Hydrophilic reflective article

ES 2 360 902 T3

DESCRIPTION

[0001] The present invention relates to a reflective article, in particular for rear-view mirrors for motor vehicles, which has hydrophilic properties and an attenuated reflection factor. The present invention also relates to a process for the production of such an article.

[0002] Mirrors are known that comprise a metallic layer (generally made of silver, aluminum or chromium) applied to the rear face of a transparent substrate, that is to say on the face away from the observer, or on the front face of the substrate, by therefore the face directed towards the observer. With a metallic layer of chromium having a thickness on the order of 40 to 60 nm, a light reflection of about 65% is obtained, which is perfectly satisfactory for use as a rear view mirror. However, with more significant light reflections the rear view mirror has the disadvantage of dazzling the driver.

[0003] Mirrors with a surface, which has been made hydrophilic, are also known (see EP 689 962, EP 1 022 588 or JP 2001033607, for example).

[0004] The hydrophilic character of a surface increases its surface energy, which allows water droplets to spread on a film instead of forming droplets. Rain forms droplets on a non-hydrophilic mirror, obstructing visibility. In a mirror with a hydrophilic surface, the water spreads to form a film to allow better visibility. Various materials are known for their inherent hydrophilic properties, in particular titanium oxide and silicon oxide.

[0005] In addition to its hydrophilic properties, titanium oxide, particularly when it crystallizes in the anatase form, is also well known for its inherent photocatalytic properties, ie it is capable of degrading organic matter when stimulated by light or UV irradiation.

[0006] Patent applications EP 978 494 and EP 1 099 671 describe anti-fog mirrors comprising a reflective metallic layer respectively on the rear and front face and a TiO2 / SiO2 coating stack on the front face.

[0007] Given that the TiO2 layer has a high refractive index (n = 2.4), the refractive factor of the coating stack in the visible spectrum is high, of the order of 80% for a neutral coloration stack. To reduce glare, the thickness of the layers should be selected so that the wavelength of the reflected light has a maximum between 400 and 510 nm, which gives a reflected blue color and a light reflection of the order of 60%. . EP 1 099 671 stipulates that a reflection adjusting layer can be added between the reflective film and the TiO2 layer to prevent excessive reduction of light reflection.

[0008] Coating stacks with alternating high and low refractive index layers are commonly used to increase light reflection. Documents EP 456 488 and EP 1 040 963 describe mirrors with high light reflection (> 70%) that use a metallic layer as a reflective layer, and a succession of layers of low index (SO2) and layers of high index (TO2 ) to increase reflection.

[0009] There is a need to provide a reflective article with a photocatalytic and hydrophilic effect to allow good visibility in the event of rain, while maintaining a moderate reflection factor to decrease glare. It should be possible in a simple manner to provide such an article with moderate reflection both in neutral reflected tones and in shades of colors, for example in the blue spectrum.

[0010] The purpose of the invention is to remedy the disadvantages described above. In particular, an object of the present invention is to provide a reflective article, which has hydrophilic and photocatalytic properties, and a light reflection, which is maintained at a level of reflection that is not excessive even with neutral coloring.

The object of the present invention is a composite article comprising a substrate, a reflective layer (generally referred to as a reflector) composed of an oxidized or nitrided metal, possibly in a sub-stoichiometric state, possibly covered by a barrier layer, then a layer based on titanium dioxide with photocatalytic properties, then possibly a thin, porous hydrophilic layer composed in particular of silicon oxide. This surface layer can be discontinuous.

In particular, the reflective layer is a Cr_xN_Y wherein x is between 0.67 and 0.9, preferably between 0.7-0.8 and y is between 0.1-0.33, preferably between 0.2-0.3.

According to the embodiment shown in figure 1, the layers are arranged on the same face of the substrate. In a comparative example, the reflective layer is arranged on the rear face, that is, on the face away from the observer, and the photocatalytic layer on the front face, as shown in figure 2.

[0014] The thickness of the photocatalytic layer can be in the range of between 20 and 120 nm and preferably between 40 and 75 nm. This thickness of the surface layer is, in turn, generally in the range between 2 and 10 nm and preferably between 3 and 8 nm. The latter allows the hydrophilic character of the surface to be preserved longer after the irradiation of light has ceased. The very thin thickness of this outer layer allows the photocatalytic effect of the TiO2 layer to be preserved to some extent.

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When a barrier layer is arranged between the reflective layer and the photocatalytic layer, this barrier layer is advantageously composed of silicon oxide. Its thickness can be between 10 and 80 nm and preferably between 20 and 60 nm. As a result of this barrier layer, the migration of alkaline constituents of the glass, in particular Na ions⁺, towards the titanium oxide layer can be reduced and prevented, and also the titanium oxide layer can be separated from the reflector.

[0016] The reflective layer is composed of partially oxidized or nitrided chromium. Its thickness can be between 20 and 150 nm, preferably between 40 and 120 nm.

According to the invention, the reflective article described above has a reflection of light (integrated throughout the visible spectrum) in the range of between 40 and 75% and preferably between 45 and 70% of the incident visible light.

When the reflected color of the article according to the invention is neutral (that is to say when the coefficients a * and b * of the Lab system are between -5 and 5), it is advantageous that the reflection factor is between 55 and 75%, preferably between 60 and 70%, and when the reflected color is in the blue spectrum (that is, a * is between -10 and 0 and b * is less than -10), it is advantageous that the reflection factor is between 40 and 55%, preferably between 40 and 50%. The coefficients a * and b * are measured with illuminant D65 at an angle of incidence of 2 °.

According to the invention, the light transmission of the article must be very low and preferably less than 3%, in fact less than 2%.

[0020] The present invention also relates to a process for the production of a reflective and hydrophilic article, comprising the following steps:

depositing a slightly oxidized or nitrided metallic layer (20) on the front or rear face of a support by magnetron sputtering in a controlled reactive atmosphere with a metallic target;

possibly the deposition of a barrier layer of SiÜ2 on the front face of the support by sputtering with magnetron in a reactive atmosphere with a Si target;

depositing a layer of Ti Ti2 on the front face by magnetron sputtering, for example in a reactive atmosphere with a Ti target;

heat treatment at a temperature in the range between 300 and 500 ° C, in particular between 350 and 450 ° C, for a period that can vary between 15 minutes and 6 hours, in particular between 30 minutes and 4 hours, which allows that the TiÜ2 crystallizes in the anatase form while preventing the formation of microcracks of the TiÜ2 and the turbidity that would result from it.

In particular, a process according to the invention also comprises a step of depositing a thin surface layer of SiÜ2 by magnetron sputtering in a reactive atmosphere with a Si target.

When the reflective layer is deposited on the rear face, it is advantageously deposited first. The barrier and photocatalytic layers and the surface layer are then deposited on the opposite face. The entire covered substrate can then be heat treated.

[0023] The present invention is described below by means of non-restrictive practical examples.

Example 1:

[0024] A coating stack comprising glass / CrxO_Y/ SiO₂/Uncle₂/ SiO₂ of neutral coloration, as shown in figure 1, is formed on a transparent sodium-calcium glass (10) with a thickness of 2 mm by sputtering with magnetron.

[0025] The deposition conditions of the different layers that form the stack are as follows:

[0026] A first layer (20) of slightly oxidized chromium is deposited on the substrate (10) from a metallic chromium target in an atmosphere of 80% by mass of argon and 20% by mass of oxygen. The thickness of the layer is of the order of 45 nm.

[0027] A barrier layer (30) of SiO2 is deposited on the first layer approximately of a metallic Si target in an atmosphere of 75% by mass of argon and 25% by mass of oxygen. The thickness of the layer is of the order of 40 nm.

[0028] A TiO2 layer (40) is deposited on the barrier layer from an oxidized titanium target in an atmosphere of 75% by mass of argon and 25% by mass of oxygen. The thickness of the layer is of the order of 60 nm.

[0029] A very thin last layer of SiO2 (50) is then deposited on the coating stack. The deposition is made from a metallic Si target in an atmosphere of 75% by mass of argon and 25% by mass of oxygen. The thickness of the layer is of the order of 5 nm.

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[0030] The coated substrate is then subjected to a heat treatment for 1 hour at 400 ° C. The temperature rise occurs rapidly but the cooling is carried out very gradually (approximately 3 ° C per minute).

[0031] The light reflection factor (LR) integrated over the entire visible spectrum is measured according to the SAE J 964 standard with an integrating photometer. The substrate coated according to Example 1 has an LR of 65%, whereas the same stacking of SiO2 / TiO2 / SiO2 on a chromium metal layer of the same thickness would have produced an LR of 80% and would therefore have produced , too glare for use as a rear view mirror (see figure 3).

[0032] The reflected color of the coating stack is determined by the colorimetric coordinates L *, a *, b * based on the illuminant D65 with an angle of incidence of 2 °. The values ​​obtained are compiled in the table below. Very low values ​​for a * and b * show that the coating stack does not have any significant reflected color.

The transmission of light (LT) integrated in the visible spectrum is 0.9%.

Example 2:

[0034] A coating stack comprising glass / CrxNy / SiO2 / TiO2 / SiO2 of blue coloration, as also shown in figure 1, is formed on a transparent sodium-calcium glass (10) with a thickness of 2 mm by means of magnetron sputtering.

[0035] The deposit conditions of the different layers that form the stack are as follows:

[0036] A first layer (20) of slightly nitrided chromium is deposited on the substrate from a metallic chromium target in an atmosphere of 50% by mass of argon and 50% by mass of nitrogen. The thickness of the layer is of the order of 45 nm.

[0037] A barrier layer (30) of SiO₂ with a thickness of the order of 25 nm, then a layer of TiO₂ (40) with a thickness of the order of 40 nm, and then a last layer of SiO2 (50) with a thickness of the order of 5 nm are successively deposited under the same conditions as those described in Example 1.

[0038] The coated substrate is then subjected to a heat treatment under the same conditions as those described in Example 1.

The light reflection factor (LR) integrated over the entire visible spectrum is measured according to the SAE J 964 standard with an integrating photometer. The substrate coated according to Example 2 has an LR of 43%, whereas the same SiO2 / TiO2 / SiO2 coating stack on a chromium metal layer of the same thickness would have produced an LR of 56% (see Figure 4 ).

[0040] The reflected color of the coating stack is determined by the colorimetric coordinates L *, a *, b * based on the illuminant D65. The values ​​obtained are compiled in the table below. Negative values ​​for b * and very slightly negative values ​​for a * show that the coating stack has a slightly greenish reflected blue color.

The transmission of light (LT) integrated in the visible spectrum is 1.5%.

Example 3:

[0042] A coating stack comprising glass / CrxNy / SiO2 / TiO2 / SiO2 of neutral color, as also shown in figure 1, is formed on a transparent sodium-calcium glass (10) with a thickness of 2 mm by means of Magnetron sputtering under the same conditions as in Example 2.

[0043] The thicknesses of the layers are: 75 nm for the CrxNy layer (20), 55 nm for the SiO2 barrier layer (30), 50 nm for the TO2 layer (40) and approximately 5 nm for the layer higher than SO2 (50).

[0044] The coated substrate is then subjected to a heat treatment under the same conditions as those described in Example 1.

[0045] The nitriding level of the CrxNy layer was analyzed. The index x is evaluated at 0.7 and y at 0.3.

[0046] The substrate coated according to Example 3 has an LR of 68%, whereas the same SiO2 / TiO2 / SiO2 coating stack on a chromium metal layer of the same thickness would have produced an LR of 76% (see figure 5).

[0047] The colorimetric coordinates L *, a *, b * of the reflected color are compiled in the table below. Very low values ​​for a * and b * show that the coating stack does not have any significant reflected color.

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Table 1:

<td></td><td>LR</td><td>L *</td><td>to*</td><td>b *</td>

<td>Example 1</td><td> 65</td><td> 85,8</td><td> -3,8</td><td> -1,4</td>

<td>Example 2</td><td> 43</td><td> 75,1</td><td> -6,4</td><td> -16,4</td>

<td>Example 3</td><td> 68</td><td> 76</td><td> -3,73</td><td> -2,36</td>