Glass with easy maintenance

1. Field of the invention

The field of the invention is that of glass substrates provided with a chemically and mechanically durable coating which gives them a certain hydrophilicity, a property making it possible to facilitate the maintenance of said substrates.

Glass is a material widely used not only in architecture but also in the automobile or in interior applications such as mirrors, shower glasses, decoration, household appliances ... There is a demand for the industry to offer substrates whose maintenance is facilitated in a sustainable way over time.

2. Prior art solutions

It is known that titanium dioxide, in particular in the anatase form, when subjected to UV irradiation, has a photocatalytic effect which allows it to degrade the organic dirt which comes into contact with it. <patcit id="pcit0001" dnum="EP1304366A1"><text>EP1304366A1</text></patcit> and <patcit id="pcit0002" dnum="WO9710186A1"><text>WO97 / 10186A1</text></patcit> largely present the different characteristics of this layer, its mode of operation and its production methods. Besides these photocatalytic properties,<patcit id="pcit0003" dnum="EP1304366A1"><text>EP1304366A1</text></patcit> and <patcit id="pcit0004" dnum="EP1366000A2"><text>EP1366000A2</text></patcit> show that titanium dioxide, still under UV irradiation, also has a hydrophilic character which results in a very low contact angle with water. This additional characteristic allows the formation of a film of water which, when flowing, facilitates the removal of residual dirt deposited on the glass. Furthermore and as described<patcit id="pcit0005" dnum="EP882686B1"><text>EP882686B1</text></patcit>, the TiO layer₂ is also used to prevent fogging, a phenomenon which can be responsible for a significant loss of visibility. The effects and advantages of this oxide are therefore multiple and very interesting.

To deposit titanium dioxide, several methods well known in the prior art exist (<patcit id="pcit0006" dnum="WO1997010186A1"><text>WO1997010186A1</text></patcit>, <patcit id="pcit0007" dnum="EP1304366A1"><text>EP1304366A1</text></patcit>). Each method has advantages and disadvantages that will determine the choice. In particular, the TiO film₂ can be deposited by gas phase pyrolysis (CVD), wet (sol-gel) or by vacuum gas phase deposition (PVD). The last process is generally done cold and makes it possible to obtain a layer of amorphous titanium dioxide which therefore requires annealing to be crystallized. Depending on the annealing temperature used, the crystalline phase obtained will be anatase or rutile, the first being generally preferred for its better photocatalytic activity. The deposition by sol-gel generally results in a thick and more porous layer, the preparation of which is also more complex. Finally the gas phase pyrolysis involves precursors which are degraded under the effect of the high temperature, to form a layer on the glass. This process can be performed directly online at the time of glass production, making this route particularly attractive and inexpensive. Especially since the resulting layer is a harder, denser layer and having significant mechanical and chemical resistance properties. Such a layer can in particular be used outdoors, without protective coating. Finally, by the method, the deposition temperature is very high and we obtain TiO₂ directly with a high crystallization rate.

Generally, such a layer obtained by CVD has a fairly large roughness. By way of illustration, we find in<patcit id="pcit0008" dnum="EP1497236A1"><text>EP1497236A1</text></patcit> than a hydrophilic TiO coating₂ deposited by CVD has a roughness characterized by an Rq of 7 to 10 nm. This roughness, generally preferred because it contributes to better photocatalytic activity and better hydrophilicity, is also responsible for greater fouling by encrustation of dirt in the roughness of the surface, as well as a certain difficulty in encrusting these impurities. In addition, the roughness, if it is too high, can make the layer more sensitive to scratches, marks, stains, etc. For those skilled in the art, such sensitivity is problematic during the various manipulations of the glass.

What the invention proposes to improve is precisely the problem linked to the question of the roughness of the TiO layer₂. How to get a layer of TiO₂ which allows to maintain good hydrophilicity while having a slightly rough surface, which seems antagonistic in view of the prior art?

3. Objectives of the invention

The invention particularly aims to overcome the drawbacks of the prior art by providing a substrate provided with a coating showing good hydrophilicity and yet having a roughness fairly low to avoid fouling by encrustation and facilitate removal dirt. Such a coating must also be more resistant to scratches. In addition, the coating of the invention must be subjected to heat treatments such as quenching or bending, without its optical properties being deteriorated.

Finally, the invention relates to an economical and easy to implement process for depositing a coating having a strong hydrophilic character and demonstrating good chemical and mechanical durability.

4. Statement of the invention

The invention relates to a glass substrate which comprises on one of its faces a hydrophilic coating.

The substrate is preferably a substrate made of clear, extra-clear or colored glass, float of the silica-soda-lime type, the thickness of which is between 0.2 and 20 mm.

According to one embodiment of the invention, this hydrophilic coating comprises a first barrier layer against alkaline ions, preferably deposited by CVD. In fact, when the coated glass is subjected to intensive heating, alkaline ions can migrate from the glass to the functional layer which is thereby degraded. This barrier layer is based on silicon and chosen from oxides, nitrides, oxynitrides, carbides, silicon oxycarbons. More particularly, the first layer is a stoichiometric layer of SiO₂ or a sub-stoichiometric of silicon oxide containing carbon and denoted SiO_xVS_y. Even more preferably, the alkali barrier layer is a layer of SiO_xVS_y with a C / Si atomic ratio of between 0.10 and 0.60, preferably between 0.20 and 0.40. This first layer has a thickness between 10 and 120 nm, preferably between 15 and 80 nm, even more preferably between 20 and 50 nm. Preferably, this first layer is in direct contact with the substrate.

The hydrophilic coating according to the invention comprises a second layer, this second layer having a hydrophilic character is preferably deposited by CVD on the first layer and preferably in direct contact with the latter. According to a preferred embodiment, this second layer is the last layer of the hydrophilic coating.

According to the invention, the hydrophilic layer of the hydrophilic coating is chosen from oxides of Ti, Sn, W, Zn, Si, Al, Ag, Co and mixtures of one or more of these oxides. The thickness of this hydrophilic layer is between 5 and 150 nm, preferably between 8 and 50 nm and even more preferably between 10 and 20 nm. According to the invention, the roughness Rq of the hydrophilic coating is less than 3 nm, preferably less than 2 nm and even more preferably less than 1 nm. The coating of the invention is characterized by a contact angle with water at most equal to 10 °, preferably at most equal to 6 °, after having been subjected to irradiation at 40 ° C for 30 minutes by means of '' UVA (340 nm) with a power of 40 W / m².

According to a particularly preferred embodiment, this hydrophilic layer is a layer of TiO₂, the thickness of which is between 5 and 150 nm, preferably between 8 and 50 nm and even more preferably between 10 and 20 nm. The TiO layer₂ is mainly obtained in anatase form. The TiO layer₂ can be doped, in particular with tin in atomic percentages of Sn / Ti less than 10%, preferably less than 5%.

More particularly, the invention also relates to the formation of a hydrophilic coating provided with a first barrier layer against alkaline ions and with a second layer of TiO₂, the thickness of which is between 5 and 150 nm, preferably between 8 and 50 nm and even more preferably between 10 and 20 nm.

According to one embodiment, the hydrophilic coating according to the invention has been polished after the deposition of all the layers, for example on a float line, so that its roughness decreases to reach roughness values ​​Rq of less than 3 nm, preferably less than 2 nm and even more preferably less than 1 nm.

According to one embodiment, the coated glass substrate has undergone a heat treatment after polishing, such as for example tempering or bending. This heat treatment involves temperatures above 600 ° C and maintaining the substrate at these temperatures for periods which are adapted to the thickness of the substrate according to a process well known to those skilled in the art.

The silicon-based barrier layer can be deposited in accordance with methods well known to those skilled in the art and described in the prior art, preferably on a glass production line. Alternatively, it can also be deposited by any process well known to those skilled in the art.

According to a preferred embodiment of the invention, the TiO layer₂ is formed by chemical vapor deposition, preferably on a glass production line, optionally following the barrier layer. It is obtained by pyrolysis of the precursors well known to those skilled in the art for producing such a layer. Among the precursors generally used, there is titanium tetraisopropoxide (Ti [OCH (CH₃)₂]₄ hereafter called TTIP), titanium tetrachloride (TiCl₄), titanium tetrabutoxide (Ti (OCH₂CH₂CH₂CH₃)₄), titanium ethoxide (IV) (Ti (OC₂H₅)₄) or any mixture of these precursors. More particularly, the TTIP is sprayed above the glass either in the tin bath where the temperature of the glass is between 750 and 620 ° C., or at the start of the gallery where the glass is at a temperature between 620 and 550 ° C. The coating comprising the TiO layer₂, is then polished so as to reduce its roughness. In accordance with the knowledge of a person skilled in the art, it has been shown that this polishing has a negative impact on the hydrophilicity of the coating.

However, very surprisingly, the inventors have observed that if the glass thus coated and polished is heat treated, the layer of TiO₂ regains its hydrophilic nature as measured before polishing, while retaining a lower roughness. This observation is contrary to the teaching of the prior art which shows that a layer of TiO₂ polished and therefore significantly less rough, has poorer hydrophilicity. This completely surprising behavior therefore makes it possible to obtain a coated glass substrate which has both a low roughness and a high hydrophilicity, thus circumventing the limitations of the prior art.

The glass substrates according to the invention can be part of a single or multiple glazing, it can be used for the automobile or in interior applications. The coated surface of the glazing is an exterior surface.

For the sake of clarity throughout this document, we adopt the following conventions:<ul id="ul0001" list-style="dash"><li>The tests were carried out on soda-lime glass substrates whose thickness is 4 mm.</li><li>By contact angle (AC), we mean the angle made by the tangent to a drop of water with the surface of the substrate. Depending on the case, the contact angle was measured with or without prior activation by UV radiation. This activation of the hydrophilic nature by UV irradiation is carried out at 40 ° C for a period of 30 minutes using UVA with a power of 40 W / m2 (UVA-340 nm 40 W / m², from a Q-Panel device, from Q-Lab, Cleveland, Ohio).</li><li>The roughness Rq is the quadratic mean of the height z deviations on the evaluation surface and measured with respect to the mean height z. The quadratic mean of the deviations of a profile is evaluated by an atomic force microscope (AFM) on a surface of 10 μm times 10 μm in N = 512 lines of M = 512 measurement points according to the following formula:<maths id="math0001"><math display="block"><mrow><msub><mi>R</mi><mi>q</mi></msub><mo>=</mo><msqrt><mrow><mfrac><mn>1</mn><mi mathvariant="italic">MN</mi></mfrac><mrow><mstyle displaystyle="false"><mrow><munderover><mrow><mo>∑</mo></mrow><mrow><mi>x</mi><mo>=</mo><mn>1</mn></mrow><mi>NOT</mi></munderover></mrow></mstyle><mrow><mstyle displaystyle="false"><mrow><munderover><mrow><mo>∑</mo></mrow><mrow><mi>y</mi><mo>=</mo><mn>1</mn></mrow><mi>M</mi></munderover></mrow></mstyle><mrow><msup><mfenced><mi>z</mi><mfenced separators=","><mi>x</mi><mi>y</mi></mfenced><mo>−</mo><mover><mi>z</mi><mrow><mo>‾</mo></mrow></mover><mfenced separators=","><mi>NOT</mi><mi>M</mi></mfenced></mfenced><mn>2</mn></msup></mrow></mrow></mrow></mrow></msqrt><mn>.</mn></mrow></math><img file="EP3431455A1_D0001.tif" /></maths></li></ul>

The measurements were carried out in intermittent contact mode (tapping mode) with a Bruker NCHV type probe, made of antimony doped silicon, of stiffness k between 20 and 80 N / m, with a resonance frequency between 334 and 401 kHz and whose nominal radius of the tip is 10 nm.<ul id="ul0002" list-style="dash"><li>The thicknesses of the indicated layers were determined by X-ray fluorescence (XRF) on the basis of a calibration curve. These are geometric or physical thicknesses.</li><li>the measurement of the colorimetric variations of the transmitted or reflected light is carried out from the coordinates of the CIELAB system (illuminant D65) in accordance with standard EN410. The colorimetric variation is expressed by the expression denoted ΔE *, an expression corresponding to the formula:<maths id="math0002"><math display="block"><mrow><mi mathvariant="normal">ΔE</mi><mo>*</mo><mo>=</mo><msup><mfenced><msup><mi mathvariant="normal">ΔL</mi><mrow><mo>*</mo><mn>2</mn></mrow></msup><mo>+</mo><msup><mi mathvariant="normal">Δa</mi><mrow><mo>*</mo><mn>2</mn></mrow></msup><mo>+</mo><msup><mi mathvariant="normal">Δb</mi><mrow><mo>*</mo><mn>2</mn></mrow></msup></mfenced><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msup></mrow></math><img file="EP3431455A1_D0002.tif" /></maths><ul id="ul0003" list-style="none"><li>where ΔL * represents the difference between the colorimetric coordinates L * of the glazing before and after heat treatment,</li><li>Δa * represents the difference between the colorimetric coordinates a * of the glazing before and after heat treatment,</li><li>Δb * represents the difference between the colorimetric coordinates b * of the glazing before and after heat treatment,</li></ul></li></ul>

More particularly, and preferably, the glazing according to the invention exhibits a colorimetric variation in transmission, ΔE *_τι: <ul id="ul0004" list-style="none" compact="compact"><li>AE *_TL= (ΔL * TL2 + Δa *_TL²+ Δb *_TL²)^1/2 is less than 3, preferably less than 2, more preferably less than 1, when said glazing is subjected to a temperature of at least 630 ° C and at most 670 ° C for 3 to 10 minutes.</li></ul>

Preferably, the glazing according to the invention additionally exhibits a colorimetric variation in reflection, on the coating side, ΔE *_RC, such as :<ul id="ul0005" list-style="none" compact="compact"><li>ΔE *_Rc= (ΔL *_Rc²+ Δa *_Rc²+ Δb *_Rc²)^1/2 is less than 3, preferably less than 2, when said glazing is subjected to a temperature of at least 630 ° C and at most 670 ° C for 3 to 10 minutes.</li></ul>

5. Description of preferred embodiments of the invention

The invention is illustrated by the following examples, which in no way limit the scope of the invention. Table 1 provides the parameters used in the examples to produce samples of coated glass according to the invention.

In these examples, the first layer, a barrier to the migration of alkaline ions from the glass, and the second, hydrophilic layer, are obtained by chemical vapor deposition directly on a production line for clear soda-lime glass, advancing at a speed of 15 m / min and whose thickness is 4 mm.

Examples 1 and 2 according to the invention underwent a polishing step. Counterexamples 3 and 4 have not been polished.<tables id="tabl0001" num="0001"><table frame="all"><title>Table 1: gas injection parameters</title><tgroup cols="8"><colspec colnum="1" colname="col1" colwidth="19mm" /><colspec colnum="2" colname="col2" colwidth="14mm" /><colspec colnum="3" colname="col3" colwidth="14mm" /><colspec colnum="4" colname="col4" colwidth="14mm" /><colspec colnum="5" colname="col5" colwidth="14mm" /><colspec colnum="6" colname="col6" colwidth="13mm" /><colspec colnum="7" colname="col7" colwidth="17mm" /><colspec colnum="8" colname="col8" colwidth="20mm" /><thead><row><entry morerows="2" align="center" valign="top">examples</entry><entry namest="col2" nameend="col5" align="center" valign="top">SiO_xVS_y</entry><entry namest="col6" nameend="col7" align="center" valign="top">TiO₂</entry><entry morerows="2" valign="top">Polishing</entry></row><row><entry align="center" valign="top">NOT₂</entry><entry align="center" valign="top">VS₂H₄</entry><entry align="center" valign="top">SiH₄</entry><entry align="center" valign="top">CO₂</entry><entry align="center" valign="top">TTIP</entry><entry align="center" valign="top">NOT₂</entry></row><row><entry align="center" valign="top">(kg / h)</entry><entry align="center" valign="top">(kg / h)</entry><entry align="center" valign="top">(kg / h)</entry><entry align="center" valign="top">(kg / h)</entry><entry align="center" valign="top">(l / h)</entry><entry align="center" valign="top">(Nm³/ h)</entry></row></thead><tbody><row><entry align="center">1</entry><entry align="center">0,80</entry><entry align="center">4,40</entry><entry align="center">0,57</entry><entry align="center">8,80</entry><entry align="center">2,0</entry><entry align="center">850</entry><entry>Yes</entry></row><row><entry align="center">2</entry><entry align="center">0,80</entry><entry align="center">4,40</entry><entry align="center">0,57</entry><entry align="center">8,80</entry><entry align="center">2,5</entry><entry align="center">850</entry><entry>Yes</entry></row><row><entry align="center">3</entry><entry align="center">0,80</entry><entry align="center">4,40</entry><entry align="center">0,57</entry><entry align="center">8,80</entry><entry align="center">2,5</entry><entry align="center">850</entry><entry>No</entry></row><row><entry align="center">4</entry><entry align="center">0,80</entry><entry align="center">4,40</entry><entry align="center">0,25</entry><entry align="center">8,80</entry><entry align="center">2,5</entry><entry align="center">850</entry><entry>No</entry></row></tbody></tgroup></table></tables>

A first coating device located above the tin bath, in an area where the glass temperature is around 745 ° C, allows by injection of silane (SiH₄), nitrogen (N₂), carbon dioxide (CO₂) and ethylene (C₂H₄), to obtain a layer of SiO_xVS_y (with a C / Si atomic ratio between 0.13 and 0.33) and whose thickness is between 10 and 30 nm.

The deposition of titanium dioxide is obtained by injecting TTIP and nitrogen via a second coating device above the glass at the entrance to the gallery where the glass is at a temperature of around 600 ° C. The layer of titanium dioxide thus obtained is mainly in anatase form.

After these deposits, for Examples 1 and 2, the coating was polished. Table 2 below shows the main characteristics of Examples 1 to 4 described in Table 1 above. Table 2 clearly shows the impact of polishing on roughness. The final roughness has a value of Rq which is between 1 and 2 nm in the case of Examples 1 and 2 which have been polished and which is greater than 4 in Examples 3 and 4 unpolished.<tables id="tabl0002" num="0002"><table frame="all"><title>Table 2: characterization of the products obtained under the conditions described in Table 1</title><tgroup cols="6"><colspec colnum="1" colname="col1" colwidth="24mm" /><colspec colnum="2" colname="col2" colwidth="35mm" /><colspec colnum="3" colname="col3" colwidth="22mm" /><colspec colnum="4" colname="col4" colwidth="35mm" /><colspec colnum="5" colname="col5" colwidth="35mm" /><colspec colnum="6" colname="col6" colwidth="17mm" /><thead><row><entry align="center" valign="top">examples</entry><entry align="center" valign="top">thickness SiO_x (XPS)</entry><entry align="center" valign="top">C / Si ratio</entry><entry align="center" valign="top">TiO thickness₂ (XRF)</entry><entry align="center" valign="top">P (polished) / NP (unpolished)</entry><entry align="center" valign="top">R_q (nm)</entry></row></thead><tbody><row><entry align="center">1</entry><entry align="center">30 nm</entry><entry align="center">0,30</entry><entry align="center">11 nm</entry><entry align="center">P</entry><entry align="center">1,6</entry></row><row><entry align="center">2</entry><entry align="center">27 nm</entry><entry align="center">0,33</entry><entry align="center">14 nm</entry><entry align="center">P</entry><entry align="center">1,7</entry></row><row><entry align="center">3</entry><entry align="center">28 nm</entry><entry align="center">0,32</entry><entry align="center">16 nm</entry><entry align="center">NP</entry><entry align="center">4,1</entry></row><row><entry align="center">4</entry><entry align="center">13 nm</entry><entry align="center">0,13</entry><entry align="center">16 nm</entry><entry align="center">NP</entry><entry align="center">4,8</entry></row></tbody></tgroup></table></tables>

Examples 1 to 4 obtained were then subjected to an intense heat treatment (670 ° C. for 200 s) and a set of analyzes were carried out in order to control their optical stability during said heat treatment.

Tables 3 and 4 show that, in accordance with the objective of the invention, the optical parameters measured before and after quenching are preserved. In fact, examples 1 and 2 of coated glass according to the invention present very satisfactory optical parameters in light transmission and in reflection on the layer side. It appears in particular that after heat treatment, the light transmission remains high and the light reflection on the layer side is less than 15%. The color of the coated substrate in transmission and reflection remains pleasant and corresponds to market demand. The heat treatment practically did not modify the optical parameters.<tables id="tabl0003" num="0003"><table frame="all"><title>Table 3: colorimetric parameters in light transmission before and after heat treatment.</title><tgroup cols="10"><colspec colnum="1" colname="col1" colwidth="22mm" /><colspec colnum="2" colname="col2" colwidth="12mm" /><colspec colnum="3" colname="col3" colwidth="15mm" /><colspec colnum="4" colname="col4" colwidth="15mm" /><colspec colnum="5" colname="col5" colwidth="12mm" /><colspec colnum="6" colname="col6" colwidth="15mm" /><colspec colnum="7" colname="col7" colwidth="15mm" /><colspec colnum="8" colname="col8" colwidth="15mm" /><colspec colnum="9" colname="col9" colwidth="15mm" /><colspec colnum="10" colname="col10" colwidth="14mm" /><thead><row><entry morerows="1" align="center" valign="top">examples</entry><entry namest="col2" nameend="col4" align="center" valign="middle">before quenching</entry><entry namest="col5" nameend="col7" align="center" valign="middle">after quenching</entry><entry morerows="1" align="center" valign="middle">Δa *</entry><entry morerows="1" align="center" valign="middle">Δb *</entry><entry morerows="1" align="center" valign="middle">ΔE_TL</entry></row><row><entry align="center" valign="middle">TV</entry><entry align="center" valign="middle">at*</entry><entry align="center" valign="middle">b *</entry><entry align="center" valign="middle">TV</entry><entry align="center" valign="middle">at*</entry><entry align="center" valign="middle">b *</entry></row></thead><tbody><row><entry align="center" valign="middle">1</entry><entry align="center" valign="middle">86</entry><entry align="center" valign="middle">-0,61</entry><entry align="center" valign="middle">1,92</entry><entry align="center" valign="middle">86</entry><entry align="center" valign="middle">-0,61</entry><entry align="center" valign="middle">2,10</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">-0,18</entry><entry align="center" valign="middle">0,2</entry></row><row><entry align="center" valign="middle">2</entry><entry align="center" valign="middle">84</entry><entry align="center" valign="middle">-0,55</entry><entry align="center" valign="middle">2,98</entry><entry align="center" valign="middle">84</entry><entry align="center" valign="middle">-0,55</entry><entry align="center" valign="middle">3,08</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">-0,1</entry><entry align="center" valign="middle">0,2</entry></row><row><entry align="center" valign="middle">3</entry><entry align="center" valign="middle">84</entry><entry align="center" valign="middle">-0,54</entry><entry align="center" valign="middle">3,1</entry><entry align="center" valign="middle">84</entry><entry align="center" valign="middle">-0,53</entry><entry align="center" valign="middle">3,22</entry><entry align="center" valign="middle">-0,01</entry><entry align="center" valign="middle">-0,12</entry><entry align="center" valign="middle">0,1</entry></row><row><entry align="center" valign="middle">4</entry><entry align="center" valign="middle">85</entry><entry align="center" valign="middle">-0,6</entry><entry align="center" valign="middle">3,15</entry><entry align="center" valign="middle">83</entry><entry align="center" valign="middle">-0,54</entry><entry align="center" valign="middle">3,21</entry><entry align="center" valign="middle">-0,06</entry><entry align="center" valign="middle">-0,06</entry><entry align="center" valign="middle">0,6</entry></row></tbody></tgroup></table></tables><tables id="tabl0004" num="0004"><table frame="all"><title>Table 4: colorimetric parameters in reflection on the layer side before and after heat treatment.</title><tgroup cols="10"><colspec colnum="1" colname="col1" colwidth="22mm" /><colspec colnum="2" colname="col2" colwidth="12mm" /><colspec colnum="3" colname="col3" colwidth="15mm" /><colspec colnum="4" colname="col4" colwidth="15mm" /><colspec colnum="5" colname="col5" colwidth="12mm" /><colspec colnum="6" colname="col6" colwidth="15mm" /><colspec colnum="7" colname="col7" colwidth="15mm" /><colspec colnum="8" colname="col8" colwidth="15mm" /><colspec colnum="9" colname="col9" colwidth="15mm" /><colspec colnum="10" colname="col10" colwidth="13mm" /><thead><row><entry morerows="1" align="center" valign="top">Examples</entry><entry namest="col2" nameend="col4" align="center" valign="middle">before quenching</entry><entry namest="col5" nameend="col7" align="center" valign="middle">after quenching</entry><entry morerows="1" align="center" valign="middle">Δa *</entry><entry morerows="1" align="center" valign="middle">Δb *</entry><entry morerows="1" align="center" valign="middle">ΔE_Rc</entry></row><row><entry align="center" valign="middle">Rc</entry><entry align="center" valign="middle">at*</entry><entry align="center" valign="middle">b *</entry><entry align="center" valign="middle">Rc</entry><entry align="center" valign="middle">at*</entry><entry align="center" valign="middle">b *</entry></row></thead><tbody><row><entry align="center" valign="middle">1</entry><entry align="center" valign="middle">11</entry><entry align="center" valign="middle">-0,3</entry><entry align="center" valign="middle">-6,41</entry><entry align="center" valign="middle">11</entry><entry align="center" valign="middle">-0,19</entry><entry align="center" valign="middle">-6,62</entry><entry align="center" valign="middle">-0,11</entry><entry align="center" valign="middle">0,21</entry><entry align="center" valign="middle">0,7</entry></row><row><entry align="center" valign="middle">2</entry><entry align="center" valign="middle">14</entry><entry align="center" valign="middle">-0,4</entry><entry align="center" valign="middle">-8,64</entry><entry align="center" valign="middle">13</entry><entry align="center" valign="middle">-0,33</entry><entry align="center" valign="middle">-8,69</entry><entry align="center" valign="middle">-0,07</entry><entry align="center" valign="middle">0,05</entry><entry align="center" valign="middle">0,7</entry></row><row><entry align="center" valign="middle">3</entry><entry align="center" valign="middle">14</entry><entry align="center" valign="middle">-0,39</entry><entry align="center" valign="middle">-8,94</entry><entry align="center" valign="middle">14</entry><entry align="center" valign="middle">-0,34</entry><entry align="center" valign="middle">-8,91</entry><entry align="center" valign="middle">-0,05</entry><entry align="center" valign="middle">-0,03</entry><entry align="center" valign="middle">0,7</entry></row><row><entry align="center" valign="middle">4</entry><entry align="center" valign="middle">13</entry><entry align="center" valign="middle">-0,2</entry><entry align="center" valign="middle">-9,53</entry><entry align="center" valign="middle">14</entry><entry align="center" valign="middle">-0,21</entry><entry align="center" valign="middle">-9,27</entry><entry align="center" valign="middle">0,01</entry><entry align="center" valign="middle">-0,26</entry><entry align="center" valign="middle">0,4</entry></row></tbody></tgroup></table></tables>

Finally, Table 5 provides the measured values ​​of the angle of contact with water for the different samples, polished or unpolished, before and after quenching depending on whether the sample has been activated by UV irradiation or not. With regard to the UV activation of the hydrophilicity, the UV irradiation is carried out at 40 ° C. for a period of 30 minutes by means of UVA with a power of 40 W / m² (UVA-340 nm, 40 W / m², from a Q-Panel device, from Q-Lab, Cleveland, Ohio).<tables id="tabl0005" num="0005"><table frame="all"><title>Table 5: measurement of the contact angle</title><tgroup cols="5"><colspec colnum="1" colname="col1" colwidth="19mm" /><colspec colnum="2" colname="col2" colwidth="18mm" /><colspec colnum="3" colname="col3" colwidth="20mm" /><colspec colnum="4" colname="col4" colwidth="18mm" /><colspec colnum="5" colname="col5" colwidth="20mm" /><thead><row><entry morerows="2" align="center" valign="middle">examples</entry><entry namest="col2" nameend="col5" align="center" valign="middle">Contact angles</entry></row><row><entry namest="col2" nameend="col3" align="center" valign="middle">before quenching</entry><entry namest="col4" nameend="col5" align="center" valign="middle">after quenching</entry></row><row><entry align="center" valign="middle">at the beginning</entry><entry align="center" valign="middle">30 min UV</entry><entry align="center" valign="middle">at the beginning</entry><entry align="center" valign="middle">30 min UV</entry></row></thead><tbody><row><entry align="center" valign="middle">1</entry><entry align="center" valign="middle">37°</entry><entry align="center" valign="middle">21°</entry><entry align="center" valign="middle">31°</entry><entry align="center" valign="middle">5°</entry></row><row><entry align="center" valign="middle">2</entry><entry align="center" valign="middle">36°</entry><entry align="center" valign="middle">18°</entry><entry align="center" valign="middle">43°</entry><entry align="center" valign="middle">4°</entry></row><row><entry align="center" valign="middle">3</entry><entry align="center" valign="middle">38°</entry><entry align="center" valign="middle">6°</entry><entry align="center" valign="middle">35°</entry><entry align="center" valign="middle">4°</entry></row><row><entry align="center" valign="middle">4</entry><entry align="center" valign="middle">34°</entry><entry align="center" valign="middle">6°</entry><entry align="center" valign="middle">35°</entry><entry align="center" valign="middle">5°</entry></row></tbody></tgroup></table></tables>

As described in the prior art, Table 5 confirms that when the TiO layer₂ is polished, and therefore less rough, hydrophilicity in general is less good. Indeed, the contact angle with water after a UV irradiation of 30 minutes is between 18 ° and 21 ° whereas the same irradiation on an unpolished sample makes it possible to reach a contact angle of the order of 6 °.

On the other hand, when comparing the contact angle with water of a polished and heat-treated coating, to the great surprise of the inventor, the titanium dioxide layer behaves in the same way as a TiO layer₂ unpolished. Indeed, we can clearly see that the TiO layer₂ polished and heat treated, when irradiated for 30 minutes has a contact angle of 5 °. This observation shows, against all expectations, that a layer of polished titanium dioxide can recover very satisfactory hydrophilicity values, after heat treatment.

At the same time the surface has a very low roughness, which slows down fouling and allows easier cleaning. Table 6 gives the roughness measurements carried out on a polished and quenched sample and on an unpolished and quenched sample. The measurements confirm that the roughness of a sample after quenching remains lower. The product of the invention, both smooth and hydrophilic, which makes it reluctant to clog, easy to clean and less scratchable.<tables id="tabl0006" num="0006"><table frame="all"><title>Table 6 roughness measurement after quenching</title><tgroup cols="3"><colspec colnum="1" colname="col1" colwidth="24mm" /><colspec colnum="2" colname="col2" colwidth="27mm" /><colspec colnum="3" colname="col3" colwidth="27mm" /><thead><row><entry align="center" valign="top">examples</entry><entry align="center" valign="top">R_q before quenching</entry><entry align="center" valign="top">R_q after quenching</entry></row></thead><tbody><row><entry align="center">2</entry><entry align="center">1,7</entry><entry align="center">1,9</entry></row><row><entry align="center">3</entry><entry align="center">4,1</entry><entry align="center">4,1</entry></row></tbody></tgroup></table></tables>

The products obtained in accordance with the invention were subjected to the standardized test EN 1096-5 which evaluates the hydrophilic and self-cleaning properties. The test of this standard is a measure of the haze on several samples subjected to a simulation of climatic conditions. The evaluation criterion is that the variation of the haze before and after the test (ΔH) must be less than 1%.

The results described in Table 7 are in agreement with the observations of the invention. Indeed, it clearly appears that if the unpolished and therefore rough glass passes the test before and after heat treatment, the product of the invention, that is to say polished and therefore less rough, passes the standard test only after heat treatment. This last test therefore confirms that, very surprisingly, a coated glass according to the invention not only has a low roughness but also has the properties of a hydrophilic self-cleaning glass.<tables id="tabl0007" num="0007"><table frame="all"><title>Table 7. variation of the haze (ΔH in%) after exposure to simulated climatic conditions according to EN 1096-5.</title><tgroup cols="4"><colspec colnum="1" colname="col1" colwidth="43mm" /><colspec colnum="2" colname="col2" colwidth="36mm" /><colspec colnum="3" colname="col3" colwidth="36mm" /><colspec colnum="4" colname="col4" colwidth="44mm" /><thead><row><entry valign="middle" /><entry align="center" valign="middle">Trial 1 (polished)</entry><entry align="center" valign="middle">Trial 2 (unpolished)</entry><entry align="center" valign="middle">Clear glass (reference)</entry></row></thead><tbody><row><entry valign="middle">Before heat treatment</entry><entry align="center" valign="middle">1,2</entry><entry align="center" valign="middle">0,6</entry><entry align="center" valign="middle">2,9</entry></row><row><entry valign="middle">After heat treatment</entry><entry align="center" valign="middle">0,7</entry><entry align="center" valign="middle">0,6</entry><entry align="center" valign="middle">4,7</entry></row></tbody></tgroup></table></tables>