Lead-free alkali metal-free glass compositions

Details Lead-free alkali metal-free glass compositions Lead-free alkali metal-free glass compositions

1998-12-04

2001-07-03

Sample, David R (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S016000, C501S017000, C501S020000, C501S025000, C501S026000, C501S032000, C501S078000, C501S079000, C428S427000, C428S428000, C428S432000

Reexamination Certificate

active

06255239

ABSTRACT:

This invention relates to lead-free alkali metal-free glass compositions, to glass enamel compositions and enamel paste compositions containing them as well as to glass and ceramic substrates coated with such enamel paste compositions.
BACKGROUND OF THE INVENTION
Low temperature melting lead-free glass compositions are known in the art. Such glasses are environmentally friendly and frits obtained from these glasses are useful in the preparation of glass enamel paste compositions which can be coated on glass or ceramic substrates and fused to provide decorative glazes and functional coatings on the substrates. Examples of such glass enamel paste compositions are those which are used as coatings for automotive and architectural glasses. The composition of these lead-free glass compositions is critical to the performance of the low melting glass frits prepared therefrom.
Reference can be made to the glass compositions disclosed in my copending U.S. patent application Ser. Nos. 09/066,533 and 09/066,534, both filed on Apr. 27, 1998 and Ser. No. 08/908,953, filed Aug. 8, 1997. Particular attention may also be directed to the following:
U.S. Pat. No. 4,554,258,
U.S. Pat. No. 4,892,847,
U.S. Pat. No. 5,252,521 and U.S. Pat. No. 5,326,591,
U.S. Pat. No. 4,970,178,
U.S. Pat. No. 5,308,803,
U.S. Pat. No. 5,629,247,
U.S. Pat. No. 5,093,285, No. 5,203,902 and
European Patent Application No. 0 370 683
U.K. Patent Publication No. 2 301 100 A, and
U.S. Pat. No. 5,559,059 and No. 5,616,417.
Further illustrative of patent publications disclosing lead-free glass compositions are the following:
U.S. Pat. No. 4,446,241,
U.S. Pat. No. 4,537,862,
U.S. Pat. No. 4,224,074,
U.S. Pat. No. 4,312,951,
U.S. Pat. No. 4,376,169,
U.S. Pat. No. 5,504,045,
U.S. Pat. No. 5,578,533, and
International Application No. PCT/EP94/00403.
Finally, there may be mentioned the following patent publications:
U.S. Pat. No, 5,643,636,
U.S. Pat. No. 5,244,848,
U.S. Pat. No. 5,733,828, and
Japanese patent publication No. 9-268026.
All of the glass compositions disclosed by these patent publications and copending applications differ in certain critical respects from the novel compositions disclosed herein.
DISCLOSURE OF THE INVENTION
The present invention provides certain new and useful glass compositions which are lead-free and alkali metal-free and which provide beneficial characteristics which make them particularly useful in the formulation of glass enamel compositions and enamel paste compositions for application to glass and ceramic substrates such as automotive and architectural glasses. They also, however, will find use in developing glass markets such as the Plasma Display Panel (PDP) or other Flat Panel Display industries because of their electrical characteristics. There may be other electronic glass industries such as sealing and semi-conductor where these novel glasses will find use.
Thus, a principle field for the use of these glasses is expected to be in the PDP industry for use as the undercoating layers or barrier layers and for use in forming the rib structures of the display panels. See, for example, U.S. Pat. No. 5,674,634 which is incorporated herein by reference. The advantage of these glass chemistries are their low melting temperatures and thermal expansion/contraction coefficients specifically for sealing to glass substrates. Also particularly desirable should be the electrical properties of these glasses. The absence of alkali metal ions in the composition should provide for very low conductivities and very high breakdown voltages. Additionally, bismuth is known to have a very high electrical resistance and to have the highest Hall effect of any metal (see CRC Handbook of Chemistry and Physics, 57th Edition). All of these characteristics should result in extremely desirable electrical properties.
The glass compositions of the invention are believed to have excellent/superior electrical characteristics, chemical durability, broad temperature firing ranges, low stress and low expansion. For example, certain of the glasses have expansion properties in the range of 64-90×10
7
/° C.
The glass compositions of the invention are lead-free bismuth-borosilicate glass systems formulated without the use of alkali metal ions and possess the following compositional ranges:
Broad
Preferred
More
Additional
Oxide
Range
Range
Preferred
High Bi
Component
(wt %)
(wt %)
Range (wt %)
Range (wt %)
Bi
2
O
3
50-90
67-84
68-84
78-88
SiO
2
 5-20
 6-17
 7-14
6.5-11 
B
2
O
3
2-9
3-9
3.5-8.7
  4-8.5
Al
2
O
3
0.1-10 
1-9
1-8
0.1-7  
TiO
2
0-8
0-3
0-2
0-2
ZnO
0-9
0-8
0-6
0-6
ZrO
2
 0-10
0.1-7  
0.5-3  
0-3
F
−1
0-4
0-3
0-2
0-2
Sro
up to 10
CaO
up to 7 
MgO
up to 7 
CeO
up to 10
MnO
up to 10
SnO
up to 10
P
2
O
5
up to 7 
Sb
2
O
3
up to 10
Fe
2
O
3
up to 10
Nb
2
O
5
up to 10
It is worthy to note that the compositions contain 0.1 to 10 weight % Al
2
O
3
. It is believed that this is an advantage to the compositions in terms of reducing refractory corrosion during the melting process.
Also of specific note are compositions which contain fluorine in an amount of 0.2 to 4.0 weight % as these compositions are believed to have particularly desirable properties.
It is noted that certain prior art glass compositions contain rather large required content of BaO and SrO (see Japanese Patent Publication No. 9-268026). This results in glasses with very high expansions which would not be suitable for soda-lime glass substrates or similar expansion materials when the B
2
O
3
content is within the range of the compositions of this invention. It is preferable that in the compositions of the present invention the SrO content not exceed 5 weight %.
The glass compositions of the invention possess excellent to outstanding thermal expansion properties for sealing to a glass substrate, an excellent to outstanding low temperature fusing or sealing range of about 535 to 600° C. so that no distortion of the glass substrate occurs, good chemical durability and, even more importantly, these alkali metal-free compositions are believed to have excellent to outstanding electrical properties.
The glass compositions are formed in a known manner as, for example, blending the known starting materials and melting at a temperature of about 1000° to 1300° C. for about forty (40) minutes to form a molten glass having the desired composition. The molten glass formed can then be suddenly cooled, e.g., water quenched, in a known manner to form a frit. The frit can then be ground using conventional milling techniques to a fine particle size, preferably between 2 to 6 microns. This component comprises the disclosed glass frit compositions.
The glass frit component can be a single composition of the invention or, alternatively, can be a mixture of these frits. Also, at least one frit of the present invention may be combined with an additional low melting frit having a composition outside the scope of those of the invention to the extent that this other frit does not deteriorate the qualities of the enamel which results.
The invention also provides glass (ceramic) enamel compositions employing the above-described glass frit compositions. These compositions comprise from about 30 to 95 wt. % solids of a glass frit component.
The finely ground glass frit can be combined with a mixed metal oxide pigment, any other type of metal powder, metal resonate, or other material of choice. Typical mixed metal oxide pigments used to produce black colors in the automotive industry would include oxides of copper, chrome, iron, cobalt, nickel, manganese, and the like. Although these black spinel pigments are preferred for use in the automotive industry, other metal oxide pigments to produce other various colors, may be combined with the glass frit compositions in this invention. Other end uses could include, and are not limited to, the architectural, appliance, and beverage industries. The pigment component would generally comprise from 5 to 40% by weight of the glass frit, depending upo

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