1. Field of the Invention

The invention relates to an article comprising a matted glass sheet, which is translucent and has a particular aesthetical aspect. The glass sheet of the invention may be used for decorative and/or privacy purposes.

Z. Description of the Related Art

In the field of decorative applications, matted glass sheets are known for a long time. By matted glass sheet, it is intended a glass which is translucent but diffuses light and has a frosted satin-like appearance. Such type of glass sheet could be obtained by removing some quantity of glass material at the top of its surface, giving a specific texture and roughness to that surface. It is mainly used for decorative and/or privacy purposes in both residential and commercial settings (doors, tables, shelves, shower screens, furniture, wall panelling, ...). The main known processes to obtain matted glass sheets are chemical etching (controlled chemical attack with acid or base) and sandblasting (mechanical attack). Matted glass sheet which is treated on one or both faces are known. The treatment of both faces of a glass sheet allows reaching a higher degree of privacy compared to the treatment of only one face. Several matting steps may also be implemented on the same face in order to increase the degree of privacy but, in that case, the roughness is much higher and then detrimental to the desired "soft touch" of the glass product.

In the same field, it is also known a glass sheet coated on one side with a satin-finish paint which mimics the translucent appearance of matted glass. Such a product, like the Lacomat® product commercialized by AGC Flat Glass Company, provides more privacy than acid-etched or sandblasting glass, coming from a higher diffusion of light. Moreover, due to the presence of the paint layer, it could also have a colour tint if the paint comprises pigments. For example, an aesthetically pleasing flat glass product is known with a whitish tint (Lacomat® White). Nevertheless, this painted glass sheet has several disadvantages: (i) it cannot be thermally tempered once coated because the paint would not resist to the heat-treatment required for tempering and (ii) it cannot be laminated. Moreover, it is known that such a whitish tint could not be obtained with a simply matted glass, by, for example, modifying or adapting (i) the composition of attack solution or (ii) the conditions of this attack (time, temperature, ... ) .

Finally, it is also known a glass sheet which is acid-etched on one side and painted with an opacifying coating on the other side (Matelac® commercialized by AGC Flat Glass Company). This product is however an opaque glazing even if it may provide, when looking from the acid-etched face, an aesthetically pleasing colour combined with a satin look due to acid-etching.

3. Objectives of the Invention

The invention aims to solve the disadvantages of known products described above. More particularly, an objective of the present invention is to provide a translucent glass article which shows a pleasant whitish aesthetical aspect, similar to that of the Lacomat® White, and which could be thermally tempered.

Another objective of the present invention is to provide a solution to the disadvantages of known products which is simple and cost effective.

4. Summary of the Invention

The invention concerns an article comprising at least one glass sheet which comprises a first surface and a second surface.

According to an embodiment, the first surface is a matted surface.

According to another embodiment, the article comprises:

- particles partially embedded in said second surface; and/or - particles totally embedded in the glass bulk close to said second surface; and/or

- particles onto said second surface.

According to the invention, the combination of a first matted surface and a second surface with particles partially and/or totally embedded and/or particles onto said second surface provides a glass product which solves the drawbacks of known products and which therefore solves the posed technical problem. The inventors have indeed surprisingly found that such a glass article is translucent with a desired degree of privacy and it shows a pleasant whitish tint. Moreover, such an article may be thermally tempered.

5. Brief Decription of the Drawings

Other characteristics and advantages of the invention will more clearly appear with the reading of the following description of at least one preferred embodiment, given as simple illustrative and non restrictive example, and annexed drawings among which:

figure 1 is an enlarged, cross-sectional view of an article according to a particular embodiment,

figure 2 is an enlarged, cross-sectional view of an article according to another particular embodiment,

figure 3 is an enlarged, cross-sectional view of an article according to another additional embodiment,

figure 4 is a combination of embodiments of Figures 1 and 2, figure 5 is a combination of embodiments of Figures 1, 2 and 3, figure 6 is a picture obtained by transmission electronic microscopy of an article according to the invention,

figure 7 is a picture obtained by transmission electronic microscopy of another article according to the invention, figure 8 is a picture obtained by scanning electronic microscopy of another article according to the invention.

6. Description of at least one embodiment of the Invention

As illustrated in Figures 1 to 5, the article according to the invention comprises at least one glass sheet (2).

The glass sheet (2) may be made of soda-lime glass. By soda-lime glass, it is meant a glass having the following composition, expressed in percentages by weight:

SiO ₂ 60 to 75%,

Na ₂ O 10 to 20%,

CaO 0 to 16%,

K ₂ O 0 to 10%,

MgO 0 to 10%,

Al ₂ O ₃ 0 to 5%,

BaO 0 to 2%, with both further conditions: alkaline-earth oxides (BaO + CaO + MgO) totalising from 10 to 20%, alkaline oxides (Na ₂ O + K ₂ O) totalising from 10 to 20%.

Minor additives may as well be present in very small proportions in the glass composition, like redox components (NaNO ₃ , Na ₂ SO ₄ , coke, ...), for example.

The glass sheet (2) according to the invention may be a float glass. It may have a thickness of from 0.5 to 15 mm. The glass sheet may be made of clear or extra-clear glass. By extra-clear glass, it is intended a glass which comprises a total amount of iron, expressed as Fe ₂ O ₃ , lower than about 0.04 weight % and particularly, lower than 0.02 weight %. By clear glass, it is intended a glass which comprises a total amount of iron, expressed as Fe ₂ O ₃ , which may vary from about 0.04 to about 0.4 weight %. The glass sheet (2) of the article comprises a first surface (3) and a second surface (4).

According to the invention, said first surface (3) is a matted surface. By matted surface, it is intended a surface for which some quantity of glass material has been removed, giving a specific texture and roughness to that surface, decreasing light transmitted by the glass. A proportion of the light transmitted through such a matted surface will also be diffused resulting in reduced spectral reflection.

The matted first surface (3) according to the invention may be produced by any known method. The matted first surface (3) according to the invention is preferably (i) an acid-etched surface obtained by a controlled chemical attack with acid, (ii) a base-etched surface obtained by a controlled chemical attack with base, or (iii) a sandblasted surface obtained by a mechanical attack. Acid-etched matted surface according to the invention may be produced conventionally by means of a controlled chemical attack with an aqueous solution of hydrofluoric acid. The acid attack may be made in one or several steps. Generally, attack aqueous solutions of hydrofluoric acid have a pH of from 0 to 5, and they may comprise, in addition to hydrofluoric acid itself, salts of that acid, other acids like HC1, H ₂ SO ₄ , HNO ₃ , acetic acid, phosphoric acids and their salts (e.g. Na ₂ SO ₄ , K ₂ SO ₄ , (NH ₄ ) ₂ SO ₄ , BaSO ₄ , ...) and optional adjuvants in minor proportions (e.g. acid/base buffer compounds, or compounds facilitating spreading of the solution, ... ). Alkaline salts and ammonium salts are generally preferred, like sodium, potassium and ammonium hydrofluoride and/or bifluoride. Base-etched matted surface according to the invention may be produced conventionally by means of a controlled attack with an alcohol-water solution of an alkali (LiOH, NaOH or KOH) at high temperature (300°C or above) . The basic attack may be made in one or several steps. Generally, attack basic solutions have a pH higher than 9 or, preferably, higher than 10. Sandblasted matted surface according to the invention may be conventionally obtained by blasting at high speed an abrasive grain material on the said surface. Such matting treatments produce a matted surface with a degree of surface roughness resulting from the creation of irregularities on the surface.

The article further comprises particles. The particles according to the invention are:

- particles partially embedded (5) in the second surface (4); and/or

- particles totally embedded (6) in the glass bulk close to the second surface (4); and/or

- particles (7) onto the second surface (4).

Figures 1-3 illustrate three particular embodiments of the invention in which particles are either partially embedded (5) in the second surface (Figure 1), or totally embedded (6) in the second surface (Figure 2) or onto the second surface (7) (Figure 3). According to the invention, these three last embodiments may be combined. Figures 4 and 5 illustrate two of the combinations covered by the invention.

By a particle partially embedded (5) in the second surface (4), it is intended a particle which lies at the same time inside the glass bulk and outside the glass bulk. In other words, the particle (5) is not completely surrounded by glass and it has thus a part of its volume in the glass sheet (2) and the other part of its volume outside the glass sheet (2).

By a particle totally embedded (6) in the glass bulk, it is intended a particle which is completely surrounded by glass and which has thus the totality of its volume in the glass sheet (2) . According to the invention, the particles totally embedded (6) in the glass bulk are close to the second surface (4). By close to the second surface, it is intended that the particles (6) are present in a glass thickness from the second surface (4) which is not higher than 100 μΐΏ and preferably, not higher than 50 μιτι. By a particle (7) onto the second surface (4), it is intended a particle which is deposited onto said surface and which sticks to it. For example, sticking occurs through covalent, dipole-dipole or van der Waals bonds.

According to the invention, the particles are at least partially crystallized. Preferably, the particles are totally crystallized. By totally crystallized, it is intended that the particles comprise at least a proportion of 90 % of their weight constituted of crystals.

The particles according to the invention may be isolated or alternatively, they may be present in the form of an assembly of several particles.

The particles according to the invention have a size which is not less than 5 nm. The particles have a size which is not higher than 10 μιτι. By size, it is intended the larger dimension of particles.

The particles according to the invention are composed of at least an inorganic oxide. The inorganic oxide is selected amongst oxides of titanium, cerium, zinc, magnesium, calcium, strontium, scandium, yttrium, lanthanum, aluminium, niobium, tantalum, and silicon. The particles may comprise one inorganic oxide from this group. Alternatively, the particles may comprise mixtures of two or more inorganic oxides from this group, in various proportions. The use of these particular oxides in the invention allows reaching a better aesthetical aspect, in particular a better whitish tint. Advantageously, the particles comprise titanium oxide. Alternatively, the particles comprise cerium oxide. The use of these oxides is particularly advantageous as it allows obtaining the most satisfactory aesthetical results. This result is furthermore surprising because titanium oxide or cerium oxide containing glasses are known but they do not display a whitish tint. Contrary, the addition of such components in glass composition gives rise to the apparition of a blue or green colour for cerium and a neutral tint for titanium. The particles according to the invention may be obtained by any known method in the art and able to generate particles and embed them in or deposit them onto a glass surface. A non-limiting example of such process is flame- assisted spraying: the particles are generated by atomization of a solution of at least a chemical precursor in an aerosol transported in a flame where combustion takes place to provide solid particles. These particles may then be deposited onto the glass surface or embedded in this surface (totally and/or partially), the energy required for embedding being provided by the flame as temperature.

The article according to the invention is preferably made in a two-steps process aimed at producing (i) the matted surface and (ii) the second surface with particles. The matted surface may be produced first or alternatively, it may be produced after producing the particles.

The surface roughness of the matted surface (3) of the article according to the invention may be characterized by the Rz and RSm parameters and the relation between both parameters Rz/RSm. Rz and RSm are typical measures of surface roughness (expressed in μιτι) . All roughness measurements herein were obtained with a Taylor-Hobson Form Talysurf apparatus, in roughness mode. The samples have been measured with the following parameters:

Shape: LS line

Filter type: 2CR-PC

Sample length: 20 mm

Cut-off: "use the whole selected data length"

Short range filter: 0.008 mm

Long range filter: 0.8 mm

Rz (also called Rtm) is the average of all of the values Rzl, Rz2 .... etc. over the entire profile (Rzl is the greatest difference in altitude between the highest peak and the lowest valley over the first cut-off portion of the sample, Rz2 is the greatest difference in altitude between the highest peak and the lowest valley over the second cut-off portion of the sample, and so on for Rz3, Rz4, ...) . RSm (also called Sm) is the average of the distance between each time the profile crosses the average line; it represents an indication of the average distance between the main peaks (resulting from irregularities) of the profile. The short range filter and long range filter, as commonly used in the art of measuring surface roughness, are used to separate a characteristic measurement of surface roughness from an overall "waviness" of the sample and from very short wavelength effects.

The matted surface (3) of the article according to the invention has a surface roughness defined by a Rz value greater than 1 μιτι and less than 20 μπ , and a Rz/RSm ratio greater than 0.01 and less than 0.5. Preferably, the article has a surface roughness defined by a Rz greater than 9 μπ and less than 18 μπ , and a Rz/RSm ratio greater than 0.12 and less than 0.16.

The article according to the invention is translucent but diffuses the transmitted light resulting in a frosted satin-like appearance. The article according to the invention further displays a pleasant whitish tint which is similar to that of known Lacomat® White product.

The optical properties of the article according to the invention are characterized by the total light transmission, the haze and clarity values (characterizing diffusion of transmitted light) and the CIELab values: L*, a* and b* (characterizing colour aspect of the article). The optical properties of the article are considered in the present invention from the first matted surface but these properties when considered from the second surface do not significantly change.

The total light transmission with illuminant D (TLD) in the following description is considered for a thickness of 4 mm (TLD4) at a solid angle of observation of 2°. The light transmission represents the percentage of light flux emitted between wavelengths 380 nm and 780 nm which is transmitted through the article. It is desirable that the article according to the invention has a TLD4 of less than 80%.

CIE L*a*b* parameters are considered in the following description in reflection and with the following measurement parameters: illuminant D, 10°. It is desirable that the article according to the invention has a L* value higher than 35 when measured from the first matted surface. Preferably, the article according to the invention has a L* value higher than 50 when measured from the first matted surface.

Advantageously, if it is desired to enhance its resistance to breakage, the article of the invention may be chemically or thermally tempered without impairing its optical properties.

The invention is not limited to the described embodiments but also covers combinations of embodiments and/or alternatives.

The invention will now be illustrated below by examples aiming at better describing the invention, without by no means trying to limit its scope. Example 1 is a comparative example corresponding to a matted glass sheet while Examples 2, 3 and 4 are in accordance with the invention.

Example 1 (comparative example, non-compliant to the invention) A sheet of clear glass, 4 mm in thickness (20 cm x 20 cm) has been cleaned with an aqueous detergent and carefully rinsed with water and then dried.

The sheet has then been acid-etched in a known manner: an acidic attack solution composed of 17 ml 40% HF, 10 g Na ₂ CO ₃ , 17 ml glacial acetic acid and 66 ml water at 25°C has been drawn onto the glass sheet and the attack has been allowed to take place for 8 minutes. The attack acid solution has further been rinsed with water and a final cleaning of the glass sheet with an aqueous detergent solution has been performed. Example 2 (compliant to the invention)

A sheet of clear glass, 4 mm in thickness (20 cm x 20 cm) has been cleaned with an aqueous detergent and carefully rinsed with water and then dried. The sheet has then been acid-etched in a known manner: an acidic attack solution composed of 17 ml 40% HF, 10 g Na ₂ CO ₃ , 17 ml acetic acid glacial and 66 ml water at 25°C has been drawn onto the glass sheet and the attack has been allowed to take place for 8 minutes. The attack acid solution has further been rinsed with water and a final cleaning of the glass sheet with an aqueous detergent solution has been performed.

The sheet has then been treated nine times on the surface opposite to that acid-attacked, as follows: Hydrogen and oxygen has been introduced in a punctual burner with one nozzle in order to generate a flame. The glass sheet, previously matted, has been heated beforehand in an oven at 600°C and it has been placed under the burner placed above the glass sheet at a distance of 160 mm. In order to cover the whole surface of the sheet, the burner is mobile in both space directions comprised in the sheet plan. The burner head has moved continuously in one direction at a speed of 5 m/min and, in the other direction, perpendicular to the first one, with step of 2 cm.

The solution introduced in the flame has been titanium tretra- isopropoxide (TTIP) dissolved in isopropanol (IPA) with a dilution ratio TTIP:IPA of 1:10 (flow : 6 ml/min). Particles of titanium oxide have therefore been generated.

The glass sheet has finally been cooled down at room temperature and then analyzed by scanning electron microscopy (SEM), transmission electronic microscopy (TEM) and X-ray diffraction. These analyses have been implemented from the side treated by the flame process.

As illustrated by Figure 6, TEM analyses have shown that titanium oxide particles are totally embedded in the glass. They are present as stick-shaped crystals of TiO ₂ with a size varying from about 200 nm to about 0.3 μχη, in a glass thickness slightly higher than ΙμΐΉ. They are furthermore composed mainly of the rutile phase but show also minor amounts of anatase phase.

The roughness of the matted surface has been measured by a Taylor- Hobson Talysurf analysis of surface roughness, as commonly used for analysing surface roughness. The analysis consists of arranging a fine stylus having a calibrated point in contact with the matted surface to be analysed and slowly displacing the stylus across the surface so as to record all variations in the altitude of the surface. The parameters cited above have been used to carry out this analysis. The following results have been obtained for this article:

Rz= 9.7 /xm

RSm= 68.0 / m

Rz/RSm=0.14

Example 3 (compliant to the invention)

A sheet of extra-clear glass, 4 mm in thickness (20 cm x 20 cm) has been cleaned with an aqueous detergent and carefully rinsed with water and then dried.

The sheet has first been treated one time on a first surface, as follows: Hydrogen and oxygen has been introduced in a punctual burner with one nozzle in order to generate a flame. The glass sheet has been heated beforehand in an oven at 650°C and it has been placed under the burner placed above the glass sheet at a distance of 160 mm. The burner head has moved continuously in one direction at a speed of 3 m/min and, in the other direction, perpendicular to the first one, with step of 2 cm.

The solution introduced in the flame has been cerium nitrate, Ce(NO ₃ ) ₃ .6H ₂ O dissolved in methanol with a dilution ratio cerium nitrate: methanol of 1:5 (flow : 9.5 ml/min). Particles of cerium oxide have therefore been generated. The glass sheet has finally been cooled down at room temperature and, finally acid-etched in the same manner as in Example 2, on the surface opposite to that first treated with particles.

The glass sheet has been then analyzed by scanning electron microscopy (SEM), transmission electronic microscopy (TEM) and X-ray diffraction. These analyses have been implemented from the side treated by the flame process.

As illustrated by Figure 7, TEM analyses have shown that the article comprises cerium oxide particles which are totally embedded in the glass. They are present as spherical crystals of CeO ₂ with a size varying from about 10 nm to about 0.5 μΓη, in a glass thickness reaching 2.5 μιτι. They are furthermore composed mainly of CeO ₂ with a cubic structure. Moreover, the picture of Figure 8 displays that the glass article also comprises particles which are onto the analyzed surface.

The following roughness results have been obtained for this article: Rz= 10.6 μχη

RSm= 71.0 /mi

Rz/RSm=0.15

Example 4 (compliant to the invention)

The article from Example 3 has been thermally tempered in a classical manner: it has been heated up to 670°C during 195 seconds and then rapidly cooled with an air blower.

The optical properties of Lacomat White® (4mm in thickness), comparative Example 1 and Examples 2-4 compliant with the invention have been determined by measuring the total light transmission, the haze and clarity values and the CIELab values: L*, a* and b*. These optical properties have been measured from the matted or coated side of each article. The total light transmission has been measured for a thickness of 4 mm and with illuminant D (TLD4), as defined by the Commission Internationale de l'Eclairage (CIE), at a solid angle of observation of 2°. The standard ASTM O 1003-61 defines the haze as the percentage of transmitted light, which, while passing through the sample, deviates from the incident beam by an angle of more than 2.5° (also called wide-angle scattering). Clarity, also called narrow-angle scattering, defines the percentage of transmitted light, which, while passing through the sample, deviates from the incident beam by an angle of less than 2.5°. CIE L*a*b* parameters have been measured in reflection with a Perkin Elmer spectrometer (lambda 950) equipped with an integration sphere (150 mm diameter); using the following measurement parameters: illuminant D, 10°.

The articles from Examples 2 and 3, in accordance with the invention, have the following optical properties which may be compared to comparative Example 1 and the known coated Lacomat White® product:

a measurement from the coated side

b measurement from the matted side

Comparison of the known Lacomat White® and Example 2 compliant to the invention leads to the conclusion that the ΔΕ* value, defining by the CIE as (AL* ² + Aa* ² + Ab* ² ) ^½ and representing the "distance" between two "colors" reaches 8.5. This value is relatively low and therefore translates the fact that both articles are rather similar in term of color. Same conclusion may be made in the case of Example 3 for which ΔΕ* value reaches 10.4. The ΔΕ* value is 27.9 while comparing Example 2 and Comparative Example 1.

While comparing Example 3 and Example 4, which is the article from Example 3 which has been thermally tempered, once may notice that the thermal treatment carried out in Example 4 has not impaired the optical properties of the original article from Example 3. These properties are not modified significantly by tempering and in particular, the color is not affected by such a treatment (the ΔΕ* value is close to zero).