without any other precision and for the whole text, values are given in nm and are geometric thicknesses.

[0030] Table 2

[0031] In a second embodiment of the invention, a supplementary CVD oxide layer with a high refractive index is deposited under the first CVD oxide layer of the stack described in the table 2. The refractive index of said supplementary CVD oxide layer, is at least 1.7, preferably at least 1.8 and more preferably at least 1.9. Advantageously, said supplementary CVD oxide layer comprises titanium oxide, tin oxide or mixture thereof. Advantageously the thickness of said supplementary CVD oxide layer is comprised between 5 and 35 nm, preferably between 8 and 30 nm.

[0032] In any of the first and second embodiments, none of the oxide layers that are deposited on the air side of the glass substrate is a conductive oxide layer such as for example a doped tin oxide or a doped zinc oxide layer.

[0033] In a third embodiment the second CVD oxide layer of the stack described in the table 2 is a transparent conductive oxide layer. Advantageously, the transparent conductive oxide layer of this third embodiment is a doped tin oxide layer. The doping element is chosen from fluoride, antimony or mixture thereof.

[0034] This third embodiment allows to add a low-emissive property to the anti- reflective coated article. This supplementary CVD oxide layer may also be deposited on the glass surface of the second embodiment. Alternatively, the supplementary CVD oxide layer of the second embodiment is also a doped tin oxide layer.

[0035] In the third embodiment of the invention, the CVD coated article is characterized by an emissivity that is at most 0.20 and allow to reach a II value of at most 1.6 for a standard DGU configuration (16 mm gap fill with 90% argon, 4 mm glass) when the coated article of the invention is used in a double glazing unit. Preferably, the CVD coated article of the third embodiment is characterized by an emissivity that is at most 0.15 and allow to reach a II value of at most 1 .5 for a standard DGU configuration (16 mm gap fill with 90% argon, 4 mm glass). More preferably, the CVD coated article of the third embodiment is characterized by an emissivity that is at most 0.10 and allow to reach a U value of at most 1.3 for a standard DGU configuration (16 mm gap fill with 90% argon, 4 mm glass).

[0036] Alternatively for any of the previous described embodiments or alternatives, the third CVD oxide layer is replaced by a low refractive index oxide layer that is deposited by an offline PVD or PECVD process. The low refractive index oxide layer deposited by an offline PVD or PECVD process is a single silica-based layer or a combined double silica based layer in which the two silica-based part are different in composition. In this latter embodiment, any or both of the silica-based layer deposited by an offline PVD or PECVD process, may contain aluminium or zirconium. Preferably, the second part of the double silica based layer contains 0 to 45 weight % of zirconium oxide.

[0037] Practically the reflectance of the CVD coated substrate, for any embodiment, is at most 7%, preferably at most 6.5% and more preferably at most 6%.

[0038] For any of the previous embodiments, the resulting CVD coated substrate is then transferred in a magnetron coating installation and the uncoated main surface of the CVD coated substrate is conducted through the magnetron line under the targets where at least 4 PVD oxide layers are deposited on the so called tin-side of the substrate, the side which is opposite to the CVD coated surface. The 4 PVD oxide layers are characterized by a succession of high and low refractive index. The first and third PVD oxide layers of the stack have a refractive index that is at least 1.8, preferably at least 1.9. The second and third PVD oxide of the stack have a refractive index that is at most 1 .8, preferably at most 1 .7.

[0039] Advantageously, the PVD low refractive index oxide layers are based on silica and they may contain other elements, as for example aluminium and zirconium. When the silica PVD low refractive index layer contains aluminium, preferably the aluminium weight proportion is at most 12% (Al ratio related to the total Al and Si content). When the silica PVD low refractive index layer contains zirconium, preferably the zirconium weight proportion is at most 28% (Zr ratio related to the total Zr and Si content).

[0040] Advantageously the PVD high refractive index oxide layers are based on titanium. Preferably the PVD high refractive index oxide layers are a mixed oxide comprising titanium oxide and zirconium oxide. Preferably the mixed oxide has a weight composition of TiO2/ZrO2 (TZO) comprised between 50/50 and 75/25. More preferably the mixed oxide layer comprising titanium oxide and zirconium oxide has a weight composition of TiO2/ZrO2: 65/35. In order to get the low reflectance, not only the nature but also the thickness of each layer must be adjusted. The table 3 illustrates the composition of the PVD coating of the invention. The first PVD oxide layer is the layer which is closest to the glass substrate. The second, third and fourth oxide layers are deposited successively above the first oxide layer.

[0041] On a preferred alternative, when the coated glass article of the invention requests to be heat treated, the PVD high refractive layers are based on both titanium and zirconium since the presence of zirconium oxide keeps a better appearance after heat treatment (see for example EP3385236A1).

[0042] Table 3 [0043] In a fourth embodiment, the fourth PVD oxide layer of the stack described in the table 3 is a combination of 2 successive silica-based oxide layers. The upper layer is a mixture of silicon oxide and zirconium oxide (SiZrO _x ) with a content of at most 45 weight% of zirconium oxide and at least 55 weight% of silicon oxide. Under said upper layer, another silicon oxidebased layer is deposited. This other silicon oxide based layer is deposited from a silicon target that contains from 0 to 12 weight% of aluminium.

[0044] In this fourth embodiment, the SiO _x layer has a thickness comprised between 50 and 80 nm and the SiZrOx has a thickness comprised between 10 and 40 nm.

[0045] Advantageously, at least one of the oxide layer of the stack described in the table 3 is deposited through a PECVD process, following well known practice of the art.

[0046] The PVD coated surface together with the CVD coated surface are characterized by a very low reflectance value, this reflectance value being lower than the one expected by the previous simulation study. The resulting reflectance of the double side coated substrate of the invention is at most 1.2%, preferably at most 1.1 % and more preferably at most 1.0%. These values are the ones measured after heat treatment (670°C, 3 min for 4mm glass).

[0047] The simulation study has been made following an usual manner known by the man in the art. Simulation is using mathematical modelling to obtain simulated values characterizing a glazing without the necessity of building or prototyping a sample. This is made by using a database of glazing components and material properties, allowing to determine according to international standards, glazing specifications, ranging from optical properties (solar energy, visible light, colour appearance) to thermal properties (U-value, solar factor). More particularly the Transfer Matrix Method is a commonly used tool in Optics. Transmittance and reflectance are calculated for each interface in the glazing as well as attenuation in each component. The theory behind this calculation is described in literature (L.A.A. Petterson, J. of Appl. Phys. 1999, 86, 487 ; P.Peumans, J. of Appl. Phys. 2003, 3, 3693 and V.Wittwer, Proceedings SPIE The international Society for Optical Engineering, Optical materials Technology for Energy Efficiency and Solar Energy conversion XIII, April 1994).

[0048] Systematically, by comparing the real values (measurement) with the calculated ones (simulation), it appears that the visible reflectance which is measured is at most 71 % of the calculated value (meaning at least 29 % improvement and more). This very unexpected observation shows that a particular synergic effect exists by combining an anti-reflective OVD coating on the air-side with an anti-reflective PVD coating on the tin-side of a glass substrate. Up to now, we have found no explanation to this phenomena. Nevertheless, this invention allows the easy, effective and low cost manufacturing of a highly anti-reflective coated article.

[0049] The coated glass article of the invention has on both sides a class A coating, which is conform to the norm EN 1096-2 2012E.

Description of embodiments / examples

[0050] Six different CVD anti-reflective coatings have been deposited on the airside of a clear soda-lime glass substrate (examples 2-6) or an extra clear soda-lime glass substrate (example 1) during its manufacturing float process. The composition of the six examples of the invention is given in the table 4 with geometrical thicknesses given in parentheses and expressed in nm

[0051] On the tin-side of the coated substrates of the 6 examples of the invention, a PVD stack has been deposited. The PVD stack was the same for all examples and has the following structure:

Glass / TZO (10 nm) / SiO _x (28 nm) / TZO (120 nm) / SiO _x (60 nm) / SiZrO _x (25 nm)

[0052] The reflectances indicated in the table 4 are:

R1 : visible reflectance measured on the article with only the CVD coating R2: visible reflectance measured on the article with both CVD and PVD coating

R3: visible reflectance simulated (see § [0047]) for the article with both CVD and PVD coatings. [0053] The relation between the measured value of reflectance and the simulated value is given through the ratio R2 divided by R3. As can be seen this ratio is at maximum 0.71 (instead of 1 for an ideal simulation), showing that the measured value is at most 71 % of the simulated value.

[0054] The last row indicates the measured visible light transmission (Tv) of the coated article of the invention (coated on both sides).

[0055] All the values that are given in the table 4, measured or simulated, correspond to the article of the invention that has been submitted to a heat treatment (670°C during 3 minutes for 4 mm glass).

[0056] Table 4

[0057] As can be seen from the table 4, all examples of the invention are very low-reflective glass articles (R2) and the still non elucidated difference in reflection between simulations and measurements is quite high and amazing (compare R3 with R2).

[0058] All samples have been submitted to the durability tests conform to the norm EN 1096-2 2012E and all examples for both coated surfaces have successfully passed the tests as class A articles.

[0059] In table 5 we show that the colour in reflection of the coated article of the invention is less affected after heat treatment than an antireflecting article having both sides coated by a PVD process (compare example 1 of the invention with the counter example 7). The counter-example is a glass substrate with the PVD coating described in paragraph [0051] deposited on both sides.

[0060] Table 5

[0061] Finally we have repeated the example 5 with the same stacks but both sides were coated through a PVD process (example 5B). The purpose of this very last test was to check if the unexpected enhance anti-reflective effect is only resulting of the process of the invention. In the table 6, we compare for both example 5 and 5B. The results of this test are given in table 6. For the example 5B, R1 is the reflectance measured with the PVD stack corresponding to the CVD stack of the example 5. For both examples, R2 is the reflectance measured on the double sides coated article and R3 is the simulated reflectance of the double sides coated article.

[0062] Table 6

[0063] What appears immediately from the table 6 is that the amazing effect that we have observed is only observed when the air-side is coated through a CVD process while the tin-side is coated through a PVD process. The reason of this remains unknown, we only can observe this very interesting phenomena. We also note that despite reflectance in example 5 is lower than in example 5B, the transmittance is also lower, leaving questions about the absorbance of the coated article of the invention. Another interesting point is that the heat treatment was not well supported by the product of example 5B (double PVD coating) because, the finale reflectance was higher than before heat treatment.