Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
2000-05-23
2002-12-10
Elve, M. Alexander (Department: 1725)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C501S026000, C501S021000, C501S079000, C313S118000, C427S126200
Reexamination Certificate
active
06492289
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lead-free glaze, a spark plug on which it is used, and a method of producing the spark plug.
2. Description of the Related Art
A spark plug insulator is an example of an insulator coated with a glaze. The glaze is coated onto the insulator after which the insulator is fired simultaneous to sealing parts in the hole in the insulator.
It is necessary that the conditions under which parts are sealed into the hole of this insulator are such that the temperature is no higher than 900° C. to prevent oxidation of the stem.
There has been a demand for lead-free glaze in recent years to accommodate environmental concerns. However, it is difficult to fire lead-free glaze onto an insulator at a temperature of 900° C. or lower. Thus, it is no longer possible to perform firing simultaneous to sealing parts in the hole of the insulator.
In consideration of this problem of the prior art, the object of the present invention is to provide a lead-free glaze that allows firing at low temperatures, a spark plug in which it is used, and a method of producing the glaze.
SUMMARY OF THE INVENTION
A first aspect of the present invention is a lead-free glaze for coating ceramic materials containing 16-49 wt % of SiO
2
, 15-35 wt % of B
2
O
3
, 0-10 wt % of Al
2
O
3
and 0-10 wt % of ZnO.
As a result of having the above constitution, the lead-free glaze of the present invention can be fired onto an insulator even at a temperature of 900° C. or lower. In addition, since this lead-free glaze does not contain lead, it is suitable for environmental protection.
In addition, since the lead-free glaze of the present invention can be fired at a low temperature of 900° C. or lower, if the ceramic material is a spark plug insulator, oxidation of the stem inserted into the hole of the insulator can be prevented. Consequently, firing of the coated glaze and sealing of parts in the hole of the insulator can be carried out simultaneously.
The following provides an explanation of the composition of the lead-free glaze of the present invention.
SiO
2
and B
2
O
3
are the main components of borosilicate glass. Regarding SiO
2
and B
2
O
3
, the melting point of a glaze tends to increase as the amount of SiO
2
increases, and the ratio of SiO
2
/(SiO
2
+B
2
O
3
) is preferably 50-70 wt %. If the ratio is less than 50 wt %, the water resistance of the glaze decreases resulting in the risk of the glass component eluting in water and deteriorating. If the ratio exceeds 70 wt %, the melting point rises resulting in a risk of the smoothness of the glazed surface decreasing.
The content of SiO
2
is 16-49 wt %. If the SiO
2
content is less than 16 wt %, there is the risk of the water resistance of the glaze decreasing. If the SiO
2
content exceeds 49 wt %, the melting point of the glaze rises resulting in a risk of the smoothness of the glazed surface decreasing.
The content of B
2
O
3
is 15-35 wt %. If the B
2
O
3
content is less than 15 wt %, the melting point of the glaze rises resulting in a risk of the smoothness of the glazed surface decreasing. If the B
2
O
3
content exceeds 35 wt %, there is the risk of the water resistance of the glaze decreasing.
Al
2
O
3
demonstrates the effect of improving the water resistance of the glaze when added in a minute amount, and prevents the glass component from eluting and deteriorating in water. The content of Al
2
O
3
is 0-10 wt %. If the Al
2
O
3
exceeds 10 wt %, the viscosity during firing increases resulting in the risk of the smoothness of the glazed surface decreasing. The content of Al
2
O
3
is preferably 2-10 wt %. If less than 2 wt %, there is the risk of a reduction in the effect of improving the water resistance of the glass.
ZnO stabilizes the glass without increasing the viscosity during firing. In addition, ZnO also has the effect of suppressing increases in the coefficient of linear expansion of the glaze. The content of ZnO is 0-10 wt %. If the ZnO content exceeds 10 wt %, the transparency of the glazed surface becomes poor.
The above lead-free glaze also preferably contains one type or two or more types of components selected from the group consisting of CaO, BaO and MgO. This is because BaO, CaO and MgO stabilize the glass without increasing the viscosity during firing.
The above lead-free glaze also preferably contains one type or two or more types of components selected from the group consisting of Bi
2
O
3
, ZrO
2
, TiO
2
, CeO and FeO.
Although Bi
2
O
3
lowers the melting point of the glaze, if added in large amounts, it results in the risk of the glazed surface losing it smoothness.
ZrO
2
has the effect of stabilizing the glass and lowering the coefficient of linear expansion, while also increasing the ceramic strength. On the other hand, the addition of ZrO
2
in large amounts causes clouding.
Although TiO
2
, CeO and FeO have the effect of preventing discoloration of the ceramic material by increasing weather resistance, addition of these components in large amounts conversely colors the glaze.
Thus, these components are preferably blended so that the necessary coefficient of linear expansion is obtained. As a result, the glass components in the glaze can be stabilized, discoloration of the ceramic material can be prevented, and the melting point of the glaze can be lowered.
Moreover, the above lead-free glaze also preferably contains one type or two or more types of components selected from the group consisting of Li
2
O, Na
2
O and K
2
O. Li
2
O, Na
2
O and K
2
O are alkaline metal oxides that lower the melting point of the glaze. The addition of these components improves the smoothness of the glazed surface.
The above lead-free glaze further preferably contains 2-30 wt % of BaO. BaO has a potent effect of suppressing increases in viscosity during firing, and results in a smooth glazed surface when added in an amount of 2 wt % or more. If the BaO content is less than 2 wt %, there is the risk of the viscosity of the glaze increasing. In addition, if the BaO content exceeds 30 wt %, there is the risk of an increase in the coefficient of linear expansion.
Moreover, the above lead-free glaze preferably contains 1-10 wt % of ZrO
2
. ZrO
2
stabilizes the glass in the glaze and has the effect of lowering the coefficient of linear expansion. Consequently, the strength of the ceramic material can be increased by coating a ceramic material with glaze containing ZrO
2
. On the other hand, if the ZrO
2
content is less than 1 wt %, there is the risk of an increase in the coefficient of linear expansion of the glaze, while if the ZrO
2
content exceeds 10 wt %, there is the risk of the glaze becoming clouded.
The above lead-free glaze also preferably contains 1-25 wt % of Bi
2
O
3
. Bi
2
O
3
has the effect of lowering the melting point of the glaze. If the Bi
2
O
3
content is less than 1 wt %, there is the risk of reducing the effect of lowering the melting point of the glaze. If the Bi
2
O
3
content exceeds 25 wt %, there is the risk of the glazed surface losing its smoothness.
The above lead-free glaze preferably contains the following components:
SiO
2
: 35-49 wt %
B
2
O
3
: 20-35 wt %
Al
2
O
3
: 2-10 wt %
ZnO: 0-10 wt %
BaO: 2-25 wt %
ZrO
2
: 1-10 wt %
Bi
2
O
3
: 1-15 wt % and,
at least one type of LiO
2
, Na
2
O or K
2
O: 0-10 wt %.
If the content of SiO
2
is less than 35 wt %, the water resistance of the glaze decreases resulting in the risk of the glass component eluting in water and deteriorating. If the SiO
2
content exceeds 49 wt %, the melting point of the glaze rises resulting in the risk of decreased smoothness of the glazed surface.
If the content of B
2
O
3
is less than 20 wt %, the melting point of the glaze rises resulting in the risk of decreased smoothness of the glazed surface. If the B
2
O
3
content exceeds 35 wt %, there is the risk of the water resistance of the glaze decreasing.
If the content of Al
2
O
3
is less than 2 wt %, there is the risk of decreasing the effect of improving the water resistance of the glaze by addition of Al
Morita Yoshiki
Nakamura Toshiya
Suzuki Hirofumi
Cooke Colleen P.
Denso Corporation
Elve M. Alexander
Nixon & Vanderhye P.C.
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