Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF FORMING COATED L~YER OF FLUORESCENT
SUBSTANCE ON INNER SURFACE OF BIJLB
_CKGRO~ND OF THE INVENTION
The present invention relates to a method of
forming a coated layer of a fluorescent substance on an
inner surface of a bulb of a fluorescent lamp.
Heretofore, when a fluorescent substance layer
is formed on an inner surface of a bulb of a fluorescent
lamp or a mercury lamp, an aqueous lacquer is prepared by
dissolving a water soluble organic polymer and a surfac-
tant in water and suspending a fluorescent substance and a
small amount of binder for improving bond strength of the
fluorescent substance particles on the surface of glass
bulb in the lacquer to form a suspension of a fl-uorescent
substance, and coating the suspension on the inner surface
of the bulb and drying it :in a desired condition and then,
burning out the organic polymer and -the surfactant by
heating the bulb to form the fluorescent substance layer.
In general, colloidal alumina of fine powdery
aluminum oxide is used as the binder for the fluorescent
substance. Thus the colloidal alumina has significant
effect for increasing bond strength of the fluorescent
substance; however, the colloidal alumina has a character-
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istic that it is converted to have high activity for a gas
absorption after heating in the bulb heat-treating step.
Accordingly, in the fluorescent substance layer
formed by the conventional method, the binder in the
fluorescent substance l.ayer absorbs or adsorbs large
amounts of moisture and carbon dioxide gas in air on the
surface of the binder. The absorbed gases are not easily
evacuated in the following evacuating step of evacuating
the bulb whereby the absorbed gases remain as impurity
gases in the bu]b and the lamp characteristics such as
luminous flux maintenance factor of the lamp are impaired.
SUMMARY OF THE INVENTION
The present invention is to .overcome the dis-
advantages and to provide a method of forming a fluores-
cent substance layer which does not cause the deteriora-
tion of the lamp by preventing the activation of the
binder for gas absorption in the bulb heat-treating step.
In detail, the present invention is to provide a
method of forming a stable fluorescent substance layer
which has hi.gh bond strengt.h on a glass surface and does
not cause a deterioration of characteristics of the lamp
which comprises a coating step of coating a suspension of
a fluorescent substance on an inner surface of a bulb to
form a fluorescent substance layer wherein said suspension
is prepared by dissolving an organic water soluble polymer
and an organic surfactant in water to prepare an aqueous
solution of a lacquer and suspending a fluorescent sub-
stance and a fine powdery alumlnum o~ide as binder for the
fluorescent substance in the aqueous solution of the
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lacquer and incorporating boric acid and hydrogen peroxide,
and a bulb heat-treating step oE burning out the organic
polymer and surfactant remaining in the fluorescent sub-
stance layer and melt-coating boric acid on the surface of
the fine powdery aluminum oxide to inactivate the surface
by heating the bulb.
DESCRIPTION OF THE PREFERRED EMBODIME~TS
In general, when aluminum oxide is heat-treated,
the surface of the aluminum oxide is activated for a gas
absorption. This tendency is especially significant in
the case of colloidal fine powder of aluminum oxide. In
order to inactivate the surface of the aluminum oxide to
overcome the tendency, it has been considered to pre-
viously absorb a stable substance on the surface of the
aluminum oxide.
It has been found that boric acid is an excel-
lent substance for inactivating the surface of the fine
powdery aluminum oxide for gas absorption without inhibit-
ing the effect of the aluminum oxide as the binder.
2n When boric acid is added to the suspension of
the fluorescent substance in an aqueous solution of the
lacquer, the boric acid is rnelted before completely burn-
ing out the organic materials of the lacquer components in
the calcining step following the coated-layer-forming step
whereby the contact of oxygen required for the complete
combustion is prevented. As a result, carbon remains in
the calcined fluorescent substance layer and the luminous
efficiency of the fluorescent substance is decreased.
In order to overcome the disadvantages, it has
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been determined that when hydrogen peroxide or its' pre-
cursor is incorporated into the suspension of the fluores-
cent substance and boric acid, the combwstion of the
organic materials of the lacquer componen-ts is signifi-
cantly accelerated while maintaining the effect of boric
acid for inactivating the fine powdery aluminum oxide in
the bulb heating step, whereby the trouble of residual
carbon in the calcined fluorescent substance layer caused
by the addition of boric acid, can be prevented. In the
case a precursor of the hydrogen peroxide, such as urea
adduct (CO(NH2)2 H2O), for examp]e, is added to the lac-
quer suspension, the added amount is calculated on the
basis of the hydrogen peroxide content thereof.
Other minor lacquer components which may be used
are well known in the art such as 0.05% by weight of the
lacquer of a defoaming agent such as sorbitan oleate.
The content of boric acid is usually in a range
of 100% to 10% preferably 70% to 30% (wt.%) of the alumi-
num oxide.
The content of hydrogen peroxide expressed as a
30% solution is usually in a range of 100% to 10% (wt.%)
of the total organic material in the suspension.
The present invention will be further illus-
trated by certain examples.
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48,208-2
EXAMPLE 1
Water 150 cc
Hydroxyethyl cellulose 3 g
(Cellosize QP-40 manufactured by ~CC~
Surfactant--Dispersing Agent (polyoxyethylene 0.3 g
alkyl phenyl ether type) (NP-lO manufactured
by Nikko Chemicals Co., Ltd. Tokyo, Japan
Fine powdery aluminum oxide (0.02 micron) 0.5 g
(Alon-C manufactured by Degussa)
Boric Acid 0.3 g
Hydrogen peroxide 0.9 g
(30% aq. sol.)
Calcium halophosphate fluorescent substancelO0 g
These components were mixed to prepare a suspen-
sion of the fluorescent substance, and the suspension was
coated on an inner surface of a glass tube for a 40 W
fluorescent lamp and it was dried and the coated layer was
calcined by heating the glass tube at 600C in a furnace
and then, the fluorescent lamp was prepared in accordance
with the conventional method of the preparation of the
fluorescent lamp.
The initial intensity of illumination and the
luminous flux maintenance factor of the resulting lamp
were compared with those of the lamp prepared by the same
method except preparing the suspension of the fluorescent
substance without incorporating boric acid and hydrogen
peroxide.
The results are shown in Table 1.
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TABLE 1
Luminous flux main-
Initial Intensity tenance factor after
of illumination 1000 hours lighting
.. ... ... . _
Lamp (the present3300 lum~ns 92%
invention)
_
Lamp (Reference_ 3300 l~nens _ _ 89%
As shown from the data of Table 1, the luminous
flux maintenance factor after lO00 hours lighting of the
lamp of the present invention is improved by 3% in compari-
son with the conventional lamp.
The bond strength of the fluorescent substance
to the glass surface was not deteriorated by the incorpor-
ation o:E boric acid and hydrogen peroxide.
During the lacquer forming operation which
involves stirring, hydrogen peroxide is gradually decom-
posed to form oxygen. To inhibit this decomposition, a
small amount of phosphoric acid or uric acid preferably is
added as a stabilizer for hydrogen peroxide, and the
decomposition of hydrogen peroxide is significantly con-
trolled. The content of the phosphoric acid acid or uric
acid stabilizer is usually in a range of 0.5% to 0.05%
preferably 0.~% to 0.1% (wt.%) taken with respect to a 30%
hydrogen peroxide solution.
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EXAMPIAE 2
~ater 150 cc
Hydroxyethyl cellulose 3 g
(Cellosize QP-40 manufactured by UCC)
Surfactant--Dispersing Agent 0.3 g
(NP-10 manufactured by ~ik~o Chemicals
Co., Ltd.
Fine powdery aluminum oxide (0.02 micron) 0.5 g
Boric Acid 0.3 g
0 Hydrogen peroxide 0.9 g
(~0/O aq. sol.)
Phosphoric acid 0.001 g
Calcium halophosphate fluorescent substance 100 g
These components were mixed to prepare a suspen-
sion of the fluorescent substance and suspension was
coated on an inner surface of a glass tube for a 40 W
fluorescent lamp and it was dried and the coated layer was
calcined by heating the glass tube at 600C in a furnace
and then, the fluorescent lamp was completed in accordance
with conventional practices.
The initial intensity of illumination and the
luminous flux maintenance factor of the resulting lamp
were compared with those of the lamp prepared by the same
method except for the preparation of the suspension of the
fluorescent substance without incorporating boric acid and
hydrogen peroxide.
The results are shown in Table 2.
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TA~LE 2
~ uminous flux main-
Initial Intensity tenance factor after
of illumination 1000 hours lighting
Lamp (the present 3300 lumens 92%
invention~
. . _ .
Lamp (Reference) 3300 lumens ~9%
_ _ . _ _ _ . _ _ _ _ . _ _ _ _ _ _ _ _ _ _ ~ . _ _ _ _ _ _ _ . .
In accordance with the present invention, the
fine powdery aluminum oxide is incorporated as the binder
for the fluorescent substance and boric acid and hydrogen
peroxide are added to the suspension of the fine powdery
aluminum oxide and the fluorescent substance, and the
suspension is coated on an inner surface of the bulb and
dried. The coated fluorescent substance layer is then
calcined to melt-coat boric acid on the surface of the
fine powdery aluminum oxide, whereby the gas absorption of
the resulting fluorescent substance layer after the cal-
cination can be controlled and the characteristics of the
lamp such as the luminous flux maintenance factor of the
lamp are improved.
