Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
2001-05-22
2003-09-09
Sample, David (Department: 1755)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C501S017000, C501S073000
Reexamination Certificate
active
06617269
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a sealing material having a low sealing temperature and, in particular, to lead free glass used in the sealing material.
BACKGROUND OF THE INVENTION
The sealing material has been used for sealing glass, ceramics and/or metals to each other. The sealing material is usually consists essentially of glass and fillers. For sealing electronic parts, the sealing material is desired to have a low sealing temperature.
Lead borate glass, typically, lead-zinc borate glass has conventionally been used as the low temperature glass in the sealing material which preferably has a sealing temperature of 430-500° C. and a thermal expansion coefficient (TEC) of 70-100×10
−7
/° C.
However, it is desired to avoid use of lead compounds for the health and safety.
SUMMARY OF THE INVENTION
It is an object of this invention provide to lead-free tin silicate-phosphate glass of an improved mechanical strength and a weather resistance by using common oxide SiO
2
as a glass forming element other than P
2
O
5
.
It is another object of this invention to provide a sealing material comprising fillers and lead-free tin silicate-phosphate glass containing silica as a glass forming element.
According to this invention, a lead-free tin silicate-phosphate glass as a sealing material is obtained which consists essentially of, by molecular percent, 30-80%, preferably, 40-60% SnO, 5.5-20%, preferably, 5.5-10% SiO
2
, 10-50%, preferably, 24.1-40% P
2
O
5
.
The lead free tin silicate-phosphate glass can contains at least one of glass stabilizing elements including 0-35% ZnO, 0-20% B
2
O
3
, 0-10% Al
2
O
3
, 0-20% WO
3
, 0-20% MoO
3
, 0-15% Nb
2
O
5
, 0-15% TiO
2
, 0-15% ZrO
2
, 0-35% R
2
O (R is Li, Na, K, and/or Cs), 0-10% CuO, 0-10% MnO, 0-15% R′O (R′ is Mg, Ca, Sr and/or Ba), a total content of at least one of the glass stabilizing elements being up to 40%.
According to an embodiment of this invention, a sealing material comprises the lead free tin silicate-phosphate glass described above of 50-100% in volume and the balance of refractory fillers. As refractory fillers, cordierite, tin dioxide, diniobium pentaoxide can be used. Zirconium phosphate, willemite and mullite can also be used as the fillers.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The lead-free glass used together with fillers in a sealing material according to this invention is a tin silicate-phosphate (SiO
2
—P
2
O
5
—SnO) glass which consists essentially of, by molecular percent, 30-80% SnO, 5.5-20% SiO
2
and 10-50% P
2
O
5
.
SnO of 30-80% is contained to lower a melting point of the resultant glass. SnO content less than 30% excessively raises the viscosity of the resultant glass so that the sealing material using the glass has a disadvantageous high sealing temperature. If SnO content is more than 80%, the resultant material does not glass.
SiO
2
is used as a glass-forming element and contained by an amount of 5.5-20%, preferably 5.5-10%. In use of SiO
2
content less than 5.5%, the resultant glass has insufficient improvement of the mechanical strength and the weather resistance. SiO
2
content more than 20% excessively raises the viscosity of the resultant glass.
P
2
O
5
of 10-50%, preferably 24.1-40%, is contained together with SiO
2
as glass-forming elements. If P
2
O
5
is less than 10%, the resultant material does not form glass. If P
2
O
5
is more than 50%, drawback inherent to phosphate glass is remarkably present in the resultant glass.
SiO
2
—P
2
O
5
—SnO glass according to this invention may contain at least one of glass stabilizing elements. The glass stabilizing elements include ZnO, B
2
O
3
, Al
2
O
3
, WO
3
, MoO
3
, Nb
2
O
5
, TiO
2
, ZrO
2
, R
2
O (R is Li, Na, K, and/or Cs), CuO, MnO R′O (R′ is Mg, Ca, Sr and/or Ba). The total content of at least one of the glass stabilizing elements is up to 40%. If the stabilizing-element content is more than 40%, the resultant glass is rather unstable and is readily devitrified at a shaping process, which is disadvantageous.
ZnO has a function for lowering a melting point as well as stabilizing glass and may be contained by 0-35%, preferably, 3-25%. ZnO content more than 35% increases crystallization of the resultant glass and lowers flowability of the glass.
B
2
O
3
content is 0-20%, preferably, 0-10%, and more preferably 0-4.9%. B
2
O
3
content more than 20% disadvantageously increases viscosity of the glass.
When B
2
O
3
is contained in the glass, it is desired to determine (B
2
O
3
content)/(P
2
O
5
content)<0.20 in order to suppress raise of glass transition point.
Al
2
O
3
content is 0-10%, preferably, 0-5%. Al
2
O
3
content more than 10% disadvantageously increases viscosity of the glass.
Each of WO
3
and MoO
3
contents is 0-20%, preferably, 0-10%. When any one of them is contained more than 20%, the resultant glass increases in the viscosity disadvantageously.
Each of Nb
2
O
5
, TiO
2
, and ZrO
2
contents is 0-15%, preferably, 0-10%. More than 15% content disadvantageously increases crystallization of the glass.
R
2
O content is 0-35%, preferably, 0-15%. More than 35% content disadvantageously increases crystallization of the glass.
Each of CuO and MnO contents is 0-10%, preferably, 0-5%. More than 10% makes the glass unstable.
R′O content is 0-15%, preferably, 0-10%. More than 15% makes the glass unstable.
Further, it is possible to contain F so as to lower the melting point of the glass. The F content is selected to determine F/(F+O)≦0.3, preferably, F/(F+O)≦0.1, in molecular percent. When F/(F+O) is larger than 0.3, the glass is unstable.
The lead-free SiO
2
—P
2
O
5
—SnO glass according to this invention has a glass transition point of 250-350° C. and an excellent flowability at a temperature of 500° C. or less. The TEC of the glass is 90-150×10
−7
/° C.
The SiO
2
—P
2
O
5
—SnO glass according to this invention itself can be used as a sealing material, without fillers, for materials having a compatible TEC. In use for sealing other materials having TEC non-compatible to the glass, for example, alumina having TEC of 70×10
−7
/° C., window glass plate having TEC of 85×10
−7
/° C. and others, the glass of this invention is mixed with refractory fillers of low expansion coefficient and is used as a composite type sealing material. The refractory fillers can be mixed with the glass of this invention not only for adjusting the TEC but also for improving the mechanical strength of the seal as formed.
In a composite type sealing material, refractory fillers are mixed by 50 volume % or less with the glass of this invention of the balance. Mix of refractory fillers more than 50 volume % makes the flowability of the sealing material low to a level insufficient for sealing because the glass content is excessively low.
Though various refractory fillers can be used, cordierite, tin dioxide, and diniobium pentaoxide are preferable fillers because their mixture with the glass are stable in the alter glass. Zircon, zirconium phosphate, willemite, mullite, and the like can be used as fillers in the sealing material.
In production of the sealing material using the lead free SiO
2
—P
2
O
5
—SnO glass according to this invention, a glass batch is prepared and then melted to produce glass. The melting must be carried out with care so that SnO is not oxidized into SnO2 during the melting process. To this end, it is recommended that the melting is conducted in a non-oxidizing atmosphere such as N2 atmosphere.
Thereafter, the molten glass is shaped, ground and classified to obtain glass powder. Thereafter, refractory fillers are mixed with into the glass powder if it is desired. Thus, a powdery sealing material is obtained.
In use of the sealing material, the powdery sealing material is mixed with an organic solvent to form a paste. The paste is applied or coated onto bonding surfaces of target objects to be joined and sealed. Then, the target objects are brought into contact with each other at their bonding surfaces and are subjected to baking
Bolden Elizabeth
Collard & Roe P.C.
Nippon Electric Glass Co. Ltd.
Sample David
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