Compositions: coating or plastic – Coating or plastic compositions – Heavy metal compound containing
Reexamination Certificate
1999-12-03
2001-11-27
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Heavy metal compound containing
C106S197010, C106S198100, C106S286200, C501S032000, C445S058000, C524S413000
Reexamination Certificate
active
06322623
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a light-screening film paint and film for a highly luminous automobile discharge lamp and a method of production thereof.
BACKGROUND OF THE INVENTION
FIG. 1
is a structural drawing of a highly luminous D
2
R-type discharge lamp for an automobile front lamp. This discharge lamp is constructed so that a metal iodide sealed in a quartz emissive section
5
emits light as a high tension is applied between the metal tungsten electrodes
1
a
and
1
b
. The emissive section
5
is covered with an external quartz tube
2
. In comparison with a halogen lamp chiefly presently employed as the front lamp for automobiles, the halogen lamp of
FIG. 1
advantageously provides a threefold luminosity at 70% consumed power. Besides, since unlike halogen lights, no filament is used in the lamp of
FIG. 1
, the service life is very long and not shorter than 1,500 hours.
In this discharge lamp, a light-screening film
4
is formed on the surface of an outer quartz tube
2
to control the projected light region. This light-screening film is about 20&mgr;m thick, and the shape and size thereof are such to be in compliance with the International Standard. The present invention relates also to a method for producing a light-screening film to be placed on the discharge lamp.
Using ferric oxide or cupric oxide as a pigment and sodium silicate or aluminum phosphate as a binder, a conventional light-screening film for lamps has been formed by mixing the pigment and the binder to form a paint; this paint is then applied to the glass surface of a lamp and the coat is fired at a temperature of from about 100° C. to about 250° C.
When such a lamp is lit, the temperature of the glass surface of the lamp rises; accordingly, the temperature of the light-screening film formed thereon rises also. Especially with a highly luminous automobile discharge lamp, the temperature of the lamp's glass surface rises to about 700° C. during the lighting and, accordingly, the light-screening film on the glass surface is exposed to a temperature of 700° C. also.
As mentioned above, a light-screening film made in accordance with prior art techniques uses ferric oxide or the like as pigment. Although cupric oxide is black at room temperature, this oxide is known to turn into red powder as oxidation progresses at about 350° C.
Thus, if a light-screening film is formed on a highly luminous discharge lamp for automobiles using prior art methods, the color of the light-screening film changes from black to red or white due as the temperature rises during lighting. When the color of the light-screening film turns from black to red or white, the absorbance of light changes, thereby leading to a decline in light-screening performance, which, of course, leads to various drawbacks. Discoloration of a light-screening film causes not only a decline in light-screening performance but the lamp also gives a bad appearance to the user; this, accordingly, has become a serious problem. Thus, there is a desire for a light-screening film material that undergoes no discoloration for a 1,500-hour lighting period.
Another problem results if a light-screening film is formed on a highly luminous automobile discharge lamp using prior art techniques. A heat cycle constituting ups and downs of temperature caused by the repetition of turning the lamp on and off causes cracking or peeling of the light-screening film, thereby resulting in loss of light-screening performance. To address this problem, a light-screening film material free of cracking or peeling due to lighting and extinction (turning the lamp on and off) over 1,500 hours is desirable.
DISCLOSURE OF THE INVENTION
In order to solve these prior art problems discussed above, the present invention is directed to a light-screening film paint for lamps comprising (1) at least one compound of either manganese oxide or an iron oxide compound doped with a metallic manganese and having the formula (Fe
x
Mn
1−x
)
2
O
3
where 0.95>x>0.70, and (2) powder glass containing at least one of silica, zinc oxide, is boron oxide and aluminum oxide.
The present invention is also directed to a light-screening film for lamps made by firing a light-screening film paint at a high temperature, containing a compound of manganese oxide, iron oxide and zinc oxide, and, in addition, powder glass containing at least one of silica, zinc oxide, boron oxide and aluminum oxide.
The present invention is also directed to a method for producing a light-screening film for lamps, including the steps of: preparing a light-screening film paint for lamps containing (1) at least one compound of either manganese oxide or an iron oxide compound doped with a metallic manganese and having the formula (Fe
x
Mn
1−x
)
2
O
3
where 0.95>x>0.70, and (2) powder glass containing at least one of silica, zinc oxide, boron oxide and aluminum oxide, applying the above paint to the surface of a lamp and forming a light-screening film by firing at a temperature not higher than 1200° C.
After a tentative drying step following application of a paint, a paint film is formed on the glass surface by the binder action of methyl cellulose, poly(vinyl alcohol) and acrylic resin. Methyl cellulose also functions to inhibit the sedimentation, coagulation or separation of pigment powder in a paint. The paint can be stabilized by adding 0.2 to 2 parts of methyl cellulose to 100 parts of powder. By setting the solid fraction in the paint to be not less than 40% by weight, dry contraction or liquid dripping after the paint has been applied can be suppressed, thereby permitting a high precision light-screening film pattern to be formed.
Preferably, by adding 0.2 to 2 parts of either silica having a primary grain size of not greater than 100 nm or mineral clay containing silica to 100 parts of powder, the paint can be made thixotropic, so that it is possible stably to apply the paint by using a coater.
During firing at a temperature not higher than 150° C., methyl cellulose, poly(vinyl alcohol) and acrylic resin are thermally decomposed; consequently, their residue in the paint film vanishes. During firing at a temperature not higher than 1500° C., powder glass contained in the paint melts and functions as a binder. By using glass that contains mainly zinc oxide and silica as powder glass, a light-screening film having a high adhesion strength to the surface of quartz glass is formed. By using powder glass having a melting point of not higher than 1000° C. and setting the firing temperature at not higher than 1000° C., one can prevent the deterioration of lamp performance.
By using powder glass having a thermal expansion coefficent not higher than 10
−6
, the difference in thermal expansion coefficient between the film and a quartz glass tube decreases and the peeling of a light-screening film due to localized ups and downs of temperature caused by the lighting and extinction of a lamp hardly occurs.
By using powder glass that will crystallize under a temperature not lower than 600° C., the deterioration of light-screening film strength due to a rise in temperature caused by lighting the lamp after firing can be prevented.
By allowing the firing to proceed under any of a nitrogen atmosphere, an inert atmosphere, or a vacuum atmosphere of not more than 10
−2
Torr, the metal electrode material for a main lamp body is kept from being oxidized, so that a light-screening film can be formed without deterioration of the lamp performance.
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patent: 4099080 (1978-07-01), Dawson et al.
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patent: 4576922 (1986-03-01), O'Brien et al.
patent: 5168126 (1992-12-01), Matsumoto et al.
patent: 5326728 (1994-07-01), Boury et al.
patent: 5410212 (1995-04-01), Reisman
patent: 5619102 (1997-04-01), Scholler
patent: 6015592 (2000-01-01), Mifune et al.
patent: 102 010 (1973-11-01), None
patent: 2 073 857 (1971-09-01), None
patent: 2 146 800 (1973-02-01), None
paten
Mifune Tatsuo
Ohata Tsumoru
Sakamoto Kazunori
Watanabe Masaru
Brunsman David
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P.
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