MXPA01002710A - Glass composition - Google Patents

Abstract

A high performance green glass composition containing at least 14.5%by weight Na2O, at least 10.5%by weight CaO, at least 0.5%by weight total iron (measured as Fe2O3) and is substantially magnesium-free, the glass thus produced having a ferrous value of at least 30%and a performance (light transmission minus Direct Solar Heat Transmission) of at least 28%at at least one thickness of 2.8 mm to 5 mm. The invention also relates to glasses made from such composition and to a laminated glass assembly in which two sheets of glass sandwich a polymeric material, at least one, preferably both, of the sheets of glass having such a composition.

Description

GLASS COMPOSITION The present invention relates to a glass composition. More particularly, the present invention relates to a glass composition for producing high performance green glass, which contains iron oxide. A "high performance" glass is one in which the light transmission of the glass is greatly in excess of its heat transmission. The transmission of light from a glass is of primary importance if the glass is for use in automobile vehicles. This is because many countries require that any window in a vehicle ahead of the B-post, have a light transmission of at least 70%. Heat transmission is usually ded by the abbreviation "DSHT", which represents Direct Solar Heat Transmission. The transmission of heat is dependent on the ability of glass to absorb radiation in the infrared region of the electromagnetic spectrum and, to a lesser extent, in the visible portion of the spectrum. In some cases, it is also convenient to absorb the radiation in the ultraviolet region of the spectrum. Iron oxide is well known as a dye in glass compositions and it has the advantage that it consists of a mixture of both ferrous and ferric iron. Radiation absorbs ferrous iron in the infrared region and radiation absorbs ferric iron in the ultraviolet region of the spectrum. To produce high performance glass, it is obviously convenient to increase the ratio of ferrous iron to ferric iron in the iron added to the glass composition. However, particularly when the glass is going to be obtained by the flotation process, merely the increase of the ferrous iron content is possible. One problem is that iron is very good at absorbing heat. Absorbs heat in the melting tank and bottom of the tank, therefore it cools. By doing so, the glass becomes more difficult to melt and the problems of devitrification and formation of silica foam arise. It is possible to use special techniques, such as vacuum refining, to achieve high ferrous ratios in the glass. However, such techniques are extremely expensive to operate. The most usual way to achieve a high ferrous ratio is to use a reducing agent, such as coal, in the batch of raw materials. However, the use of carbon can lead to the problem of foam formation of silica. In passing, it is d that the silica foam is an undissolved silica layer, which is placed over the a YSy -... - surface of molten glass and can, in some cases, form a floating mass, which extends over the entire surface of the glass. To minimize this problem, it is customary to add sulfate to the batch. This sulfate is generally in the form of sodium sulfate or calcium sulfate. However, sulfate is only an agent that aids in the melting of glass, but also acts as an oxidizing agent. Thus, sulfate tends to react with carbon leaving less carbon to reduce ferric iron to ferrous iron. Therefore, although the addition of carbon appears to be a simple way to increase the ferrous ratio in the glass, in practice this is achieved or at least to a desired extent. Most glasses also contain sodium.

In many patent specifications, the amount of sodium present is reported to be 10 to 20%. However, in practice, the amount of sodium present is within the range of 12 to 13%. There are three main reasons for this. First, the greater the amount of sodium in the composition, the higher the cost of the glass. More importantly, high amounts of sodium in the glass have adverse effects on the viscosity of the glass. The third major problem, associated with the use of high - < £. ^ F ¿¿. A,, * a ~ a-j- zS? - ü? Ü? A? 1 '* e * j¡ quantities of sodium, is that the glass obtained desJ • same has low durability, often evident by the stained glass that makes it unacceptable to the users of this glass. Calcium is also used in glass, but has the disadvantage that, if used in large quantities, it causes devitrification. The approximate upper limit, before this happens, is 11% by weight. Magnesium is also used in glass. If the magnesium content in the glass is reduced, the minimum absorption of ferrous iron, which is usually centered at around 1050 nm in the conventional float glass, is shifted to a longer wavelength. This leads to both improved light transmission and reduced solar heat transmission, both of which are clearly beneficial in a high performance glass. Also, magnesium is generally an expensive component of the batch and its removal will reduce the cost of glass. However, magnesium decreases the rate of crystal growth in glass and its removal means that it increases the rate of crystal growth, which manifests itself in devitrification. Likewise, it is believed that magnesium improves the durability of the glass and generally that its removal will adversely affect the durability of the glass.

The present invention is directed to a green glass composition, which contains iron, which has a performance in excess of 28%, ideally greater than 30%, with a ferrous content in excess of 30%, but which can easily be melted , without the disadvantages outlined here above. According to the present invention, a green glass composition is provided, which contains at least 14.5% by weight of Na0, at least 10.5% of CaO and at least 0.5% of total iron (measured as Fe203), the glass being substantially free of magnesium, and this glass, thus produced, has a ferrous value of at least 30% and a performance (transmission of light minus transmission of direct solar heat) of at least 28% and with a thickness of at least 2.8 mm up to 5 mm. As will be apparent to those skilled in the art, the term "magnesium-free" denotes that magnesium is not added to the composition. However, the magnesium will be present in the glass as impurities or a trace element in the batch materials or as a residual exchange from a previous operation in a furnace. In practical terms, therefore, the maximum amount of magnesium present in the composition will remotely exceed 0.2% by weight of the total composition.

We have found, surprisingly, that the composition supplies a glass which has the difference between its light transmission and its DST of at least 28 percentage points, usually in excess of 30%. Although the ferrous value is in excess of 30%, such a composition can be melted in a flotation furnace with all the disadvantages expected by the prior art being obviated or at least minimized. In a preferred embodiment of the present invention, the produced glasses have a light transmission of at least 70% and a performance of at least 30%. Conveniently, the glass contains at least 0.8% of the total iron. It is advantageous if the ferrous value is at least 35%. We have found that if the composition contains a higher content of conventional amounts, both sodium and calcium, the composition is easier to melt. By doing this, the amount of sulfate can be reduced, which is normally added to the batch composition simply to facilitate melting. The reduction of ferric iron to ferrous iron is done using a reducing agent, the most common of which is carbon. However, as mentioned above, it will be readily appreciated that if a reducing agent and an oxidizing agent, such as sulfate, are i ** - < The two are present in the batch, they tend to cancel out from each other and the desired ferrous ratio is not achieved Without, in the present invention, the amount of sulphate needed to facilitate the fusion is Clearly, therefore, carbon acts as a reducing agent for ferric iron, rather than sulfate, and high ferrous ratios can be achieved, Conversely, the amount of sulfate can be kept substantially constant, while However, excessive amounts of calcium, present in the composition, can cause problems of devitrification in the furnace, for this reason, it is convenient if the amount of CaO present in the composition is limited to a value greater than 12%, but preferably below 11% The composition of the present invention may be free of potassium and aluminum (in addition to the amounts present as impurities in the sand). However, either or both of these materials may be present in the composition of the present invention, if desired. Potassium increases the coefficient of thermal expansion of glass and aluminum improves the durability of glass. If present, the amount of potassium is conveniently less than or equal to 1%. Similarly, it & Do you prefer if the amount of aluminum is limited to a maximum -7 of 1.6%. * Likewise, the zirconium can also be present in the composition, in order to improve the durability of the glass, but it is preferred if its amount is not greater than 1%. Likewise, titanium may be present in the composition. Titanium has the advantage that it reduces the ultraviolet transmission of glass, thus accentuating the effect produced by ferric iron, in comparison with ferrous iron, in glass. In this aspect, it is convenient, if titanium is included in the composition, if the titanium is in the ilmenite form. This ilmenite is the ferrous titanate and, therefore, also helps in the production of glass, which has a high ferrous ratio. However, if present, it is advantageous if the amount of titanium, measured as Ti02, present, is limited to a maximum of 1%. Advantageously, the amount of titanium is in the range of 0.20 to 0.60%. Cerium and / or vanadium, both of which act as absorbers of ultraviolet radiation, can also be included in the composition. The glass sheets, obtained from the composition of the present invention, can have a performance of at least 28%, with a thickness of 5 mm. If the glass is to be obtained in a relatively thin form, for example of "* ~ .8 mm, the composition of the present invention allows this glass to have a performance of at least 28% .In a preferred embodiment of the present invention , a glass sheet is obtained from a composition comprising 70 to 75% (by weight) of Si02, 0.25 to 0.55% of Ti02 and 0.75 to 0.95% of Fe203, the glass has a ferrous value of 33 to 37% and a light transmission of at least 70%, with a nominal thickness of 4 mm Another preferred embodiment supplies a glass sheet, formed of a composition comprising 70 to 75% (by weight) of SiO2, 0.25 to 0.45 % of Ti02, and 0.95 to 1.05% of Fe203, this glass has a ferrous value of 33 to 37% and a transmission of light of at least 70%, with a nominal thickness of 3.15 mm In still another preferred embodiment, a glass sheet is provided, formed of a composition comprising 70 to 75% (by weight) of SiO2, 0.50 to 0.65% of Fe 203 and 0.25 to 0.55% of Ti02, this glass has a ferrous value between 33 and 37% and a transmission of light of at least 70%, with nominal thicknesses of 4.6 mm. In all the above cases, the glass is in monolithic form. However, in each case, particularly that described in the immediately preceding paragraph, the glass may be in the form of a laminate, comprising two hours of glass sandwiched in an inner layer. In such a case, at least one of the glass sheets, preferably both, are obtained from a composition according to the present invention. The inner layer, in such case, is advantageously polyvinyl-butyral. The invention will be described, only in the form of illustration, with reference to the following Examples. In the Examples, Table 1 shows the composition of a number of glasses, according to the present invention, Table 2 shows various physical and optical properties of the glasses of Table 1, and Table 3 shows details of certain glasses of the Tables 1 and 2, converted to different thicknesses. In Table 2, light transmission was measured using the Illuminant A, which is well known in the art. The Direct Solar Heat Transmission was measured according to international standard 9050 / ISO 9050) in Air Mass 2, over the range of 350 to 2100 nm. The ultraviolet transmission of Table 2 was measured according to the Parry-Moon Rectangular Rule, which is also known in the art. Similarly, the values a * and b * are the color coordinates of the glass, measured according to the Cie-Lab system under the Illuminant C. Both the The Cie-Lab system as the Illuminant C are terms known in art. m or aSt-fc ^^^ iL. • ^ ^ ^ S ^ Y Table 2 Table 3 The glasses of the present invention are primarily intended for use in automobiles. When used in laminated form, a film of suitable lamination material, such as polyvinyl-butyral, can be sandwiched between a glass sheet, having a composition according to the present invention, and a second glass sheet, which It has appropriate properties. Preferably, however, the lamination film is sandwiched between two glass pieces having a composition according to the present invention. It will be readily appreciated that, to meet the legal requirements in many countries, particularly with respect to the lights located in front of the B-post, the laminated structure must have a light transmission of at least 70%. Clearly, it is convenient to select the glasses that form the outer layers of the laminate, so that the laminated structure still has a performance of not less than 28%. It will be readily apparent to those skilled in the art that several minor changes can be made to the glass of the present invention, without departing from its scope. Thus, for example, the glass of the present invention could be used for architectural purposes.

Claims (21)

1. CLAIMS 1. A green glass composition, which contains at least 14.5% by weight of Na20, at least 10.5% by weight of CaO and at least 0.5% by weight of total iron (measured as Fe203), glass is substantially free of magnesium, this glass, thus produced, has a ferrous value of at least 30% and a performance (transmission of light minus transmission of direct solar heat) of at least 28% and with a thess of at least 2.8 to 5 mm.
2. 2. A composition, as claimed in claim 1, wherein the amount of CaO is equal to, or less than, 12%.
3. 3. A composition, as claimed in claim 2, wherein the amount of CaO is less than 11%.
4. 4. A composition, as claimed in any of the preceding claims, which additionally contains K20, in a maximum amount of 1% by weight.
5. 5. A composition, as claimed in any of the preceding claims, which additionally contains Ti02 in a maximum amount of 1% by weight.
6. 6. A composition, as claimed in claim 5, wherein the Ti02 is present in, an amount of 0.20 to 0.60% by weight.
7. 7. A composition, as claimed in claim 6, in which the source of Ti02 is ilmenite.
8. 8. A composition, as claimed in any of the preceding claims, which additionally contains Al203 in a maximum amount of 1.5% by weight.
9. 9. A composition, as claimed in any of the preceding claims, which additionally contains Zr02 in a maximum amount of 1% by weight.
10. 10. A composition, as claimed in any of the preceding claims, which additionally contains at least one of Ce02 and V203.
11. 11. A sheet of glass, having a composition, as claimed in any of the preceding claims, having a performance of at least 28%, with a thess of 2.8 mm.
12. 12. A glass sheet, having a composition, as claimed in any of claims 1 to 10, having a performance of at least 28%, with a thess of 5 mm.
13. 13. A glass sheet, having a composition, as claimed in any of claims 1 to 10, having a light transmission of at least 70%.
14. 14. A glass sheet, having a composition, as claimed in any of claims 1 to 10, comprising from 70 to 75% (by weight) of SiO2, from 0.25 to 0.55% of TiO2 and from 0.75 to 0.95% of Fe203, this glass has a ferrous value of 33% to 37% and a transmission of light of at least 70%, with a nominal thess of 4 mm.
15. 15. A glass sheet, having a composition, as claimed in any of claims 1 to 10, comprising 70 to 75% (by weight) of SiO2, 0.25 to 0.45% of TiO2 and 0.95 to 2.05% of the Fe203, this glass has a ferrous value of 33 to 37% and a transmission of light of at least 70%, with a nominal thess of 3.15 mm.
16. 16. A glass sheet, having a composition, as claimed in any of claims 1 to 10, which comprises 70 to 75% (by weight) of Si02, 0.50 to 0.65% of Fe203, and 0.25 to 0.55% of Ti02 this glass has a ferrous value of 33 to 37% and a light transmission of at least 70%, with a nominal thess of 4.6 mm.
17. 17. A glass, formed of a composition as claimed in any of the preceding claims, in a monolithic form.
18. 18. A laminate, comprising two sheets of glass, separated by an inner layer, in which at least one of the glass sheets is formed of a composition, as claimed in any of claims 1 to 15.
19. 19. A laminate, as claimed in claim 17, wherein both glass sheets are formed of a composition as claimed in any of claims 1 to 15.
20. 20. A laminate, as claimed in claim 17 or claim 18, wherein the inner layer is polyvinyl butyral.
21. 21. A laminate comprising two sheets of glass, formed of a composition as claimed in claim 15, each sheet having a thickness of 2.3 mm and an internal layer of polyvinyl-butyral, this laminate has a light transmission of at least 70%