Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
2001-04-27
2004-04-27
Sample, David (Department: 1755)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C501S069000, C501S070000
Reexamination Certificate
active
06727198
ABSTRACT:
TECHNICAL FIELD
This invention relates to an infra-red absorption glass for a reed switch, which glass is suitable for encasement of a reed switch using magnetic wire members made of Fe—Ni based alloy (52 alloy).
BACKGROUND ART
A reed switch comprises confronting contact points including magnetic wire members and a glass tube enclosing those points and performs open/close operations of the contact points by applying a magnetic field from the outside of the glass tube. The encasement of the magnetic wire members into the glass tube is carried out by heating, softening, and sealing both ends of the glass tube in an inert gas, in a reducing gas, or in a vacuum in the state where the magnetic wire members are inserted in the glass tube. In the heating operation, use is made of a heat source available under the above-mentioned atmosphere, for example, an infra-red radiation type heat source using a halogen lamp with a reflecting plate for light convergence.
Under the above-mentioned circumstances, an infra-red absorption glass specially developed is used as a glass for a reed switch. Presently, use is widely made of the infra-red absorption glass having a characteristic such that an infra-red transmittance at a wavelength of 1050 nm is on the order of 15% to 20% when the glass has a thickness of 0.5 mm.
In the meanwhile, the reduction in size of electronic components is strongly desired as an essential condition in order to achieve the reduction in size and weight of electronic apparatuses which is remarkably accelerated in recent years. For the reed switch, reduction in size similarly proceeds. Accordingly, the reduction in diameter, length, and thickness of the glass tube which determines the size of the reed switch is carried out.
However, as the reduction in diameter, length, and thickness of the glass tube for a reed switch proceeds further, the following problems are caused in a conventional infra-red absorption glass to decrease the process yield and to place a limit in further reduction in size.
A first problem is as follows. Specifically, an infra-red ray from the halogen lamp forms a spot having the spread on order of 10 mm in diameter even if converged. When the center of the infra-red spot is brought into coincidence with the center of a sealing portion of the reed switch using the glass tube having a short length and a small thickness, a peripheral portion of the spot hits and heats the contact points of the switch which should not be heated in its nature. Therefore, it is necessary to intentionally deviate the center of the spot from the center of the sealing portion and to heat the sealing portion by the peripheral portion of the spot. However, the peripheral portion of the spot is low in infra-red energy and is unstable. Accordingly, the sealing requires a long time so that the productivity is decreased. In addition, nonuniformity in sealed pattern is increased so that the yield is deteriorated.
Next, a second problem is as follows. Upon sealing, the glass is in a softened state at about 1000° C. and a glass component is evaporated although in a very small amount. Such evaporated component is again solidified on a surface of metal material and/or of the glass of the reed switch which are present in the vicinity and still relatively low in temperature. In case of the reed switch having a short length, the evaporated glass component is again solidified around the contact points of the switch to thereby cause contact fault (electrical connection defect) of the switch.
In view of the above-mentioned problems, this invention has been made. It is an object of this invention to provide an infra-red absorption glass suitable for efficiently producing a small-sized reed switch.
DISCLOSURE OF THE INVENTION
The present inventors have found out that the problems accompanying the reduction in size of a reed switch can be solved by limiting an infra-red transmittance of a glass to an appropriate lower range and by strictly restricting Cl content included as a small amount of impurity in the glass and propose this invention.
Specifically, an infra-red absorption glass for a reed switch of this invention is characterized in that an infra-red transmittance at a wavelength of 1050 nm is not greater than 10% when the glass has a thickness of 0.5 mm and the content of Cl in the glass is not greater than 150 ppm.
BEST MODE FOR EMBODYING THE INVENTION
Description will be made in detail about this invention.
An infra-red absorption glass for a reed switch of this invention has an infra-red transmittance at a wavelength of 1050 nm which is not greater than 10% when the glass has a thickness of 0.5 mm.
The low infra-red transmittance is a characteristic essential to absorb heat radiation. It is assumed that the infra-red transmittance at a wavelength of 1050 nm exceeds 10% when the glass has a thickness of 0.5 mm. In this event, upon manufacturing a small-sized reed switch using the glass having a small diameter, a short length, and a small thickness, infra-red absorption from a halogen lamp is not sufficient so that an additional time and an extra energy are required for sealing. In addition, since the amount of infra-red rays transmitted through the glass to reach the inside of the reed switch is increased, contact point portions of the switch are heated so that magnetic characteristics would be deteriorated.
Furthermore, in the infra-red absorption glass for a reed switch of this invention, the content of Cl is extremely small.
Cl is contained as one of impurities in raw materials for the glass. If the glass prepared by the use of the above-mentioned raw materials is heated, salt such as NaCl and KCl is liable to evaporate. The evaporated salt is again solidified inside the reed switch to cause a contact fault (electrical connection defect). Therefore, in this invention, the content of Cl in the glass is limited to 150 ppm or less, preferably 100 ppm or less.
The content of Cl being greater than the above-mentioned range will remarkably increase the evaporation of the salt from the glass softened by the heat for sealing. In case of the small-sized reed switch, the salt is solidified in the vicinity of the contact points to cause the contact fault.
It is noted here that F exists as a component similar to Cl. F is sometimes contained as another impurity in the glass raw material and is sometimes positively introduced into the glass because it serves to reduce the viscosity of the glass or has a very strong action as a melting agent. However, if a large amount of F is contained in the glass, the salt such as NaF and KF is evaporated to possibly cause a problem similar to that mentioned in conjunction with Cl. Therefore, the content thereof is preferably limited. In this case, the content of F is desirably not greater than 5000 ppm, in particular, not greater than 1500 ppm.
In addition, it is important that a coefficient of thermal expansion of the glass in a temperature range between 30° C. and 3800° C. is limited to an extent of 85-100×10
−7
/° C. If the coefficient of thermal expansion is out of the above-mentioned extent, matching with the 52 alloy as magnetic wire members of the reed switch are impossible. This results in a leak (leakage of airtightness) at a sealing portion and, in the worst case, a damage of the glass.
As the glass having the above-mentioned characteristics, use is advantageously made of the infra-red absorption glass having a composition consisting essentially of, by weight percent, 60-75% of SiO
2
, 1-10% of Al
2
O
3
, 0-10% of B
2
O
3
, 3.5-10% of RO (R being one or more selected from Ca, Mg, Ba, Sr, and Zn), 0.5-5% of Li
2
O, 8-17% of Na
2
O+K
2
O, 2-10% of Fe
3
O
4
.
In this invention, the reason why the composition of the glass is restricted as described above is as follows.
At first, SiO
2
is a main component required to form a frame structure of the glass. If the content is more than 75%, the coefficient of thermal expansion is excessively low and the meltability is deteriorated. If the content is less than 60%, the chemical durability is de
Hashimoto Koichi
Kosokabe Hiroyuki
Collard & Roe P.C.
Nippon Electric Glass Co. Ltd.
Sample David
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