Amber-free reduced blue glass composition

Details Amber-free reduced blue glass composition Amber-free reduced blue glass composition

2001-10-26

2003-07-22

Sample, David (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S071000, C065S134300

Reexamination Certificate

active

06596660

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The invention is directed to a blue glass composition and method of producing; a blue glass with an improved infrared absorption.
BACKGROUND OF THE INVENTION
It would be extremely advantageous to improve the infrared absorption of glass products while maintaining a high level of visible transmission and to also have a good absorption in the ultraviolet portion of the spectrum. As is well known in the art, iron oxide is commonly used to provide a green color to glass. Iron oxide exists in two chemical forms in the glass, an oxidized form which is yellow: Fe
2
O
3
, and a reduced form which is blue FeO. Advantageously, the oxidized form of iron oxide absorbs a portion of the ultraviolet light passing through the glass product and the reduced form of iron oxide absorbs a portion of the infrared light passing through the glass product. Under typical furnace firing conditions arid batching conditions, when the total iron oxide in the glass product is within the range of about 0.3 to 0.8 wt. % as Fe
2
O
3
, the iron oxide equilibrium is such that the redox ratio of FeO/total Fe as Fe
2
O
3
is about 0.23-0.26.
It is desirable to increase the proportion of reduced iron oxide (FeO) in the glass to improve its infrared absorption. In addition, by shifting the iron oxide away from the oxidized form (Fe
2
O
3
) the glass will change color from green to blue. The total iron oxide concentration may be decreased to maintain a high visible transmittance of the glass as the reduced iron absorbs more in the visible portion of the spectrum than the oxidized iron.
One way commonly employed to shift the redox equilibrium of iron oxide in the glass, and hence its UV and IR properties, is by increasing the fuel to the furnace. Increasing the amount of fuel, however, has several undesirable consequences: the combustion heating of the furnace becomes inefficient and requires an air increase or the unburnt fuel will burn in the checker system of the furnace. Excess fuel can also reduce the glass to an amber color that sharply lowers the visible transmittance of the glass product.
An amber color arises when the iron reacts with sulfur that has been reduced to form iron sulfide. Amber colored glass containers are normally melted in like manner by using anthracite coal together with iron oxide and sulfate. The amber iron sulfide chromophore, once produced, significantly decreases the visible transmittance of the glass and the glass could not be used where a high transmittance is required.
Therefore, there is a need in the glass industry to produce amber free blue glass that has high transmittance yet having an improved infrared light absorption and an ultra violet absorption.
SUMMARY OF THE INVENTION
The present invention is a blue soda-lime-silica glass composition that is heat absorbing. The composition comprises 68 to 75% SiO
2
, 10 to 18% Na
2
O, 5 to 15% CaO, 0 to 10% MgO, 0 to 5% Al
2
O
3
, and 0 to 5% K
2
O, where CaO+MgO is 6 to 15% and Na
2
O+K
2
O is 10 to 20%, and colorants consisting essentially of: 0.3 to 0.8 wt. % total iron oxide as Fe
2
O
3
wherein the ratio of FeO/total Fe as Fe
2
O
3
is greater than 0.35 but less than 0.62; 0.05 to 0.5 wt. % manganese compound as MnO
2
; 0 to 0.30 wt. % titanium oxide as TiO
2
, and 0 to 0.8 wt. % cerium oxide as CeO
2
.
Glass products made according to the embodiment of the invention have the following spectral properties at 4.0 mm. Thickness 65 to 81% light transmittance using Illuminant A (LTA) and using Illuminant C has a dominant wavelength greater than 488 but less than or equal to 494 nanometers with an excitation purity greater than 4 and less than 11%. Generally, as the quantities of the colorants increase, both the % LTA and % IR transmittance will go down. Similarly, as the glass thickness increases for a given glass composition, the transmittance of the thicker glass will decrease.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Flat soda-lime-silica glass, used in the automotive and architectural industries and conveniently made by the float glass process, is generally characterized by the following basic composition, the amounts of the components being based on a weight percentage of the total glass composition:
TABLE I
Base Glass Components
Weight %
SiO
2
68 to 75
Al
2
O
3
0 to 5
CaO
 5 to 15
MgO
 0 to 10
Na
2
O
10 to 18
K
2
O
0 to 5
The blue glass composition of the present invention employs this basic soda-lime-silica glass composition wherein, additionally, CaO+MgO is 6 to 15 wt. % and Na
2
O+K
2
O is 10 to 20 wt. %. Preferably SO
3
is 0.02 to 0.20 wt. %, more preferably 0.02 to 0.10 wt. %. In addition, the blue glass composition consists essentially of the following coloring components: iron oxide; manganese compound; and optionally any of titanium dioxide or cerium oxide or both.
The total iron oxide as Fe
2
O
3
present in the invention composition in quantities of 0.3 to 0.8 wt. % Fe
2
O
3
. Typically, this ingredient is added with the batch ingredients in the oxide form, Fe
2
O
3
. The iron oxide incorporated in the composition lowers both the ultraviolet and the infrared transmittance of the glass products. When iron is used in a glass composition in normal commercial production, the redox ratio defined as equal to FeO/total Fe as Fe
2
O
3
is 0.23-0.26, while glass of the invention has a higher redox ratio of 0.35-0.62. If the redox ratio goes above 0.62, the undesirable amber chromophore may form.
The most important factor of glass of the invention is the one step batch admixing of the components to feed a conventional siemens float glass furnace. Sodium sulfate is mixed in the batch together with anthracite coal to shift the iron oxide equilibrium toward the reduced form of iron. Manganese dioxide is necessary in the batch to prevent the formation of the amber iron sulfide. All of the batch components are mixed together in a single step and then metered into the furnace. The glass product made with this method becomes blue and the infrared absorption of the product is measurably improved. When glass products made in this manner are used in vehicles, the blue glass absorbs solar heat and there is less total heat build up in the vehicle. The load on vehicle air conditioners is reduced such that there is less heat build up to cool and comfort to the passengers occurs quickly. Glass made with the instant invention can also be used for architectural products and provides a similar reduction in air conditioner load.
A manganese compound is present in an amount of 0.05 to 0.5 wt.% based on MnO
2
in the blue glass invention composition to prevent the formation of the amber color. This manganese compound can be added to the batch glass components in a variety forms, e.g., but not limited to MnO
2
, Mn
3
O
4
, MnO, MnCO
3
, MnSO
4
, MnF
2
, MnCl
2
, etc.
Table II discloses the amounts of raw material batch ingredients that are preferably used to form the embodiments of blue glass compositions according to the present invention.
TABLE II
Batch Material
Range Mass (Lbs)
Sand
1000
Soda Ash
290 to 350
Limestone
70 to 90
Dolomite
215 to 260
Salt cake
 5 to 15
Rouge (97% Fe
2
O
3)
 3.5 to 11.5
Manganese Dioxide
0.65 to 6.5 
Titanium Dioxide
  0 to 4.2
Cerium Oxide
  0 to 11.5
Anthracite coal
  1 to 2.5
Nepheline Syenite
 0 to 150
CARBOCITE is anthracite coal from the Shamokin Filler Company. Graphite could be used as a substitute for anthracite coal in an amount of about 70% that of anthracite coal because anthracite coal contains about 70-72% carbon, the typical range would be from 0.7 to 2.1 pounds of graphite per 1000 pounds of sand. MELITE, a coal slag processed by Calumite Corporation could partially or wholly substitute for rouge in the batch up to about 55 pounds Melite per 1000 pounds of sand. MELITE has about 80% of the total iron oxide in the reduced form and thus would require less anthracite coal to generate similar spectral properties.
The equilibrium reactions that occur in the glass melt which cause a shif

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