Transparent substrate with a stack of thin layers acting on solar and/or infra-red radiation.

The invention relates to transparent substrates, in particular glass, which are coated with a stack of thin layers comprising at least one layer, in particular metallic, which can act on solar radiation and / or on infrared radiation.

The invention also relates to the use of substrates thus coated to manufacture glazing, very particularly suitable for thermal insulation and / or sun protection. These glazings are intended both to equip buildings and vehicles, with a view in particular to reducing the air conditioning effort and / or reducing any excessive overheating caused by the ever increasing importance of the glazed surfaces in premises or interiors.

One type of stack of thin layers known to give substrates such properties consists of one or more metallic layers such as silver layers, interspersed with layers of dielectric material such as metal oxide layers. This stack is generally obtained by a succession of deposits made by a technique using the vacuum of the cathode sputtering type assisted by magnetic field.

Increasing the number of metal layers in the stack makes it possible to optimize sun protection, which can result in a reduction in the solar factor of the glazing. (Remember that the solar factor of a glazing is the ratio between the total energy entering the room through the glazing and the incident solar energy). However, this also leads, in parallel, to a reduction in the transparency of the glazing, reflected in a drop in the value of the light transmission T_L said glazing.

A compromise is therefore to be found between anti-solar performance and transparency, without forgetting the industrial feasibility of such a stack.

US Pat. No. 5,071,206 proposes in particular a substrate on which is deposited a stack consisting of three silver-based layers alternated with four layers of metal oxide such as indium oxide, the three silver layers being substantially equal thicknesses although the "central" layer is slightly thicker than the other two. However, as long as such a substrate is not incorporated in a laminated glazing, the face of the substrate coated with the stack being in contact with the thermoplastic interlayer film of polyvinyl butyral type PVB, the appearance in reflection of said substrate is unattractive: in reflection, it appears reddish, a color little appreciated by architects, all the more so since the color is relatively intense.

The object of the invention is therefore to overcome this drawback by developing a substrate coated with a stack comprising at least three layers with infrared reflection properties, in particular metallic, and which has a high selectivity, c is a T ratio_L/ FS as high as possible for a value of T_L given, while guaranteeing an appearance, in particular in external reflection, which is pleasing to the eye, this means that the substrate is used as monolithic glazing, incorporated in multiple insulating glazing of the double-glazing type, or even in glazing laminated.

The subject of the invention is a transparent substrate, in particular made of glass, provided with a stack of thin layers comprising essentially successively, counting from the substrate, a first layer of dielectric material, a first layer with properties of reflection in the infrared, in particular metallic, a second layer of dielectric material, a second layer with reflective properties in infrared, especially metallic, a third layer of dielectric material, then finally a third layer with infrared reflection properties, in particular metallic, surmounted by a fourth layer of dielectric material. The thicknesses of the three layers with properties in the infrared are chosen, in accordance with the invention, so that the thickness of the third layer is greater than that of the second layer, itself greater than that of the first layer.

This asymmetry in the thicknesses of the three layers with infrared reflection properties, in particular metallic, is preferably adjusted so that the ratios on the one hand of the thickness of the third layer to that of the second , on the other hand, the thickness of the second layer over that of the first, are between 1.40 and 1.05 and preferably between 1.30 and 1.10.

The fact that the layers with reflection properties in the infrared are thicker the further they are from the substrate, makes it possible to obtain glazings with very high selectivity, ie having a ratio T_L/ FS of at least 1.8 or even 2 or more. By modulating the thicknesses of the layers, one can control the transparency of the glazing, and obtain values ​​of T_L in the range of 58 to 68%, a range particularly suitable for glazing intended for the building trade. Similarly, solar factors FS of the order of 28 to 36% can be achieved.

However, the major advantage of the invention is that these good performances in terms of sun protection do not operate at the expense of the visual appearance of the substrate.

Indeed, whether it is used as monolithic glazing or incorporated into a multiple glazing type double glazing, the substrate coated with the stack of layers according to the invention has a coloration in pleasant and soft external reflection, in the range of blues or blue-green (dominant wavelength values ​​of the order of 470 to 500 nanometers). In addition, this coloration appears neutral, "washed white" and not shiny, which is confirmed by in particular purity values ​​in reflection of less than 6% and of external reflection R_L less than 10%.

A final point: this visual aspect remains almost unchanged regardless of the angle of incidence with which the glazing is observed. This means that an outside spectator, in view of a facade of a building fully equipped with such glazing, does not have the impression of a significant inhomogeneity of color, or appearance, which is much sought after. architects currently.

It should be noted that in internal reflection the substrates mounted in glazing also have a color in blues or in blues-greens, neutral and not shiny. This implies that, when it is dark outside a room lit and equipped with such glazing, a person inside the room sees these colored glazing in a pleasant manner.

The colorimetry of the substrates according to the invention is further optimized if the thickness of the three layers with infrared reflection properties increases progressively and regularly, that is to say if the ratio of the thickness of the third layer on that of the second and the ratio of the thickness of the second layer to that of the first are substantially equal. These neighboring ratios are preferably chosen from 1.13 to 1.15.

The preferred embodiment of the invention thus consists in choosing the first layer of thickness 8 to 12 nanometers, in particular 9.5, the second layer of thickness 10 to 13 nanometers, in particular 11, and finally the third layer of thickness approximately 11 to 15 nanometers, in particular 12.5.

The choice of the thicknesses of the four layers of dielectric material is not indifferent either. Thus, it is preferable that the thickness of the fourth layer of dielectric material is equal to that of the first and possibly a little greater, and this in a ratio of between 1 and 1.20.

Likewise, the thicknesses of the layers of "intermediate" dielectric materials, that is to say the second and third layers are preferably chosen to be close, in particular in a ratio of between 0.9 and 1.1. These layers are also chosen significantly thicker than the first and fourth layers.

Advantageously, the thickness of each of the second and third layers is chosen to be greater than or equal to the sum S of the thicknesses of the first and fourth layers, and in particular of a value between the product S x 1.1 and the product S x 1 , 2.

To verify these conditions, the thickness of the first layer can be chosen between 27 and 34 nanometers, and in particular equal to approximately 27 or 32 nanometers. The thickness of the second and third layers can be chosen between 70 and 80 nanometers, and in particular equal to 72, 73 or 77 nanometers. The thickness of the fourth layer can be chosen between 32 and 37 nanometers and be equal to 34 or 35 nanometers.

In terms of choice of materials, it is recommended to use layers with infrared reflection properties which are made of metal, especially based on silver. As for the layers of dielectric material, they can be made of metal oxide such as tantalum, zinc or tin oxide, or a mixture of at least two of these oxides, each of these oxides has its own advantages. Thus, tin or zinc oxide can be deposited at high speeds when a reactive sputtering technique is used, which is industrially very advantageous. On the other hand, tantalum oxide provides increased durability in the face of mechanical or chemical attack. It is also not obligatory to choose the same oxide for all the layers of dielectric material. Thus the first two or three layers can be made of tin oxide, to increase the production rates, the last layer being made of tantalum oxide to best protect the stack. In addition, this choice consisting in that the four layers of dielectric material are not all of the same oxide advantageously makes it possible to adjust more or less certain photometric values ​​of the stack, in particular the value of T_L and / or the solar factor FS and possibly modulating its colorimetry.

The layers of dielectric material can also be of different nature, and in particular based on sulphide such as zinc sulphide Zns, which easily lends itself to a thin layer deposition by vacuum evaporation techniques. It is thus possible to deposit all of the layers of the stack either by evaporation or by sputtering.

It should also be noted that it is preferable to each overcome the layers with infrared reflection properties, especially when they are metallic, with a thin metallic "barrier" layer, a metal other than silver such as a nickel-chromium alloy, tantalum or titanium and this especially when the layers of dielectric material are deposited by reactive sputtering in the presence of oxygen. These barrier layers thus protect the underlying layers, in particular metallic layers, from contact with oxygen by oxidizing themselves partially.

It is also possible to provide for depositing, under each of the layers with reflection properties in the infrared, a thin layer known as "bonding", in particular intended to improve the adhesion to the underlying layer of dielectric material. These bonding layers are in particular of the same nature as the “barrier” layers mentioned above, that is to say metallic and made of a metal other than silver and for example based on alloys of the nickel- chromium, or based on tantalum or titanium.

We also note that the presence of these "barrier" layers and / or these "bonding" layers can allow the stack of layers as a whole to better withstand subsequent heat treatments that the substrate may have to undergo. carrier, annealing, bending or quenching treatments.

The details and advantageous characteristics of the invention appear from the following nonlimiting examples, illustrated with the aid of FIG. 1.

It is specified that in the two examples which follow, the successive depositions are carried out by sputtering assisted by magnetic field, but that any other deposition technique can be envisaged since it allows good control of the thicknesses of the layers to be deposited. The substrates on which the stacks are deposited are silica-soda-lime substrates 4 millimeters thick. They are then assembled in double glazing to an identical but bare substrate by means of a 10 mm gas slide.

Figure 1 shows the stack according to the invention and does not respect the proportions as to the thicknesses of the layers so that its reading is facilitated. We see there the substrate 1, the three layers 3, 5, 7 with properties of reflection in the infrared, here in silver and the four layers in dielectric material, here in tin or tantalum oxide 2, 4, 6, 8. The thin barrier layers of Ni-Cr do not appear above each of the silver layers 3, 5, 7.

The deposition installation comprises at least one spraying chamber provided with cathodes equipped with targets made of suitable materials under which the substrate 1 passes successively. These deposition conditions by each of the layers are as follows:<ul id="ul0001" list-style="none"><li>The silver-based layers 3, 5, 7 are deposited using a silver target, under a pressure of 0.8 Pa in an argon atmosphere,</li><li>The layers 2, 4, 6, 8 when they are based on SnO₂, are deposited by reactive spraying using a tin target, under a pressure of 0.8 Pa and in an argon atmosphere / oxygen including 36% by volume of oxygen,</li><li>· Layers 2, 4, 6, 8 when they are based on Ta₂O₅, are deposited by reactive spraying using a tantalum target, under a pressure of 0.8 Pa and in an argon / oxygen atmosphere of which about 10% by volume of oxygen,</li><li>· The three barrier layers based on Ni-Cr are deposited using a nickel-chromium alloy target, always under the same pressure and in an argon atmosphere.</li></ul>

The power densities and the running speeds of the substrate 1 are adjusted in a known manner to obtain the desired layer thicknesses.

Example 1 relates to such a stack, the four dielectric layers of which are made of tin oxide, while Example 2 relates to such a stack, the four dielectric layers of which are made of tantalum oxide.

Table 1 below specifies the thicknesses in nanometers of the layers of the two stacks:<tables id="tabl0001" num="0001"><img file="EP0645352A1_D0001.tif" /></tables>

Table 2 below indicates for each of the two examples the light transmission values ​​T_L in percentage, of solar factor FS calculated according to DIN 67 507 (Annex A 233) in percentage, of exterior and interior light reflections R_L-ext and R_L-int in percentage, as well as the dominant wavelengths in nanometers Lambda-int and Lambda-ext and the purities in percentage p-ext and p-int which are associated with it: (values ​​measured on the substrate mounted in double-glazing and with reference to the illuminant D₆₅).<tables id="tabl0002" num="0002"><img file="EP0645352A1_D0002.tif" /></tables>

From this last table, the following conclusions can be drawn:

The glazings according to the invention have a ratio T_L/ High FS, close to 2, and therefore offer good sun protection in a range of light transmissions particularly suitable for equipping buildings.

In addition, the colors in interior and exterior reflections remain in the range of blues-greens, colors appreciated on the aesthetic level. These colors are very neutral, since they have purities at worst of 6% and reflection values ​​remaining below or close to 10%.

In addition, these glazings do not see their appearance in reflection perceptibly changed if the angle from which they are observed varies.