Grey glass composition and method of making same

Details Grey glass composition and method of making same Grey glass composition and method of making same

1999-03-29

2001-05-22

Sample, David R (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S027000, C501S031000, C501S065000, C501S066000, C501S070000, C501S071000, C065S027000

Reexamination Certificate

active

06235666

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to grey glass compositions and methods of making same. More particularly, this invention relates to erbium-containing grey glass compositions having low light transmittance in the UV and IR range while, at the same time, having high light transmittance in the visible range, thus making such glasses suitable for use as windows and windshields in the automotive industry and architectural field, as well as, in certain embodiments, as eyeglass lenses.
BACKGROUND OF THE INVENTION
The automotive industry, for a number of years, has centered on the color grey, sometimes referred to as “neutral grey”, as the aesthetic color of choice for automotive windows. At the same time, this industry, as well as the eyeglass art, have demanded that transmission in the UV and IR range of the light spectrum be minimized. This is also desirable at certain times in the architectural field. Governmental regulations in the automotive industry, moreover, simultaneously insist that the visible light transmittance be at least 70% or greater in certain, if not all, vehicular windows when provided by the original equipment manufacturer of the vehicle (e.g. GM, Ford, Chrysler etc., in the U.S.A.). A need is thereby created in these diverse industries for a glass which achieves these properties.
A glass window, windshield or other glass article is said to have the desirable color “grey”, sometimes referred to as “neutral grey”, if it manifests a dominant wavelength from about 435 nm, and preferably from about 470 nm, to less than about 570 nm, in combination with an excitation purity of less than about 4.5%. This, then, defines the meaning of the term “grey” as used herein. A still more preferred range of dominant wavelength, thus defining a more preferred “grey” as used herein, is about 480 nm-550 nm, and in like manner, a more preferred range of purity is about 0.2-4.5%. The appearance of such glass, thus defined, has been found to be of a truly “grey” color, rather than wandering into an objectionable hew of bronze, green or purple, or some other color. This “grey” color, as aforesaid, has found a unique demand in the automotive market, but it also has potential utility in the architectural and eyeglass markets as well.
At the same time that a true “grey” color is to be achieved, there is the usually required need to achieve rather strict levels of light transmission defined conventionally by:
LTa as visible light transmission,
UV as ultraviolet light transmission,
IR as infrared light transmission, and
T
s
as total solar transmission.
In order to specify the parameters of these characteristics, it is generally necessary to specify the thickness of the glass which is the subject of the measurement. As used herein, in this respect, the term “a nominal thickness of about 1 mm-6 mm,” and in certain embodiments, “about 3 mm-4 mm” means that the characteristics of the glass are those experienced when the thickness of the actual glass under investigation is adjusted for that nominal thickness range. Such thickness ranges, in this respect, are generally recognized as conventional thicknesses for glass sheets made by the float glass process, as well as a recognized thickness range for the automotive industry.
When measured at the specified nominal thickness (e.g. 3.2 mm or 4 mm) the important characteristic of color achieved by this invention may be reported by the conventional CIE LAB technique (see U.S. Pat. No. 5,308,805). Such a technique is reported in CIE Publication 15.2 (1986) and ASTM: E 308-90 [Ill. C 2° observer].
“Luminous transmittance” (LTa) [2° observer] is a characteristic and term well understood in the art, and is used herein in accordance with its well known meaning [see U.S. Pat. No. 5,308,805]. This term is also known as Ill. A visible transmittance (380-780 nanometers inclusive), and its measurement is made in accordance with CIE Publication 15.2 (1986) and ANSI test method Z26.1.
“Total solar energy transmittance” (T
s
) (300-2100 nm inclusive, integrated using Simpson's Rule at 50 nm intervals using Parry Moon Air Mass=2) is another term well understood in the art [see U.S. Pat. No. 5,308,805]. It is used herein according to this well known meaning. Its measurement is conventional and well known.
The terms, and characteristics, of “ultraviolet light transmittance” (% UV), “infrared energy transmittance” (% IR), “dominant wavelength” (DW) and “excitation purity” (i.e. % “purity”, or Pe) are also well understood terms in the art, as are their measurement techniques. Such terms are used herein, in accordance with their well known meaning [see U.S. Pat. No. 5,308,805].
“Ultraviolet transmittance” (% UW) is measured herein using Parry Moon Air Mass=2 (300-400 nm inclusive, integrated using Simpson's Rule at 10 nm intervals). Such a measurement is well known in the art.
“Infrared transmittance” (% IR) is conventionally measured using Simpson's Rule and Parry Moon Air Mass=2 over the wavelength range 800-2100 nm inclusive at 50 nm intervals. Such a measurement is well known in the art.
“Dominant wavelength” (DW) is calculated and measured conventionally in accord with the aforesaid CIE Publication 15.2 (1986) and ASTM: E 308-90. Its calculation and measurement are also well known in the art. As used herein, therefore, the term “dominant wavelength” includes both the actual measured wavelength and, where applicable, its calculated complement.
“Excitation purity” (Pe or % “purity”) is measured conventionally in accord with CIE Publication 15.2 (1986) and ASTM: E 308-90.
For automotive windows (including windshields) it is desirable that the glass have the following characteristics (when measured at a nominal thickness of about 3 mm-4 mm and preferably at about either 3.2 mm or 4 mm as the particular situation may require), and often in the ultimate product as well:
LTa, greater than about 70%
UV, less than about 42%, preferably less than about 38%
IR, less than about 37%, preferably less than about 28%
T
s
, less than about 47%.
Generally speaking, the prior art has at times been able to meet these automotive requirements, including the achievement of the necessary, aesthetic “grey” color by using as the essential ingredients of the colorant portion in an otherwise conventional silicate glass composition (e.g. a typical soda-lime-silica float glass composition), a combination of cobalt admixed with one or more of selenium, nickel, and cerium, along with an essential amount of iron. In many instances this combination was thought critical to achieving both a grey color and the requisite light transmission properties, or at least a “neutral bronze color.” See, for example, U.S. Pat. Nos. 4,101,705; 5,061,659; 5,264,400; 5,318,931; 5,380,685; and Japanese Patent JP4-280834.
Unfortunately, these prior art combinations often had various problems associated with them. For example, cerium, being a well known UV absorber when present in glass in its reduced form, Ce
3+
, should be avoided for the following reason. Iron is conventionally introduced into glass in the form of Fe
2
O
3
, part of which should be reduced to FeO to achieve the requisite low IR transmittance value. Cerium, which is introduced into glass in the form of CeO
2
, is known to oxidize divalent iron to trivalent iron either directly or by competition with any reducing agent present in the glass melt. Therefore, coexistence of iron oxide and cerium oxide will inevitably lead to a decrease in the concentration of FeO in the glass and thus will reduce its IR absorbing power.
The use of nickel in these prior art compositions presented the problem of nickel sulfide stones forming in the ultimate product. Selenium, furthermore, is difficult to retain in the glass during glass making. The loss of selenium created a difficulty in controlling the redox ratio in the glass, which ultimately adversely affected transmittance values. Without some, or all, of these aforesaid key ingredients, cobalt used by itself with

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