Electric lamp and discharge devices – With luminescent solid or liquid material – With gaseous discharge medium
Reexamination Certificate
1999-04-20
2001-08-28
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
With gaseous discharge medium
C313S635000
Reexamination Certificate
active
06281625
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a fluorescent lamp having a protective layer formed on the inner surface of a glass tube, and to a method for producing the same.
BACKGROUND OF THE INVENTION
There has been a problem with a conventional fluorescent lamp in that its long-time operation results in blackening of a glass tube and reduced luminous flux. It is considered that such blackening is caused, for example, by the factors as follows: (1) reaction between mercury enclosed in the fluorescent lamp and alkali components in the glass tube forms amalgam; (2) metal mercury penetrates into the glass tube; and (3) solarization occurs due to ultraviolet ray. Thus, it is known that blackening of a glass tube is prevented and reduction in luminous flux is inhibited by forming a protective film comprising metal oxides between the glass tube and a fluorescent layer.
It is desired that the protective film is a dense, homogeneous film, which does not have non-uniformity or falling-off, so that its function as a protective film can be fully displayed. Generally, fine particles with an average particle diameter of about 1 &mgr;m or less are used as the metal oxides in such a protective film. The fine particles are uneven in shapes, and they have a needle-shape, or a dendritic or feather-like shape. Because such fine particles tend to aggregate easily, preparation of a suspension of these particles with good dispersibility has been difficult. When a suspension not fully dispersed is applied to a glass tube, it is likely that pinholes are developed due to non-uniform coating or falling-off of the particles. Particularly, a thin film tends to be significantly non-uniform and become discontinuous, so that it cannot fully display its function as a protective film. On the other hand, a film with increased thickness tends to generate cracks or falling-off, so that its function as a protective film cannot be obtained adequately.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a fluorescent lamp having a dense, homogeneous protective film, which prevents blackening of a glass tube and inhibits the reduction in luminous flux.
In order to attain the above object, a fluorescent lamp of the present invention comprises a glass tube, a protective film formed on the inner surface of the glass tube, and a fluorescent layer formed on the protective film, in which the protective film is mainly composed of substantially spherical metal oxide particles.
Furthermore, a method for producing a fluorescent lamp including a glass tube, a protective film formed on the inner surface of the glass tube, and a fluorescent layer formed on the protective film of the present invention comprises steps of:
preparing a suspension containing a dispersoid mainly composed of substantially spherical metal oxide particles; and
applying the suspension to the inner surface of the glass tube followed by burning to form the protective film on the inner surface of the glass tube.
In the fluorescent lamp of the present invention, it is preferable that 60% or more, most preferably 80% or more, of the spherical metal oxide particles in the protective film are substantially spherical. In the method for producing a fluorescent lamp of the present invention, it is preferable that 60% or more, most preferably 80% or more, of the spherical metal oxide particles included as the dispersoid in the suspension are substantially spherical.
As a result of various researches, the inventors of the present invention have found that a dense, homogeneous protective film can be formed by mainly using spherical or approximately spherical metal oxide particles.
That is, increased flowability of such metal oxide particles enables the preparation of a suspension with excellent dispersibility. Furthermore, because the suspension has an improved coating property for the surface of a glass tube, a dense, homogeneous protective film can be formed with very little non-uniformity. Moreover, because this suspension has excellent dispersibility, the particles are difficult to aggregate when allowed to stand for a long time, so that it also has excellent stability. In addition, even if particle aggregation develops, the suspension can be re-dispersed easily.
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Amano Toyokazu
Inagaki Fumihiro
Otaka Yoshinori
Tachibana Hirokazu
Matsushita Electronics Corporation
Merchant & Gould P.C.
Patel Vip
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