Patent Application
20080096754
In certain example embodiments of this invention, an ultraviolet (UV) transmissive soda-lime-silica based glass is provided. In certain example embodiments of this invention, the UV transmissive soda-lime-silica based glass may be made via the float process. In certain example embodiments of this invention, a soda-lime-silica based glass has a UV transmission of at least 84%, more preferably of at least 86%, even more preferably of at least 88%, and most preferably of at least 90%. In certain example embodiments of this invention, a soda-lime-silica based glass has a transmission at 320 nm (in the UV range) of at least 60%, more preferably of at least 65%, even more preferably of at least 70%, still more preferably of at least 75%, and possibly of at least 78%. In certain example embodiments of this invention, the soda-lime-silica glass has a visible transmission of at least about 80%, more preferably of at least about 85%, and most preferably of at least 90% or 91%. These optical characteristics may be provided at an example non-limiting reference glass thickness of about 3 mm.
In certain example embodiments of this invention, the glass is soda-lime-silica based and may be made via the float process, or any other suitable process such as in a patterned glass line. In addition to the base soda-lime-silica composition/glass, the soda-lime-silica based glass may also include a colorant portion. In certain example embodiments of this invention, it is desired for the glass to have a high visible transmission in combination with high UV transmission. An exemplary soda-lime-silica base glass according to certain embodiments of this invention, on a weight percentage basis, includes the following basic ingredients:
In addition to the base glass (e.g., see Table 1 above), in making glass according to certain example embodiments of the instant invention the glass batch includes materials (including colorants and/or reducing agent(s)) which cause the resulting glass to have a reduced amount of ferric iron and/or the like, high UV transmission, high visible transmission, and/or stabilization against UV degradation. These materials may either be present in the raw materials (e.g., small amounts of iron), or may be added to the base glass materials in the batch (e.g., reducing agents). Moreover, in addition to the ingredients in Table 1 above, other minor ingredients, including various conventional refining aids, such as SO3 and the like may also be included in the base glass. In certain embodiments, for example, glass herein may be made from batch raw materials silica sand, soda ash, dolomite, limestone, with the use of materials such as carbon, silicon, and/or the like as refining agents. In certain example embodiments, soda-lime-silica based glasses herein include by weight from about 10-15% Na2O and from about 6-12% CaO.
Glass raw materials (e.g., silica sand, soda ash, dolomite, and/or limestone) typically include certain impurities such as iron, which is a colorant for glass. The total amount of iron present is expressed herein in terms of Fe2O3 in accordance with standard practice. However, typically, not all iron is in the form of Fe2O3. Instead, iron is usually present in both the ferrous state (Fe2+; expressed herein as FeO, even though all ferrous state iron in the glass may not be in the form of FeO) and the ferric state (Fe3+). Iron in the ferrous state (Fe2+; FeO) is a blue-green colorant, while iron in the ferric state (Fe3+) is a yellow-green colorant. The yellow-green colorant of ferric iron (Fe3+) is of particular concern when seeking to achieve a highly UV transmissive glass because ferric iron is much more of a UV absorber than is ferrous iron. Thus, high ferric iron amounts are not desirable in certain example embodiments of this invention.
In certain example embodiments of this invention, the soda-lime-silica glass is made using a reduced batch process so as to provide the glass with a high glass redox and/or a low ferric iron content. As mentioned above, ferric iron in significant amounts is undesirable in that it absorbs significant amounts of UV radiation. Thus, glasses according to certain example embodiments of this invention limit the amount of ferric iron in the glass. This may be done by reducing the amount of total iron in the glass and/or by providing a high glass redox. Because the glass may include more ferrous than ferric iron in certain example embodiments of this invention, the glass may be bluish and/or greenish in color due to the blue-green colorant nature of ferrous iron.
In certain example embodiments of this invention, the glass is essentially or substantially free of UV absorbing compounds such as ferric iron, chromium oxide, lead oxide, titanium oxide, vanadium oxide, and heavy metal sulfides. In certain example embodiments of this invention, a low total iron content glass batch is reduced so that much ferric iron is transformed into less UV absorbing ferrous iron. The reducing agents that may be used without significantly contaminating the batch are, for example and without limitation, metallic silicon, aluminum metallic, calcium silicide, silicon monoxide, tin monoxide. Optionally, though less preferred, carbon may also or instead be used as a refining aid for reducing purposes. Moreover, in certain example embodiments of this invention, the batch may be based on substantially non-oxidizing refining with sodium chloride and/or temperature in order to prevent or reduce the formation of ferric iron. In certain example embodiments, the glass may be made using a negative batch redox in order to reduce generation of significant amounts of sulfides.
In certain example embodiments of this invention, in order to improve UV transmission characteristics, the glass may contain one or more of elements such as Li, Al and/or Zn (including oxides thereof). One or more of these materials may be introduced into the batch as batch materials lithium carbonate, alumina and/or zinc oxide, respectively. The final glass may contain, for example, from 0-5% of one, two or all of lithium oxide (e.g., Li2O), aluminum oxide (e.g., Al2O3), and/or zinc oxide (e.g., ZnO). The presence of one or more of these elements in the body of the glass is advantageous in that it provides a certain level of stabilization against UV degradation. The degradation effect (e.g., oxidation by UV radiation) may also or instead be reduced by heat treatment which may occur naturally or in the manufacturing process. Moreover, zinc for example may also be advantageous in that it may both cause a reducing effect and remove/reduce sulfides. For instance, zinc oxide in the glass batch may lead to substantially colorless zinc sulfide thereby preventing or reducing the generation of brown iron sulfide.
In certain example embodiments of this invention, the UV transmissive glass is achieved without the need for significant amounts of materials such as one or more of arsenic, antimony, vanadium, cerium, selenium, and lead (including oxides thereof). In certain example embodiments of this invention, the glass contains no more than 0.1%, more preferably no more than 0.05%, even more preferably no more than 0.01%, more preferably no more than about 0.005%, still more preferably no more than about 0.0005%, and possibly no more than about 0.0001% of one, two, three, four, five or all of arsenic, antimony, erbium, nickel, vanadium, cerium, selenium, and/or lead (including oxides thereof). In certain example embodiments of this invention, the glass is free of (has 0% of) one, two, three, four, five or all of arsenic, antimony, erbium, nickel, vanadium, cerium, selenium, and/or lead (including oxides thereof). In certain example embodiments, one, two, three, four, five, six, seven or all of these elements are not present even in trace amounts. As with all material percentages herein, these amounts are in terms of wt. %. Oxides as used herein include different stoichiometries; for example and without limitation the term cerium oxide as used herein includes Ce2O3, CeO2, or the like, as with certain other elements mentioned herein. In certain example embodiments of this invention, the colorant portion is substantially free of colorants other than iron (other than potentially trace amounts).
It is noted that glass according to certain example embodiments of this invention is often made via the known float process in which a tin bath is utilized. It will thus be appreciated by those skilled in the art that as a result of forming the glass on molten tin in certain exemplary embodiments, small amounts of tin or tin oxide may migrate into surface areas of the glass on the side that was in contact with the tin bath during manufacture (i.e., typically, float glass may have a tin oxide concentration of 0.05% or more (wt.) in the first few microns below the surface that was in contact with the tin bath).
In view of the above, glasses according to certain example embodiments of this invention achieve high visible transmission in combination with high UV transmission. In certain embodiments, resulting glasses according to certain example embodiments of this invention may be characterized by one or more of the following transmissive optical, composition, or color characteristics (for the optics, an example non-limiting reference thickness of about 3 mm is used). Note that Lta is visible transmission %, and % T is percent transmission at 320 nm which is in the UV range.
As can be seen from Table 2 above, glasses of certain embodiments of this invention achieve desired features of high visible transmission and/or high UV transmission.
Example glasses were made and tested according to example embodiments of this invention, as shown in
It is noted that the term UV transmission is well known in the art. UV transmission may, for example, be calculated using Parry Moon Air Mass=2 (300-400 nm inclusive, integrated using Simpson's Rule at 10 nm intervals), or via any other suitable technique for this range.
Once given the above disclosure many other features, modifications and improvements will become apparent to the skilled artisan. Such features, modifications and improvements are therefore considered to be a part of this invention, the scope of which is to be determined by the following claims:
