Dark gray colored glass

Details Dark gray colored glass Dark gray colored glass

2000-06-13

2002-01-15

Marcheschi, Michael (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S904000, C501S905000

Reissue Patent

active

RE037514

ABSTRACT:

The present invention relates to a dark gray colored glass having low visible light transmittance, low ultraviolet ray transmittance, low solar radiation transmittance and low excitation purity, which is suitable for a sun roof or rear window glass of an automobile.
A typical neutral gray colored heat absorbing glass containing Fe
2
O
3
, Se, CoO, NiO, Cr
2
O
3
, etc., is known.
However, nickel is not desirable, since it sometimes forms nickel sulfide in glass. Nickel sulfide is almost indistinguishable by naked eyes and presents no adverse effects to glass in a usual state. However, it has a large thermal expansion coefficient and thus sometimes causes a thermal stress sufficient to break the glass e.g. when the glass is subjected to quenching for toughening.
The following glasses may be mentioned as gray colored glasses which contain no nickel and which have sufficiently low visible light transmittance to be useful for sun roof or rear window glasses of automobiles.
U.S. Pat. No. 4,873,206 discloses a glass which contains total iron in an amount of from 0.6 to 1.0 wt %, as calculated as Fe
2
O
3
, and Se and CoO, and which does not contain nickel or chromium. However, this glass has high solar radiation transmittance and is not necessarily suitable for sun roof of an automobile.
JP-A-4-275943 (which corresponds to U.S. Pat. No. 5,393,593) discloses glasses which contain total iron in an amount of from 1.0 to 1.7 wt %, as calculated as Fe
2
O
3
, and Se and CoO, and which do not contain nickel or chromium. However, most of glasses specifically disclosed in this publication contains FeO in an amount exceeding 0.30 wt %. Accordingly, they are poor in the thermal efficiency during melting and likely to freeze at the bottom of the melting furnace which is remote from the heating source. In Example 4 of this publication, the content of FeO is 0.264 wt %, but the glass is strongly bluish probably due to a poor color forming efficiency of Se. In Examples 1 and 3 thereof, the content of FeO is not too high, and the bluish or reddish color may be within a not distinctive range, as judged from the dominant wavelength, but the amount of total iron is so large that the excitation purity is high. No dark gray colored glass having a low excitation purity has been obtained within a range where the content of FeO is not higher than 0.30 wt %.
U.S. Pat. No. 5,352,640 discloses a glass which contains total iron in an amount of from 1.4 to 4 wt %, as calculated as Fe
2
O
3
, and optionally CoO, Se and Cr
2
O
3
. However, this glass may sometimes be difficult to melt since the amount of total iron is large. Further, no Examples are disclosed for a combination of Se and Cr
2
O
3
, and glasses specifically disclosed in Examples all have a high excitation purity.
Further U.S. Pat. No. 5,411,922 discloses a glass composition which does not contain nickel or chromium. However, no specific Examples for the composition are disclosed.
It is an object of the present invention to solve the above problems of the prior art and to provide a glass which is readily meltable and can be produced by a conventional float glass production process and which exhibits a dark gray color with the visible light transmittance controlled to be as low as possible, and with the solar radiation transmittance and ultraviolet ray transmittance lowered substantially, whereby the excitation purity is low, and a neutral color can readily be obtained.
The present invention provides a dark gray colored glass comprising 100 parts by weight of a soda lime silicate glass as a matrix component and coloring components essentially consisting of from 0.8 to 1.5 parts by weight of total iron calculated as Fe
2
O
3
, from 0.1 to 0.3 part by weight of FeO, from 0 to 1.0 part by weight of TiO
2
, from 0.0005 to 0.015 part by weight of Se, from 0.02 to 0.05 part by weight of CoO and from 0.002 to 0.05 part by weight of Cr
2
O
3
.
Now, the reasons for defining the above coloring components will be described.
If the content of the total iron calculated as Fe
2
O
3
is less than 0.8 part by weight, per 100 parts by weight of the matrix component, the visible light transmittance tends to be too high. The content is preferably at least 1.0 part by weight. On the other hand, if it exceeds 1.5 parts by weight, per 100 parts by weight of the matrix component, it tends to be difficult to obtain a low excitation purity. The content is preferably at most 1.4 parts by weight, more preferably at most 1.35 parts by weight, per 100 parts by weight of the matrix component.
Among the total iron, the content of ferrous (bivalent) iron calculated as Fe
2
O
3
is preferably from 10 to 30%, more preferably from 15 to 25%, based on the total iron calculated as Fe
2
O
3
. If the content of ferrous iron is less than 10%, the solar radiation transmittance tends to be high. If it exceeds 30%, SO
3
used as a refining agent tends to be reduced, whereby the refining effects will decrease, or due to formation of ferric sulfide, an amber color is likely to form. Further, evaporation of Se tends to be vigorous during melting, whereby it tends to be difficult to incorporate an adequate amount of Se.
If the content of FeO exceeds 0.3 part by weight, per 100 parts by weight of the matrix component, the thermal efficiency during melting tends to be poor, and the glass melt is likely to freeze at the bottom of the furnace which is remote from the heating source. The content is preferably at most 0.26 part by weight, per 100 parts by weight of the matrix component. On the other hand, if the content is less than 0.1 part by weight, per 100 parts by weight of the matrix component, it tends to be difficult to attain sufficiently low solar radiation transmittance. The content is preferably at least 0.22 part by weight, per 100 parts by weight of the matrix component.
TiO
2
is not essential, but may be incorporated to adjust the visible light transmittance.
TiO
2
is usually regarded as a component to be incorporated to reduce the ultraviolet ray transmittance T
uv
. However, as a result of a detailed study on the effect of its incorporation within the range of the glass composition of the present invention, the present inventors have found that when TiO
2
is incorporated in a small amount, the visible light transmittance T
va
can be adjusted without presenting no substantial influence to T
uv
. Its effect is such that when TiO
2
is incorporated in an amount of 0.06 part by weight, per 100 parts by weight of the matrix component, T
va
is reduced by 0.3% in a thickness of 5 mm. With the glass of the present invention, the absolute value of T
va
is small, and incorporation of TiO
2
is accordingly very effective for fine adjustment of T
va
.
Specifically, incorporation of TiO
2
in an amount of at least 0.05 part by weight, per 100 parts by weight of the matrix component, is effective to adjust the visible light transmittance. On the other hand, from the view-point of economical efficiency, TiO
2
may be incorporated in an amount of up to 1.0 part by weight, per 100 parts by weight of the matrix component. However, this effect saturates at a relatively small amount, and it is preferred to control the content of TiO
2
to a level of at most 0.095 part by weight, per 100 parts by weight of the matrix component.
If the content of Se is less than 0.0005 part by weight, per 100 parts by weight of the matrix component, the color of the glass tends to be bluish. The content is preferably at least 0.001 part by weight. On the other hand, if the content exceeds 0.015 part by weight, per 100 parts by weight of the matrix component, the excitation purity tends to be high, and the glass tends to be yellowish, whereby it tends to be difficult to obtain a gray colored glass. The content is preferably at most 0.005 part by weight, per 100 parts by weight of the matrix component.
If the content of CoO is less than 0.02 part by weight, per 100 parts by weight of the matrix component, the visible light transmittance tends to be too high. The content is preferably at least 0.021 part by weight. On t

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