Ultraviolet and infrared radiation absorbing glass

An ultraviolet and infrared radiation absorbing glass having excellent ultraviolet radiation absorbing power and green tint, which is suitably used as a window glass for automobiles and constructional materials. The glass comprises, in % by weight: basic glass components comprising 65 to 80% SiO.sub.2, 0 to 5% Al.sub.2 O.sub.3, 0 to 10% MgO, 5 to 15% CaO, 10 to 18% Na.sub.2 O, 0 to 5% K.sub.2 0, 5 to 15% MgO+CaO, 10 to 20% Na.sub.2 O+K.sub.2 O, and 0 to 5% B.sub.2 O.sub.3, and coloring components comprising 0.4 to 1.5% total iron oxide (T-Fe.sub.2 O.sub.3) in terms of Fe.sub.2 O.sub.3, 0 to 3.0% CeO.sub.2, 0 to 2.0% TiO.sub.2, and 0.025 to 6.0% La.sub.2 O.sub.3, wherein 25 to 40% of said T-Fe.sub.2 O.sub.3 in terms of Fe.sub.2 O.sub.3 is FeO.

FIELD OF THE INVENTION 
The present invention relates to an ultraviolet and infrared radiation 
absorbing glass having a green tint. More specifically, it relates to an 
ultraviolet and infrared radiation absorbing glass which is used as a 
glass for automobiles. 
BACKGROUND OF THE INVENTION 
In order to meet the demand for the protection of interior trim of 
automobiles against deterioration, which has been increasing with the 
recent trend to luxury of the interior trim, and to reduce the load of air 
conditioning, a green-tinted glass having ultraviolet and infrared 
radiation absorbing power has recently been proposed as window glass of 
automobiles. 
For example, there has been known a green-tinted glass having an 
ultraviolet transmission reduced to about 38% or less and a total solar 
energy transmission reduced to about 46% or less while maintaining a 
visible light transmission of at least 70% for securing the vision from 
the inside of automobiles. There is a recent trend that a bluish green 
tint is preferred for such a green-tinted glass for automobiles. 
It is known that the total solar energy transmission can be decreased by 
increasing the absolute amount of ferrous oxide (FeO) of the iron oxides 
introduced into a glass. Almost all of the conventional infrared radiation 
absorbing glasses have used this method. 
On the other hand, various methods have conventionally been proposed as 
methods for decreasing ultraviolet transmission. For example, an infrared 
and ultraviolet radiation absorbing glass disclosed in JP-A-4-193738 (the 
term "JP-A" as used herein means an "unexamined published Japanese patent 
application") contains cerium oxide and titanium oxide. More specifically, 
the glass comprises, in % by weight, as basic glass components, 68 to 72% 
SiO.sub.2, 1.6 to 3.0% Al.sub.2 O.sub.3, 8.5 to 11.0% CaO, 2.0.to 4.2% 
MgO, 12.0 to 16.0% Na.sub.2 O, and 0.5 to 3.0% K.sub.2 O, and as coloring 
components, 0.65 to 0.75% Fe.sub.2 O.sub.3, 0.20 to 0.35% CeO.sub.2 and 
0.2 to 0.4% TiO.sub.2. 
The green-tinted ultraviolet radiation absorbing glass disclosed in 
JP-A-6-564668 comprises, in % by weight, basic glass components of 
soda-lime-silica glass and having incorporated therein 0.53 to 0.70% total 
iron oxide in terms of Fe.sub.2 O.sub.3, 0.5 to 0.8% CeO.sub.2, and 0.2 to 
0.4% TiO.sub.2 as coloring components, wherein 30 to 40% of the total iron 
oxide in terms of Fe.sub.2 O.sub.3 is FeO. 
Further, the green-tinted ultraviolet and infrared radiation absorbing 
glass disclosed in JP-B-6-88812 (the term "JP-B" as used herein means an 
"examined published Japanese patent application") comprises, in % by 
weight, as basic glass components, 65 to 75% SiO.sub.2, 0 to 3% Al.sub.2 
O.sub.3, 1 to 5% MgO, 5 to 15% CaO, 10 to 15% Na.sub.2 O, and 0 to 4% 
K.sub.2 O, and as coloring components, 0.65 to 1.25% total iron oxide in 
terms of Fe.sub.2 O.sub.3, 0.2 to 1.4% CeO.sub.2, or 0.1 to 1.36% 
CeO.sub.2 and 0.02 to 0.85% TiO.sub.2. 
Because cerium oxide is expensive, an ultraviolet and infrared radiation 
absorbing glass having a decreased cerium oxide content has also been 
proposed. 
For example, JP-A-4-231347 discloses a green-tinted ultraviolet radiation 
absorbing glass having a basic glass composition of soda-lime-silica glass 
and further containing, in % by weight, as coloring components, more than 
0.85% total iron oxide (T-Fe.sub.2 O.sub.3) in terms of Fe.sub.2 O.sub.3, 
with a FeO/T-Fe.sub.2 O.sub.3 ratio smaller than 0.275, and less than 0.5% 
CeO.sub.2. 
The above-described conventional ultraviolet and infrared radiation 
absorbing glasses have an ultraviolet radiation absorbing power imparted 
by ultraviolet absorption due to Fe.sub.2 O.sub.3, CeO.sub.2 and TiO.sub.2 
and interactions among them. Of these components, it is CeO.sub.2 that can 
enhance the ultraviolet radiation absorbing power best without giving a 
yellowish tint unfavorable as a glass for automobiles. However, CeO.sub.2 
is expensive. Therefore, in order to minimize the amount of CeO.sub.2 
used, compositions are controlled such that the CeO.sub.2 content is 
decreased and the decreased ultraviolet radiation absorbing power 
corresponding to such a decreased amount is compensated for by using 
Fe.sub.2 O.sub.3 and TiO.sub.2. However, the ultraviolet absorption of 
Fe.sub.2 O.sub.3 or the interaction between TiO.sub.2 and FeO is extended 
over the visible light region. Therefore, if one tries to increase the 
ultraviolet absorption of a glass, the transmission of visible light in 
the short wavelength region is also decreased, so that the glass has a 
yellowish tint. 
SUMMARY OF THE INVENTION 
The present invention has been made in light of the above-described 
problems associated with the conventional techniques. 
Accordingly, an object of the invention is to provide a green-tinted 
ultraviolet and infrared radiation absorbing glass at a low cost which has 
high ultraviolet and infrared radiation absorbing power and is free from 
yellowing that is unfavorable for use in automobiles. 
The ultraviolet and infrared radiation absorbing glass according to the 
present invention comprises, in % by weight: 
basic glass components comprising 
65 to 80% SiO.sub.2, 
0 to 5% Al.sub.2 O.sub.3, 
0 to 10% MgO, 
5 to 15% CaO, 
10 to 18% Na.sub.2 O, 
0 to 5% K.sub.2 O, 
5 to 15% MgO+CaO, 
10 to 20% Na.sub.2 O+K.sub.2 O, and 
0 to 5% B.sub.2 O.sub.3, and 
coloring components comprising 
0.4 to 1.5% total iron oxide (T-Fe.sub.2 O.sub.3) in terms of Fe.sub.2 
O.sub.3, 
0 to 3.0% CeO.sub.2, 
0 to 2.0% TiO.sub.2, and 
0.025 to 6.0% La.sub.2 O.sub.3, 
wherein 25 to 40% of said T-Fe.sub.2 O.sub.3 in terms of Fe.sub.2 O.sub.3 
is FeO. 
In the above embodiment, when the glass has thickness of 4.75 to 6.25 mm, 
the ultraviolet and infrared radiation absorbing glass of the present 
invention preferably comprises, in % by weight: 0.45 to 0.65% T-Fe.sub.2 
O.sub.3 in terms of Fe.sub.2 O.sub.3. 
In another preferred embodiment, when the glass has thickness of 3.25 to 
4.0 mm, the ultraviolet and infrared radiation absorbing glass of the 
present invention preferably comprises, in % by weight: 0.55 to 1.0% 
T-Fe.sub.2 O.sub.3 in terms of Fe.sub.2 O.sub.3, more preferably, 0.55 to 
0.85% T-Fe.sub.2 O.sub.3 in terms of Fe.sub.2 O.sub.3. 
Further, it is preferable that the glass comprises 0.5 to 2.0% CeO.sub.2 
and 0.05 to 1.5% La.sub.2 O.sub.3, wherein 30 to 40% of the T-Fe.sub.2 
O.sub.3 in terms of Fe.sub.2 O.sub.3 is FeO. 
The ultraviolet and infrared radiation absorbing glass of the present 
invention preferably has a visible light transmission of 70% or more, as 
measured in a wavelength region of 380 to 770 nm with the CIE standard 
illuminant A; a dominant wavelength of 495 to 535 nm and an extinction 
purity of 1.5 to 3.5% as measured in a wavelength region of 380 to 770 nm 
with the CIE standard illuminant C; a total solar energy transmission of 
less than 50% as measured in a wavelength region of 300 to 2100 nm; and a 
total ultraviolet transmission of less than 12% as measured according to 
ISO 9050, when the glass has a thickness of 3.25 to 6.25 mm. 
DETAILED DESCRIPTION OF THE INVENTION 
The reasons for limitations of the glass composition of the ultraviolet and 
infrared radiation absorbing glass according to the present invention are 
explained below. Hereinafter, all percents are by weight. 
SiO.sub.2 is a main component forming the skeleton of glass. If the 
SiO.sub.2 content is less than 65%, the glass has poor durability. If the 
content exceeds 80%, it is difficult to melt the glass composition. 
Al.sub.2 O.sub.3 serves to improve the durability of glass. If the Al.sub.2 
O.sub.3 content exceeds 5%, it is difficult to melt the glass composition. 
A preferred Al.sub.2 O.sub.3 content is from 0.1 to 2%. 
MgO and CaO both serve to improve the durability of glass and to control 
the liquidus temperature and viscosity of a glass composition when forming 
a glass. If the MgO content exceeds 10%, the liquidus temperature rises. 
If the CaO content is less than 5% or higher than 15%, the liquidus 
temperature rises. If the total content of MgO and CaO is less than 5%, 
the durability of the resulting glass deteriorates. If the total content 
exceeds 15%, the liquidus temperature rises. 
Na.sub.2 O and K.sub.2 O are used as a glass melting accelerator. If the 
Na.sub.2 O content is less than 10%, or if the total content of Na.sub.2 O 
and K.sub.2 O is less than 10%, the effect of melting acceleration is 
poor. If the Na.sub.2 O content exceed 18%, or if the total content of 
Na.sub.2 O and K.sub.2 O exceeds 20%, the durability of glass decreases. 
It is not preferable that the K.sub.2 O exceeds 5%, because it is more 
expensive than Na.sub.2 O. 
While B.sub.2 O.sub.3 is a component generally used for improvement of the 
durability of glass or as a melting aid, it also functions to enhance 
ultraviolet absorption. If the B.sub.2 O.sub.3 content exceeds 5%, 
exertion of the ultraviolet transmission decreasing effect is extended to 
the visible region, so that not only does the tint tend to be yellowish, 
but also disadvantages occur in forming a glass due to volatilization of 
B.sub.2 O.sub.3 and the like. Accordingly, the upper limit of the B.sub.2 
O.sub.3 content should be 5.0%. 
Iron oxide is present in glass in the form of Fe.sub.2 O.sub.3 (Fe.sup.3+) 
and FeO (Fe.sup.2+). Fe.sub.2 O.sub.3 is a component which serves to 
enhance ultraviolet absorption together with CeO.sub.2 and TiO.sub.2, and 
FeO is a component which serves to enhance the absorption of heat rays. 
Where the total iron oxide (T-Fe.sub.2 O.sub.3) content is within the range 
of from 0.4 to 1.5%, the FeO/T-Fe.sub.2 O.sub.3 ratio is preferably in the 
range of from 0.25 to 0.40 in order to obtain desired total solar energy 
absorption. In the above ratio, the FeO content is usually expressed in 
terms of Fe.sub.2 O.sub.3 content. When the thickness of the glass is from 
4.75 to 6.25 mm, the total iron oxide content preferably is from 0.45 to 
0.65%, and in this embodiment, the FeO/T-Fe.sub.2 O.sub.3 ratio is 
preferably in the range of from 0.25 to 0.40. 
When the thickness of the glass is from 3.25 to 4.00 mm, the total iron 
content preferably is from 0.55 to 1.0%, and in this embodiment, the 
FeO/T-Fe.sub.2 O.sub.3 ratio is preferably 0.30 to 0.40. 
CeO.sub.2 is a component which serves to enhance ultraviolet radiation 
absorbing power, and is present in glass in the form of Ce.sup.3+ or 
Ce.sup.4+. Especially, Ce.sup.3+ is effective in ultraviolet absorption 
because of having a small amount of absorption in the visible light 
region. If the CeO.sub.2 content is too large, the absorption in the short 
wavelength side of the visible light region is too large, and the glass 
becomes yellowish, and at the same time, the cost of the glass extremely 
increases. Therefore, the CeO.sub.2 content is 3.0% or less. In order to 
obtain a further desirable ultraviolet radiation absorbing power and tint, 
the CeO.sub.2 is preferably used in an amount of 0.5 to 2.0%. 
La.sub.2 O.sub.3 is effective not only in decreasing the viscosity of the 
glass but also in accelerating the melting of the glass. Further, it also 
improves the chemical durability of the glass, such as water resistance. 
It has been found that the ultraviolet transmission is decreased by adding 
La.sub.2 O.sub.3 to the glass containing Fe.sub.2 O.sub.3 and CeO.sub.2. 
If the glass containing Fe.sub.2 O.sub.3 and CeO.sub.2 is tempered, the 
ultraviolet transmission and solar energy transmission can be decreased. 
It has also been found that such an effect can be enhanced by the addition 
of La.sub.2 O.sub.3. Although the detailed mechanism of this effect is not 
yet clarified, it can be considered that when La.sup.3+ is introduced 
into the glass, it distorts the structure around ions such as Ce.sup.3+, 
Fe.sup.3+ and Fe.sup.2+, because of the large ion radius of La.sup.3 +, 
so that each ion absorption is increased. When the La.sub.2 O.sub.3 
content is less than 0.025%, such an effect is insufficient. If the 
content exceeds 6.0%, the specific gravity of the glass is too high so 
that problems may arise, for example, that the molten glass is difficult 
to be replaced with other glasses at the time of the production. The 
preferable La.sub.2 O.sub.3 content is 0.05 to 1.5%. La.sub.2 O.sub.3 can 
be added in the form of a raw material containing a high concentration of 
La.sub.2 O.sub.3. However, such a raw material is required to be refined, 
resulting in increasing cost. In view of lowering the cost of the raw 
material, it is preferable that La.sub.2 O.sub.3 is added in the form of a 
mixture with CeO.sub.2 which is produced together with La.sub.2 O.sub.3 
and which is not separated or in the form of an impurity remaining in 
CeO.sub.2 having a low degree of purification. 
TiO.sub.2, while not essential, can be added in order to enhance 
ultraviolet radiation absorbing power in such a small amount that does not 
impair the optical characteristics intended in the present invention. The 
upper limit of the TiO.sub.2 content is 2.0%, preferably 0.5%, and more 
preferably 0.2%. If the TiO.sub.2 content exceeds the upper limit, the 
glass tends to be yellow-tinted. 
The glass having the above-described composition may further contain other 
coloring components, e.g., CoO, NiO, MnO, V.sub.2 O.sub.5, MnO.sub.3, 
etc., and SnO.sub.2 as a reducing agent in a total amount of 0 to 1%, so 
long as the green tint intended in the present invention is not impaired. 
In particular, CoO gives a blue tint and is therefore effective in 
preventing the glass from being yellow-tinted due to Fe.sub.2 O.sub.3, 
CeO.sub.2 or TiO.sub.2 added in increased amounts. A preferred amount of 
CoO added is from 3 to 20 ppm. 
The ultraviolet and infrared radiation absorbing glass according to the 
present invention has a green tint and exhibits high ultraviolet 
absorption, high infrared absorption, and high visible light transmission, 
especially high ultraviolet absorption. 
The present invention will now be described in more detail by reference to 
the following Examples, but it should be understood that the invention is 
not construed as being limited thereto. Unless otherwise indicated, all 
parts, percents, ratios and the like are by weight.

EXAMPLES 1 TO 3 
A typical soda-lime-silica glass batch was appropriately compounded with 
ferric oxide, titanium oxide, cerium oxide, and a carbonaceous material as 
a reducing agent. In Example 1, La.sub.2 O.sub.3 was added in a given 
amount by using cerium oxide containing about 5% of La.sub.2 O.sub.3 as a 
raw material of cerium oxide. In Example 2, a mixture containing CeO.sub.2 
and La.sub.2 O.sub.3 at a weight ratio of about 5:3 was used as a raw 
material of CeO.sub.2 and La.sub.2 O.sub.3. In Example 3, this mixture was 
added until the CeO.sub.2 content reached a given amount and a deficient 
amount of La.sub.2 O.sub.3 was added in the form of lanthanum oxide. These 
raw materials were melted at 1,500.degree. C. for 4 hours in an electric 
furnace. The molten glass was cast on a stainless steel plate and annealed 
to obtain a glass plate having a thickness of about 10 mm. The resulting 
glass plate was cut into a square having a size of 10 cm, and then 
polished so as to have a given thickness, The polished glass was heated to 
about 660.degree. C. in the electric furnace, and the heated glass was 
then taken out of the furnace and tempered under ordinary conditions. 
Regarding the tempered glass thus obtained, a visible light transmission 
(YA) measured with the CIE standard the illuminant A, a total solar energy 
transmission (TG), an ultraviolet transmission (Tuv), and a dominant 
wavelength (Dw) measured with the CIE standard illuminant C, and an 
excitation purity (Pe) were obtained. 
Table 1 shown below shows T-Fe.sub.2 O.sub.3 concentration, FeO (in terms 
of T-Fe.sub.2 O.sub.3)/T-Fe.sub.2 O.sub.3 ratio, TiO.sub.2 concentration, 
CeO.sub.2 concentration, La.sub.2 O.sub.3 concentration, and optical 
characteristics of the samples. In Table 1, concentrations are all % by 
weight. 
TABLE 1 
______________________________________ 
Example 1 Example 2 
Example 3 
______________________________________ 
T-Fe.sub.2 O.sub.3 
0.55 0.63 0.63 
FeO/T-Fe.sub.2 O.sub.3 
0.31 0.34 0.33 
TiO.sub.2 0.11 0.15 0.03 
CeO.sub.2 1.50 1.70 1.00 
La.sub.2 O.sub.3 
0.075 1.00 5.00 
Thickness (nm) 
5.0 4.0 3.5 
YA (%) 74.5 73.5 75.9 
TG (%) 47.5 44.4 49.7 
Tuv (%) 8.6 7.1 9.7 
Dw (nm) 507 515 525 
Pe (%) 2.8 2.1 1.7 
______________________________________ 
As is apparent from Table 1, the sample, the glass according to the 
Examples having a thickness of 3.25 to 6.25 mm, has optical 
characteristics that a visible light transmission (YA) is 70% or more as 
measured with the CIE standard illuminant A, a dominant wavelength (DW) is 
495 to 535 nm, an excitation purity (Pe) is 1.5 to 3.5% as measured with 
the CIE standard illuminant C, a total solar energy transmission (TG) is 
less than 50%, and an ultraviolet transmission (TUV) defined according to 
ISO 9050 is less than 12%. 
COMATIVE EXAMPLES 1 TO 3 
Comparative Examples to the present invention are shown in Table 2 below. 
Comparative Examples 1 to 3 show examples having the compositions 
corresponding to those of Examples 1 to 3 except that La.sub.2 O.sub.3 was 
not included. 
TABLE 2 
______________________________________ 
Comparative 
Comparative 
Comparative 
Example 1 Example 2 Example 3 
______________________________________ 
T-Fe.sub.2 O.sub.3 
0.55 0.63 0.63 
FeO/T-Fe.sub.2 O.sub.3 
0.31 0.34 0.33 
TiO.sub.2 0.11 0.15 0.03 
CeO.sub.2 1.50 1.70 1.00 
La.sub.2 O.sub.3 
0 0 0 
Thickness (nm) 
5.0 4.0 3.5 
YA (%) 74.7 73.8 76.2 
TG (%) 47.6 44.5 49.8 
Tuv (%) 9.1 8.1 12.5 
Dw (nm) 504 510 503 
Pe (%) 3.1 2.5 2.7 
______________________________________ 
It can be seen from the results shown in Tables 1 and 2 above that by 
containing La.sub.2 O.sub.3, an ultraviolet transmission was decreased and 
an ultraviolet absorption was increased. 
In order to examine chemical durability of the glass of Examples 2 and 3 
and Comparative Examples 2 and 3, the glass was placed into a constant 
temperature and humidity bath kept at 80.degree. C. under the condition of 
saturated humidity. After 200 hours, the glass was taken out of the bath 
and cooled. The reflectance of the cooled glass was determined, and the 
difference of the reflectance before or after introducing into the bath 
was determined. According to this method, since the reflectance is 
decreased when the glass surface is modified, the modification of the 
glass can be conveniently evaluated based on the degree of decrease in the 
reflectance. The reflectance of each glass is shown in Table 3 below. 
TABLE 3 
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Change of reflectance (%) 
______________________________________ 
Example 2 -0.80 
Example 3 -0.41 
Comparativw Example 2 
-1.40 
Comparative Example 3 
-1.98 
______________________________________ 
As is apparent from the results shown in Table 3 above, the glass of the 
Examples has a decreased reflectance smaller than that of the Comparative 
Examples, so that the surface of such a glass is difficult to be modified. 
That is, it can be seen that the glass of the Examples has a high chemical 
durability. 
As described in detail above, the present invention can provide an 
ultraviolet and infrared radiation absorbing glass having a high visible 
light transmission and excellent ultraviolet radiation absorbing power 
without yellowing the tint, and also having an excellent chemical 
durability. 
Further, according to the ultraviolet and infrared radiation absorbing 
glass of the present invention, CeO.sub.2 and La.sub.2 O.sub.3 can be 
added in the form of an inexpensive raw material having a low degree of 
purification. Thus, an ultraviolet and infrared radiation absorbing glass 
having excellent ultraviolet radiation absorbing power and chemical 
durability can be produced at low cost. 
While the invention has been described in detail and with reference to 
specific examples thereof, it will be apparent to one skilled in the art 
that various changes and modifications can be made therein without 
departing from the scope thereof.