DESCRIPTION
GLASS TUBE FOR FLUORESCENT LAMP, FLUORESCENT LAMP, AND LIGHTING SYSTEM
Technical Field
The present invention relates to a glass tube for a fluorescent
lamp, a fluorescent lamp, and a lighting apparatus.
Background Art
In recent years, in terms of protection of the global environment,
there has been demand for saving of natural resources and reduction
of CO2 emission. In the technical field of fluorescent lamps, methods
for reducing the thickness of the glass bulb (hereinafter simply
called "glass") can be adopted for the saving of natural resources
and the reduction of CO2 emission. That is, it is possible to reduce
the amount of the glass used as the material of the bulb by reducing
the thickness of the bulb, which results in the saving of natural
resources. Also, the reduction of the glass usage reduces the
consumption of the combustion gas by the melting furnace in the
production of the glass, which results in the reduction of CO2 emission.
However, fluorescent lamps that use a bulb with a reduced
thickness are easily damaged, due to its reduced glass strength.
To solve this problem, Patent Document 1, for example, discloses
a technique to increase the glass strength by forming a film made
of an oxide such as a zirconium oxide on the surface of a lamp bulb,
to increase the glass strength.
Prior Art Documents
Patent Document

Patent Document 1: Japanese Laid-open Patent Application No.
2001-332222
Summary of the Invention
Problems to be solved by the Invention

In an experiment, the inventors observed that in the case of
a lamp bulb without a phosphor layer, it was possible to increase
the glass strength by forming a film on the surface of the bulb.
However, in the case of a fluorescent lamp having a phosphor layer,
it was impossible to increase the glass strength by forming a film
on the surface of the bulb. Thus, in the case of a fluorescent lamp,
it was difficult to reduce the thickness of the bulb.
In view of the problem explained above, the main object of
the present invention is to provide a glass tube for a fluorescent
lamp with which the bulb thickness of the fluorescent lamp can be
reduced. Another object of the present invention is to provide a
fluorescent lamp and a lighting apparatus that are appropriate for
saving natural resources and reducing CO2 emission.
Means for solving the problems

To achieve the objects, the present invention provides a glass
tube for a fluorescent lamp, comprising: a main body that is made
of glass containing 60wt% to 75wt% of a silicon oxide material and
5wt% to 18wt% of an alkaline earth metal oxide material; and a film
that is formed at least on a circumference surface of the main body
and is made of at least one oxide selected from among a tin oxide,

a titanium oxide, a zirconium oxide and a silicon oxide.

Note that the content rates of the oxides described in this
Description are expressed in terms of oxides unless otherwise
specified. Also note that each of the numerical ranges specified
in this Description includes the lower limit and the upper limit.
For example, a numerical range "60wt% to 75wt%" includes both 60wt%
and 75wt%. Further, the glass constituting the main body of the glass
tube and the oxides constituting the film may include a negligible
amount of impurities in addition to the constituents specified above.

According to the glass tube for a fluorescent lamp pertaining
to the present invention, the glass constituting the main body of
the glass tube contains 5wt% or more of an alkaline earth metal oxide
material. Thus it is possible to realize a fluorescent lamp bulb
with a thin glass wall.

In the glass, the alkali metal exists as univalent metal ions,
and accordingly has a high mobility in the network structure in the
glass. In particular, sodium has a high mobility because of its small
atomic radius. Alkali metal with a high mobility is easily eluted
to the glass surface, as an alkaline constituent. Especially, when
the glass temperature is high, the mobility of the metal ions is
high, and the alkaline constituent is more easily eluted.

Usually, the manufacturing processes of fluorescent lamps
include a sintering process for sintering the phosphor layer. Since
the glass tube is heated in the sintering process, the alkaline

constituent is easily eluted from the glass tube. If the alkaline
constituent is eluted, the film will be subjected to chemical attacks
(i.e. chemically damaged), and the capability of the film of increasing
the glass strength will be degraded. The inventors found out that
in the case of fluorescent lamps, this is the reason why the film
formed on the surface of the bulb does not improve the glass strength.
[0012]
Note that it is not only due to the heating in the sintering
process that the alkaline constituent is eluted form the glass. In
addition to the sintering process, a bulb curving process for curving
a bulb, a glass sealing process for sealing the ends of the glass
tube, a connecting process for connecting glass tubes and so on are
included in the manufacturing processes of fluorescent lamps. In
each of these processes, the heat is applied to the glass tube and
the heat makes the alkaline constituent be easily eluted. Note that
the curved glass tube is a non-straight glass tube formed through
curving of a straight glass tube. For example, the curved glass tube
may be a ring-shaped bulb, a U-shaped bulb, a spiral bulb, or the
like.
[0013]
The glass tube for a fluorescent lamp pertaining to the present
invention suppresses the elution of the alkaline constituent by
containing an alkaline earth metal. In the glass, the alkaline earth
metal exists as bivalent metal ions, and accordingly has a low mobility
in the network structure in the glass. Also, the ion radius is
relatively large. Thus, they inhibit the alkaline metal ions from
moving in the glass. As the main body of the glass tube contains
5wt% or more of the alkaline earth metal oxide material, the alkaline

constituent does not easily elute from the glass of the main body
of the tube. As a result, the film is prevented from being subjected
to the chemical attacks, and the capability of the film of increasing
the glass strength will not be easily deteriorated. Note that the
content rate of the alkaline earth metal oxide is preferably 5wt%
to 18wt%. In particular, 10wt% to 18wt% is further preferable, and
the optimum range is 12wt% to 18wt%.
FIG. 1 and FIG. 2 each show compositions and properties of
glass that constitutes the main body of the glass tube for a lamp
pertaining to the embodiment of the present invention. As FIG. 1
and FIG. 2 show, the inventors found out that the glass strength
of the bulb is high enough in the case the content rate of the alkaline
earth metal constituting the glass of the main body was 5wt% or more.
On the other hand, in the case the content rate was less than 5wt%,
the glass strength of the bulb was not enough.

In the glass tube for a fluorescent lamp pertaining to the
present invention, the content rate of the alkaline earth metal oxide
contained in the main body of the glass tube is 18wt% or less, and
thus it has a high workability.

As the content rate of the alkaline earth metal is increased,
the viscosity of glass changes greatly according to the temperature.
Such glass is easily cooled down and the workability of the glass
is poor. If the main body of the glass tube is made of such glass,
the workability of the glass tube is also poor. In order to realize
a glass tube with a high workability, it is necessary to determine

the content rate of the alkaline earth metal included in the glass
contained in the glass tube to be 18wt% or less. Here, note that
glass with a high workability is glass whose softening point is within
a range from 650 °C to 720°C and working point is within a range from
960°C to 1050°C. It is preferable that the softening point is within
a range from 670°C to 700°C and the working point is within a range
from 960°C to 1000°C.

As FIG. 1 and FIG. 2 show, in the case the content rate of
the alkaline earth metal is 18wt% or less, the softening point and
the working point of the glass were within the ranges shown above,
and thus the workability of the glass was high. On the other hand,
in the case the content rate of the alkaline earth metal is more
than 18wt%, the workability of the glass was poor.

At least, the film should be made of at least one oxide selected
from among a tin oxide, a titanium oxide, a zirconium oxide and a
silicon oxide. However, it is preferable that the film is made of
a tin oxide. In the case the film is made of a tin oxide, the glass
of the main body of the glass tube will not be colored nor devitrify.
On the other hand, in the case the film is made of a zirconium oxide,
zirconium might react with constituents of the glass and work as
a nuclear product, and the crystal nucleus of the zirconium might
grow when heated in the succeeding processes and devitrify the glass
of the main body of the glass tube. Also, in the case the film is
made of a titanium oxide, the glass of the main body of the glass
tube might be clouded as the grain size of the titanium grows greatly.

The alkaline earth metal oxide material may consist of at least
one of a magnesium oxide and a calcium oxide. If this is the case,
the glass tube can be manufactured at low cost. This is because a
magnesium oxide and a calcium oxide can be obtained from natural
ore such as dolomite, and it costs lower than other alkaline earth
metal oxides.

The alkaline earth metal oxide material may consist of a
magnesium oxide and a calcium oxide, and a molar ratio of the calcium
oxide to the magnesium oxide may be 0.5 to 3. If this is the case,
the main body of the glass tube can be structured from glass that
is not likely to devitrify and elutes less alkaline constituent.
Since calcium has a larger ion radius than magnesium, calcium can
achieve a greater effect of suppressing the alkaline elution than
magnesium. On the other hand, too much calcium generates crystals
of calcium and alkaline metal, and the glass easily causes the
devitrification due to the crystals. Thus, it is preferable that
the molar ratio of the calcium oxide to the magnesium oxide is within
the range specified above.

As FIG. 1 and FIG. 2 show, in the case the molar ratio of the
calcium oxide to the magnesium oxide (CaO/MgO) is less than 0.5,
the softening point and the working point of the glass is not included
within the preferable ranges in some cases, which easily results
in poor workability. Also, in the case the molar ratio of the calcium
oxide to the magnesium oxide (CaO/MgO) is more than 3, the glass
might devitrify in some cases.

The glass constituting the main body may further contain 8wt%
to 20wt% of an alkali metal oxide material in total. If the content
rate of the alkaline metal oxide is more than 20wt%, the electrical
conductivity, which will be explained below, exceeds 57 uS/cm in
some cases. Such glass elutes a relatively large amount of the
alkaline constituent. If the content rate of the alkaline metal oxide
is less than 8wt%, the working point is not included in the preferable
range in some cases, which results in poor workability.

50wt% or more of the at least one oxide constituting the film
may have a tetragonal crystal structure.
In the case where more than a half of the oxides constituting
the film has a tetragonal crystal structure, the glass strength of
the bulb is increased. With such a structure, it is possible to realize
a thinner bulb wall. The reason why the glass strength is increased
by the tetragonal crystal structure of the oxide is as follows: Since
the cristobalite structure (i.e. the crystal structure of the SiO2
as the main constituent of the glass) is tetragonal, if the crystal
structure of the oxide constituting the film is tetragonal as well,
the film can be easily formed on the glass surface. Also, if the
crystal structure is tetragonal, the formed film firmly fixes to
the glass and is unlikely to fall off.
In the case the oxide constituting the film is a tin oxide,
it is preferable that the oxide is not SnO, but SnO2. This is because
SnO2 is stable as a crystal having the tetragonal crystal structure,
whereas the structure of SnO tends to change to a cubic structure.
Note that the tin oxide easily falls into the state of SnO if the

temperature of the glass tube on which the film is formed is 500°C
or more.

A wall thickness t [mm] and an outside diameter φ [mm] of the
glass tube may satisfy t ≤ 0.7 or t /φ ≤ 0.42. If this is the case,
the bulb is likely to be damaged due to the thin wall of the glass
tube, and thus the structure pertaining to the present invention
is particularly effective.

Another aspect of the present invention is a fluorescent lamp
comprising a bulb manufactured from the glass tube described above.
With such a structure, the fluorescent lamp is unlikely to be damaged.
[0021]
Another aspect of the present invention is a lighting apparatus
comprising the fluorescent lamp described above. With such a
structure, the lighting apparatus is unlikely to be damaged.
Advantageous Effects of the present Invention
With the glass tube for a fluorescent lamp pertaining to the
present invention, the capability of the film of increasing the glass
strength will not be de degraded even if the glass tube is heated
in the manufacturing processes of the fluorescent lamp. Thus, the
glass tube realizes a thin wall of the bulb of the fluorescent lamp.
Brief Description of the Drawings

FIG. 1 shows compositions and properties of glass that

constitutes a main body of a glass tube for a lamp, pertaining to
an embodiment of the present invention;
FIG. 2 shows compositions and properties of the glass that
constitutes the main body of the glass tube for a lamp, pertaining
to the embodiment;
FIG. 3 shows results of experiment in which effects of a film
thickness on glass strength and clouding were tested;
FIG. 4 is a partial cutaway plan view of a lamp pertaining
to the embodiment;
FIG. 5 is a perspective view showing an overall structure of
a lighting apparatus pertaining to the embodiment;
FIGs. 6A - 6D explain a manufacturing method of a fluorescent
lamp, where FIG. 6A explains a phosphor application process, FIG.
6B explains a sintering process, FIG. 6C explains a bulb sealing
process, and FIG. 6D explains a bulb curving process;
FIGs. 7A and 7B explain a method for measuring a thickness
of a film;
FIG. 8 explains a method for measuring an amount of alkaline
elution; and
FIG. 9 shows correlation between an amount of alkaline elution
measured with an alkaline elution testing method based on the JIS
and an electrical conductivity measured by an alkaline elution testing
method pertaining to the present invention.
Best Mode for Carrying Out the Invention
The following explains a glass tube for a fluorescent lamp
(hereinafter simply called "glass tube"), a fluorescent lamp and
a lighting apparatus pertaining to an embodiment of the present

invention, with reference to the drawings.

- Structures of the glass tube, the fluorescent lamp and the lighting
apparatus

The glass tube pertaining to the present invention includes
a tube body and a film formed at least on the outer surface of the
tube body.

Regarding the tube body, it is preferable that t ≤ 0. 7 or t/φ
≤ 0.42, where t [mm] is the wall thickness of the tube body and φ
[mm] is the outside diameter of the tube body. In particular, it
is preferable that 0.4 ≤ t ≤ 0.6 and 1 ≤ φ ≤ 10.

It is also preferable that the thickness of the film is from
5 ran to 100 nm, and particularly preferable that the thickness is
from 5 nm to 50 nm. FIG. 3 shows the results of experiment in which
effects of the film thickness on the glass strength of the glass
tube and clouding were tested. As FIG. 3 shows, in the case the film
thickness is no less than 5 nm (i.e. examples 14 to 20 and 23 to
25), the glass strength was rated as "o" (which means "excellent") .
However, in the case the film thickness is less than 5 nm (i.e. examples
21 and 22), the glass strength was rated as "∆" (which means "not
bad") . Also, in the case the film thickness is no greater than 50
nm, clouding did not occur in the part of the glass tube where was
heated during the bulb sealing process and so on. However, in the
case the film thickness is greater than 50 nm, clouding occurred
in the heated part. Here, it can be assumed that the clouding occurred

due to the grain growth of the heated coating grains of a tin oxide.
Such clouding is undesirable because it degrades the appearance of
the fluorescent lamp, and disturbs the appearance test for detecting
flaws and so on.

If the film thickness exceeds 500 run, the visible light
transmission of the glass tube decreases, and the visible light
transmission of a bulb manufactured with use of such a glass tube
decreases accordingly. If a fluorescent lamp is manufactured with
use of this bulb, it decreases the light extraction efficiency, and
also decreases the total luminous flux of the lamp. Note that the
film may be formed not only on the outer surface of the tube body,
but also on the inner surface and the end faces. Also, the film is
not necessarily formed on the entire outer surface of the tube body.
That is, the film may not cover the part where is to be covered with
a base when it is built into a bulb.

It is preferable that the tube body is made of glass including
the following constituents: 60wt% to 75wt% of SiO2; 0.5wt% to 5wt%
of Al2O3; 0wt% to 5wt% of B2O3; 0.5wt% to 7wt% of Li2O; 3wt% to 17wt%
of Na2O; lwt% to 12wt% of K2O; lwt% to 4wt% of MgO; lwt% to 7.3wt%
of CaO; 0wt% to 8wt% of SrO; 0wt% to 10wt% of BaO; 0wt% to 10wt%
of ZnO; 0wt% to 5wt% of ZrO; 0.01wt% to 0.2wt% of Fe2O3; 0wt% to Iwt%
of Sb2O3; and 0wt% to lwt% of CeO2.

SiO2 is the main constituent that forms glass framework. Too
little SiO2 content decreases the viscosity of the glass, which results
in poor workability. With toomuch SiO2 content, the viscosity becomes

too high and it becomes hard to deform the glass. The preferable
content rate of SiO2is 60wt% to 75wt%.
Al2O3 is a constituent for improving the chemical durability.
Too little Al2O3 decreases the chemical durability of the glass. Yet,
too much Al2O3 makes the glass inhomogeneous and increases the striae.
The preferable content rate of Al2O3 is 0.5wt% to 5wt%.

B2O3 is an optional constituent. The addition of small amount
of B2O3 decreases the expansion coefficient and prevents the
devitrification. However, too much B2O3 lowers the working point,
and narrows the range of the working point, which results in poor
workability. The preferable content rate of B2O3 is Owt% to 5wt%.
The addition of Na2O has the effect of decreasing the viscosity
and increasing the expansion coefficient. Too little Na2O can not
realize suchan effect. Toomuch Na2O degrades the chemical durability.
The preferable content rate of Na2O is 3wt% to 17wt%.
The addition of K2O has the effect that is similar to the effect
of Na2O. However, K2O increases the expansion coefficient by a larger
amount. Also, in combination with Na2O, K2O realizes the mixed alkali
effect, and increases the electrical resistivity as well. Too little
K2O can not realize such effects, and too much K2O leads to too large
expansion coefficient. The preferable content rate of K2O is lwt%
to 12wt%.

The addition of Li2O has the effect that is similar to the

effect of Na2O and K2O. However, Li2O increases the expansion
coefficient by a smaller amount than Na2O does. Also, in combination
with Na2O and K2O, Li2O realizes an additional mixed alkali effect,
and further increases the electrical resistivity. Too little Li2O
can not realize such effects, and too much Li2O might lead to phase
separation of the glass . The preferable content rate of Li2O is 0. 5wt%
to 7wt%.

The addition of MgO and CaO has the effect of improving the
chemical durability, in addition to the effect of preventing the
alkaline elution. Too little MgO and CaO can not realize the effects,
and too much MgO and CaO might cause the devitrification of the glass.
The preferable content rate of MgO is lwt% to 4wt%. The preferable
content rate of CaO is lwt% to 7.3wt%.
SrO, BaO and ZnO have the effect of increasing the electrical
resistivity, in addition to the effect of preventing the alkaline
elution. Also, they provide the electrical insulation property. If
the content rates of these constituents are greater than 10wt%, the
glass easily causes the devitrification. The preferable content rate
of SrO is Owt% to 8wt%. The preferable content rate of BaO is Owt%
to 10wt%. The preferable content rate of ZnO is Owt% to 10wt%. These
content rates realize a preferable glass for a fluorescent lamp.
ZrO is an optional constituent. The addition of ZrO increases
the hardness. Too much Zro might crystallize the glass. The
preferable content rate of ZrO is 0wt% to 5wt%.

Fe2O3 is an impurity substance that can be included in various
materials of the glass. However, it is possible to adjust the amount
of Fe2O3 by the material refining. The addition of Fe2O3 has the effect
of ultraviolet absorption. Too little Fe2O3 can not achieve the effect,
and too much Fe2O3 makes a stain on the glass. The preferable content
rate of Fe2O3 is 0.01wt% to 0.2wt%.

Sb2O3 is an optional constituent that has the effect of
effectively clarifying the gas generated from the materials in the
melting furnace. However, too much Sb2O3 makes a stain on the glass.
The preferable content rate of Sb2O3 is 0wt% to lwt%.

CeO2 is an optional constituent. The addition of CeO2 has the
effect of ultraviolet absorption. However, too much CeO2 might make
a stain due to ultraviolet radiation, which is so-called solarization.
The preferable content rate of CeO2 is 0wt% to lwt%.

FIG. 4 a partial cutaway plan view of a ring-shaped fluorescent
lamp pertaining to an embodiment of the present invention. As FIG.
4 shows, the ring-shaped fluorescent lamp 10 (FCL30ECW/28) pertaining
to the embodiment of the present invention includes a ring-shaped
bulb 20, stems 30 and 30' attached to the both ends of the bulb 20,
and a base 40 attached to cover the both ends.

The bulb 20 is manufactured from the glass tube pertaining
to the present invention. A protective layer (not illustrated) and
a phosphor layer (not illustrated) are laminated on the inside surface

of the bulb 20 in order. A piece of amalgam 21 for providing mercury
vapor and an argon gas as a rare gas are enclosed within the bulb
20. Electrodes 31 and 31', each including a filament coil and a pair
of lead wires, are respectively mounted on the stems 30 and 30'.
The base 40 including a main body 41 for accommodating the
ends of the bulb 20, and a plurality of connection pins 42 disposed
on the main body 41.

FIG. 5 is a perspective view showing an overall structure of
a lighting apparatus pertaining to an embodiment of the present
invention. As FIG. 5 shows, a lighting apparatus 100 pertaining to
this embodiment includes, as the light source, the fluorescent lamp
10 explained above. The fluorescent lamp 10 is housed in an apparatus
body 101 of the lighting apparatus 100, and is started to light by
a lighting unit 102.

- Manufacturing methods of the glass tube and the lamp
Manufacturing method of glass tube>
First, various kinds of glass materials are blended according
to the content rates stated above so that a mixture of the materials
are obtained. Next, the mixture of the materials is put into a melting
furnace and is melted at 1500°C to 1600°C to be vitrified, and a
glass melt is obtained. After that, the glass melt is drawn into
a tube through the Danner process or the like, and is cut into a
prescribed size and processed to be the glass tube.

The film is formed through the deposition of the vapor, which

is generated as the organic metal is heated, and is sprayed onto
the glass tube that is being drawn into a tube in the draft chamber.
For example, the organic metal is heated at 180°C so that 10 g of
the organic metal vapors per minute, and the generated vapor is splayed
onto the glass tube for 1 minute at the flow speed of 5L/min. It
is possible to control the thickness of the film by adjusting the
vaporization temperature, the usage amount of the organic metal,
the splaying speed, the splaying time, and so on. Note that there
are alternative methods for forming the film. For example, the organic
metal may be dissolved in water or organic solution and be sprayed,
or the tube body may be immersed in the solution of the organic metal
for application of the solution onto the glass tube.

The organic metal for use in the film formation includes, for
example, stannum, titanium, zirconium, or silicon as the metal
constituent. Specifically, it includes tin tetrachloride, titanium
tetrachloride, zirconium tetrachloride, silicon tetrachloride,
dimethyldichloro tin, dimethyldichloro titanium, dimethyldichloro
zirconium, dimethyldichloro silicon, acetylacetone tin,
acetylacetone titanium, acetylacetone zirconium, acetylacetone
silicon, and so on.

Manufacturing method of the lamp>
FIGs. 6A - 6D explain a manufacturing method of a fluorescent
lamp. FIG. 6A explains a phosphor application process, FIG. 6B
explains a sintering process, FIG. 6C explains a bulb sealing process,
and FIG. 6D explains a bulb curving process.

Firstly, in the phosphor application process as FIG. 6A shows,
a three-wavelength phosphor suspension 50 is poured into the glass
tube 21 to be saturated. Here, a protective film has been formed
on the inside surface of the glass tube 21. Next, hot air (25°C to
30°C) is blown into the glass tube to dry the phosphor suspension
50. After that, as FIG. 6B shows, the glass tube is sintered in the
oven for approximately one minute for the formation of the phosphor
layer. In the oven, the atmosphere is controlled to be about 550°C
to 660°C. In this way, since the glass tube is heated in the sintering
process, the alkaline constituent is easily eluted from the glass
tube.

Next, in the bulb sealing process, portions of the phosphor
layer near the both ends of the glass tube 21 are removed. After
that, the stems 30 and 30' are inserted into the glass tube 21 and
sealed at the both ends as FIG. 6C shows. In the subsequent bulb
curving process, as FIG. 6D shows, the straight glass tube 21 is
curved to shape a ring in the oven in which the atmosphere is controlled
to be about 700°C to 900°C. In this way, since the glass tube is
heated in the bulb curving process, the alkaline constituent is easily
eluted from the glass tube.

After that, in an exhausting process, an impurity gas is
exhausted from within the bulb 20 via an exhaust pipe 32 which has
not been sealed, so that the bulb 20 is almost evacuated. Then the
bulb 20 is filled with an argon gas . Further, in an amalgam enclosing
process, the piece of amalgam 21 is put into the bulb 20 through
the exhaust pipe 32.

- Evaluation method
The glass tubes for a fluorescent lamp were evaluated in the
experiment in the following manner.

The thickness of the film was measured with use of a hot end
coating measurement system: HECM-S, which is a product of American
Glass Research.
FIGs. 7A and 7B explain a method for measuring the thickness
of the film. As a sample, a glass tube cut into a 20-centimeter-long
piece was prepared. For each of three positions shown in FIG. 7A,
which are at both end positions and the central position of the glass
tube, the film thickness was measured at four measurement points
located equiangularly (i.e. each two points form a right angle) as
FIG. 7B shows (Thus the film thickness was measured at twelve points
in total) . The average of the thicknesses measured at the twelve
measurement points was determined as the film thickness. Note that
the incident angle of the light at each measurement point was 45°.

The hot end coating meter shows the film thickness in terms
of unique units "ctu (coating thickness units)". 1 ctu is equal to
0.2 nm to 0.3 rati in terms of the International System of Units. In
the present Application, it is assumed that 1 ctu = 0.25 nm.

First, in the experiment, a straight glass tube with a film

formed on the circumference surface thereof was used. The outside
diameter and the inside diameter of this glass tube is 4 mm and 3
mm, respectively. The film had been formed in the following manner:
powder dimethyldichloro tin is heated at 120°C for one minute; and
the vapor generated from the powder is splayed onto the glass tube
that is being drawn into a tube in the draft chamber. The thickness
of the film, which includes a tin oxide, is 100 ran.

Next, the glass tube, on which the film had been formed, was
put into a silica tube whose inside diameter is 20 mm, and was rotated
at a speed of 20 rpm for five minutes in a 500°C atmosphere so that
scars were formed on the surface of the glass tube as the surface
was rubbed against the silica tube.

After that, the flexural strength of the glass tube with the
scars were measured with use of Autograph AG-IS (a product of Shimadzu
Corporation) . The flexural strength was measured in the following
manner: The glass tube was fixed at two points such that the span
between them is 40 mm, and a load was applied onto the center of
the glass tube at a load velocity of 1 mm/min; and the value of the
load at the time the glass tube was destroyed was measured.

In the case the scars decreased the flexural strength by 30%
or more, the glass strength was evaluated as "x", which means that
the glass strength is not sufficient. In the case the scars decreased
the flexural strengthby less than 30%, the glass strength was evaluated
as "A" (the flexural strength was decreased by 15% or more but less
than 30%) or "o" (the flexural strength was decreased by 0% or more

but less than 15%), which bothmean that the glass strength is sufficient.
The reason why the glass strength was evaluated as not sufficient
in the case the scars decreased the flexural strength by 30% or more
is that if fluorescent lamps are manufactured from such glass tubes,
yield of the lamps greatly decreases.

The clouding was evaluated visually, "o" means that clouding
was not found by sight, and "x" means that clouding was found by
sight.

For measurement of the softening point and the working point
of the glass, samples were manufactured according to the following
steps: First, themixtureof thematerials resultant from the blending
of the glass materials is put into a platinum crucible, and the glass
materials in the platinum crucible are melted to be vitrified in
an electrical furnace at 1500 °C for three hours. After being melted,
the glass melt is poured into a metal mold, and gradually cooled
(i.e. annealed) for 12 hours, which is enough time length for
eliminating distortion. The molded glass block is processed with
a cutter or the like into samples in the shapes that are suitable
for the series of measurement shown blow.
The softening point is the temperature at which the viscosity
of the glass is 107.65dPa.s. The glass has fluidity while the
temperature is no less than the softening point. For use in a
fluorescent lamp, it is preferable that the softening point is within

the glass tube may be hard glass or soft glass. However, the structure
of the present invention is particular effective in the case of soft
glass with a low glass strength.

The fluorescent lamp pertaining to the present invention is
not limited to the embodiment above. It is commonly applicable to
various types of fluorescent lamps, such as a straight fluorescent
lamp, a ring-shaped fluorescent lamp, a cold cathode fluorescent
lamp, a double ring-shaped fluorescent lamp, a square-shaped
fluorescent lamp, a double square-shaped fluorescent lamp, and a
twin fluorescent lamp.

The lighting apparatus pertaining to the present invention
is not limited to the embodiment above. For example, it is commonly
applicable to various types of lighting apparatuses, such as a room
lighting apparatus, an outdoor lighting apparatus, a desk lighting
apparatus, a portable lighting apparatus, a display light source,
a backlight for a liquid crystal display and a lighting apparatus
for an image reader.
Industrial Applicability
The glass tube for a fluorescent lamp, pertaining to the present
invention, is applicable to various products for lighting.
Explanation of numerals

10 lamp
20 bulb

21 glass tube for fluorescent lamp
22 main body
23 film
100 lighting apparatus

We Claim:
1. A glass tube for a fluorescent lamp, comprising:
a main body that is made of glass containing 60wt% to 75wt%
of a silicon oxide material and 5wt% to 18wt% of an alkaline earth
metal oxide material; and
a film that is formed at least on a circumference surface of
the main body and is made of at least one oxide selected from among
a tin oxide, a titanium oxide, a zirconium oxide and a silicon oxide.
2. The glass tube of Claim 1, wherein
the alkaline earth metal oxide material consists of at least
one of a magnesium oxide and a calcium oxide.
3. The glass tube of Claim 1, wherein
the alkaline earth metal oxide material consists of a magnesium
oxide and a calcium oxide, and a molar ratio of the calcium oxide
to the magnesium oxide is 0.5 to 3.
4. The glass tube of Claim 1, wherein
the glass constituting the main body further contains 8wt%
to 20wt% of an alkali metal oxide material in total.
5. The glass tube of Claim 1, wherein
50wt% or more of the at least one oxide constituting the film
has a tetragonal crystal structure.
6. The glass tube of Claim 1, wherein
a wall thickness t [mm] and an outside diameter φ [mm] of the

glass tube satisfy t ≤ 0.7 or t/φ ≤ 0.42.
7. A fluorescent lamp comprising a bulb manufactured from the
glass tube defined in Claim 1.
8. A lighting apparatus comprising the fluorescent lamp defined
in Claim 7.


but less than 15%), which both mean that the glass strength is sufficient.
The reason why the glass strength was evaluated as not sufficient
in the case the scars decreased the flexural strength by 30% or more
is that if fluorescent lamps are manufactured from such glass tubes,
yield of the lamps greatly decreases.

The clouding was evaluated visually. "o" means that clouding
was not found by sight, and "×" means that clouding was found by
sight.

For measurement of the softening point and the working point
of the glass, samples were manufactured according to the following
steps: First, themixture of thematerials resultant from the blending
of the glass materials is put into a platinum crucible, and the glass
materials in the platinum crucible are melted to be vitrified in
an electrical furnace at 1500°C for three hours. After being melted,
the glass melt is poured into a metal mold, and gradually cooled
(i.e. annealed) for 12 hours, which is enough time length for
eliminating distortion. The molded glass block is processed with
a cutter or the like into samples in the shapes that are suitable
for the series of measurement shown blow.
The softening point is the temperature at which the viscosity
of the glass is 107.65dPa.s. The glass has fluidity while the
temperature is no less than the softening point. For use in a
fluorescent lamp, it is preferable that the softening point is within

a range from 650°C to 720°C, and further preferable that it is within
a range from 670°C to 700°C. If the softening point is lower than
650°C, the bulb might be deformed in the phosphor printing process,
due to the heat applied for volatizing the binder included in the
phosphor suspension. On the other hand, if the softening point is
hither than 720°C, it is necessary to increase the temperature of
the glass tube for the sealing process, and accordingly it is necessary
to increase the burning capability of the melting furnace.

The working point is the temperature at which the viscosity
of the glass is 104dPa.s. The glass is processed at this temperature
or lower. For use in a fluorescent lamp, it is preferable that the
working point is within a range from 960°C to 1050°C, and further
preferable that it is within a range from 960°C to 1000°C. If the
working point is lower than 960°C, the range of the working point
becomes narrow, which results in poor workability. On the other hand,
if the working point is hither than 1050°C, the melting point of
the glass becomes too high, which also results in poor workability,
and the cost of the melting processing increases in cost.

As a method for measuring the alkaline elution, a testing method
for glassware for use in chemical analysis based on JIS (Japanese
Industrial Standards R 3502) is common. The following provides a
simple explanation of this method: First, the glass sample is
pulverized into a ground glass (grain diameter: 250 urn - 420 urn)
in a mortar or the like. Next, fine glass powders are removed from
the ground glass by washing of it in ethyl alcohol. The washed ground

glass is heated in boiled water for 60 minutes. As a result, the
alkaline constituent is eluted from the ground glass, and an alkaline
elution is obtained. After that, the neutralization titration with
use of sulfuric acid is conducted on the alkaline elution, and the
amount of the alkaline elution can be calculated according to the
obtained value.
Such a testing method based on the JIS might leave the fine
glass powders in the ground glass if the washing in ethyl alcohol
is not done enough. The existence of the fine glass powders is
problematic because it greatly increases the total surface area of
the glass in distilled water, and makes it impossible to precisely
measure the amount of the alkaline elution. Also, such a testing
method requires troublesome steps, including the removal of the fine
glass powders by washing, the neutralization titration, and so on.
Thus there is a demand for a more precise and easier method for measuring
the amount of the alkaline elution.

In view of this demand, the inventors have established a new
method for measuring the amount of the alkaline elution, which is
more precise and easier than the conventional testing method based
on the JIS. According to the measurement method pertaining to the
present invention, a glass sample in the shape of a block is immersed
in distilled water so that the alkaline constituent is eluted from
the glass sample to the distilled water, the electrical conductivity
of the obtained alkaline elution is measured, and the measured
conductivity value is converted to the amount of the alkaline elution.

FIG. 8 shows the method for measuring the amount of the alkaline
elution, pertaining to this embodiment. The following specifically
explains the procedures of the measurement method pertaining to the
present invention.

First, the glass sample is cut into a block, and is left in
a basin enclosing an atmosphere with constant temperature and humidity
(temperature: 75°C - 85°C, humidity: 85% - 95%) for 45 hours to 50
hours so that the glass sample contains moisture. Note that in order
to realize high measurement accuracy, it is preferable that the
temperature, the humidity and the time length are 80°C, 90% and 48
hours respectively, which are almost the middle values of the ranges
mentioned above.

Next, as FIG. 8 shows, 100 ml of distilled water 2 at temperature
of 70°C to 80°C is stored in a tank 1, and a glass sample 3 after
the moisture containing process is immersed in the distilled water
2 for one hour. According to the measurement method pertaining to
the present invention, the alkaline constituent is eluted at a
relatively low temperature (70°C to 80°C) . Thus, in comparison with
the testing method based on the JIS in which the alkaline constituent
is forced to be eluted in boiling distilled water, the measurement
method pertaining to the present invention realizes more practical
measurement of the amount of the alkaline elution based on practical
usage of the glass.
Before the immersion into the distilled water 2, the shape
of the glass sample 3 is adjusted such that its total surface area

is 4500 mm2 to 5500 mm2 (preferably about 5000 mm2) . For example,
eight pieces of the glass sample 3, each having been cut into a
rectangular parallelepiped of about 15 mm* 15 mm* 2.5mm may be
immersed in the distilled water 2.
After that, the glass sample 3 is removed from the distilled
water 2, and an alkaline elution is obtained. Then, the temperature
of the alkaline elution is stabilized at 25°C, and the electrical
conductivity of the alkaline elution is measured with a commercially
available handheld-type electrical conductivity meter 4 (Trade name:
Twin Cond B-173) with a sensor for immersion testing.
FIG. 9 is a graph showing correlation between an amount of
alkaline elution measured with the alkaline elution testing method
based on the JIS and an electrical conductivity measured by the alkaline
elution testing method pertaining to the present invention. The
amount of the alkaline elution and the electrical conductivity have
a correlation as shown in FIG. 9. It is considered that glass with
alkaline elution of no greater than 270 µg/g is suitable for a bulb
of a fluorescent lamp. As seen from FIG. 9, an alkaline elution value
270 µg/g corresponds to an electrical conductivity value 57 µS/cm.
This means that glass with electrical conductivity of no greater
than 57 µS/cm is suitable as glass for the bulb.

Electrical conductivity indirectly indicates the amount of
alkaline elution. As glass that is suitable for fluorescent lamps,
it is preferable that the electrical conductivity is no greater than
57 µS/cm at 25°C. If the electrical conductivity is greater than

57 µS/cm, various problems become pronounced due to generation of
amalgam.
Since glass material in the shape of a block is used in the
measurement method explained above, it is easy to adjust the total
surface area of the glass to be immersed in the distilled water.
Thus, in comparison with the testing method based on the JIS, the
method pertaining to this embodiment can measure the alkaline elution
more precisely. Also, since the method pertaining to this embodiment
measures the alkaline elution based on the electrical conductivity,
the measurement accuracy does not degrade even if the alkaline elution
increases.
Further, since glass material that is cut into blocks is immersed
in the distilled water in the measurement method explained above,
this method does not require the procedures including pulverizing
of the glass material and removal of the fine glass powders by washing.
Also, the electrical conductivity of the alkaline elution can be
measured through simple operations of immersing the electrode of
the electrical conductivity meter 4 into the alkaline elution, and
the troublesome neutralization titration is unnecessary. Thus, the
method pertaining to this embodiment is much easier than the measuring
method based on the JIS.

The inventors evaluated the devitrification of the glass when
melting the glass to vitrify it, by visually checking whether or
not the glass would be crystallized and devitrify. "o" means that

the devitrification was not found, and "×" means that the
devitrification was found.

First, in the experiment, a straight glass tube with a film
formed on the circumference surface thereof was used. The outside
diameter and the inside diameter of this glass tube is 4 mm and 3
mm, respectively. The film had been formed in the following manner:
powder dimethyldichloro tin is heated at 120°C for one minute; and
the vapor generated from the powder is splayed onto the glass tube
that is being drawn into a tube in the draft chamber. The thickness
of the film is 100 nm.
Next, the inventors observed the crystal structure of an oxide
included in the film on the glass tube, using an X-ray dif fractometer.

- Modification examples
The fluorescent lamp and the glass tube for the fluorescent
lamp that pertain to the present invention are explained above based
on the embodiment. However, the glass tube for the fluorescent lamp,
the fluorescent lamp, and the lighting apparatus that pertain to
the present invention are not limited to the embodiments.

In addition to the use for manufacturing a bulb, the glass
tube for the fluorescent lamp pertaining to the present invention
are suitable for a flare, an exhaust pipe and so on, which are to
be heated in the manufacturing process and are demanded to have a
thin glass wall. Also, the glass that constitutes the main body of

The present invention provides a glass tube for a fluorescent
lamp, comprising: a main body that is made of glass containing 60wt%
to 75wt% of a silicon oxide material and 5wt% to 18wt% of an alkaline
earth metal oxide material; and a film that is formed at least on
a circumference surface of the main body and is made of at least
one oxide selected from among a tin oxide, a titanium oxide, a zirconium
oxide and a silicon oxide.