Flat glass composition

Abstract

The invention relates to a flat glass composition comprising the following constituents, the sum of said constituents representing at least 95% of the composition, the percentages being expressed by weight relative to the total weight of the composition: - from 60% to 75% silicon dioxide (SiO2); - from 8% to 12% sodium oxide (Na2O); - from 6% to 12% calcium oxide (CaO); - from 6% to 10% aluminium oxide (Al2O3); - from 0% to 5% potassium oxide (K2O); - from 0% to 3.5% magnesium oxide (MgO); wherein the sum of the contents by weight of CaO and MgO is from 6% to 12% and the content by weight of BaO and / or SrO is preferably at most 0.5%. The invention also relates to a method for preparing a flat glass comprising a composition according to the invention, and also to a glass sheet comprising a composition according to the invention.

Description

Description Title of the invention: Flat glass composition. TECHNICAL FIELD

[0001] The invention relates to a flat glass composition (or float glass), of the soda-lime-silica type, in particular for applications in the building or automotive sectors. The present invention also relates to a method for manufacturing such flat glass, and its use as glazing. TECHNOLOGICAL BACKGROUND

[0002] The manufacturing process for float glass involves melting a mixture of raw materials in a glass furnace at temperatures ranging from 1300 to 1700°C, then forming a ribbon of molten glass over a molten tin bath. The ribbon is then slowly cooled, annealed, and then cut.

[0003] As with any industrial process, there is a growing need to decarbonize flat glass production processes in order to limit their impact on the environment. Development efforts are therefore generally focused on the use of renewable energy or fuels, increasing the proportion of raw materials from recycling or industrial waste recovery channels in glass-forming mixtures, or energy recovery at various stages of the process.

[0004] At the same time, float glass compositions are subject to standards in order to obtain a set of desired physical or mechanical properties and to define quality criteria. Thus, classic glass products are of the soda-lime-silica type and have the following chemical composition, expressed by convention in oxides of the constituent elements (in mass percentages): - from 69% to 74% silicon dioxide (SiO2); - from 5% to 14% calcium oxide (CaO); - from 10% to 16% sodium oxide (Na2O); - from 0% to 6% magnesium oxide (MgO); - from 0% to 3% aluminum oxide (AI2O3); - from 0% to 5% of other oxides (Fe2O3, K2O, ZnO, SrO, B2O3, etc.).

[0005] These standard compositions allow the production of flat glasses of satisfactory quality and durability (optical qualities, vitrification, refining, resistance to surface abrasion, surface durability to weathering, etc.) with controlled process constraints and production costs (including various aspects: minimized melting temperature, less corrosion of refractories, hardenability, etc.).

[0006] To reduce environmental impacts, it is proposed to reduce the energy required to melt raw materials. For example, document US 5,071,796 proposes flat glass compositions with lower melting temperatures. These compositions are obtained in particular by slightly reducing the silica content and compensating for it with a higher alkali content (Na2O). However, the glasses obtained have a substantially higher coefficient of thermal expansion (TEC) than standard float glasses (10.44 x 10' 6 °C' 1 against 8.62 x 10' 6 °C' 1 ), which can alter their thermal shock resistance properties.

[0007] WO 2014 / 128714 describes soda-lime-silica flat glass compositions that allow energy savings during production and also reduce carbon dioxide (CO2) emissions related to the reaction of raw materials. These compositions are obtained by substituting sodium carbonate and limestone (sources of Na2O and CaO) with borax pentahydrate (source of B2O3) in the raw materials used. They also reduce the coefficient of thermal expansion and improve surface durability to weathering.However, boron compounds are harmful to health (classified as "CMR") and to aquatic ecosystems, which poses constraints both in terms of use during manufacturing (exposure in the form of fine dust or vapors with partial volatilization during glass melting) and in terms of recyclability (boron releases can accumulate in soils and waters, and affect plant growth and aquatic life).

[0008] More generally, a change in composition by varying one or more constituents impacts the glass structure and the vitreous network, and possible beneficial effects are often accompanied by detrimental effects on one or more other properties (such as hydrolytic resistance, viscosity at high temperatures, reduction of the temperature range in which the glass can be formed without devitrification, etc.). It is therefore complex to modify and formulate float glass compositions, allowing both to reduce environmental impacts and to satisfy the various production and performance criteria (including the conditions for good "floatability" and refining, the durability of the glass, etc.). More specific oxides (such as B2O3, BaO, ZrO or ZrO2) are sometimes used to improve certain properties of the glass or to limit other negative effects of the composition, but their use is not always beneficial for the environment (conditions of extraction and purification of the oxides, more energy-intensive processing, recyclability of the resulting glass).

[0009] Thus, alternative compositions are still being researched and there is still a need for compositions that can reduce environmental impacts without increasing production costs and without deteriorating the thermal, mechanical and durability properties of the glasses. In particular, there is still a need for compositions that can become new standards compatible with the "float" process, making it possible to meet current environmental challenges (minimization of energy impacts and / or CO2 emissions, compositions compatible with the use of recycled materials, recyclability of the glasses produced), while meeting the various requirements of standard glasses, particularly for glazing, in terms of quality and durability (absence of optical defects, homogeneity, thermal expansion, hydraulic resistance, hardness, etc.).

[0010] It is to the applicant's credit that it proposes a flat glass composition which, surprisingly, makes it possible to reduce the carbon footprint of the product, whilst satisfying both the process constraints and the quality and durability requirements. SUMMARY OF THE INVENTION

[0011] According to a first aspect, the invention relates to a flat glass composition comprising the following constituents, their sum representing at least 95% of the composition, the percentages being expressed by mass relative to the total mass of the composition: - 60% to 75% silicon dioxide (SiO2); - 8% to 12% sodium oxide (Na2O); - from 6% to 12% calcium oxide (CaO); - from 6% to 10% aluminum oxide (AI2O3); - from 0% to 5% potassium oxide (K2O); - from 0% to 3.5% of magnesium oxide (MgO); in which the sum of the mass contents of CaO and MgO is from 6% to 12%. In addition, the mass content of SrO and / or BaO may advantageously be at most 0.5%.

[0012] The composition according to the invention has the advantage of allowing the use of a wider variety of alternative raw materials. Surprisingly, the inventors have demonstrated that, although the composition according to the invention has a higher refining temperature (Tiogz) than standard compositions, it allows a significant reduction in overall CO2 emissions, taking into account both emissions linked to the melting of raw materials (reactions of raw materials), emissions linked to the combustion of natural gas (energy required for the temperature increase) and other emissions linked to the use and production of synthetic raw materials. In addition, the composition according to the invention has all the desired properties in terms of quality and durability without requiring the use of particular oxides.This composition is also compatible with the use of a larger proportion of cullet, which further improves the environmental impact. Finally, it is itself more easily recyclable, since it is essentially made up of "classic" oxides of soda-lime-silica type compositions.

[0013] The invention also relates, according to a second aspect, to a method for manufacturing a flat glass, comprising: - a step of melting a mixture of selected raw materials so as to obtain a target composition according to the invention; - a step of forming the molten mixture into a glass ribbon by floating.

[0014] According to another aspect, the invention also relates to a window comprising a composition according to the invention.

[0015] The invention relates to the use of a composition according to the invention as glazing, preferably for buildings. DETAILED DESCRIPTION

[0016] General terms used in this text are defined below.

[0017] The expression "comprising" includes the expression "consisting of".

[0018] The expression "from ... to ..." must be understood inclusively.

[0019] Unless explicitly stated, the term “free”, within the meaning of the present invention, means a mass content of substance less than or equal to 0.1%, preferably less than or equal to 0.05% relative to the total mass of the composition.

[0020] The composition according to the invention comprises the following constituents, their sum representing at least 95% of the composition, the percentages being expressed by mass relative to the total mass of the composition: - 60% to 75% silicon dioxide (SiO2); - 8% to 12% sodium oxide (Na2O); - from 6% to 12% calcium oxide (CaO); - from 6% to 10% aluminum oxide (AI2O3); - from 0% to 5% potassium oxide (K2O); - from 0% to 3.5% magnesium oxide (MgO); in which the sum of the mass contents of CaO and MgO is from 6% to 12%.

[0021] It is understood that this is the composition expressed, by convention, in oxides of the constituent elements (SiO2, Na2O, CaO, K2O, AI2O3, Fe2O3, etc.). Indeed, glass is a substance of variable composition, resulting from complex reactions forming a random network. Although classically the compositions of glass are expressed in oxides of different elements, glass is not a mixture of these different oxides and does not contain these oxides as such.

[0022] In the composition according to the invention, the sum of the mass contents of SiO2, Na2O, CaO, AI2O3, K2O and MgO represents at least 95%, relative to the total mass of the composition. More preferably, the sum of the mass contents of SiO2, Na2O, CaO, AI2O3, K2O and MgO represents at least 98%, preferably at least 99%, relative to the total mass of the composition.

[0023] The composition according to the invention comprises 60% to 75% SiO2. Silicon dioxide (SiO2), also called silica here, is the main network-forming element in glass. Too low levels lead to a deterioration in the hydrolytic resistance of the glass, particularly in basic environments. On the other hand, Contents above 75% lead to too great an increase in the viscosity of the glass, which is problematic for melting the mixture of raw materials and for forming the glass. The silica can be provided by raw materials such as sand, cullet, feldspar and / or wollastonite. Preferably, in the composition according to the invention, the mass content of SiO2 is at most 73%, more preferably at most 71%, relative to the total mass of the composition. Preferably, in the composition according to the invention, the mass content of SiO2 is from 65% to 73%, more preferably from 65% to 71%, relative to the total mass of the composition.

[0024] The composition according to the invention comprises 6% to 10% of AI2O3. Aluminum oxide (AI2O3) is also a network-forming element in glass. According to ISO 16293, applicable to building glazing, the standard AI2O3 content is 0% to 3%. Indeed, a higher aluminum oxide content increases the melting temperature of the glass (and therefore the energy required for melting), increases the viscosity at high temperatures (which complicates the shaping of the glass), and can promote the formation of undesirable crystals (optical defects and / or embrittlement of the glass structure). Going against these prejudices, the inventors have developed a glass composition with specific contents of different oxides, compatible with the float process and surprisingly making it possible to significantly reduce the carbon footprint of the glass produced while maintaining satisfactory properties in terms of quality, durability and processability.Aluminum oxide can in particular be provided by raw materials such as aluminosilicates, in particular feldspars. Preferably, in the composition according to the invention, the mass content of AI2O3 is from 7% to 10%, more preferably from 8% to 10%. Advantageously, the mass content of AI2O3 can be from 7.5% to 9%, more preferably from 8% to 9%, relative to the total mass of the composition. This content, combined with the other oxide contents, advantageously makes it possible to combine a substantial reduction in the carbon footprint of the product while satisfying the quality and durability requirements of the glass (in particular a large forming margin, a limited risk of crystallization and good wear resistance).

[0025] Alkali oxides (Na2O and K2O) are network modifiers. They reduce the high-temperature viscosity of the molten glass composition but can also have a negative impact on the hydrolytic resistance of the glass. These elements can, for example, be provided by raw materials such as sodium carbonate, cullet, aluminosilicates, in particular feldspars. The composition according to the invention comprises 8% to 12% of Na2O. Preferably, the mass content of Na2O is 8% to 11%, more preferably 9% to 11%, relative to the total mass of the composition. The composition according to the invention comprises 0% to 5% of K2O. Preferably, in the composition according to the invention, the mass content of K2O is 0.1% to 5%, more preferably 0.5% to 5%, even more preferably 1% to 4%, relative to the total mass of the composition.

[0026] Alkali earth metal oxides (CaO and MgO) are network modifiers. They reduce the high-temperature viscosity of the molten glass composition but can also increase the liquidus temperature and / or increase the risk of devitrification. These elements can, for example, be introduced into the raw material mixture by limestone, wollastonite, talc, lime, cullet and / or dolomite. The composition according to the invention comprises 6% to 12% of CaO. Preferably, the mass content of CaO is at most 11%, preferably at most 10%, even more preferably at most 9%, relative to the total mass of the composition. Preferably, the mass content of CaO is 6% to 11%, more preferably 7% to 10%, even more preferably 7% to 9%, relative to the total mass of the composition. The composition according to the invention comprises 0% to 3.5% of MgO.Preferably, the mass content of MgO is at most 3%, preferably at most 2.5%, even more preferably at most 2%, relative to the total mass of the composition. Preferably, the mass content of MgO is from 0.1% to 3.5%, more preferably from 0.1% to 3%, more preferably from 0.5% to 2.5%, even more preferably from 1% to 2%, relative to the total mass of the composition.

[0027] Preferably, the sum of the mass contents of CaO and MgO is at most 11%, preferably at most 10%, more preferably at most 9%, relative to the total mass of the composition. Preferably, the sum of the mass contents of CaO and MgO is from 6% to 11%, more preferably from 7% to 10%, better still from 7% to 9% relative to the total mass of the composition. This makes it possible to optimize the carbon footprint while maintaining or even improving the forming properties (in particular the buoyancy criterion) and the durability of the glass.

[0028] More preferably, the sum of the mass contents of alkaline earth metal oxides, in particular CaO, MgO, SrO and BaO, is at most 11%, preferably at most 10%, more preferably at most 9%, relative to the total mass of the composition. Preferably, the sum of the mass contents of alkaline earth metal oxides, in particular CaO, MgO, SrO and BaO, is 6% to 11%, more preferably 7% to 10%, better still 7% to 9% relative to the total mass of the composition. This makes it possible to optimize the environmental balance while maintaining or even improving the properties for forming and the durability of the glass.

[0029] Preferably, the sum of the mass contents of Na2O and K2O is less than 15%, relative to the total mass of the composition. Preferably, the sum of the mass contents of Na2O and K2O is between 13% and 15%, relative to the total mass of the composition.

[0030] More preferably, the sum of the mass contents of alkali metal oxides, in particular Na2O, K2O and Li2O, is less than 15%, relative to the total mass of the composition, preferably between 13% and 15%.

[0031] Advantageously, in the composition according to the invention, the sum of the mass contents of Na2O and CaO is from 14% to 20%, preferably from 14% to 19%, relative to the total mass of the composition. This allows good properties to be obtained, particularly in terms of durability of the glass.

[0032] Advantageously, in the composition according to the invention, the ratio R of the sum of the mass contents of SiO2 and AI2O3 to the sum of the mass contents of CaO, MgO, Na2O and K2O, is 3 to 4. This makes it possible to maintain good properties for the forming and durability of the glass.

[0033] Preferably, in the composition according to the invention, the sum of the mass contents of B2O3, SrO, BaO and ZrO2 is less than 1%, preferably less than 0.5%, more preferably less than 0.2%, relative to the total mass of the composition. The particular composition according to the invention makes it possible to obtain good optical and mechanical properties without requiring the use of substantial contents of such oxides.

[0034] Preferably, in the composition according to the invention, the sum of the mass contents of B2O3, SrO, BaO, ZrO2, TiO2, ZnO and SnO2 is less than 1%, preferably less than 0.5%, more preferably less than 0.2%, relative to the total mass of the composition. The particular composition according to the invention allows obtaining good optical and mechanical properties without requiring the use of substantial contents of such oxides.

[0035] Preferably, the composition according to the invention is free of boron oxide (B2O3). This oxide generally improves the mechanical and / or chemical resistance of glasses. However, it has a complex effect on the thermal expansion of the glass, which depends on its concentration and the overall composition of the glass (interactions and combination with other oxides), which requires a suitable dosage and formulation to control its effects. In addition, its use complicates the recyclability and reuse of glasses produced with this oxide.

[0036] Preferably, the composition according to the invention comprises a mass content of Li2O of less than 0.5%, preferably less than 0.2% relative to the total mass of the composition. More preferably, the composition according to the invention is free of lithium oxide (Li2O). This oxide is generally used to facilitate the melting of glass and / or improve its mechanical properties. However, in addition to its rarity and high cost, it tends to evaporate at high temperature, which can complicate the precise control of the composition of the glass during melting.

[0037] Preferably, the composition according to the invention is free of ZnO. This oxide is generally added for its beneficial effects on the hardness, chemical resistance and optical properties of the glass. However, depending on the other oxides present and their content, it can promote crystallization (devitrification) which can lead to a loss of transparency and / or affect the mechanical properties of the glass.

[0038] Preferably, the composition according to the invention is free of ZrO2. This oxide is often used, particularly in the field of plasma glass compositions, to improve properties such as the mechanical strength and hardness of the glass. However, the extraction and purification of this oxide are more complex than those of other oxides (therefore generally not consistent with an ecological approach). In addition, this oxide, which is very refractory, is dense and more difficult to melt, which increases the risk of infusibility and / or the energy required for melting. Finally, ZrO2-based glasses are more difficult to recycle.

[0039] Preferably, the composition according to the invention is free of SnO2. This oxide can influence several properties of the glass such as transparency, chemical resistance or electrical conductivity. However, in addition to its high cost, it increases the viscosity of the glass and may tend to induce crystallization, defect formation or heterogeneity problems.

[0040] Preferably, the composition according to the invention comprises a mass content of BaO and / or SrO of at most 1%, preferably at most 0.5%, more preferably at most 0.2%, relative to the total mass of the composition. In other words, the sum of the BaO and SrO contents is less than or equal to these percentages. These oxides make it possible to lower the viscosity, just like CaO and MgO, but have less negative impact on the increase in the liquidus temperature. However, in addition to their rarity and the significant increase in the cost of the composition, these oxides are very dense and, depending on the compositions, they can pose problems of homogeneity. In addition, barium can be toxic in certain forms and requires precautions during the manufacture and recycling of the glass. More preferably, the composition according to the invention is free of BaO and / or SrO.This makes it possible to obtain glass compositions essentially made up of more traditional oxides and which can be more easily recycled.

[0041] Preferably, the composition according to the invention comprises a mass content of Fe2O3 of at most 2%, preferably at most 1%, more preferably at most 0.6%, relative to the total mass of the composition.

[0042] The composition according to the invention may optionally contain other components or impurities, such as for example sulfur oxide (SO3), often in low levels (for example less than 1%). The SO3 element may in particular come from refining agents (such as sodium sulfate).

[0043] According to a preferred embodiment, the composition according to the invention comprises the following constituents, the percentages being expressed by mass relative to the total mass of the composition: - from 60% to 71% SiO2; - from 8% to 11% of Na2O; - from 6% to 11% CaO, preferably from 6% to 10% CaO; - from 6% to 10% of AI2O3, preferably 7.5% to 9% of AI2O3; - from 0% to 5% K2O; - from 0% to 3% of MgO; and the sum of the mass contents of CaO and MgO being from 6 to 11%. This composition may further include one or more of the features previously described.

[0044] According to another preferred embodiment, the composition according to the invention comprises the following constituents, the percentages being expressed by mass relative to the total mass of the composition: - from 60% to 71% of SiO2, preferably from 65% to 71% of SiO2; - from 8% to 11% of Na2O; - from 6% to 10% CaO; - from 6% to 10% of AI2O3, preferably 7.5% to 9% of AI2O3; - from 0% to 5% K2O; - from 0% to 3% of MgO; and the sum of the mass contents of CaO and MgO being from 6% to 10%. This composition may further comprise one or more of the characteristics previously described.

[0045] According to a particularly preferred embodiment, the composition according to the invention comprises the following constituents, their sum representing at least 98% of the composition, preferably at least 99% of the composition, the percentages being expressed by mass relative to the total mass of the composition: - from 60% to 75% SiO2; - from 8% to 11% of Na2O; - from 6% to 10% CaO; - from 7.5% to 9% of AI2O3, preferably 8% to 9% of AI2O3; - from 0% to 5% K2O; - from 0% to 3% of MgO; and the sum of the mass contents of CaO and MgO being from 6% to 10%, preferably from 6% to 9%. This composition may further comprise one or more of the characteristics previously described.

[0046] The composition according to the invention has the advantage of being able to be melted and transformed into a glass ribbon at temperatures suitable for the manufacture of flat glass, in particular using the float process. In addition, it has very good properties, in particular an improved service life. The composition according to the invention may also have other advantageous properties in terms of processability.

[0047] The composition according to the invention may have a refining temperature (T| Og2 ) above 1450°C, or even above 1500°C. Preferably, the refining temperature ( og2 ) is lower than 1700°C, more preferably lower than 1600°C. The refining temperature (Ti og2), represents the temperature at which the molten glass composition has a viscosity of 100 poises (enabling the refining of the molten glass to be facilitated). Thus, the compositions according to the invention have a higher refining temperature than standard compositions.

[0048] The composition according to the invention may have a liquidus temperature (Ti iq ) of at most 1200°C, for example from 1000°C to 1150°C. The liquidus temperature (Ti iq ), represents the temperature from which the mixture is entirely liquid (no more coexistence of liquid and solid forms).

[0049] Advantageously, the composition according to the invention has a forming margin (AT=Ti og 3.5-Ti iq ), greater than 50°C, preferably greater than 75°C, more preferably greater than 80°C, more preferably greater than 100°C. The temperature Ti og3.5, is the temperature at which the molten glass composition reaches a viscosity v such that log v=3.5 (viscosity of 3160 Poises) and represents the temperature beyond which the viscosity is too low to operate the forming of the glass. Thus the forming margin AT corresponds to the temperature zone where the molten mixture can be "formed" and can spread sufficiently over the tin bath. On an industrial level, it is generally preferred to use compositions which have an AT greater than 20°C, or even greater than 50°C (floatability criterion) in order to limit the risks of crystallization or devitrification during forming on the float. Against all expectations, the compositions according to the invention have a particularly advantageous forming margin AT.

[0050] The composition according to the invention may have a lower annealing temperature (Ti ogi4.s) of at least 500°C, for example from 500°C to 600°C. The lower annealing temperature (Ti og i4.s), represents the temperature below which the glass no longer has viscous behavior (viscosity of the order of 10 14 ' 5 Poises) and allows you to assess the temperature resistance of a glass.

[0051] The compositions according to the invention allow the use of a greater diversity of raw materials, including those which contain, among others, the element aluminum. The compositions according to the invention have higher liquidus and refining temperatures than standard compositions. Despite this, and unexpectedly, the compositions according to the invention are not only compatible with the float process for producing flat glass but also allow a significant reduction in overall CO2 emissions by allowing for more diversified raw materials. Indeed, without wishing to be bound by any theory, it is observed that even if the compositions require a higher furnace temperature, the mixture of raw materials "melts" better while requiring less energy.

[0052] The present invention also relates to a method for manufacturing a flat glass, comprising: - a step of melting a mixture of selected raw materials so as to obtain a target composition according to the invention; - a step of forming the molten mixture into a glass ribbon by floating.

[0053] The mixture of raw materials is prepared according to known techniques so as to arrive at a target composition according to the invention. The raw materials may be selected, for example, from synthetic mineral materials and / or natural mineral materials. In the case of natural mineral materials in particular, the constituent elements may be determined using appropriate techniques (for example, chemical analysis, X-ray diffraction, etc.) and, on the basis of this initial determination of the composition of the mineral material, the necessary proportions of components (silica, carbonate, limestone, etc.) are calculated and adjusted to arrive at the target composition. Examples of raw materials that may be used include sand, wollastonite, aluminosilicates, sodium carbonate, limestone, dolomite, lime, talc, cullet, etc.According to an advantageous embodiment of the process, the mixture of selected raw materials comprises aluminosilicates, for example sodium, potassium and / or calcium.

[0054] The mixture of raw materials is then heated, generally in a furnace, until a molten glass is obtained. The heating is carried out at a higher or lower temperature and for a longer or shorter time depending on the quality of the glass required, in particular depending on the degree of tolerance for unmelted particles (called "unmelted") and bubbles. Generally, the maximum heating temperature of the The temperature of molten glass is between 1200 and 1700°C. For the transformation of the raw material mixture into molten glass, glass melting techniques well known to those skilled in the art can be used. This transformation can be carried out in any type of furnace such as an electric electrode furnace, an overhead burner furnace such as a cross-fired furnace or a loop furnace.

[0055] The molten glass is then introduced onto a bath of molten tin to form a glass ribbon (the well-known "foat" process). The glass ribbon can then be annealed using an annealing furnace.

[0056] The present invention also relates to a mixture of raw materials selected so as to obtain a target composition according to the invention. Preferably, the mixture of raw materials comprises aluminosilicates, in particular sodium, potassium and / or calcium.

[0057] According to another aspect, the invention relates to a glass sheet having a composition according to the invention.

[0058] The present invention also relates to a glazing comprising a glass sheet according to the invention. The present invention also relates to the use of a glazing according to the invention for buildings or automobiles, preferably for buildings. Examples

[0059] The invention is illustrated using the non-limiting examples below where two compositions are compared, in particular in terms of CO2 emissions: - a known comparative composition “A”, representative of a classic “float” glass composition - a composition “B” according to the invention. The element contents of these compositions are detailed in Table 1.

[0060] The compositions are made by melting the raw materials in a furnace and glass plates are obtained by cutting after forming the mixture of materials on a tin bath using the well-known float process.

[0061] The properties of the compositions and glasses obtained are also evaluated and listed in Table 1 below (liquidus temperatures, margin of training, etc.). ^Table 1]

[0062] Composition B according to the invention has a refining temperature ( og2 ) substantially higher than standard composition A (1562°C versus 1422°C). But this remains acceptable on an industrial level. As regards the glass transition temperature (T g ) and the lower annealing temperature (T| Og i4.5), they remain comparable to those of standard composition A. Advantageously, and surprisingly, composition B according to the invention has a particularly wide AT forming margin (of 145°C). In addition, composition B according to the invention shows a better coefficient of thermal expansion (TEC).

[0063] Hydrolytic resistance is also assessed using the DGG (Deutsche Glass Gesellschaft) method. This method applies to all types of glass and allows to give, in addition to the quantity of alkalis dissolved in water, the mass of dry residue. This method consists of immersing 10 grams of crushed glass grains (previously sieved to obtain a particle size of 355 to 400 micrometers) in beakers of demineralized water. The whole is brought to a boil for 5 hours at using an oil bath. After rapid cooling, the solution is filtered and a determined volume of the filtrate is evaporated to dryness. The weight of the dry matter obtained makes it possible to calculate the quantity of glass dissolved in water (in milligrams, per gram of glass tested). The quantity of alkalis is also measured by titration using a 0.01 mol / L hydrochloric acid solution (the colored indicator being methyl red at 2g / L in 60% ethanol). The results show that the composition according to the invention has very good hydrolytic resistance.

[0064] The average hardness H (which represents scratch resistance) and the Young's modulus E (which characterizes the deformation of the glass before breakage) are also evaluated. The measurements are made by nanoindentation, according to the NF EN ISO 14577 standard. Surprisingly, the composition according to the invention also has an H / E ratio (which characterizes wear resistance) as good as that of the standard composition.

[0065] To obtain each of the two compositions A and B detailed above, two mixtures of raw materials were used, in order to evaluate the impact of the compositions according to the invention on CO2 emissions (whatever the raw materials used): - two mixtures Al and B1 are made with the same types of raw materials called “carbonated”, the proportions of which are adapted so as to obtain the compositions according to A and B respectively; - two other mixtures A2 and B2 are made with the same types of raw materials called “decarbonated”, with the proportions allowing the target compositions A and B to also be obtained. These raw material mixes are detailed in Table 2 below. ^Table 2]

[0066] CO2 emissions are calculated for each composition and each of the raw material mixtures. The results are listed in Table 2. They show that the composition according to the invention allows a reduction in overall CO2 emissions of 24% in the first case of raw material mixtures. "carbonated". A significant drop in emissions is also observed in the second case of "decarbonated" raw material mixtures (22% drop). Thus, regardless of the raw materials used ("decarbonated" or not), the composition according to the invention makes it possible to significantly reduce overall carbon dioxide emissions, which was not obvious given its refining temperature Ti og 2 higher. Advantageously, by combining the composition according to the invention produced with the “decarbonated” raw materials, we even achieve a reduction in overall emissions of 32% compared to the reference composition.

[0067] In conclusion, the particular composition according to the invention not only allows a significant reduction in the carbon footprint of the product, but also to satisfy the quality and durability requirements of flat glass by combining all the desired properties (such as a melting temperature usable for the float process, a wide forming margin, a good coefficient of thermal expansion, very good surface durability, etc.). In addition to limiting its impact during glass manufacturing, the composition according to the invention also allows the use of a greater proportion of recycled materials (conventional cullet). In addition, it has the advantage of being itself more easily recycled and reused, due to its limited content of particular oxides (such as SrO, BaO, ZrO2 or others), and its high content of "conventional" oxides of at least 95%, or even at least 98% or even 99%, and this without giving up all the desired properties.Thus, the specific composition according to the invention makes it possible to satisfy the quality requirements. and durability of glass without the need to resort to particular oxides and is fully part of an ecological approach from the manufacture of the glass to its recycling and reuse.

Claims

Claims 1. Flat glass composition comprising the following constituents, their sum representing at least 95% of the composition, the percentages being expressed by mass relative to the total mass of the composition: - 60% to 75% silicon dioxide (SiO2); - 8% to 12% sodium oxide (Na2O); - from 6% to 12% calcium oxide (CaO); - from 6% to 10% aluminum oxide (AI2O3); - from 0% to 5% potassium oxide (K2O); - from 0% to 3.5% magnesium oxide (MgO); in which the sum of the mass contents of CaO and MgO is from 6 to 12%, and the mass content of BaO and / or SrO is at most 0.5%.

2. Composition according to claim 1, in which the sum of the mass contents of SiO2, Na2O, CaO, AI2O3, K2O and MgO represents at least 98%, preferably at least 99%, relative to the total mass of the composition.

3. Composition according to any one of the preceding claims, in which the mass content of aluminum oxide (AI2O3) is from 7.5% to 9%, preferably from 8% to 9%, relative to the total mass of the composition.

4. Composition according to any one of the preceding claims, in which the sum of the mass contents of CaO and MgO is at most 11%, preferably at most 10%, more preferably at most 9%, relative to the total mass of the composition.

5. Composition according to any one of the preceding claims, in which the sum of the mass contents of alkaline earth metal oxides, in particular CaO, MgO, SrO and BaO, is at most 11%, preferably at most 10%, more preferably at most 9%, relative to the total mass of the composition.

6. Composition according to any one of the preceding claims, in which the sum of the mass contents of Na2O and K2O is less than 15%, relative to the total mass of the composition.

7. Composition according to any one of the preceding claims, in which the sum of the mass contents of Na2O and CaO is from 14% to 20%, preferably from 14% to 19%, relative to the total mass of the composition.

8. Composition according to any one of the preceding claims, in which the ratio R of the sum of the mass contents of SiO2 and AI2O3 to the sum of the mass contents of CaO, MgO, Na2O and K2O, is from 3 to 4.

9. Composition according to any one of the preceding claims, in which the sum of the mass contents of B2O3, SrO, BaO and ZrO2 is less than 1%, preferably less than 0.5%, relative to the total mass of the composition.

10. Composition according to any one of the preceding claims, in which the sum of the mass contents of B2O3, SrO, BaO, ZrO2, TiO2, ZnO and SnO2 is less than 1%, preferably less than 0.5%, relative to the total mass of the composition.

11. Composition according to any one of the preceding claims, the composition being free of boron oxide (B2O3) and zinc oxide (ZnO).

12. Composition according to any one of the preceding claims, in which the mass content of lithium oxide (Li2O) is less than 0.5%, preferably less than 0.2%, relative to the total mass of the composition, more preferably the composition is free of lithium oxide (Li2O).

13. Composition according to any one of the preceding claims, the composition comprising a mass content of BaO and / or SrO of at most 0.2%, relative to the total mass of the composition.

14. Composition according to any one of the preceding claims, the composition comprising a mass content of Fe2O3 of at most 2%, preferably at most 1%, more preferably at most 0.6%, relative to the total mass of the composition.

15. Composition according to any one of the preceding claims, the composition having a difference AT=Tiog3,5-Ti iq greater than 50°C, preferably greater than 75°C, preferably greater than 80°C, more preferably greater than 100°C.

16. Method of manufacturing a flat glass, comprising: - a step of melting a mixture of selected raw materials so as to obtain a target composition according to any one of claims 1 to 15; and - a step of forming the molten mixture into a glass ribbon by floating.

17. Mixture of raw materials selected so as to obtain a target composition according to any one of claims 1 to 15, comprising aluminosilicates, preferably sodium, potassium and / or calcium.

18. Glass sheet having a composition according to any one of claims 1 to 15.

19. Glazing comprising a glass sheet according to claim 18.

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