Colored glass

Details Colored glass Colored glass

2000-05-18

2001-12-25

Group, Karl (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S064000, C501S071000, C501S904000, C501S905000

Reexamination Certificate

active

06333287

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a colored glass containing at least 0.5% total iron oxide (T-Fe
2
O
3
) in terms of Fe
2
O
3
. More particularly,the invention relates to a colored glass which is air-quench tempered and used as a window glass for buildings or automobiles or in other applications and in which the generation of nickel sulfide (NiS) has been eliminated or diminished without impairing glass appearance or productivity.
DESCRIPTION OF THE RELATED ART
Nickel sulfide stones rarely generate in glasses. These nickel sulfide stones, which range from small ones having a particle diameter of about tens of micrometers to visually observable ones having a particle diameter of about hundreds of micrometers, are known to considerably impair the reliability (quality) of glass products.
Namely, the presence of nickel sulfide stones often poses serious problems in air-quench tempered glasses obtained by heating a glass to a temperature around the softening point thereof and then rapidly cooling the glass surfaces generally with air to form a tough compressive stress layer on each glass surface and a tensile stress layer inside and thereby improve the strength of the glass.
Nickel sulfide in a glass is known to undergo phase transition at temperatures lower than the softening point of the glass. When the glass is heated to a temperature around the softening point thereof during air-quench tempering, the nickel sulfide stones modify into a high temperature-stable phase (&agr; phase). These nickel sulfide stones are present as the a phase in the glass even after the glass has been cooled to room temperature, and then undergo gradual phase transition to a room temperature-stable phase (&bgr; phase) with the lapse of time. Since the &agr;-to-&bgr; phase transition of nickel sulfide stones is accompanied by a considerable volume change, high local stresses generate around the nickel sulfide stones and occasionally develop cracks. If these cracks reach the tensile stress layer present inside the air-quench tempered glass, the glass breaks in a moment.
In general, a long time is required for a tempered glass containing nickel sulfide stones to break due to the phase transition of the nickel sulfide stones. It is therefore extremely important that, from the standpoint of not impairing the reliability of products and hence of glass manufacturers, glasses containing nickel sulfide stones should not be provided as building or automotive window glasses or the like for which air tempering is conducted.
For preventing the generation of nickel sulfide stones, it is primarily necessary to prevent a nickel source from coming into the glass melting furnace. However, it is highly difficult to avoid the inclusion of a minute amount of nickel impurities. This is partly because welding rod pieces used in a construction work or stainless steel parts employed in the mechanical equipment can be causative of the inclusion of nickel impurities. There also are cases where nickel oxide is purposely added as a coloring material for glasses. In any event, it is generally difficult to completely avoid the inclusion of a nickel impurity.
Several techniques for preventing a glass containing a nickel impurity from generating nickel sulfide stones have hence been devised.
For example, U.S. Pat. No. 4,919,698 discloses a method in which the generation of nickel sulfide stones in a glass is diminished by using a furnace in which a zone close to the bottom and at least the part between the inlet and the spring zone are kept in an electrically oxidized state.
JP-A-7-144922 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) discloses a method for diminishing the formation of nickel sulfide stones which comprises adding to crude batch materials at least 0.010% by weight one or more substances selected from the group consisting essentially of molybdenum, arsenic, antimony, bismuth, copper, silver, potassium dichromate, iron chromite and combinations of two or more of these.
Furthermore, JP-A-9-169537 discloses a process for producing a soda-lime glass which comprises adding a slight amount of a zinc compound to batch materials to thereby produce a melt-formed glass in which nickel sulfide is inhibited from generating from a nickel compound which was contained in the batch materials and/or from a nickel compound which came into the batch materials during the melting thereof.
The method for diminishing the generation of nickel sulfide stones disclosed in U.S. Pat. No. 4,919,698 has a drawback that the furnace is considerably limited in structure and operating conditions. In particular, this method cannot be used for the production of heat-absorbing glasses, which especially necessitates a measure against nickel sulfide, because the inside of the furnace for producing a heat-absorbing glass should be kept in a reduced state so as to sufficiently incorporate bivalent iron ions, showing heat-absorbing ability, into the glass.
The method for diminishing the formation of nickel sulfide stones disclosed in JP-A-7-144922 has a drawback, as stated in the specification, that the addition of molybdenum, copper, iron dichromate or iron chromite changes the color tone of the glass. This coloring cannot be overlooked especially in applications where an attractive appearance is important, as in automotive window glasses. In addition, arsenic and antimony cannot be used in float glass production because these elements volatilize in the float bath to foul the atmosphere in the bath, while use of bismuth or silver is unsuitable for float glass production, for which mass production is a premise, because bismuth and silver sources are highly expensive.
Furthermore, the method for diminishing the formation of nickel sulfide stones disclosed in JP-A-9-169537, which is characterized by adding a slight amount of a zinc compound to batch materials to thereby inhibit nickel sulfide generation, has a drawback that since the zinc added to the batch materials volatilizes considerably in the float bath, it not only fouls the atmosphere in the float bath but also drops off as zinc oxide from the ceiling of the float bath to impair glass quality and reduce the yield.
SUMMARY OF THE INVENTION
The present invention has been achieved in view of the problems of the conventional techniques described above.
An object of the present invention is to provide a colored glass, particularly a colored glass to be air tempered and used as a window glass for buildings or automobiles or in other applications, in which the generation of nickel sulfide (NiS) stones has been eliminated or diminished, without impairing glass appearance or productivity, by regulating the glass so as to contain 0.5 to 4% total iron oxide in terms of Fe
2
O3 and 0.0002 to less than 0.01% molybdenum in terms of Mo.
The present invention provides a colored glass containing, in % by weight, 0.5-4% total iron oxide (T-Fe
2
O
3
) in terms of Fe
2
O
3
and 0.0002 to less than 0.01% molybdenum in terms of Mo.
The colored glass preferably has a basic glass composition which comprises, in % by weight,
65-80% SiO
2
,
0-5% Al
2
O
3
,
0-10% MgO,
5-15% CaO,
5-15% MgO+CaO,
10-18% Na
2
O,
0-5% K
2
O,
10-20% Na
2
O+K
2
O, and
0-5% B
2
O
3
.
The colored glass preferably contains, in % by weight, 0.5-2.2% total iron oxide (T-Fe
2
O
3
) in terms of Fe
2
O
3
, 0.0002 to less than 0.01% molybdenum in terms of Mo, and at least one coloring component selected from the group consisting of TiO
2
, CeO
2
, NiO, CoO, Se, MnO, Cr
2
O
3
, V
2
O
5
, Nd
2
O
3
and Er
2
O
3
.
A preferred embodiment of the colored glass comprises, in % by weight,
a basic glass composition comprising
65-80% SiO
2
,
0-5% Al
2
O
3
,
0-10% MgO,
5-15% CaO,
5-15% MgO+CaO,
10-18% Na
2
O,
0-5% K
2
O,
10-20% Na
2
O+K
2
O, and
0-5% B
2
O
3
;
a coloring component comprising
0.5-2.2% total iron oxide (T-Fe
2
O
3
) in terms of Fe
2
O
3
,
0.01-1.0% TiO
2
, and
0.1-2.0% CeO
2
; and
0.0002 to less than 0.01% molybdenum in terms of Mo for inhibiting the generation of nickel s

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