MXPA00000391A - A nitrate-free method for manufacturing a blue glass composition - Google Patents

Abstract

The invention is nitrate-free method to manufacture a blue soda-lime-silica glass composition and improving the ultraviolet light absorption thereof while maintaining a high visible light transmission. The method comprises the steps of:adding colorants, during molten glass formation, consisting essentially ofa manganese compound along with a cobalt compound, iron oxide and optionally titanium oxide to a soda-lime-silica base glass composition, and adding no sodium nitrate into the batch during molten glass formation, the materials are added in quantities sufficient to form said blue glass composition having at a 4.0 mm. thickness:477 - 494 dominant wavelength and 6 - 40%purity of excitation. The blue glass composition, by weight, comprises a base glass composition of:68 to 75%SiO2, 10 to 18%Na2O, 5 to 15%CaO, 0 to 10%MgO, 0 to 5%al2O3, and 0 to 5%K2O, where CaO + MgO is 6 to 15%and Na2O + K2O is 10 to 20%;and colorants consisting essentially of:0.4 to 2.0%total iron oxide as Fe2O3, 0.15 to 2.00%manganese oxide as MnO2;0. 005 to 0.025%cobalt oxide as Co, and 0 to 1.00%titanium oxide as TiO2. The glass is useful for automotive or architectural applications. The method preferably involves the use of a reducing agent like anthracite coal during melting operations.

Description

NITRATE EXEMPT METHOD FOR THE MANUFACTURE OF A BLUE GLASS COMPOSITION Reference is made to the related US patent application serial number .... entitled "A BLUE GLASS COMPOSITION ITH IMPROVED UV AND IR ABSORPTION" (COMPOSITION OF BLUE GLASS WITH ABSORPTION IMPROVED UV AND IR) presented concurrently and commonly assigned with this. The invention focuses on a nitrate-free method for the manufacture of a blue glass composition having improved absorption of ultraviolet (UV) and infrared (IR) light together with a low shadow coefficient. More particularly, the blue glass is a glass of soda-lime-silica whose dyes are iron oxide, cobalt oxide, manganese oxide, and optionally titanium oxide. The method can employ, for example, anthracite as a reducing agent. BACKGROUND OF THE INVENTION Blue glass is especially useful for architectural applications such as glass for buildings and has been considered for application as glass in the automotive industry. The blue glass has been manufactured using iron oxide, cobalt, and selenium, as dyes, the cobalt providing a blue color to the glass, in accordance with that indicated in the North American patent RE 34,639 of Boulos et al. In US Patent No. 34,760, Boulos et al., Present a blue glass produced by the use of iron oxide, cobalt and nickel, and in another embodiment, a blue glass also including selenium, both patents are paired with the present invention. . Selenium however is an expensive colorant and tends to volatilize from glass while nickel tends to form undesirable nickel sulfide "stones" in the glass. Another blue glass composition is presented in U.S. Patent 5,344,798, the glass including iron oxide and cerium oxide, optionally together with limited amounts of titanium oxide, zinc oxide, manganese oxide, and cobalt oxide, and having a specific supply Fe + 2 / Fe + 3. The use of cerium oxide, which is known to improve the absorption of UV light, is less than desirable from a commercial perspective because cerium oxide is extremely expensive. Iron oxide exists in two forms in glass, the reduced form (Fe + 2) and the oxidized form (Fe + 3). Another blue glass composition, presented in US Pat. No. 3,779,733, incorporates tin oxides to form more of the reduced iron blue (Fe + 2) having IR light absorption properties. This decreases the amount of yellow oxidized iron, however, which has the property of UV light absorption. Others have used a combination of zinc oxide and tin to similarly reduce iron and form a pale blue glass, as in US Pat. No. 5,013,487, with a resultant decrease in UV light absorption. A pale blue glass is obtained in U.S. Patent 4,792,536 using a unique melting furnace to reduce iron oxide, without using zinc tin oxides, which again decreases the absorption of UV light. As can be seen, the absorption properties of UV and IR light from iron oxide are especially valuable when the glass is to be used in buildings. When the heat is absorbed by the glass, the load on the air conditioners of the building is reduced and when the absorption of ultraviolet light is improved, less damage is observed with the passage of time on the colors of the articles that are inside. of the building, also offering greater comfort. Therefore, the control of these spectral properties of the glass is important. The addition of iron oxide to the glass under normal furnace conditions improves both the absorption of ultraviolet light and the absorption of infrared light from the glass since the concentration of both forms of iron is increased correspondingly, but this is best at the expense of the visible transmittance since the reduced form is darker in terms of its color. That is to sayAs iron oxide is added, the color of the glass becomes obscured in such a way that the visible transmittance is correspondingly diminished which may limit the useful character of the glass. We have unexpectedly discovered that the blue glass of the present invention can include relatively large amounts of iron oxide and yet have a good transmittance of visible light and excellent UV light absorption properties, without the undesirable effects of some blue glass the prior art, through the use of a particular combination of dyes in the glass, i.e., iron oxide, cobalt oxide and manganese oxide. For example, the blue glass of the present invention provides this excellent absorption of UV light without the use of expensive UV light absorbers such as for example cerium oxide. In the United States patent application serial number 08 / 762,474 filed on December 9, 1996 and in the CIP application serial number 08 / 767,768 filed on December 17, 1996, both commonly assigned herein, the present inventors they showed a green glass of high transmittance with improved UV absorption, which dyes are iron oxide and manganese oxide, and optionally any of titanium oxide, cerium oxide, vanadium oxide, and chromium oxide. SUMMARY OF THE INVENTION The present invention is a nitrate-free method for making a blue glass composition and improving ultraviolet light absorption thereof while maintaining a high visible light transmission, said method comprising the steps of: Adding dyes, during melt glass formation, consisting essentially of a manganese compound together with a compound of cobalt, iron oxide and optionally titanium oxide to a glass composition of soda-lime-silica base, without the addition of sodium nitrate in the batch during the formation of glass in fusion, to manufacture a blue glass. According to the method, the materials are added in sufficient amounts to form a blue glass composition whose base glass composition comprises: from 68 to 75% SiO2, from 10 to 18% Na20, from 5 to 15% of CaO, from 0 to 10% of MgO, from 0 to 5% of A1203 and from 0 to 5% of K20, where CaO + MgO is from 6 to 15% and Na20 + K20 is from 10 to 20%; and whose colorants consist essentially of the following: from 0.4 to 2.0% total iron oxide as Fe0; from 0.15 to 2.00% manganese oxide as Mn02; from 0.005 to 0.025% cobalt oxide as Co, and from 0 to 1.00% titanium oxide as Ti02, all percentages by weight are based on the total weight of blue glass; the glass having a thickness of 4.0 mm: dominant wavelength 477-494 and excitation purity: 6-40%. Advantageously, embodiments of the glass composition have enhanced UV light and IR light absorption and a low shade coefficient compared to other blue glasses of similar color and visible transmittance. The shadow coefficient is a widely used indicator of solar thermal gain through a glass compared to a standard reference glass formation system. It is a significant advantage to improve the absorption of UV light and IR light, in commercially desirable form, without the use of costly absorbents such as cerium oxide as is done here, while maintaining good visible light transmittance. We have found that the manganese oxide dye of the blue glass composition of the present invention makes it possible in particular to avoid frequently added dyes such as selenium oxide or nickel while obtaining a pleasant medium to achieve a dark blue color. Accordingly, in this glassmaking method, sodium nitrate is not added during the glass melt processing. Optionally, but desirably anthracite, a reducing agent is added to the batch materials to aid in refining during the manufacturing process, particularly to cooperate with a conventional refining agent, sodium sulfate. This cooperation decreases the temperature at which S03 is released from the sulfate. The anthracite can be replaced in part or in its entirety by other reducers such as blast furnace slag, slag from coal furnace, coke, or graphite in the batch. In the present invention, the use of reducing agents of this type can act to modify certain of the oxidizing effects of the manganese oxide dye or of the sodium sulfate refining agent without destroying the blue color of the glass. These and other advantages of the present invention will be apparent from the following detailed description. DETAILED DESCRIPTION OF THE INVENTION A soda-lime-silica glass used in the automotive industry and in the construction industry is conveniently prepared by the float glass process, and is generally characterized by the following basic composition illustrated in FIG. Figure I, the amounts of the components are based on a percentage by weight of the total glass composition: TABLE I Base glass components% by weight Si02 from 68 to 75 A1202 from 0 to 5 CaO from 5 to 15 MgO from 0 at 10 Na20 from 10 to 18 K20 from 0 to 5 The blue glass composition made according to the method of the present invention employs this basic glass composition soda-lime-silica, additionally CaO + MgO is from 6 to 15% and Na20 + K20 is from 10 to 20%. In addition, the coloring components of the blue glass composition consist essentially of the following: from 0.4 to 2.0% by weight of total iron oxide as Fe203, from 0.15 to 2.00% by weight of manganese oxide, as Mn02; from 0.005 to 0.025% by weight of cobalt oxide as Co, and from 0 to 1.00% by weight of titanium oxide as Ti02. In addition, the blue glass of the present invention, considered at a thickness of 4.0 mm, has the following spectral properties: dominant wavelength: from 477 to 494 and excitation purity from 6 to 40%. The blue glass products made according to the embodiments of the present invention preferably have the following spectral properties in a thickness of 4.0 mm: light transmittance of 20 to 70% using the illuminant A (LTA) and less than 62% transmittance of ultraviolet light (UV) measured in the range of 300 to 400 nanometers and less than 54% of infrared light transmittance (IR) measured in the range of 760 to 2120 nanometers. A preferred embodiment of glasses of the present invention includes an LTA less than 60% with the UV light transmittance less than 50% and the IR transmittance less than 45%. The most preferred embodiment of glass of the present invention includes an LTA of less than 50% with a light transmittance of less than 40% and an IR light transmittance of less than 30%. In general, as the amounts of dyes in the proportion of glass rise, the percentage of LTA, the percentage of IR and UV transmittance of the glass decrease. Similarly, as the thickness of the glass is increased for a given glass composition, the transmittance of the thicker glass decreases. Preferably, the dominant wavelength is between 480 and 488 nanometers with an excitation purity of 10 to 30%. more preferably, the dominant wavelength is between 482 and 485 nanometers with an excitation purity of 10 to 20%. Fusion and refining aids are routinely included in glass manufacturing and can also be used here. A refining aid usually used to remove bubbles from the glass is sodium sulfate which generates SO3 in the glass. S03 is preferably present in the glass composition in a range of 0.10 to 0.30% by weight, more preferably this range is 0.14 to 0.25% by weight. A required dye of the blue glass of the present invention is iron oxide, where as total iron oxide (As Fe2? 3) is present in amounts of 0.4 to 2.0% by weight, more preferably 0.6 to 1.2% by weight . All percentages by weight herein are based on the total weight of the blue glass composition of the present invention.

Typically, this dye is added to the batch ingredients in the oxide form, Fe2 ?3. As previously mentioned, iron oxide exists in two forms in the glass melting. The oxidized form of iron oxide absorbs ultraviolet (UV) light and the reduced form of iron oxide absorbs infrared (IR) light, so the presence of iron oxide decreases the transmittance of UV and IR light through the glass products. Both absorbing functions of iron oxide are especially valuable when the glass product is used in construction applications, particularly in geographical areas that have a significant amount of sunlight. Another essential dye in the blue glass composition of the present invention is manganese oxide which is present in a composition in an amount of 0.15 to 2.0% by weight as Mn02, more preferably in an amount of 0.2 to 0.8% by weight. Mn02 weight. The manganese component can be added to glass materials in batches in various forms of manganese compound, including, but not limited to, MnO, Mn0, Mn30, MnS04, MnCÜ3, MnCl2, MnF2, etc., as well as mixtures of any of these. This dye is generally present in the form of manganese oxide Mn + 2 and Mn + 3 in the glass, although it may also be present in other states, such as Mn + X, for example. It is generally expected that any manganese compound used present in the glass in the form of manganese oxide. It is important that the manganese oxide Mn 3 form generally absorbs in the same spectral area as the selenium oxide or nickel which are the dyes. Accordingly we have found that it can be employed in the blue glass composition of the present invention in order to offer, in part, the coloring effect of selenium oxide or nickel to obtain the desired blue color of the glass of the present invention, however, without the drawbacks of selenium or nickel, as presented above, selenium is expensive and easily volatilized from the melting of glass. Manganese oxide, for example, is not expensive and is not subject to volatility such as selenium in such a way that it is optimal as a colorant in the blue glass composition of the present invention. The use of nickel oxide as a colorant causes the undesirable power of nickel sulphide stone formation in the glass when the sulphates are used as refining agents. The nickel sulphide stones are small ellipse-shaped structures that escape normal inspection methods during glassmaking and have been shown to cause instantaneous rupture when tempering the glass. It has been frequently suggested in the literature that the use of manganese oxide together with iron oxide should be avoided in glass compositions due to the tendency of the glass to be solarized afterwards. That is, it is known that manganese oxide causes a discoloration of the glass when it is exposed to a strong ultraviolet light. USP 5,344,798 mentioned above comments on the problem of solarization related to the inclusion of manganese oxide in the glass and limits its inclusion. In the present invention, the composition includes relatively large amounts of manganese oxide and yet we have found, as shown in the examples, that this amount of manganese oxide does not cause solarization of the glass. The manganese dye has an oxidizing capacity which we have found is useful in the present invention. We wish to oxidize the iron oxide towards its more colorless form. Oxidizing environments have been provided to glass melts in various ways, such as, for example, by providing additional air to the glass melt, by increasing sodium sulfate, calcium sulfate, or sodium nitrate in the batch or by decreasing the temperature from the oven. All these efforts have commercial drawbacks. For example, sodium nitrate can cause undesirable emissions of nitrogen oxide. We have found that the use of manganese oxide as a colorant in the glass within a range of 0.15 to 2.00% by weight of the Mn 2 form further provides oxidizing benefits for the manufacture of the blue glass of the present invention by eliminating the need for a additional oxidant, such as, for example, sodium nitrate. Thus, desirably, this blue glass composition can be manufactured without the use of sodium nitrate as is preferred here. When the manganese compound is added to the glass batch, it is reduced to its more colorless form. For example, a portion of the colored manganese oxide dye-in its oxidized form (e.g., Mn203) is converted to the more colorless, reduced Mn2 form. We have found in this way that more iron oxide can be added to the batch to increase both the absorption of ultraviolet light and the infrared light of the glass while simultaneously maintaining a high transmittance of visible light and obtaining a desired blue color of the glass . While it is expected that other manganese compounds such as MnCl2 would be equally useful and converted to oxides in the batch, it is preferred to use manganese oxide or manganese carbonate compounds as sources of the manganese oxide dye in the glass batch . Cobalt is another required dye in the blue glass composition made in accordance with the present invention. It is typically added to the batch ingredients in the form of an oxide compound thereof and is present as a coloring component in the glass in an amount of 0.005 to 0.025% by weight as Co, preferably in an amount of 0.005 to 0.015% by weight. weight and more preferably in an amount of 0.006 to 0.12% by weight as Co. The cobalt dye functions to absorb light in the range of 580 to 680 nanometers of the visible spectrum. Strong absorption in the range of 580 to 680 nanometers and the weakest absorption at the lower wavelengths is what primarily provides the blue color of the glass of the present invention. It is necessary to balance the amount of absorption from Mn02 and both FeO and Fe2? 3 with the amount of cobalt absorption to achieve the desired blue appearance of the glass composition of the present invention. Typically, in conventional glass compositions, increasing the amount of iron oxide would undesirably reduce the amount of visible light that is being transmitted through the glass. Thus, while the absorption properties of UV and IR light can be improved in conventional glass by increasing the iron oxide dye, if a glass with high visible light transmittance is desired, this can not be achieved. The present invention advantageously offers a blue glass with a good absorption of UV light in IR, while at the same time maintaining a good transmittance of visible light and a pleasant medium blue color. And it provides good absorption of UV light without the use of expensive UV light absorbers such as cerium oxide. A property of manganese dye, its oxidizing capacity towards iron oxide, acts to improve the UV absorption of the blue glass of the present invention. And, in the present invention, the total increase of the total iron concentration can improve the absorption of IR light plus decrease the absorption of UV light again. In another preferred embodiment of the present invention, discussed in more detail below, anthracite or other reducing agent is employed together in the batch with the dyes to further increase the UV and IR light absorption of the glass product. The anthracite displaces a certain part of the manganese oxide and iron oxide to its reduced form and the effect is to increase the blue color. Visible transmittance (% LTA) is decreased when manganese oxide, cobalt oxide, iron oxide and anthracite are used in the manner described above. Some part of the cobalt oxide can be removed to raise the% LTA and the glass will remain blue from the coloring effect of the reduced species of both iron oxide and manganese oxide. The particular amounts of each of the dyes employed, for example iron oxide and each form of iron oxide (Fe + 3, Fe + 2) in a form of a glass product according to the present invention will be a matter of choice and will depend, in part, on the desired spectral properties of the blue glass product, as will be apparent to those skilled in the art from the present disclosure. The selection of a glass composition of a particular embodiment will depend to a large extent on its desired application, such that a glass product for one application preferably has a higher absorption of UV light whanother glass product has an absorption of IR light better. As explained above, the method of the present invention produces a glass with improved UV light absorption whallowing the maintenance of good visible transmittance without the use of expensive additives. For example, a commercially available blue glass sample made in accordance with the US patent RE 34m639, discussed above, and commonly assigned herein, includes iron oxide, cobalt and selenium as colorants and has a UV light transmittance. of about 64.7% and an IR light transmittance of 48.8% to 64.7% LTA (composition of Example 1 here). One embodiment of the present invention of similar color appearance can be prepared which has a 63.6% LTA, a UV light transmittance of 40.0% and an IR transmittance of 40.6% as in example 3. Example 2 has a transmittance of UV light of 45.5% and IR light transmittance from 41.0% to 64.7% LTA. These examples demonstrate the significant improvement of the UV and IR properties of embodiments of the blue glass composition of the present invention compared to a blue glass available with almost the same percentage of LTA. The advantage for building applications of the blue glass produced in accordance with the present invention is apparent from the compositions of the spectral properties made above. The blue glass composition of the present invention may also include titanium oxide in the form of Ti02 in an amount of up to 1.0% by weight to improve the absorption of UV light from the glass. In general, the glass of the present invention does not require any added titanium oxide since it possesses excellent UV and IR light absorption properties. If it is desired to improve the absorption of UV light, titanium dioxide can be added and preferably when included, it will consist of about 0.4% by weight of the blue glass composition. It is known that foreign materials can penetrate the glass batch during the change of production from one glass composition to another in glass melting furnaces or from impurities that frequently accompany the raw materials used. Examples of such foreign materials are selenium, nickel oxide, molybdenum, zinc, zirconium, lithium and chromium, although this list is not limiting. Others will be apparent to those skilled in the art based on the present disclosure. These foreign materials or impurities represent small amounts, such as up to 0.0005% by weight of selenium and up to 0.005% by weight of nickel oxide in the form of NiO. According to the source of the raw materials, obviously, titanium dioxide frequently enters soda-lime-silica glass compositions as an impurity with sand, dolomite, or limestone at levels that provide in the final glass product , even when titanium dioxide has not been intentionally added, a range of titanium dioxide of about 0.015% by weight or 0.02% by weight to about 0.05% by weight. Below is a table showing a list of the ingredients that are preferably used to form the optimum modalities of the blue glass compositions prepared according to the present invention. TABLE II BATCH MATERIALS MASS RANGE (POUNDS) SAND 1000 SODIUM ANHYDRO CARBONATE from 290 to 350 DOLOMITE from 215 to 260 LIMESTONE STONE from 70 to 90 SALT CAKE from 6 to 24 RED ABRASIVE (97% Fe203) from 6 to 30 DIOXIDE FROM MANGANESE from 2.0 to 28 COBALT OXIDE (Co304; from 0.095 to 0.5 TITANIUM DIOXIDE from 0 to 14 CARBOCITO from 0 to 4 NEFELINO SIENITA from 0 to 150 In order to demonstrate the advantages of blue glass made in accordance with the present invention , detailed glass fusions were performed in all the samples in the laboratory in accordance with the following procedure: the batches were weighed, placed in glass jars approximately 2 inches in height and 2 inches in internal diameter and mixed dry for 10 minutes In a Turbula mixer, the dry batches were placed in an 80% platinum crucible / 20% rhodium that has a height of 2 inches and has an internal diameter in the top of 2.5 inches and is tapered towards the base. With an internal diameter of 1.65 inches, add an amount of 4.5 ml of water to the dry batch in the crucible and mix it with a metal spoon. After a preparation of this type, the group of 6 different batches is melted in a gas / air activated furnace at the same time for one hour at a temperature of 2600 ° F and each crucible is removed from the furnace and fryed. The glass fritting action includes coating the inside of the platinum / rhodium crucible with the melted glass and then immersing the crucible in cold water. After removing the crucible from the water and after draining the water, the broken glass particles are removed from the sides of the crucible and mechanically mixed in the crucible. The six samples are similarly fritted and all the crucibles are returned to the furnace for another one hour interval at a temperature of 2600 ° F and the fritting procedure is repeated. After the second fritting process, the crucibles are returned to the oven for 4 hours at a temperature of 2600 ° F. Each crucible is removed in turn from the furnace and each sample of melted glass is emptied into a graphite mold with an internal diameter of 2.5 inches. Each glass is then slowly cooled, marked, and placed in a tempering furnace where the temperature is rapidly raised to 1050 ° F, held for 2 hours at this temperature, and then cooled slowly by turning off the oven and removing the samples after 14 or more hours. The samples are milled and polished to a thickness of approximately 4.0 mm and subsequently the spectral properties are measured for each sample. All the laboratory mergers of the examples are made with the aforementioned procedure and employ a base composition of 100 grams of sand, 32.22 grams of anhydrous sodium carbonate, 8.81 grams of limestone, 23.09 grams of dolomite, 1.2 grams of sulfate of sodium, 2.64 grams of nepheline syenite, and the remainder of the lot includes red abrasive, manganese dioxide and cobalt oxide and may include anthracite or another reducing agent as described in exemplary mergers. Titanium dioxide may also be added to improve ultraviolet absorption, if desired. The base composition of a typical glass melt made from the batch materials above would be about 72% by weight of SiO2, 13.5% by weight of Na20, 0.15% by weight of K20, 8.4% by weight of CaO, 3.6% by weight of MgO, 0.6% by weight of AI2O3, and 0.2% of S03. The range of dyes of the embodiment examples of the present invention is: from 0.4 to 2.0% by weight of Fe203. From 0.15% to 2.00% by weight of Mn02- from 0.005 to 0.025% by weight of coO, and from 0 to 1.0% by weight of Ti0, the specific amounts are detailed in the examples, as can be observed in the subject, the Concentration in percent by weight of the base components decreases as the total amount of dyes rises. Table III shows the improvement of ultraviolet light and infrared light absorption of several examples of glass composition embodiments of the present invention (i.e., other than example 1 which is an example of comparison) which include variable amounts of manganese dioxide as a colorant. Particularly, Table III below shows the improvements in ultraviolet light absorption with an increasing amount of MnO2 at a constant level of 0.6% by weight of Fe203. By way of comparison, Example 1 is a commercially produced product based on the North American patent RE 34,639 pooled with the present in accordance with that commented above, which contains approximately 0.0002% by weight of selenium. In both Table III and Table IV, Ti02 was not added to the glass, but was present as an impurity in the glass at a level of approximately 0.02% by weight, coming from the raw materials. TABLE III EJ.l EJ.2 EJ.3 EJ.4 EJ.5 % by weight of Fe20 + 3 0.42 0.6 0.6 0.6 0.6 % by weight of FeO 0.096 0.123 0.125 0.109 0.123 ppm of Co 50 50 50 150 150 % by weight of Mn02 none 0.2 0.6 0.2 0.6 % LTA 64.7 64.7 63.6 49.3 42.9 % UV 64.7 45.5 40.0 42.9 39.3 % IR 48.8 41.0 40.6 44.1 40.5 % TSET 58.7 53.6 52.3 49.8 45.4 wavelength - 481.9 484.3 486.3 479.6 479.4 dominant% purity of 8.7 9.4 8.2 20.2 23.7 excitation EJ.6 EJ.7% by weight of Fe20 + 3 0.6 0.6% by weight of FeO 0.254 0.266 ppm of Co 150 150% by weight of Mn02 0.2 0.6% LTA 40.3 39.3% UV 50.9 46.9% IR 18.2 16.9% TSET 33.1 31.6 wavelength - 478.9 479.4 dominant% purity of 29. 8 29.5 excitation From Table III, it can be readily observed that the addition of manganese dioxide dye together with the relatively increasing amount of iron oxide dye significantly improves both the absorption of ultraviolet light and the absorption of infrared light from the glass composition of the present invention. In particular, compare the spectral properties of the exemplary commercial product with the glass of the embodiments of the present invention which are found in Examples 2 and 3. More desirably, in addition to the significant improvement in the absorption of ultraviolet light from the glass, the examples of the present invention also conserve the transmittance of visible light of the glass, in accordance with what is evidenced by a similar LTA Percentage. Examples 4 and 5 show an increase in the intensity of the blue color by increasing the concentration of cobalt oxide with corresponding improvements in both UV light absorption and IR light absorption. Examples 6 and 7 are similar to examples 5 and 6, respectively, except that anthracite was added to the batch, such that the ratio between salt and anthracite was 7: 1 to generate reducing conditions. Reductive conditions significantly improved the absorption of IR light while also obtaining better UV light absorption than in the case of the commercial blue glass product of example 1. While Table III showed the improvement in ultraviolet light absorption of the glasses of the present invention with a constant total iron dye when the Mn02 dye was increased, table IV shows the change in ultraviolet light absorption when a constant amount of Mn02 (0.2% by weight) is added to several Fe2? 3 concentrations. The results of table IV, for the glass composition embodiments of the present invention, show that, in glass with a constant weight percentage of MnO2 (concentration), an increase in Fe2? 3, correspondingly increases the absorption of ultraviolet light . Table IV also shows that, at a given concentration of Mn02 dye, the dominant wavelength (color) tends to increase slightly as the total iron oxide in the glass increases. Example 3 (table III) is the same as example 9 in table IV. Example 8 demonstrates the improved absorption of UV light compared to Example 1 in Table III based, it is believed, on the action of the manganese dye to displace the iron oxide dye to its oxidized form. The blue color and intensity of the blue glass of a mode according to the present invention appearing in the example is similar to the commercial blue glass of example 1 and yet has the additional benefit of a higher LTA percentage. Table IV also demonstrates that the transmittance of infrared light is lower in the embodiments of the present invention as the total iron oxide is increased in the blue glass compositions of the present invention. TABLE IV EJ.8 EJ.9 EJ.10 EJ.ll EJ. 12 % by weight of Fe20 + 3 0.4 0.6 0.75 0.9 1. 2% by weight of FeO 0.091 0.125 0.228 0 0..331188 0. 450 ppm Co 50 50 50 50 50% by weight of Mn02 0.2 0.2 0.2 0.2 0. 2% LTA 68.0 64.7 58.9 54.0 46.6 % UV 56.1 45.5 41.4 36.9 27.7 % IR 50.4 41.0 21.5 12.7 6.1 % TSET 60.5 53.6 40.3 33.0 25.4 wavelength - 48.7 484.3 485.2 485.8 487.0 dominant% purity of - 9.4 9.4 12.4 14.4 16.2 excitation EJ.13% by weight of Fe20 + 3 1.6% by weight of FeO 0.644 ppm of Co 50% by weight of Mn? 2 0.2% LTA 35.1% UV 17.5% IR 1.6% TSET 16.9 wavelength - 488.5 dominant% purity of - 19.5 excitation Table V demonstrates the changes in spectral properties that occur when sodium sulfate and the anthracite vary within the embodiment of the invention. The total iron oxide, ppm of Co and% by weight of Mn02 were kept at constant values and the percentage of FeO is the only variable. The actual percentage of Fe203 varies in proportion to the respective concentration of FeO percentage to maintain the total iron oxide at a level of 0.6% by weight. Note that the anthracite has a stronger impact on the percentage concentration of Fe02 than the concentration of sodium sulfate. Examples 14 to 17 have the same percentage by weight between sodium sulphate and anthracite (7: 1), but the reducing action of anthracite overcomes the oxidizing effect of the increase in sodium sulfate. See also examples 16, 18, and 19, in constant sodium sulfate concentration, as the level of anthracite decreases, the percentage of FeO gradually falls. In Examples 14 to 19, constant cobalt oxide and manganese dioxide maintain the dominant wavelength and the excitation purity within a small range. TABLE V EJ. 14 EJ. 15 EJ. 16 EJ. 17 EJ. 18% by weight of Fe2? 3 0. 6 0. 6 0. 6 0. 6 0. 6% by weight of FeO 0.274 0.303 0.331 0.353 0.282 ppm of Co 80 80 80 80 80% by weight of Mn02 0.4 0.4 0.4 0.4 0.4 Na2SO / 1000 Si02 7.5 10 12 16 12 Anthracite / 1000 Si02 1.07 1.43 1.71 2.29 0.8% LTA 51.6 52.3 50.4 48.1 51.6 % UV 48.5 50.4 51.0 47.7 46.2 % IR 16.4 13.9 11.7 10.5 15.6 % TSET 35.4 34.1 32.1 30.0 34.5 wavelength - 482.6 483.1 483.1 484.0 483.7 % purity of ~ 19.3 18.7 19.9 19.1 17.3 excitation EJ.19% by weight of Fe20 + 3 0.6% by weight of FeO 0.274 ppm of Co 80% by weight of Mn02 0.4 Na2SO4 / 1000 Si02 12 Anthracite / 1000 Si02 0.48% LTA 52.3% UV 50.3% IR 16.3% TSET 35.7 wavelength - 482.5 dominant% purity of - 19.4 excitation Table VI below further demonstrates the impact of the use of anthracite compared to the non-use of anthracite in the lot. The manganese dioxide, sodium sulfate, and total iron oxide dye remained constant while the percentage of FeO varied due to the reducing power of the carbon. Examples 20 to 22 had no reducing agent in the batch while examples 23 to 25 each had anthracite in the batch which reduced the iron oxide to generate a higher percentage of FeO and the percentage of transmitted IR light was lower. Note that in each case as the cobalt oxide was increased, the dominant wavelength was decreased and the excitation purity percentage was increased indicating that the blue color was more intense. TABLE VI EJ.20 EJ.21 EJ.22 EJ.23 EJ.24 % by weight of Fe2? 3 0.6 0.6 0.6 0.6 0.6 % by weight of FeO 0.121 0.115 0.117 0.150 0.148 ppm of Co 65 80 95 65 80 % by weight of Mn02 0.2 0.2 0. 0.2 0.2 Na2SO4 / 1000 Si02 12 12 12 12 12 Anthracite / 1000 Si02 0 0 0 0.8 0.8 % LTA 57.9 57.6 54.2 59.7 56.3 % UV 41.3 44.9 44.8 46.2 46.5 % IR 41.2 43.1 42.4 34.6 34.9 % TSET 51.1 52.3 50.8 48.4 47.5 wavelength - 482.8 481.8 480.9 482.9 481.9 dominant% purity of 12.9 14.7 16.3 12.9 15.3 excitation EJ.25% by weight of Fe2Ü + 3 0.6% by weight of FeO 0.152 ppm of Co 95% in weight of Mn02 0.2 Na2SO4 / 1000 Si02 12 Anthracite / 1000 Si02 0.8% LTA 52.6% UV 45.9% IR 34.0% TSET 45.7 wavelength - 481.0 dominant% purity of - 18.1 excitation Table VII below shows the increase in length of dominant wave as the manganese oxide dye rises from 0.2 to 0.6% by weight plus the oxidizing effect that decreases the percentage of UV light transmitted at the highest concentration of manganese oxide and at constant levels of iron oxide. It also shows the influence of an iron oxide dye increased particularlyAs the concentration of iron oxide rises, the percentages of UV, IR percentage and LTA percentage decrease. All the examples in Table VII demonstrate the increased absorption of IR from the addition of anthracite. TABLE VII CJ.26 EJ.27 EJ.28 EJ.29 EJ.30 % by weight of Fe203 0.4 0.4 0.9 0.9 1.6 % by weight of FeO 0.163 0.160 0.373 0.367 0.622 ppm of Co 150 150 150 150 150 % by weight of Mn02 0.2 0.6 0.2 0.6 0.2 Na SO4 / 1000 Si0 12 12 12 12 12 12 Anthracite / 1000 Si02 1.71 1.71 1.71 1.71 1.71 % LTA 43.8 43.2 36.4 36.1 24.6% UV 61.6 55.2 37.8 35.6 16.4 % IR 31.5 32.1 9.1 9.4 2.0 % TSET 42.5 42.1 25.2 25.0 13.9 wavelength - 477.9 478.4 480.4 480.9 482.8 dominant% purity of 28. 5 27. 3 30 1 29. 4 31. 7 excitation EJ. 31% by weight of Fe20 + 3 1. 6% by weight of FeO 0. 644 ppm of Co 150% by weight of Mn02 0.6 Na2SO / 1000 Si02 12 Anthracite / 1000 Si02 1.71% LTA 23.3% UV 12.7% IR 1.9% TSET 12.9 wavelength - 483.9 dominant% purity of - 30.1 excitation Glass compositions Blue processed according to the present invention can be used both in the automotive industry and in construction. In general, they can be manufactured by means of well-known float glass techniques. The current regulations in the automotive industry require a minimum LTA of 70.0% measured in the actual glass thickness, in general, for glasses used in the automotive industry for example, burning coconuts can have a lower LTA. It is expected that the blue glass of the present invention will maintain its LTA throughout its useful life. Glasses containing manganese oxide and iron as colorants have been known to either solarize or discolor when exposed to a strong ultraviolet light source in accordance with the above. Tests of glass composition in the ranges of iron oxide concentrations with manganese oxide dyes of the present blue glass compositions by the inventors have shown that no solarization is observed. It is expected that the blue glass according to the present invention which also includes cobalt oxide does not present solarization since it is manganese oxide which has been repeatedly implicated in literature as a cause of solarization, not cobalt oxide. The examples demonstrate that the inventors unexpectedly discovered a useful way to improve the absorption of ultraviolet light in blue glass products while maintaining good visible light transmission and, at the same time, absorption in the infrared portion of the spectrum is improved. All this has been achieved in a remarkable way at low cost and in a friendly way for the environment, that is, by using, as one of the dyes, manganese compounds instead of the usual materials such as selenium oxide. , nickel or cerium, in the batch of glass composition. And preferably, blue glass can avoid the inclusion of sodium nitrate with the glass batch as is generally used in glass manufacture since these nitrates are a source of undesirable emissions of NOx. While embodiments of the novel method for making the blue glass composition of the present invention have been illustrated and described, it will be apparent to those skilled in the art taking into account the present disclosure that various modifications within the scope of the presentation can be carried out without leave the scope of the invention. The appended claims encompass all these modifications and equivalents that fall within the true spirit and scope of the invention.

Claims (1)

1. CLAIMS A nitrate-free method for preparing a blue glass composition and improving ultraviolet light absorption thereof while maintaining a high transmission of visible light, said method comprises the steps of: Adding dyes, during the formation of melting glass , which consist essentially of a manganese compound with cobalt compound, iron oxide and optionally titanium oxide to a glass composition of soda-lime-silica base, and do not add sodium nitrate in the batch during glass formation In melting, all the base materials and colorants are used in sufficient amounts to make a blue glass composition whose base glass composition comprises: 68 to 75% SiO2, 10 to 18% Na20, 5 to 15 CaO%, 0 to 10% MgO, 0 to 5% A1203, and 0 to 5% K20, where CaO + MgO is 6 to 15% and Na20 + K20 is 10 to 20%; and whose colorants consist essentially of the following: from 0.4 to 2.0% total iron oxide as Fe203; from 0.15 to 2.00% manganese oxide as Mn02; from 0.005 to 0.025% cobalt oxide as Co, and from 0 to 1.00% titanium oxide as Ti02, all percentages are percentages by weight based on the total weight of the blue glass composition; the glass has, in a thickness of 4.0 m, a dominant wavelength of 477 to 494 and an excitation purity of 6 to 40%. The method according to claim 1, wherein the dominant wavelength, at a thickness of 4.0 mm, is between 480 and 488 nanometers. The method according to claim 1, wherein the excitation purity, in a thickness of 4.0 mm, is between 10 and 30%. The method according to claim 1, wherein the amount of manganese dye in the blue glass composition as Mn02 is from 0.2 to 0.8% by weight. The method according to claim 1, wherein the amount of Fe 2 O 3 in the blue glass composition is within a range of 0.6 to 1.2% by weight. The method according to claim 1, wherein the amount of cobalt oxide in the blue glass composition in the form of Co is within the range of 0.005 to 0.015% by weight. The method according to claim 1, wherein it further comprises a floating melted glass made according to the method in a melted tin bath. The method according to claim 1, further comprising the use during the melt processing of a reducing agent as a raw material component. The method according to claim 8, wherein said reducing agent is selected from the group consisting of anthracite, blast furnace slag, coal furnace slag, coke, or graphite, or a mixture thereof. The method according to claim 8, wherein said reducing agent comprises at least anthracite. The method according to claim 1, wherein said blue glass composition comprises SO3 in an amount comprised between 0.10 and 0.30% by weight. The method according to claim 1, wherein the blue glass composition has an excitation purity of blue glass of 10 to 20%. The method according to claim 1, wherein the amount of cobalt oxide as Co in said blue glass composition is within a range of 0.006 to 0.012% by weight. The method according to claim 1, wherein the dominant wavelength of said blue glass composition is between 482 and 485 nanometers. The method according to claim 1, wherein said blue glass composition has the following spectral properties, in a thickness of 4.0 mm: from 20 to 70% of light transmittance using illuminant A (LTA) and less than 62% transmittance of ultraviolet (UV) light measured over a range of 300 to 400 nanometers and less than 54% of infrared (IR) light transmittance measured over the range of 760 to 2120 nanometers. The method according to claim 1, wherein said blue glass composition comprises: 68 to 75% Si02, 10 to 18% Na20, 5 to 15% CaO, 0 to 10% MgO, 0 to 5% of A1203, and 0 to 5% of K20, where CaO + MgO is from 6 to 15% and Na20 + K20 is from 10 to 20%; and dyes consisting essentially of the following: from 0.6 to 1.2% total iron oxide in the form of Fe203; from 0.2 to 0.8% manganese oxide as Mn02; from 0.005 to 0.015% cobalt oxide in the form of Co, from 0 to 1.00% titanium oxide in the form of Ti02, all percentages by weight are based on the total weight of the blue glass composition; the blue glass has, in a thickness of 4.0 mm, a dominant wavelength of 480-488 and an excitation purity of 10 to 30%. SUMMARY OF THE INVENTION The invention is a nitrate-free method for the manufacture of a blue glass soda-lime-silica composition and to improve the ultraviolet light absorption of said glass composition while maintaining a high transmission of visible light. The method comprises the steps of: adding dyes, during melt glass formation, consisting essentially of a manganese compound together with a cobalt compound, iron oxide and optionally titanium oxide to a glass base composition of soda -cal-silica, and do not add sodium nitrate in the batch during the formation of molten glass, the materials are added in sufficient quantities to form said blue glass composition having, in a thickness of 4.00 mm, 477-494 of dominant wavelength and 6-40% excitation purity. The blue glass composition, by weight, comprises a base glass composition consisting of the following: from 68 to 75% Si02, from 10 to 18% Na20, from 5 to 15% CaO, from 0 to 10 % MgO, 0 to 5% Al203, and 0 to 5% K20, where CaO + MgO is 6 to 15% and Na20 + K20 is 10 to 20%; and dyes consisting essentially of: 0.4 to 2.0% total iron oxide as Fe203, 0.15 to 2.00% manganese oxide in the form of Mn02; from 0.005 to 0.025% cobalt oxide in the form of Co, and from 0 to 1.00% titanium oxide in the form of Ti02. Glass is useful for applications in the automotive industry and in architecture. The method preferably includes the use of a reducing agent such as, for example, anthracite during melt operations.