Soda Lime Silica Glass with High Visible Light Transmittance

Abstract

The present invention provides a glass sheet having soda-lime-silica glass composition with a high visible light transmittance (L.sub.tC) of at least 89% with a dominant wavelength (DW) from about 490 to 505 nanometers and purity (Pe) of no more than 1% for control thickness of 5.66 mm. The glass composition comprising a low iron raw material, a total iron oxide (Fe.sub.2O.sub.3) of 0.02 to 0.06 wt. %, ferrous (FeO) from 0.006 to 0.02 wt. %, a redox ratio (FeO/Fe.sub.2O.sub.3) of from about 0.30 to 0.55, Cr.sub.2O.sub.3 from about 0.3 to 10 ppm, TiO.sub.2 from about 50 to 500 ppm, SnO.sub.2 from about 10 to 500 ppm, and an amount from about 0.10 to 0.25 wt. % of SO.sub.3. The low content of iron oxide is achieved in one instance through the use of a low iron dolomite with a maximum content of 0.020 wt. % Fe.sub.2O.sub.3.

Claims

1. A method of making a clear glass using a conventional float non-vacuum glass system, the method comprising: providing a glass batch having ingredients to make a glass having a basic soda-lime-silica glass composition and colorants; melting the glass batch to provide a pool of molten glass; flowing the molten glass onto a molten tin bath; moving the molten glass on the surface of the molten tin bath, while controllably cooling the glass and applying forces to the glass to provide a glass of a desired thickness; and removing the glass from the molten tin bath, wherein the glass batch comprises between 5 to 20 wt. % of a low iron dolomite where the low iron dolomite has a total iron content, expressed as Fe.sub.2O.sub.3 content, of less than 0.1 wt. %, and wherein the glass has a redox ratio (as expressed as FeO/Fe.sub.2O.sub.3) in the range of about 0.30 to 0.55.

2. The method of claim 1, wherein the conventional float non-vacuum glass system contains a furnace, wherein combustion in the furnace is produced by a firing of air and/or gas, or by a firing of oxygen/gas, to control a redox ratio in the glass (as expressed as FeO/Fe.sub.2O.sub.3) to be in the range of about 0.30 to 0.55.

3. The method of claim 2, wherein the redox ratio in the glass (as expressed as FeO/Fe.sub.2O.sub.3) of about 0.30 to 0.55 is achieved by adjusting the amount of oxygen and air in the combustion gas.

4. The method of claim 2, wherein the low iron dolomite has a total iron content, expressed as Fe.sub.2O.sub.3 content, of less than 0.025 wt. %.

5. The method of claim 4, wherein the glass batch further comprises one or more low iron materials that are selected from low iron sand, low iron limestone, low iron clear cullet, or a combination thereof.

6. The method of claim 4, wherein the low iron dolomite has a total iron content, expressed as Fe.sub.2O.sub.3 content, of less than 0.020 wt. %.

7. The method of claim 1, wherein the glass batch comprises between 5 to 20 wt. % of a low iron dolomite where the low iron dolomite has a total iron content, expressed as Fe.sub.2O.sub.3 content, of less than 0.030 wt. %, and wherein the low iron dolomite has a total CaO content of between 30 and 35 wt. % and an MgO content of between 15 and 25 wt. %.

8. The method of claim 1, wherein the glass batch comprises between 5 to 20 wt. % of a low iron dolomite where the low iron dolomite has a total iron content, expressed as Fe.sub.2O.sub.3 content, of less than 0.025 wt. %, and wherein the low iron dolomite has a total CaO content of between 31 and 33 wt. % and an MgO content of between 20 and 22 wt. %.

9. The method of claim 1, wherein the glass batch comprises between 5 to 20 wt. % of a low iron dolomite where the low iron dolomite has a total iron content, expressed as Fe.sub.2O.sub.3 content, of less than 0.022 wt. %, and wherein the low iron dolomite has a total CaO content of between 31.1 and 32.6 wt. % and an MgO content of between 20.0 and 21.1 wt. %.

10. A method of forming clear glass comprising: mixing raw materials, wherein the raw materials comprise cullet, sand, soda ash, salt cake, limestone and dolomite, wherein the dolomite comprises: TABLE-US-00022 SiO.sub.2 0 to 5 wt. % Na.sub.2O 0 to 1 wt. % CaO 30 to 35 wt. % MgO 15 to 25 wt. % Al.sub.2O.sub.3 0 to 1 wt. % SO.sub.3 0 to 1 wt. % Fe.sub.2O.sub.3 0 to 0.1 wt. % melting the raw materials to form molten glass; flowing the molten glass onto a molten tin bath; moving the molten glass on the surface of the molten tin bath while controllably cooling the molten glass and applying forces to the molten glass to form a glass of a desired thickness and a desired width; and removing the glass from the molten bath, wherein the dolomite is a low iron dolomite comprising between 5 to 20 wt. % of the low iron dolomite with the total iron content being expressed as Fe.sub.2O.sub.3 content and being in the range noted in the table above, and wherein the glass has a redox ratio (as expressed as FeO/Fe.sub.2O.sub.3) in the range of about 0.30 to 0.55.

11. The method of claim 10, wherein the raw materials are present in the following amounts: TABLE-US-00023 Cullet 0 to 15 wt. % Sand max 65 wt. % Dolomite 5 to 20 wt. % Salt Cake 0.2 to 1.0 wt. % Soda Ash 13 to 23 wt. %

12. The method of claim 10, wherein the limestone comprises: TABLE-US-00024 SiO.sub.2 0 to 5 wt. % Na.sub.2O 0 to 1 wt. % CaO 40 to 65 wt. % MgO 10 to 30 wt. % Al.sub.2O.sub.3 0 to 1 wt. % SO.sub.3 0 to 1 wt. % Fe.sub.2O.sub.3 0 to 0.5 wt. %

13. The method of claim 10, wherein the raw materials further comprise coal or graphite.

14. The method of claim 13, wherein the coal or graphite is in a range of 0.01 to 0.3 wt. %.

15. The method of claim 10, wherein the glass batch comprises between 5 to 20 wt. % of a low iron dolomite where the low iron dolomite has a total iron content, expressed as Fe.sub.2O.sub.3 content, of less than 0.030 wt. %, and wherein the low iron dolomite has a total CaO content of between 30 and 35 wt. % and an MgO content of between 15 and 25 wt. %.

16. The method of claim 10, wherein the glass batch comprises between 5 to 20 wt. % of a low iron dolomite where the low iron dolomite has a total iron content, expressed as Fe.sub.2O.sub.3 content, of less than 0.025 wt. %, and wherein the low iron dolomite has a total CaO content of between 31 and 33 wt. % and an MgO content of between 20 and 22 wt. %.

17. The method of claim 10, wherein the glass batch comprises between 5 to 20 wt. % of a low iron dolomite where the low iron dolomite has a total iron content, expressed as Fe.sub.2O.sub.3 content, of less than 0.022 wt. %, and wherein the low iron dolomite has a total CaO content of between 31.1 and 32.6 wt. % and an MgO content of between 20.0 and 21.1 wt. %.

18. A glass composition comprising: TABLE-US-00025 SiO.sub.2 65 to 75 wt. % Na.sub.2O 10 to 20 wt. % K.sub.2O 0 to 5 wt. % CaO 5 to 15 wt. % MgO 2 to 10 wt. % Al.sub.2O.sub.3 0 to 5 wt. % SO.sub.3 0 to 0.5 wt. % Cr.sub.2O.sub.3 0.00003 to 0.001 wt. % Fe.sub.2O.sub.3 0.02 to 0.07 wt. % FeO 0.005 to 0.03 wt. % Redox Ratio (FeO/Fe.sub.2O.sub.3) 0.30 to 0.55 wherein the glass composition comprises between 5 to 20 wt. % of a low iron dolomite where the low iron dolomite has a total iron content, expressed as Fe.sub.2O.sub.3 content, of less than 0.1 wt. %.

19. The glass composition of claim 18, wherein the Fe.sub.2O.sub.3 is in an amount of 0.021 to 0.053 wt. %, and the redox ratio is in the range of 0.30 to 0.46.

20. The glass composition of claim 18, wherein the low iron dolomite has a total iron content, expressed as Fe.sub.2O.sub.3 content, of less than 0.030 wt. %.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0103] FIGS. 1A and 1B are a horizontal section of a glass melting furnace that can be used in the practice of the invention; FIG. 1A is the melting section of the furnace, and FIG. 1B is the refining and homogenizing section of the furnace;

[0104] FIG. 2 is a vertical section of the melting section shown in FIG. 1A;

[0105] FIG. 3 is an elevated side view partially in cross section of a glass melting and refining apparatus that can be used in the practice of the invention; and

[0106] FIG. 4 is a fragmented side view of a glass ribbon supported on a molten tin bath.

DESCRIPTION OF THE INVENTION

[0107] As used in the following discussion, unless otherwise indicated, all numbers expressing dimensions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term about. Accordingly, unless indicated to the contrary, the numerical values set forth in the following specification and claims can vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Moreover, all ranges disclosed herein are to be understood to include the beginning and ending range values and to encompass any and all subranges subsumed therein. For example, a stated range of 1 to 10 should be considered to include any and all subranges between (and inclusive of) the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a minimum value of 1 or more and ending with a maximum value of 10 or less, e.g., 5.5 to 10. Additionally, all documents, such as but not limited to issued patents and patent applications, referred to herein, are to be considered to be incorporated by reference in their entirety.

[0108] Any reference to composition amounts, unless otherwise specified, is by weight percent based on the total weight of the final glass composition. The total iron content of the glass compositions disclosed herein is expressed in terms of Fe.sub.2O.sub.3 in accordance with standard analytical practice, regardless of the form actually present. Likewise, the amount of iron in the ferrous state is reported as FeO, even though it may not actually be present in the glass as FeO. The terms redox, redox ratio, or iron redox ratio mean the amount of iron in the ferrous state (expressed as FeO) divided by the amount of total iron (expressed as Fe.sub.2O.sub.3). As used herein soda-lime-silica glasses having a total iron (expressed as Fe.sub.2O.sub.3) in the range of greater than 0 to 0.06 wt. % is a low iron soda-lime-silica glass. Generally and not limiting to the invention, high iron soda-lime-silica glasses have total iron in the range of equal to and greater than 0.10 wt. % to 2.0 wt. %; equal to and greater than 0.10 wt. % to 1.5 wt. %; equal to and greater than 0.10 wt. % to 2.0 wt. %; and equal to and greater than 0.10 wt. % to 0.80 wt. %.

[0109] As can now be appreciated, the invention is directed to making low iron, high redox soda-lime-silica glasses and is not limited to the optical properties, e.g. ultra violet visible and IR transmission and absorption and the color of the glass and physical properties, e.g. glass thickness. In defining a non-limiting embodiment of a glass of the invention, reference can be made to specific ranges or values of ultra violet, visible and IR transmission and absorption, and/or color of the glass and/or physical properties, e.g. glass thickness to identify a specific glass of the invention and/or a glass made by the practice of the invention. Presented below are common additives, e.g. color additives that are added to the glass batch materials, and/or molten glass to alter optical and physical properties of the glasses of the invention.

[0110] The sulfur content of the glass compositions disclosed herein is expressed in terms of SO.sub.3 in accordance with standard analytical practice, regardless of the form actually present.

[0111] As used herein, visible transmittance and dominant wavelength values are those determined using the conventional CIE Illuminant C and 2-degree observer angle. Those skilled in the art will understand that properties such as visible transmittance and dominant wavelength can be calculated at an equivalent standard thickness, e.g., 5.5 millimeters (mm), even though the actual thickness of a measured glass sample is different than the standard thickness.

[0112] As is appreciated, the invention is not limited to the color additives discussed above and any color additives to a soda-lime-silica glass known in the art can be used in the practice of the invention, for example, but not limited to, the colorants selected from the group of CoO, Se, NiO, Cl, V.sub.2O.sub.5, CeO.sub.2, Cr.sub.2O.sub.3, TiO.sub.2, Er.sub.2O.sub.3, MnO.sub.2, La.sub.2O.sub.3, and combinations thereof.

[0113] As can now be appreciated, the invention is not limited to the process of, and/or equipment for, practicing the invention to make glasses of the invention, and any of the glass making processes and/or equipment known in the art can be used in the practice of the invention.

[0114] Referring to FIGS. 1 and 2 as needed, there is shown a conventional continuously fed, cross-tank fired, glass melting and non-vacuum refining furnace 20 having an enclosure formed by a bottom 22, roof 24, and sidewalls 26 made of refractory materials. The glass batch materials 28 are introduced through inlet opening 30 in an extension 32 of the furnace 20 known as the fill doghouse in any convenient or usual manner to form a blanket 34 floating on the surface 36 of the molten glass 38. Overall progression of the glass as shown in FIGS. 1A and 1B are from left to right in the figures, toward an entrance end of a glass forming chamber 40 of the type used in the art to make float flat glass.

[0115] Flames (not shown) to melt the batch materials 28 and to heat the molten glass 38 issue from burner ports 42 spaced along the sidewalls 26 (see FIG. 2) and are directed onto and across the surface 36 of the molten glass 38. During the first half of a heating cycle, the flames issue from a nozzle 43 (see FIG. 2) in each of the ports on one side of the tank 20, as the exhaust of the furnace moves through the ports on the opposite side of the furnace. During the second half of the heating cycle, the function of the ports is reversed, and the exhaust ports are the firing ports, and the firing ports are the exhaust ports. The firing cycle for furnaces of the type shown in FIGS. 1 and 2 are well known in the art. As can be appreciated by those skilled in the art, the invention contemplates using a mixture of air and fuel gas, or a mixture of oxygen and fuel gas, to generate the flames to heat the batch materials and the molten glass. For a discussion of using oxygen and fuel gas in the furnace of the type shown in FIG. 1, reference can be made to U.S. Pat. Nos. 4,604,123, 6,962,887, 7,691,763, and 8,420,928, which are hereby incorporated by reference.

[0116] The glass batch materials 28 as they move downstream from the batch feeding end or doghouse end wall 46 are melted in the melting section 48 of the furnace 20, and the molten glass 38 moves through waist 54 of refining section 56 of the furnace 20. In the refining section 56, bubbles in the molten glass 38 are removed, and the molten glass 38 is mixed or homogenized as the molten glass passes through the refining section 56. The molten glass 38 is delivered in any convenient or usual manner from the refining section 56 onto a pool of molten metal (not shown) contained in the glass-forming chamber 40. As the delivered molten glass 38 moves through the glass-forming chamber 40 on the pool of molten metal (not shown), the molten glass is sized and cooled. A dimensionally stable sized glass ribbon (not shown) moves out of the glass-forming chamber 40 into an annealing lehr (not shown). Glass making apparatus of the type shown in FIGS. 1 and 2, and of the type discussed above are well known in the art.

[0117] Shown in FIG. 3 is continuously fed glass melting and vacuum refining equipment 78 for melting glass batch materials and refining the molten glass. Batch materials 80, preferably in a pulverulent state, are fed into cavity 82 of a liquefying vessel, e.g. a rotating drum 84. A layer 86 of the batch material 80 is retained on the interior walls of the vessel 84 aided by the rotation of the drum and serves as an insulating lining. As the batch material 80 on the surface of the lining 84 is exposed to the heat within the cavity 82, it forms a liquefying layer 88 that flows out of a central drain opening at the bottom 92 of the vessel 84 to a dissolving vessel 94 to complete the dissolution of unmelted particles in the liquefied material coming from the vessel 84.

[0118] A valve 96 controls the flow of material from dissolving vessel 94 into a generally cylindrical vertically upright vessel 98 having an interior ceramic refractory lining (not shown) shrouded in a gas-tight, water-cooled casing 100. A molten stream 102 of refined glass falls freely from the bottom of the refining vessel 98 and can be passed to a subsequent stage in the glass making process. For a detailed discussion on the operation of the equipment 78 shown in FIG. 3 reference can be made to U.S. Pat. No. 4,792,536.

[0119] The glasses of the invention can be made using any known glass making process. For example, but not limiting to the invention, the low iron, high redox glasses of the invention can be made in the multi-stage melting and vacuuming-assisted refining operation shown in FIG. 3. The refining stage of this known process is performed under a vacuum to reduce the concentration of dissolved gasses and volatile gaseous components, particularly sulfur-containing components. As will be appreciated by one skilled in the art, it can be advantageous to remove sulfur-containing components from certain float glass compositions since the combination of sulfur with iron in the glass can result in amber coloration of the glass at high redox ratios, for example, iron redox ratios above 0.4, especially above 0.5, due to the formation of ferric sulfide (also conventionally referred to as iron sulfide or iron polysulfide). Ferric sulfide can form throughout the bulk glass or in streaks or layers of a glass sheet. As used herein, the term bulk glass means the internal portion of a glass piece, such as a glass sheet, that is not chemically altered in the process of forming the glass. For a 2 millimeter (mm) or thicker glass sheet made by a float glass process, the bulk glass does not include the outer region of the glass adjacent to the glass surface, for example the outer 25 microns (as measured from the glass surface). The elimination of gaseous sulfur components in the vacuum refining stage of this known process helps prevent the formation of ferric sulfide in the glass and, thus, helps prevent amber coloration.

[0120] As mentioned above and shown in FIGS. 1 and 2, conventional float glass systems typically include a furnace or melter into which the glass materials are placed for melting. In one practice of the invention, the melter can be an oxygen fuel furnace in which the fuel is mixed with oxygen to supply heat to melt the batch materials. In another practice of the invention, the melter can be a conventional air-fuel melter in which air is mixed with the combustion fuel to provide heat to melt the batch materials. In a still further practice of the invention, the melter can be a hybrid-type melter in which a conventional air-type melter is augmented with oxygen lances to supplement the heated air with oxygen before combustion.

[0121] One difference between glasses made from batch materials melted in an oxygen fuel furnace and a conventional air-fuel melter is that the glass made from batch materials melted in an oxygen fuel furnace typically has a water content in the range of 425-600 parts per million, wherein the glass made from batch materials melted in a conventional air-fuel melter typically has a water content in the range of 200-400 parts per million, and glass made from 100% cullet melted in an oxygen fuel furnace typically has a water content of about 700 parts per million. In the preferred practice of the invention, the glass batch materials are melted in an oxygen fuel furnace or a conventional air-fuel melter. In the following discussion of the invention, the invention is practiced using an oxygen fuel furnace; however, the invention is not limited thereto, and the invention can be practiced using any type of glass melting system.

[0122] In the practice of the invention, typical batch materials for making soda-lime-silica glass are introduced into the melter, the furnace 20 shown in FIG. 1 and furnace 84 shown in FIG. 3. Typical batch materials for soda-lime-silica glass composition include sand, soda ash, limestone, alumina and dolomite. In one non-limiting embodiment of the invention, low iron dolomite is used as a batch material. As will be appreciated by one skilled in the art, conventional soda-lime-silica batch materials also include melting and refining aids, such as salt cake (sodium sulfate). Salt cake can also be an oxidizer when incorporated into the glass batch.

[0123] If salt cake is totally eliminated from the batch materials, in addition to increased melting difficulties, the redox ratio of the glass can increase to the point where polysulfides can be formed in the bulk glass, thus providing the bulk glass with an amber tint. In order to control the redox ratio of the glass, non-sulfur containing oxidizers can be added to the batch materials in place of salt cake to oxidize the Fe++ to Fe+++ to decrease the redox ratio. One non-limiting example of such a material is sodium nitrate (NaNO.sub.3). While sodium nitrate can prevent the redox ratio of the glass from increasing to the point where bulk polysulfide formation results in an undesirable amber tint in the bulk glass, sodium nitrate can lead to the production of NO.sub.x emissions during the glass production process. These emissions can be treated in conventional manner before their release of the melter gasses to the atmosphere to meet governmental restrictions on NO.sub.x emissions.

[0124] A non-limiting embodiment of the present invention is practiced to make the clear glass of the present invention forming a soda-lime-silica glass composition by means of a float glass process, which is characterized by the following formulation based on the percentage by weight with respect to the total weight of the glass, these percentages were obtained by using x-ray fluorescence analysis.

TABLE-US-00015 SiO.sub.2 68 to 75 wt. %; Al.sub.2O.sub.3 0 to 5 wt. %; CaO 5 to 15 wt. %; MgO 2 to 10 wt. %; Na.sub.2O 10 to 18 wt. %; and K.sub.2O 0 to 5 wt. %.

[0125] In one non-limiting embodiment of the invention, the total iron oxide (Fe.sub.2O.sub.3) is within the range of 0.02 to 0.06 wt. %, ferrous (FeO) from 0.006 to 0.02 wt. %, redox (FeO/Fe.sub.2O.sub.3) from about 0.30 to 0.55 wt. %; Cr.sub.2O.sub.3 from about 0.3 to 10 ppm, TiO.sub.2 from about 50 to 500 ppm; and a proportion of reducing agent of SnO.sub.2 from about 10 to 500 ppm and a critical amount from about 0.10 to 0.25 wt. % of the oxidizing agent SO.sub.3. The low content of iron oxide is achieved by the partial substitution of regular raw materials by low iron raw materials, with a complete substitution of regular dolomite by a low iron dolomite with a maximum content of 0.020 wt. % Fe.sub.2O.sub.3.

[0126] In one non-limiting embodiment of the invention, the low iron dolomite in the range of 5 to 20 wt. % in the batch comprises from 5 to 15 wt. % of CaO and 2 to 10 wt. % of MgO. The low iron dolomite contains less than or equal to about 0.020% Fe.sub.2O.sub.3.

[0127] In one non-limiting embodiment, the clear glass has a high visible light transmittance (L.sub.tC) of at least 89; with a dominant wavelength (DW) from about 490 to 505 nanometers and purity (Pe) of no more than 1% for control thickness of 5.66 mm.

[0128] A clear glass with low iron has great importance in the architectural industry, but not limited to automotive industry or applications, where the high visible light transmittance and its low iron percentage, allows objects seen through this type of glass to be better appreciated, or when is used in outdoors, it allows to have spaces with greater lighting.

[0129] To achieve the described characteristics, the present invention includes a proper balance between the iron, ferric and ferrous oxide, titanium oxide, chromium oxide, tin oxide and regular coal or low iron graphite, in addition, substituting partially or totally regular raw materials with low iron raw materials, such as low iron sand with a maximum content of 0.010% Fe.sub.2O.sub.3, low iron dolomite with a maximum content of 0.020 wt. % Fe.sub.2O.sub.3, low iron calcite with a maximum content of 0.010% Fe.sub.2O.sub.3, low iron cullet with a maximum content of 0.010% Fe.sub.2O.sub.3, and low iron graphite with a maximum content of 0.010% Fe.sub.2O.sub.3.

[0130] A proper balance of low iron raw materials and clear cullet ratio can achieve the desired properties; however, in this case, the cost of formulation might be higher. Another formulation to achieve the desired characteristics could be using low iron raw materials and regular dolomite. In this case, it would be necessary to adjust the clear and low iron cullet ratio, nevertheless, the cost of this formulation might be higher.

[0131] Another variable to achieve the glass proposed in this invention is the iron redox in the glass, wherein, carbon and tin oxide are used as reducing agents and sodium sulfate is used as an oxidizing agent and refining agent. Chromium oxide and titanium oxide are allowed as coloring agents.

[0132] According to the present invention, the above-mentioned performance properties are measured as described below. The luminous transmittance (Lt.sub.C) is measured using C.I.E. standard illuminant C with a C.I.E. 2 observer over the wavelength range of 380 to 770 nanometers. Glass color, in terms of dominant wavelength (DW) and excitation purity (Pe), is measured using C.I.E. standard illuminant D65 with a 10 observer, following the procedures established in ASTM E 308-2001. The total solar ultraviolet transmittance (T.sub.UV) is measured over the wavelength range of 300 to 400 nanometers, total solar infrared transmittance (T.sub.IR) is measured over the wavelength range of 720 to 2000 nanometers, and total solar energy transmittance (T.sub.SET) is measured over the wavelength range of 300 to 2000 nanometers. The T.sub.UV, T.sub.IR and T.sub.SET transmittance data is calculated using Parry Moon air mass 2.0 direct solar irradiance data and integrated using the Trapezoidal Rule, as is known in the art.

[0133] The color variables L*, a*, and b* of the color system CIELAB 1976 are also calculated through the tristimulus values.

[0134] The glass of the present invention may be melted and refined in a continuous, large-scale, commercial glass melting operation and formed into flat glass sheets of varying thickness by the float method in which the molten glass is supported on a pool of molten metal, usually tin, as it assumes a ribbon shape and is cooled in a manner well known in the art.

[0135] The following formulations in the Table 1 have basic batch components, colorants and redox agents to produce 1 ton of glass.

TABLE-US-00016 TABLE 1 Ex 1 to 7 Ex 8 to 16 Ex 17 to 21 Ex 22 to 30 Batch weights in kg per ton of glass Cullet 150.0 150.0 150.0 80.0 Low Iron Sand 616.3 624.3 0.0 0.0 Regular Sand 0.0 0.0 619.5 668.8 Low Iron Dolomite 109.3 144.2 163.1 199.5 Low Iron Graphite 0.6 0.5 0.0 0.0 Regular Coal 0.0 0.0 0.5 0.9 Salt Cake 5.8 4.3 6.2 6.7 Regular Limestone 0.0 0.0 41.5 24.4 Low Iron Calcite 97.4 55.4 0.0 0.0 Soda Ash 201.0 201.8 199.5 216.0 Iron Oxide as required as required as required as required Tin Oxide as required as required as required as required Titanium Oxide as required as required as required as required Chromium Oxide as required as required as required as required Firing Air/Gas Oxy/Fuel Air/Gas Air/Gas Air/gas ratio 13.5 13.81 14.0 Oxygen/gas ratio 2.0

[0136] In the examples 1 to 7, low iron raw materials are used in a non-limiting formulation of the present invention: 0.6 kg of low iron graphite and 5.8 kg of salt cake per ton of glass are added to the batch formulation to control the redox in the glass and the iron percentage is adjusted by using a mixture of clear and low iron cullet.

[0137] Typical raw material composition for these examples are listed below:

TABLE-US-00017 Raw Material Sources By Weight Percent SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 CaO MgO Na.sub.2O SO.sub.3 Low Iron Sand 99.7 0.01 0.1 Soda Ash 58.6 Salt Cake 0.1 43.7 56.4 Graphite 0.01 Low Iron 0.1 0.01 53 2.1 Limestone Low Iron 0.1 0.01 31.1 21.1 0.1 Dolomite Clear Cullet 72.6 0.2 0.10 10.0 3.1 13.8 0.2 Low Iron Culler 72.7 0.1 0.01 10.3 2.9 13.8 0.2

[0138] In the examples 8 to 16, low iron raw materials are used in the formulation: 0.5 kg of low iron graphite and 4.3 kg of salt cake per ton of glass are added to the batch formulation to control the redox in the glass and the iron percentage is adjusted by using a mixture of clear and low iron cullet.

[0139] Typical raw material composition for these examples are listed below:

TABLE-US-00018 Raw Material Sources By Weight Percent SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 CaO MgO Na.sub.2O SO.sub.3 Low Iron Sand 99.7 0.01 0.1 Soda Ash 58.6 Salt Cake 0.1 43.7 56.4 Graphite 0.01 Low Iron 0.1 0.01 53.0 2.1 Limestone Low Iron 0.1 0.01 31.1 21.1 0.1 Dolomite Clear Cullet 72.8 0.3 0.10 8.8 3.9 13.8 0.1 Low Iron Culler 73.1 0.1 0.01 9.0 3.8 13.9 0.1

[0140] In the examples 17 to 21 are formulated with regular raw materials, except for low iron dolomite with a maximum content of 0.020 wt. % Fe.sub.2O.sub.3. 0.5 kg of regular coal and 6.2 kg of salt cake per ton of glass are added to the batch formulation to control the redox in the glass. These formulations represent a lower cost in final product, due a lower percentage of Fe.sub.2O.sub.3 is maintained by the substitution of regular dolomite by a low iron dolomite and low iron graphite by regular coal. In these examples recirculated cullet is used in the formulation.

[0141] Typical raw material composition for these examples are listed below:

TABLE-US-00019 Raw Material Sources By Weight Percent SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 CaO MgO Na.sub.2O SO.sub.3 Regular Sand 99.1 0.4 0.03-0.04 0.2 Soda Ash 58.6 Salt Cake 0.1 43.7 56.4 Coal 1.5 Regular 0.6 0.12 54.6 0.8 Limestone Low Iron 1 0.01-0.02 32.6 19.6 Dolomite Recirculated 72.6 0.4 0.03-0.05 8.8 3.8 13.9 0.2 Culler

[0142] The examples 22 to 30 are formulated with regular raw materials with the exception of low iron dolomite with a maximum content of 0.020 wt. % Fe.sub.2O.sub.3, 0.9 kg of regular coal and 6.7 kg of salt cake per ton of glass are added to the batch formulation to control the redox in the glass. In these examples low iron dolomite is used to achieve a lower percentage of Fe.sub.2O.sub.3 in the glass, therefore, the amount of regular limestone is decreased. Recirculated cullet is used in the formulation.

[0143] Typical raw material composition for these examples are listed below:

TABLE-US-00020 Raw Material Sources By Weight Percent SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 CaO MgO Na.sub.2O SO.sub.3 Regular Sand 99.1 0.4 0.03-0.04 0.2 Soda Ash 58.6 Salt Cake 0.1 43.7 56.4 Coal 1.50 Regular 0.6 0.12 54.6 0.8 Limestone Low Iron 1 0.01-0.02 32.6 19.6 Dolomite Recirculated 72.4 0.3 0.03-0.05 8.7 4.1 14 0.2 Culler

[0144] The following are examples of soda-lime-silica compositions presented in Table 2, according to what is proposed in the present invention, reporting the physical properties of light transmission (L.sub.tC), UV light (T.sub.UV), infrared (T.sub.IR), and total solar transmittance (T.sub.SET) at control thickness of about 5.66 mm.

[0145] The composition of the following glasses was calculated by x-ray fluorescence.

TABLE-US-00021 TABLE 2 Ex 1 Ex 2 Ex 3 Ex 4 Ex 5 Ex 6 Ex 7 SiO.sub.2 (Weight %) 72.7 72.7 72.7 72.6 72.6 72.6 72.6 Na.sub.2O (Weight %) 13.8 13.8 13.8 13.8 13.8 13.8 13.8 K.sub.2O (Weight %) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 CaO (Weight %) 10.2 10.2 10.2 10.2 10.2 10.2 10.1 MgO (Weight %) 3.0 3.0 3.0 3.0 3.0 3.0 3.0 Al.sub.2O.sub.3 (Weight %) 0.08 0.08 0.09 0.09 0.09 0.10 0.11 SO.sub.3 (Weight %) 0.20 0.20 0.20 0.18 0.19 0.21 0.21 Fe.sub.2O.sub.3 (Weight %) 0.022 0.025 0.027 0.031 0.037 0.038 0.046 FeO (Weight %) 0.008 0.010 0.012 0.012 0.014 0.013 0.015 Redox Ratio (FeO/Fe.sub.2O.sub.3) 0.379 0.398 0.433 0.403 0.381 0.352 0.325 Cr.sub.2O.sub.3 (ppm) 1.7 0.6 0.6 0.6 0.6 0.6 0.6 TiO.sub.2 (ppm) 100 110 110 110 120 130 150 SnO.sub.2 (ppm) 63 67 56 62 59 50 47 Low iron graphite/Regular 0.06 0.06 0.06 0.06 0.06 0.06 0.06 coal in batch (Weight %) Control Thickness 5.66 mm Lt.sub.C (%) 90.8 90.7 90.5 90.4 90.3 90.3 90.1 T.sub.UV (%) 85.3 84.1 83.0 82.9 81.9 81.5 80.3 T.sub.IR (%) 85.2 84.0 82.7 82.1 80.9 81.3 80.1 T.sub.SET (%) 87.9 87.1 86.4 86.1 85.4 85.6 84.9 L* 96.3 96.3 96.2 96.2 96.1 96.1 96.1 a* 0.4 0.5 0.6 0.7 0.8 0.7 0.8 b* 0.0 0.0 0.0 0.1 0.1 0.0 0.0 DW (nm) 494 494 494 492 492 494 494 Pe (%) 0.2 0.3 0.3 0.4 0.5 0.4 0.4 Ex 8 Ex 9 Ex 10 Ex 11 Ex 12 Ex 13 Ex 14 SiO.sub.2 (Weight %) 73.2 73.2 73.2 73.2 73.0 73.0 73.0 Na.sub.2O (Weight %) 13.8 13.8 13.8 13.8 13.9 13.9 13.9 K.sub.2O (Weight %) 0.0 0.0 0.0 0.0 0.0 0.1 0.1 CaO (Weight %) 8.9 8.9 8.8 8.8 8.8 8.8 8.8 MgO (Weight %) 3.7 3.8 3.8 3.8 3.9 3.9 3.9 Al.sub.2O.sub.3 (Weight %) 0.09 0.10 0.10 0.14 0.13 0.16 0.17 SO.sub.3 (Weight %) 0.15 0.15 0.15 0.15 0.16 0.15 0.15 Fe.sub.2O.sub.3 (Weight %) 0.021 0.023 0.024 0.031 0.026 0.030 0.034 FeO (Weight %) 0.009 0.010 0.011 0.012 0.010 0.011 0.013 Redox Ratio (FeO/Fe.sub.2O.sub.3) 0.439 0.438 0.458 0.392 0.384 0.373 0.385 Cr.sub.2O.sub.3 (ppm) 1.6 1.9 1.9 3.0 2.4 2.7 2.8 TiO.sub.2 (ppm) 110 120 120 140 120 140 140 SnO.sub.2 (ppm) 414 392 380 335 339 295 285 Low iron graphite/Regular 0.05 0.05 0.05 0.05 0.05 0.05 0.05 coal in batch (Weight %) Control Thickness 5.66 mm Lt.sub.C (%) 90.7 90.6 90.5 90.4 90.5 90.4 90.2 T.sub.UV (%) 85.4 84.9 83.9 82.8 84.0 83.1 81.3 T.sub.IR (%) 84.6 83.9 83.2 82.1 83.7 82.9 81.6 T.sub.SET (%) 88.7 88.4 88.1 87.6 86.9 86.4 85.7 L* 96.3 96.3 96.2 96.2 96.2 96.2 96.1 a* 0.5 0.5 0.6 0.7 0.6 0.6 0.7 b* 0.0 0.0 0.0 0.0 0.0 0.0 0.0 DW (nm) 494 493 494 494 494 494 495 Pe (%) 0.3 0.3 0.3 0.4 0.3 0.3 0.4 Ex 15 Ex 16 Ex 17 Ex 18 Ex 19 Ex 20 Ex 21 SiO.sub.2 (Weight %) 72.9 72.8 72.7 72.6 72.6 72.7 72.7 Na.sub.2O (Weight %) 13.9 13.9 13.8 13.9 13.9 13.8 13.9 K.sub.2O (Weight %) 0.1 0.1 0.2 0.2 0.2 0.2 0.2 CaO (Weight %) 8.8 8.8 8.8 8.9 8.9 8.9 8.8 MgO (Weight %) 3.9 3.9 3.8 3.7 3.7 3.8 3.7 Al.sub.2O.sub.3 (%) 0.19 0.26 0.39 0.36 0.35 0.39 0.38 SO.sub.3 Weight (%) 0.15 0.15 0.17 0.18 0.20 0.17 0.17 Fe.sub.2O.sub.3 (Weight %) 0.038 0.053 0.035 0.035 0.035 0.036 0.044 FeO (Weight %) 0.014 0.016 0.014 0.013 0.013 0.013 0.017 Redox Ratio (FeO/Fe.sub.2O.sub.3) 0.369 0.301 0.398 0.383 0.354 0.371 0.384 Cr.sub.2O.sub.3 (ppm) 2.4 3.6 4.9 5.2 4.4 5.6 4.6 TiO.sub.2 (ppm) 160 200 370 360 350 390 380 SnO.sub.2 (ppm) 232 114 253 229 184 227 214 Low iron graphite/Regular 0.05 0.05 0.05 0.05 0.05 0.05 0.05 coal in batch (Weight %) Control Thickness 5.66 mm Lt.sub.C (%) 90.1 89.9 90.2 90.1 90.1 90.2 89.9 T.sub.UV (%) 80.0 78.4 81.9 81.8 81.4 81.8 78.7 T.sub.IR (%) 80.7 79.4 80.9 81.3 82.0 81.3 78.9 T.sub.SET (%) 85.1 84.3 85.3 85.4 85.8 85.5 84.0 L* 96.1 96.0 96.1 96.1 96.0 96.1 96.0 a* 0.8 0.9 0.9 0.8 0.8 0.8 1.0 b* 0.1 0.1 0.1 0.1 0.2 0.1 0.2 DW (nm) 495 496 497 497 499 498 498 Pe (%) 0.4 0.4 0.4 0.4 0.3 0.4 0.4 Ex 22 Ex 23 Ex 24 Ex 25 Ex 26 Ex 27 Ex 28 SiO.sub.2 (Weight %) 72.5 72.5 72.5 72.4 72.4 72.5 72.4 Na.sub.2O (Weight %) 14.0 14.0 14.0 14.0 14.0 14.0 14.0 CaO (Weight %) 8.7 8.7 8.7 8.7 8.7 8.7 8.8 MgO (Weight %) 4.1 4.1 4.1 4.1 4.1 4.1 4.1 Al.sub.2O.sub.3 (Weight %) 0.29 0.29 0.29 0.30 0.30 0.31 0.31 SO.sub.3 (Weight %) 0.17 0.17 0.18 0.18 0.18 0.19 0.19 Fe.sub.2O.sub.3 (Weight %) 0.029 0.030 0.031 0.033 0.035 0.037 0.040 FeO (Weight %) 0.013 0.012 0.013 0.013 0.012 0.013 0.013 Redox Ratio (FeO/Fe.sub.2O.sub.3) 0.434 0.418 0.399 0.378 0.351 0.337 0.324 Cr.sub.2O.sub.3 (ppm) 2.9 4.1 3.0 3.1 4.3 4.1 3.3 TiO.sub.2 (ppm) 270 280 290 300 300 300 310 SnO.sub.2 (ppm) 384 388 382 341 308 261 212 Low iron graphite/Regular 0.09 0.09 0.09 0.09 0.09 0.09 0.09 coal in batch (Weight %) Control Thickness 5.66 mm Lt.sub.C (%) 90.2 90.4 90.3 90.3 90.3 90.1 90.1 T.sub.UV (%) 83.4 83.2 82.9 82.5 81.8 80.9 80.4 T.sub.IR (%) 82.0 82.0 81.9 81.9 82.1 81.9 81.7 T.sub.SET (%) 85.8 85.9 85.9 85.8 85.9 85.7 85.6 L* 96.1 96.2 96.1 96.1 96.1 96.0 96.0 a* 0.7 0.7 0.8 0.8 0.7 0.8 0.8 b* 0.0 0.0 0.0 0.0 0.1 0.1 0.2 DW (nm) 494 494 494 495 496 498 498 Pe (%) 0.4 0.4 0.4 0.4 0.3 0.3 0.3 Ex 29 Ex 30 SiO.sub.2 (Weight %) 72.4 72.4 Na.sub.2O (Weight %) 14.0 14.0 K.sub.2O (Weight %) 0.2 0.2 CaO (Weight %) 8.8 8.8 MgO (Weight %) 4.1 4.0 Al.sub.2O.sub.3 (Weight %) 0.31 0.31 SO.sub.3 (Weight %) 0.19 0.19 Fe.sub.2O.sub.3 (Weight %) 0.043 0.043 FeO (Weight %) 0.013 0.014 Redox Ratio (FeO/Fe.sub.2O.sub.3) 0.301 0.317 Cr.sub.2O.sub.3 (ppm) 3.4 4.2 TiO.sub.2 (ppm) 300 300 SnO.sub.2 (ppm) 189 168 Low iron graphite/Regular 0.09 0.09 coal in batch (Weight %) Control Thickness 5.66 mm Lt.sub.C (%) 90.1 90.0 T.sub.UV (%) 80.1 79.4 T.sub.IR (%) 81.7 81.2 T.sub.SET (%) 85.6 85.3 L* 96.1 96.0 a* 0.8 0.8 b* 0.2 0.2 DW (nm) 498 499 Pe (%) 0.3 0.3

[0146] We now refer to the examples from Table 2, a base soda-lime-silica glass composition with a proper balance of chromium and titanium as colorants, low iron graphite or regular coal and tin oxide as redox agents. In this composition, iron oxide is maintained within 0.02 to 0.06 wt. % and sulfate is maintained in the critical amount from about 0.10 to 0.25 wt. % to avoid affecting the refining properties of the SO.sub.3. The quantity added of tin oxide and regular coal or low iron graphite depend of the initial redox conditions of the furnace, requiring different amounts of tin oxide to reach the desired redox in the glass.

[0147] In the examples 1 to 7, low iron raw materials are used with a mixture of clear and low iron cullet to achieve the proper balance of iron oxide, chromium oxide and titanium oxide. In these examples, less SnO.sub.2 is required to reach the redox in the glass due the redox conditions present in the furnace.

[0148] The examples 8 to 16, are also formulated with low iron raw materials and a mixture of clear and low iron cullet, with the difference that a higher amount of SnO.sub.2 is added in the composition of the glass due that the furnace presented a lower redox condition compared to the examples 1 to 7.

[0149] In the examples 17 to 21, regular raw materials are used except for low iron dolomite. In these examples the proper balance of the colorants such as iron oxide, chromium oxide and titanium oxide can be achieved by the use of regular sand in which these oxides are present as impurities. To achieve the redox required in the glass, the amount of SnO.sub.2 added varies according to the redox condition in the furnace.

[0150] In the examples 22 to 30, regular raw materials are used except for low iron dolomite. In these examples the amount of low iron dolomite is increased and the amount of regular limestone is decreased, in relation to the previous examples. The amount of SnO.sub.2 varies as required by the redox condition in the furnace. Like the examples 17 to 21, the proper balance of the colorants described can be achieve by the use of regular sand.

[0151] The examples 1 to 21 from the Table 2 maintained from about 50 to 500 ppm of TiO.sub.2. The titanium oxide in the range described above, increases the light transmission in the glass which is one of the main characteristics of the proposed glass. Additional to this, if the titanium oxide is in excess, a yellowish coloration appears on the glass.

[0152] It is appreciated by one skilled in the art that if the presence of iron oxide, titanium oxide, or chromium oxide are in quantities greater than the ranges mentioned, the light transmission decreases to values lower than those proposed in this patent application.

[0153] The addition and control of these materials confer a clear glass according to a non-limiting embodiment of the present invention, which includes about a total iron oxide (Fe.sub.2O.sub.3) of 0.02 to 0.06 wt. % ferrous (FeO) from 0.006 to 0.02 wt. %, redox (FeO/Fe.sub.2O.sub.3) from about 0.30 to 0.55; Cr.sub.2O.sub.3 from about 0.3 to 10 ppm, TiO.sub.2 from about 50 to 500 ppm; SnO.sub.2 from about 10 to 500 ppm and SO.sub.3 from about 0.10 to 0.25 wt. %. At a control thickness of 5.66 mm, the glasses from the examples have a visible light transmittance (L.sub.tC) of at least 89% with a dominant wavelength (DW) from about 490 to 505 nanometers and purity (Pe) of no more than 1%.

[0154] The disclosed herein compositions are produced by float process in a range from about 1 millimeter to 25 millimeters.

[0155] Reaching the proposed properties for a clear glass composition, according to the scope of the invention, other variations may be applied without departing from what is described in the claims that follow. Accordingly, the particular embodiments described in detail herein are illustrative only and are not limiting to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof.