Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
1998-06-23
2002-01-01
Group, Karl (Department: 1755)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C501S070000, C501S905000
Reexamination Certificate
active
06335299
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a soda-lime glass coloured dark green with a grey hue, composed of glass forming main constituents and colouring agents.
2. Description of the Related Art
The expression “soda-lime glass” is used here in the wide sense and relates to any glass which contains the following constituents (in percentages by weight):
Na
2
O
10 to 20%
CaO
0 to 16%
SiO
2
60 to 75%
K
2
O
0 to 10%
MgO
0 to 10%
Al
2
O
3
0 to 5%
BaO
0 to 2%
BaO + CaO + MgO
10 to 20%
K
2
O + Na
2
O
10 to 20%.
This type of glass is very widely used in the field of glazing for buildings or motor vehicles, for example. It is commonly manufactured in the form of ribbon by the drawing or float process. Such a ribbon may be cut in the form of sheets which may then be bent or subjected to a treatment for enhancing the mechanical properties, for example a thermal toughening treatment.
When referring to the optical properties of a glass sheet, it is generally necessary to relate these properties to a standard illuminant. In the present description, 2 standard illuminants are used, Illuminant C and Illuminant A defined by the International Commission on Illumination (Commission Internationale de l'Eclairage or C.I.E.). Illuminant C represents average daylight having a colour temperature of 6700 K. Above all, this illuminant is useful for determining the optical properties of windows intended for buildings. Illuminant A represents the radiation of a Planck radiator having a temperature of approximately 2856 K. This illuminant represents the light emitted by car headlights and is essentially intended to determine the optical properties of windows intended for motor vehicles. The International Commission on Illumination has also published a document entitled “Colorimetry, Official Recommendations of the C.I.E.” (May 1970) which describes a theory in which the calorimetric coordinates for the light of each wavelength of the visible spectrum are defined so as to be able to be represented on a diagram having orthogonal axes x and y, called a C.I.E. trichromatic diagram. This trichromatic diagram shows the locus representative of the light of each wavelength (expressed in nanometres) of the visible spectrum. This locus is called the “spectrum locus” and the light whose coordinates lie on this spectrum locus is said to have 100% excitation purity for the appropriate wavelength. The spectrum locus is closed by a line called the “purple boundary” which joins the points on the spectrum locus whose coordinates correspond to the 380 nm (violet) and 780 nm (red) wavelengths. The area lying between the spectrum locus and the purple boundary is that available for the trichromatic coordinates of any visible light. The coordinates of the light emitted by Illuminant C, for example, correspond to x=0.3101 and y=0.3162. This point C is regarded as representing white light and consequently has an excitation purity equal to zero for any wavelength. Lines may be drawn from point C to the spectrum locus at any desired wavelength and any point lying on these lines may be defined not only by its coordinates x and y but also as a function of the wavelength corresponding to the line on which it lies and of its distance from the point C with respect to the total length of the wavelength line. Consequently, the tint of the light transmitted by a sheet of coloured glass may be described by its dominant wavelength and its excitation purity expressed as a percentage.
In fact, the C.I.E. coordinates of light transmitted by a sheet of coloured glass will depend not only on the composition of the glass but also on its thickness. In the present description, as well as in the claims, all the values of the excitation purity P, of the dominant wavelength &lgr;
D
of the transmitted light and of the light transmission factor (TLC5) of the glass are calculated from the spectral specific internal transmissions (SIT
&lgr;
) of a sheet of glass 5 mm in thickness. The spectral specific internal transmission of a glass sheet is governed solely by the absorption of the glass and may be expressed by the Beer-Lambert law:
SIT
&lgr;
=e
−E.A&lgr;
where A
&lgr;
is the absorption coefficient (in cm
−1
) of the glass at the wavelength in question and E is the thickness (in cm) of the glass.
To a first approximation, SIT
&lgr;
may also be represented by the formula:
(
I
3&lgr;
+R
2&lgr;
)/(
I
1&lgr;
−R
1&lgr;
)
where I
1&lgr;
is the intensity of the visible light incident on a first face of the glass sheet, R
1&lgr;
is the intensity of the visible light reflected by this face, I
3&lgr;
is the intensity of the visible light transmitted by the second face of the glass sheet and R
2&lgr;
is the intensity of the visible light reflected towards the interior of the sheet by this second face.
In the description which follows, as well as in the claims, the following are also used:
the total light transmission for Illuminant A (TLA) measured for a thickness of 4 mm (TLA4). This total transmission is the result of integrating, between the 380 and 780 nm wavelengths, the expression: &Sgr;T
&lgr;
.E
&lgr;
.S
&lgr;
/&Sgr;E
&lgr;
.S
&lgr;
, in which T
&lgr;
is the transmission at the wavelength &lgr;, E
&lgr;
is the spectral distribution of the Illuminant A and S
&lgr;
is the sensitivity of the normal human eye as a function of the wavelength &lgr;;
the total energy transmission (TE), measured for a thickness of 4 mm (TE4). This total transmission is the result of integrating, between the 300 and 2150 nm wavelengths, the expression &Sgr;T
&lgr;
.E
&lgr;
/&Sgr;E
&lgr;
, in which E
&lgr;
is the spectral energy distribution of the sun at 30° above the horizon;
the selectivity (SE), measured by the ratio of the total light transmission for Illuminant A to the total energy transmission (TLA/TE); and
the total transmission in the ultraviolet, measured for a thickness of 4 mm (TUV4). This total transmission is the result of integrating, between 280 and 380 nm, the expression &Sgr;T
&lgr;
.U
&lgr;
/&Sgr;U
&lgr;
, in which U
&lgr;
is the spectral distribution of the ultraviolet radiation which has passed through the atmosphere, defined in the DIN 67507 standard.
SUMMARY OF THE INVENTION
The present invention relates in particular to green glasses with a greyish hue. When the transmission curve of a transparent substance barely varies as a function of the visible wavelength, this substance is termed “neutral grey”. In the C.I.E. system, it does not have a dominant wavelength and its excitation purity is zero. By extension, a body is regarded as grey if its spectral curve is relatively flat in the visible region but has, nevertheless, weak absorption bands making it possible to define a dominant wavelength and a low but non-zero purity. The green glass with a grey hue according to the present invention preferably has a dominant wavelength between 480 and 550 nm.
Green glasses are generally chosen for their protective properties with respect to solar radiation and their use in buildings is known. Green glasses are also used in architecture, as well as for partially glazing certain vehicles or railway carriage compartments. To prevent their contents from being seen from the outside, very dark glass is mainly used.
The present invention relates to a highly selective grey-hued dark green glass specially suitable for use in the form of vehicle windows and in particular as rear side windows and as rear windows.
Glasses with a high selectivity generally impose high absorption of infrared radiation, which makes them difficult to manufacture in conventional glass furnaces.
The invention provides a soda-lime glass coloured dark green, composed of main glass forming constituents and colouring agents, wherein it contains less than 0.4% by weight of FeO, in that it possesses an excitation purity of more than 5% and has, under Illuminant A and for a glass thickness of 4 mm, a light transmission (TLA4) of greater than
Dupont Camille
Foguenne Marc
Glaverbel S.A.
Group Karl
Marbury Piper
Rudnick & Wolfe LLP
Schneider Jerold I.
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