Glass composition.

Abstract

The invention relates to a glass composition, in particular flat glass, comprising the following constituents, in mass percentages relative to the total mass of the composition: - from 60% to 70% of SiO2; - from 2% to 18% of Na2O; - from 8% to 28% of CaO; - from 1% to 9% of MgO; - from 0% to 2% of Al2O3; - from 0% to 0.5% of K2O in which the sum of the CaO and MgO contents is from 14% to 32%. The invention also relates to a process for preparing a flat glass, comprising a composition according to the invention, as well as a glass sheet having a composition according to the invention.

Description

Title of the invention: Glass composition. Technical field

[0001] The invention relates to a glass composition of the soda-lime-silica type, in particular flat glass, as well as its manufacturing process and its use as glazing. TECHNOLOGICAL BACKGROUND

[0002] The manufacturing processes for so-called float glass consist of melting a mixture of raw materials in a glass furnace at temperatures of up to 1550°C, then forming a ribbon of molten glass on a bath of molten tin. The ribbon is then slowly cooled, annealed and then cut.

[0003] As with any industrial process, there is an increased 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 vitrifiable mixtures, or even energy recovery at the various stages of the process.

[0004] Flat glass generally has a chemical composition comprising (in mass percentages relative to the mass of the composition): - from 69% to 74% silicon dioxide (SiO2); - from 10% to 16% sodium oxide (Na2O); - from 5% to 14% calcium oxide (CaO); - from 0% to 6% magnesium oxide (MgO); - from 0% to 3% aluminum oxide (A12O3); - from 0% to 5% of other oxides (Fe2O3, K2O, ZnO, SrO, B2O3, etc.).

[0005] These compositions are popular with manufacturers to ensure both the quality and durability of the finished product and the stability of the process. It is commonly accepted that the alkaline earth oxide content, particularly CaO, must be kept relatively low in order to satisfy the floatability criterion (the float margin AT=T iog3,5-Tiiq must be greater than 20°C, or even greater than 50°C) and avoid the risk of devitrification. In particular, document US 5,071,796 describes flat glass compositions comprising a carefully controlled alkaline earth oxide (CaO + MgO) content (from 10.2 to 12% by mass), taking into account the negative effect of calcium oxide on the float margin.

[0006] Going against these prejudices, the inventors have developed a composition of soda-lime-silica glass making it possible to reduce the energy consumption required for its manufacture while satisfying both the quality and durability requirements of the finished product, particularly from the point of view of hydrolytic resistance, and industrial requirements, particularly with regard to the risks of devitrification, and the capacity for refining. Thus, it is to the applicant's credit to propose a glass composition, in particular flat glass, which, surprisingly, makes it possible to resolve all of these problems. Summary of the invention

[0007] According to a first aspect, the present invention relates to a glass composition, in particular flat glass, comprising the following constituents, in mass percentages relative to the mass of the composition: - 60% to 70% SiO2; - from 2% to 18% of Na2O; - from 8% to 28% CaO; - from 1% to 9% of MgO; - from 0% to 2% of A12O3; - from 0% to 0.5% K2O in which the sum of CaO and MgO contents is 14 to 32%.

[0008] It has in fact been demonstrated that these compositions have an advantageous viscosity range for floating over a lower temperature range than that of standard float glass, and this without risk of devitrification and with a refining capacity equivalent to standard soda-lime-silica glasses, thus making it possible to achieve significant energy savings. The applicant thus proposes glass compositions which, despite relatively high liquidus temperatures, prove compatible with industrial requirements from the point of view of the risks of devitrification, contrary to prejudices.

[0009] The invention also relates, according to a second aspect, to a method for manufacturing a glass, in particular 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.

[0010] According to other aspects, the invention also relates to a glass sheet having a composition according to the invention, a glazing comprising such a glass sheet according to the invention, and the use of such a glazing for buildings or automobiles. DETAILED DESCRIPTION

[0011] The general terms used in this text are defined below.

[0012] The expression “comprising” encompasses the expression “consisting of”.

[0013] The expression “from ... to ...” must be understood inclusively.

[0014] 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.

[0015] The composition according to the invention is of the silico-soda-lime type and comprises the following constituents, in mass percentages relative to the total mass of the composition: - 60% to 70% SiO2; - from 2% to 18% of Na2O; - from 8% to 28% CaO; - from 1% to 9% of MgO; - from 0% to 2% of A12O3; - from 0% to 0.5% K2O in which the sum of CaO and MgO contents is 14 to 32%.

[0016] It is understood that this is the composition expressed, by convention, in oxides of the constituent elements (SiO2, Na2O, CaO, K2O, Al2O3, Fe2O3, etc.). Indeed, glass is a substance of variable composition, resulting from complex reactions forming a random network. Although conventionally 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.

[0017] Advantageously, the composition according to the invention is a flat glass composition. In other words, it is compatible with industrial processes for manufacturing flat glass, in particular by floating.

[0018] Advantageously, in the composition according to the invention, the sum of the mass contents of SiO2, Na2O, CaO and MgO represents at least 95% by mass, preferably at least 98% by mass, relative to the total mass of the composition.

[0019] Silicon dioxide (SiO2) is the main network-forming element in glass. Too low contents lead to a deterioration in the hydrolytic resistance of the glass, particularly in basic media. On the other hand, high contents 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 composition according to the invention comprises 60% to 70% by mass of SiO2. Preferably, the mass content of SiO2 is 60% to 68%, more preferably 62% to 67%, relative to the total mass of the composition.

[0020] Aluminum oxide (A12O3) may be present in the composition according to the invention at a mass content of 0% to 2%, relative to the mass of the composition. Preferably, the mass content of A12O3 is 0.5% to 2%.

[0021] Alkali oxides (Na2O and K2O) are network modifiers. They make it possible to reduce the high temperature viscosity of the molten glass composition but can also have a negative impact on the hydrolytic resistance of the glass. The composition according to the invention comprises 2% to 18% by mass of Na2O. Preferably, the mass content of Na2O is from 2% to 16%, more preferably from 3% to 14%, relative to the total mass of the composition. The composition according to the invention comprises 0% to 0.5% by mass of K2O. Preferably, the mass content of K2O is from 0.05% to 0.5%, relative to the total mass of the composition.

[0022] Alkaline earth oxides (CaO and MgO) are network modifiers. They make it possible to reduce the high temperature viscosity of the molten glass composition but can also increase the liquidus temperature and / or increase the risks of devitrification. The composition according to the invention comprises 8% to 28% by mass of CaO. Preferably, the mass content of CaO is at least 9%, more preferably at least 12%, even more preferably at least 14%, relative to the total mass of the composition. Preferably, the mass content of CaO is from 9% to 28%, more preferably from 12% to 25%, relative to the total mass of the composition. The composition according to the invention comprises 1% to 9% by mass of MgO. Preferably, the mass content of MgO is from 1% to 8%, relative to the total mass of the composition.

[0023] The sum of the CaO and MgO contents in the composition according to the invention is from 14 to 32%, relative to the total mass of the composition. Preferably, the sum of the mass contents of CaO and MgO is from 16% to 32%, more preferably from 18% to 30%, relative to the total mass of the composition. This makes it possible to increase the liquidus temperature, while maintaining good properties for refining and forming the glass.

[0024] Preferably, the sum of the mass contents of Na2O, CaO and MgO is from 25 to 40%, more preferably from 30% to 37%, relative to the total mass of the composition.

[0025] Advantageously, in the composition according to the invention, the ratio R of the sum of the mass contents of SiO2 and Al2O3 to the sum of the mass contents of CaO, MgO and Na2O, is from 1.5 to 2.5, preferably from 1.7 to 2.1. This makes it possible to combine good glass properties.

[0026] Preferably, the composition according to the invention comprises a mass content of boron oxide (B2O3) of less than 1%, preferably less than 0.5%, relative to the total mass of the composition. More preferably, the composition according to the invention is free of boron oxide (B2O3).

[0027] Preferably, the composition according to the invention is free of lithium oxide (Li2O), in particular for cost reasons.

[0028] Preferably, the composition according to the invention is free of ZnO and / or ZrO2.

[0029] Preferably, the composition according to the invention comprises a mass content of phosphorus oxide (P2O5) less than 1%, preferably less than 0.5%, relative to the total mass of the composition. More preferably, the composition according to the invention is free of P2O5.

[0030] Preferably, the composition according to the invention comprises a mass content of BaO of less than 1%, preferably less than 0.5%, relative to the total mass of the composition. Advantageously, the composition according to the invention is free of BaO.

[0031] Preferably, the composition according to the invention comprises a mass content of SrO of less than 1%, preferably less than 0.5%, relative to the total mass of the composition. Advantageously, the composition according to the invention is free of SrO.

[0032] The composition according to the invention may comprise a mass content of Fe2O3 of at most 2%, relative to the total mass of the composition. This may be the case, for example, for applications in the automotive field. Preferably, the composition according to the invention comprises a mass content of Fe2O3 of at most 1%, preferably at most 0.5%, more preferably at most 0.2%, relative to the total mass of the composition. For the purposes of the present invention, the term "Fe2O3 content" means the total content of iron oxides, in particular including iron (II) and iron (III) oxides.

[0033] The composition according to the invention may optionally contain other impurities, such as for example sulfur oxide (SO3), often in low levels (for example less than 0.1%). The element SO3 may in particular come from refining agents (such as sodium sulfate).

[0034] According to an advantageous embodiment, the composition according to the invention comprises the following constituents, in mass percentages relative to the total mass of the composition: - from 60% to 68% SiO2; - from 2% to 18% of Na2O; - from 9% to 28% CaO; - from 1% to 8% of MgO; - from 0.5% to 2% of A12O3; - from 0% to 0.5% K2O in which the sum of the CaO and MgO contents is from 16 to 32%, preferably from 18% to 30%. This composition may further comprise one or more of the characteristics previously described.

[0035] According to another advantageous embodiment, the composition according to the invention includes the following constituents, in mass percentages relative to the total mass of the composition: - from 62% to 67% of SiO2; - from 2% to 16% of Na2O; - from 12% to 25% CaO; - from 1% to 8% of MgO; - from 0.5% to 2% of A12O3; - from 0% to 0.5% K2O in which the sum of the CaO and MgO contents is from 16 to 32%, preferably from 18% to 30%. This composition may further comprise one or more of the characteristics previously described.

[0036] The composition according to the invention has the advantage of being able to be melted and transformed into a glass ribbon at temperatures lower than those usually used for the manufacture of standard flat glasses, in particular according to the float process. In addition, it also allows it to be refined at a lower temperature (at temperatures lower than 1400°C) leading to glasses of high optical quality, without unmelted parts and / or bubbles and without risks of devitrification. The composition according to the invention may also have other advantageous properties in terms of processability.

[0037] The composition according to the invention may have a liquidus temperature (Tiiq) greater than 1050°C, preferably greater than 1060°C, for example from 1060°C to 1350°C. The liquidus temperature (Tiiq) represents the temperature from which the mixture is entirely liquid (no more coexistence of liquid and solid forms). Thus, the compositions according to the invention have a higher liquidus temperature than standard compositions.

[0038] The composition according to the invention may have a refining temperature (Tiog2) of less than 1400°C, preferably less than 1380°C. Preferably, the refining temperature (Tiog2) is from 1100°C to 1400°C, more preferably from 1100°C to 1380°C, and even more preferably from 1100°C to 1370°C. The refining temperature (Tiog2) 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).

[0039] The composition according to the invention may have a forming margin (AT=Tiog3>5-T iiq) of less than 20°C, for example less than 10°C. The temperature Tiog3 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- It is generally advisable to use compositions that have an AT greater than 50°C in order to limit the risks of crystallization during forming on the float. Against all expectations, and despite a low AT forming margin, the compositions according to the invention do not present any risks of crystallization, are compatible with the process of producing flat glass by float. They also allow an energy reduction by taking advantage of a lower refining temperature.

[0040] 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.

[0041] The mixture of raw materials is prepared according to known techniques so as to result in a target composition according to the invention. The raw materials may be, for example, selected from synthetic mineral materials and / or natural mineral materials. Examples of raw materials that can be used include, for example, sand, feldspar, dolomite, talc, wollastonite, sodium carbonate, sodium hydroxide, limestone, sodium sulfate, etc.

[0042] 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. Advantageously, in the case of the compositions according to the invention, the operating temperature of the furnace may be lower than 1400°C, for example between 1200 and 1400°C. For the transformation of the mixture of raw materials into molten glass, glass melting techniques well known to those skilled in the art may be used.

[0043] The molten glass mixture is then introduced onto a molten tin bath to form a glass ribbon (well-known "float" process). The glass ribbon can then be annealed using an annealing furnace.

[0044] Advantageously, in the process according to the invention, the melting step is carried out at a temperature below 1400°C, preferably at a temperature below 1380°C.

[0045] According to another aspect, the present invention also relates to a glass sheet having a composition according to the invention.

[0046] The invention also relates to glazing comprising a glass sheet according to the invention.

[0047] The invention also relates to the use of glazing according to the invention for buildings or automobiles, preferably for buildings. Examples

[0048] The invention is illustrated using the non-limiting examples below. The compositions according to the invention II to 13 and the comparative composition C1 were prepared from the following raw materials of industrial quality: sand, sodium carbonate, limestone, dolomite and cullet. These compositions are detailed in Table 1 below. Unless otherwise indicated, the percentages indicated are percentages by mass. [Tables 1] Composition (in %) Cl II 12 13 SiO2 72.7 64.3 66.0 69.0 AI2O3 0.72 0.24 0.94 1.0 Na2O 13.6 13.1 16.9 5.7 CaO 10 15.2 9.5 19.0 MgO 2.4 7.4 6.6 5.0 k2o - 0.08 0.27 0.13 Properties: Tliq (in °C, ± 5°C) 1021 1140 1070 1353 Tlog2 (in °C, ± 5°C) 1451 1321 1373 1378 AT = Tlog3.5 - Tliq (°C) > 50°C -57°C +9°C -214°C DGG (mg) 33.89 33.7 33.5 not determined Optical qualities at 1450°C: no defects at 1370°C: presence of very many defects (bubbles and unmelted) at Tiog2: no defects (with and without refining agents) at Tiog2: no defects (with and without refining agents) at Tiog2: no defects (with and without refining agents)

[0049] The compositions are made with and without the addition of refining agents, by melting the raw materials in an electric furnace at a glass-making temperature close to the estimated refining temperature (Tiog2) of the compositions. Glass plates are obtained by cutting after forming the mixture of materials on a tin bath according to the well-known float process.

[0050] The properties of the compositions and glasses obtained are also measured and listed in Table 1 above (liquidus temperatures, refining temperature, etc.). The refining temperature is determined by viscometry according to ISO 7884-2:1987.

[0051] It can be noted that the liquidus temperature of composition C1 is low and largely meets the buoyancy criterion (AT = Tiog3 5 - Tiiq > 20°C). On the other hand, the liquidus temperatures of compositions II to 13 according to the invention are higher and do not meet this criterion. However, the compositions according to the invention have a refining temperature substantially lower than that of composition C1. It can be observed that, despite a high liquidus temperature and an unfavorable forming margin, the glasses resulting from the compositions according to the invention do not have defects (bubbles or unmelted) and have not devitrified. These glasses are, however, produced at a lower temperature than the usual temperatures of standard compositions. It should be noted that compositions C1 and 12 were also produced at the same temperature of 1370°C in a flame furnace, using Pt-Rh crucibles.Here again, composition 12 does not devitrify and does not present any defects. On the other hand, composition Cl presents a very large number of defects (unmelted or bubbles).

[0052] Hydrolytic resistance is also evaluated using the DGG (Deutsche Glas s Gesellschaft) method. This method allows to give, in addition to the quantity of alkalis dissolved in water, the mass of dry residue. The 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 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 allows to calculate the quantity of glass dissolved in water (in milligrams, per gram of glass tested). The amount of alkali is also measured by titration using a 0.01 mol / L hydrochloric acid solution (the color indicator being methyl red at 2g / L in 60% ethanol).The results show that the compositions according to the invention have a hydrolytic resistance equivalent to that of standard glasses.

[0053] The energy gain of the compositions according to the invention, compared to the reference composition Cl, is also evaluated by taking into account the calculated enthalpy variation (in kWh per tonne of glass) and the no-load losses (which represent the heat losses in the furnace, in kWh per tonne of glass, calculated by taking into account the specific pull). The specific pull (or "specific pull") represents the quantity of glass that can be produced per unit of time and unit of surface area (in tonnes of glass per m2 .hour). The results are presented in Table 2 below. [Tables 2] Composition Cl II 12 13 Enthalpy variation AH of the raw material mixture (in kWh / ton) 690 682 684 702 Specific pull (in ton / m2 / h) 0.072 0.135 0.114 0.110 No-load loss (in kWh / ton) 162 87 103 107 AH + No-load loss (in kWh / ton) 852 769 787 808 Energy gain AE (compared to composition Cl) - -9.78% -7.62% -5.11%

[0054] While the enthalpy variations of the raw materials are of the same order of magnitude, once in the furnace, the compositions according to the invention consume less energy than the reference composition Cl (energy gain ranging from approximately 5% to 10%). Indeed, the significant reduction in the production temperature (thanks to a lower refining temperature of the compositions) makes it possible in particular to significantly increase the specific pull. These advantages are obtained thanks to the compositions according to the invention, with a higher alkaline earth oxide content.

[0055] Thus, it has been demonstrated that, contrary to prejudices, it is possible to obtain float glasses without defects or devitrification from the compositions according to the invention, despite a higher liquidus temperature than the standard compositions, and despite an unfavorable AT forming margin.

Claims

Claims

1. Glass composition, in particular flat glass, comprising the following constituents, in mass percentages relative to the total mass of the composition: - from 60% to 70% of SiO2; - from 2% to 18% of Na2O; - from 8% to 28% of CaO; - from 1% to 9% of MgO; - from 0% to 2% of A12O3; - from 0% to 0.5% of K2O in which the sum of the CaO and MgO contents is from 14 to 32%.

2. Composition according to claim 1, in which the sum of the mass contents of SiO2, Na2O, CaO and MgO represents at least 95% by mass, preferably at least 98% by mass, relative to the total mass of the composition.

3. Composition according to any one of the preceding claims, in which the mass content of SiO2 is from 60% to 68%, preferably from 62% to 67%, relative to the total mass of the composition.

4. Composition according to any one of the preceding claims, in which the mass content of CaO is at least 9%, preferably at least 12%, more preferably at least 14%, 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 CaO and MgO is from 16% to 32%, preferably from 18% to 30%, 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, CaO and MgO is from 25 to 40%, preferably from 30% to 37%, relative to the total mass of the composition.

7. Composition according to any one of the preceding claims, the composition comprising a mass content of boron oxide (B2O3) of less than 1%, preferably the composition being free of boron oxide (B2O3).

8. Composition according to any one of the preceding claims, the composition comprising a mass content of BaO of less than 1%, preferably less than 0.5%, relative to the total mass of the composition, more preferably the composition being free from BaO.

9. Composition according to any one of the preceding claims, the composition comprising a mass content of SrO of less than 1%, preferably less than 0.5%, relative to the total mass of the composition, more preferably the composition being free of SrO.

10. Composition according to any one of the preceding claims, the composition comprising a mass content of Fe2O3 of at most 1%, preferably at most 0.5%, more preferably at most 0.2%, relative to the total mass of the composition.

11. Composition according to any one of the preceding claims, the composition having a refining temperature (Tiog2) of less than 1400°C, preferably less than 1380°C.

12. A method of manufacturing a flat glass, comprising: - a step of melting a mixture of raw materials selected so as to obtain a target composition according to any one of claims 1 to 11; - a step of forming the molten mixture into a glass ribbon by float.

13. A method according to claim 12, wherein the melting step is carried out at a temperature below 1400°C, preferably at a temperature below 1380°C.

14. A glass sheet having a composition according to any one of claims 1 to 11.

15. Glazing comprising a glass sheet according to claim 14.