Ultraviolet ray absorbing glass

Details Ultraviolet ray absorbing glass Ultraviolet ray absorbing glass

1999-07-29

2001-07-10

Marcheschi, Michael (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S069000, C501S071000, C501S072000, C501S904000, C501S905000

Reexamination Certificate

active

06258740

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an ultraviolet ray absorbing glass that is transparent and clear (i.e., colorless or almost colorless). The glass is suitable for use in various building, vehicle and transport plane windows, showcase window, glass substrate for display, etc. The glass can be tempered and bent by heating.
There is an increasing demand for glass that is clear and capable of absorbing ultraviolet rays, which may cause various articles, particularly those made of organic materials, to deteriorate or discolor and may cause adverse effects on human body. Fe
2
O
3
is known as an ultraviolet ray absorbing component that is relatively cheap in price, and is light-absorptive within a wide range of the visible light region, thereby making a glass have a color.
Japanese Patent First Provisional Publication JP-A-6-92678 discloses an ultraviolet and infrared radiation absorbing glass comprising 0.1-0.8 wt % of Fe in terms of Fe
2
O
3
, 0.3-2 wt % of cerium oxide in terms of CeO
2
, 0-1 wt % of TiO
2
, 0-0.006 wt % of CoO, 0-0.0015 wt % of Se, and 0-0.01 wt % of NiO.
JP-A-10-226534 having a Japanese Patent Application No. 9-31830 discloses an ultraviolet ray absorbing soda-lime glass comprising 0.08-0.15 wt % of total iron in terms of Fe
2
O
3
, 1.3-1.7 wt % of CeO
2
, 0.5-0.8 wt % of TiO
2
and 0.0005-0.0015 wt % of CoO, with a proviso that the weight ratio of ferrous iron to ferric iron, Fe
2+
/Fe
3+
, is not higher than 0.05. This glass is made to have at a thickness of 5 mm a visible light transmittance of not lower than 75% and an ultraviolet ray transmittance of not higher than 13%.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an ultraviolet ray absorbing soda-lime glass that is superior in ultraviolet ray absorption capability and high in visible light transmittance.
According to the present invention, there is provided an ultraviolet ray absorbing soda-lime glass. This glass comprises less than 0.10 wt % of iron, in terms of Fe
2
O
3
, which is optionally contained as an impurity in the glass, and 0.7-2.6 wt % of CeO
2
, 0-1.3 wt % of TiO
2
, 0-0.12 wt % of V
2
0
5
, 0.08-0.30 wt % of sulfur in terms of SO
3
, and 0-0.0025 wt % of CoO. The glass at a thickness of 5 mm is not higher than 10% in ultraviolet radiation transmittance, is not lower than 80% in visible light transmittance, and is from 530 to 575 nm in dominant wavelength.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
An ultraviolet ray absorbing soda-lime glass according to the present invention will be described in detail in the following.
Similar to conventional soda-lime float glasses, the glass may contain as a soda-lime glass fundamental components of SiO
2
in an amount of 67-75 wt %, Al
2
O
3
of 0-3 wt %, CaO of 6-12 wt %, MgO of 2-6 wt %, Na
2
O of 10-15 wt %, and K
2
O of 0-3 wt %. Within these ranges of the fundamental components, the glass becomes superior in meltability, weatherability and durability and can easily and efficiently be produced using raw materials cheap in price.
As stated above, the glass comprises less than 0.10 wt % of iron, in terms of Fe
2
O
3
, which is optionally contained as an impurity in the glass. In other words, iron is not intentionally added to a batch of raw materials of the glass. Purified natural raw materials of the glass, however, such as silica sand, limestone and dolomite, may contain iron as an impurity, and therefore the glass may contain iron as an impurity in an amount that is at least 0.05 wt % and less than 0.10 wt %, in terms of Fe
2
O
3
. In fact, when the glass batch is melted, the proportions of Fe
2+
and Fe
3+
change reversibly depending on the oxidation-reduction condition of the glass melt to reach the equilibrium condition. Fe
3+
is absorptive in the ultraviolet region and also in a shorter wavelength side of the visible light region, thereby making the glass have a color. In contrast, Fe
2+
is absorptive in the near infrared region and also in longer wavelength side of the visible light region, thereby making the glass to have a color. Thus, the iron content of the glass must be less than 0.10 wt % in order to make the glass clear or substantially colorless.
The glass comprises 0.7-2.6 wt % of CeO
2
. This CeO
2
serves as a major ultraviolet-ray-absorbing agent and is capable of absorbing ultraviolet rays in a so-called boundary region between the visible and ultraviolet regions. If it is less than 0.7 wt %, the glass becomes insufficient in ultraviolet absorption capability. If it exceeds 2.6 wt %, the glass becomes absorptive not only in the ultraviolet region but also in the visible light region exceeding its lower end (380 nm) in wavelength, thereby making the glass have a yellowish color.
The glass comprises 0-1.3 wt % of TiO
2
. This TiO
2
is a material relatively cheap in price and has an ultraviolet absorbing capability similar to that of CeO
2
. Thus, TiO
2
is optionally used as a supplement to CeO
2
. If the TiO
2
content of the glass exceeds 1.3 wt %, the glass becomes also absorptive in the visible light region exceeding its lower end (380 nm) in wavelength, thereby making the glass have a yellowish color.
The glass comprises 0-0.12 wt % of V
2
O
5
. This V
2
O
5
also has a great capability of absorbing ultraviolet rays and is optionally used as a supplement to CeO
2
. V
2
O
5
is absorptive at about 440 nm and about 630 nm in the visible region. Thus, if the V
2
O
5
content of the glass exceeds 0.12 wt %, the glass is made to have a green color.
The glass comprises 0.08-0.30 wt % of sulfur in terms of SO
3
. Sulfur may be added to the glass batch in the form of sulfate (e.g., Na
2
SO
4
), and serves as a refining agent and also as an oxidizing agent. Thus, sulfur is capable of stabilizing the ultraviolet absorption by CeO
2
and TiO
2
. Furthermore, sulfur is capable of making the amount of Fe
3+
much larger than that of Fe
2+
in the glass batch. Therefore, it becomes possible to minimize the adverse effects of Fe
2+
on the glass. If the sulfur content of the glass is less than 0.08 wt %, the above-mentioned advantageous effects of sulfur become insufficient. If it is greater than 0.30 wt %, the glass melt tends to have bubbles therein. That is, the refining does not proceed properly, and thus it becomes difficult to produce a high-quality glass.
The glass comprises 0-0.0025 wt % of CoO. CoO has a plurality of absorption peaks in a range of 525-650 nm in the visible region. In fact, its absorption end on the shorter wavelength side is 450 nm and that on the longer wavelength side is 700 nm. The width therebetween is very broad, and CoO itself makes the glass have a bluish color. On the other hand, depending on the respective contents of Fe
2
O
3
(FeO), CeO
2
, TiO
2
and V
2
O
5
, the spectral transmittance (transmittance-wavelength) curve of the glass is not necessarily flat. With this, the glass may have a pale color. In this case, CoO serves to eliminate this pale color to make the glass substantially colorless. Therefore, CoO is optionally added to the glass batch. If its content exceeds 0.0025 wt %, the bluish color of the glass becomes too strong.
It is preferable to add carbon to the glass batch in order to accelerate the decomposition of the above-mentioned sulfate. This carbon, however, serves as a reducing agent, and thus its amount should be minimized. In fact, its amount may be changed depending on the amount of the sulfate and is preferably not greater than about 0.2 parts by weight relative to 100 parts by weight of the glass batch.
The glass at a thickness of 5 mm is not higher than 10%, preferably not higher than 8%, in ultraviolet radiation transmittance. With this, it becomes possible to minimize adverse effects of ultraviolet rays on human body and substantially suppress the deterioration or discoloration of various articles made of organic materials (e.g., polymers). The ultraviolet radiation transmittance is the average transmittance in a range of 300-380 nm in wavelength, and its measurement is d

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