JPH0317175B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION Field of Industrial Application The present invention relates to a method of forming a phosphor coating for a fluorescent lamp.

(Prior art) Conventionally, the phosphor coating of a fluorescent lamp is made by applying a phosphor suspension to the inner wall surface of the bulb to adhere the phosphor coating, and then drying the phosphor coating. It was formed by baking the phosphor coating to remove organic substances such as binders.

(Problem to be Solved by the Invention) At this time, ethyl acetate and butyl acetate are generally known as solvents for the phosphor suspension, but when these solvents are used for curved tube valves, straight tube valves The drawback is that the evaporation rate is slower and the production time is longer than when it is applied to Also,
When a curved bulb was used, the evaporation rate of the solvent was slow, which caused the phosphor suspension to drip and accumulate in the curved section. Therefore, when an organic solvent with a high evaporation rate, such as acetone, is used, there is a problem that a phosphor film cannot be uniformly formed. In particular, if a phosphor suspension made of a fast-evaporating solvent such as acetone is applied to a curved tube-shaped bulb and dried, even if the phosphor film is properly formed in the center of the curved tube-shaped bulb, The problem was that the evaporation rate of the solvent was too fast near the opening of the shaped valve, causing cracks. For this reason, it has not been possible to obtain an organic solvent that has an appropriate evaporation rate and is inexpensive. Therefore, conventional methods have had the disadvantage that even if the phosphor coating has a somewhat poor adhesion condition, the phosphor coating must be formed using a cost-effective solvent.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for forming a phosphor coating in a curved tube bulb at low cost and by which a uniform phosphor coating can be obtained.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a method for mixing two types of organic solvents with different evaporation rates so that the evaporation rate is 20°C per minute in an atmosphere.
A mixed solvent with a concentration of 3.5×10 ^-3 g/cm ² or more and 6.5×10 ^-3 g/cm ² or less is prepared, and a phosphor suspension obtained by mixing a phosphor in this mixed solvent is poured into a curved tube. It is applied to the inner wall surface of the bulb to form a phosphor coating. The phosphor coating is then dried and fired to form a phosphor coating.

(Function) Since two or more organic solvents having different evaporation rates are mixed in the phosphor suspension, the solvent can be obtained at low cost. In addition, the evaporation rate of the mixed solvent was set to 3.5×10 ^-3 cm ³ /g or more per minute and 6.5×10 ^-3 cm ³ /g in an atmosphere of 20°C.
g or less, the phosphor film is uniformly formed and has no cracks, and a high-quality phosphor film with no traces of liquid pools in the curved portions can be obtained. Further, the lamp manufacturing time can be shortened, and the device can be made more compact.

(Example) An example in which the present invention is applied to a substantially saddle-shaped valve shown in FIG. 1 will be described below. This substantially saddle-shaped valve is formed by bending a straight pipe valve into a substantially U-shape, and then bending it again at the center in a direction perpendicular to a plane containing this substantially U-shape. The method for forming a phosphor coating on this saddle-shaped bulb is as follows.
That is, first, a mixed solvent of butyl acetate and acetone is used as a solvent, and a phosphor is mixed into this to form a phosphor suspension. In addition to the phosphor, this phosphor suspension contains, for example, nitrocellulose as a binder.

The phosphor suspension is then poured into the saddle bulb, excess liquid is drained, and a phosphor coating is applied. After that, hot air is blown through the saddle bulb to evaporate the solvent and dry the phosphor coating. The temperature of the hot air at this time is approximately 50°C. The saddle-shaped bulb is then fired in a furnace at approximately 500°C in order to remove the nitrocellulose as a binder contained in the phosphor coating. The saddle-shaped bulb having the phosphor coating formed as described above is completed as a saddle-shaped fluorescent lamp through a sealing process for attaching electrodes, an evacuation process, a mercury filling process, etc.

In the above process, several saddle-shaped fluorescent lamps were manufactured according to the above-mentioned method by changing the mixing ratio of butyl acetate and acetone, and the results shown in FIG. 2 were obtained. Curve a represents the evaporation rate of the mixed solvent, and curve b represents the drying time of the phosphor coating. In addition, the × mark indicates that the phosphor coating is cracked or the film thickness is uneven due to the fast drying speed, and the △ mark indicates that the drying time is too long, causing problems in lamp manufacturing or curved parts. The mark ○ indicates that the phosphor suspension has accumulated and the phosphor film is not properly formed, while the circle mark indicates that the drying time was appropriate and the phosphor film was well formed. Here, the drying time is compared with the drying time of a phosphor coating that is applied by applying a phosphor suspension containing only butyl acetate to a straight tube bulb before it is formed into a saddle shape. A short drying time was considered acceptable, and a long drying time was considered unsuitable.

As shown in Figure 2, using a mixed solvent of butyl acetate and acetone, the evaporation rate was set at 3.5× per minute.
By setting the concentration to 10 ^-3 g/cm ² or more and 6.5×10 ^-3 g/cm ² or less, an appropriate evaporation rate of the solvent could be obtained and a uniform phosphor coating could be formed. Moreover, the combination of solvents makes it possible to further shorten the drying time of the phosphor coating, thereby shortening the manufacturing time of the lamp and at the same time making it possible to downsize the manufacturing equipment for drying. Furthermore, by combining low-cost solvents, a low-cost solvent can be obtained.

As for the solvent, butyl acetate and acetone are used, but ethyl acetate or alcohol may also be used.

[Effects of the Invention] The present invention mixes two or more organic solvents with different evaporation rates into a phosphor suspension, and the evaporation rate is 3.5×10 ^-3 cm ³ /g or more per minute in an atmosphere of 20°C. 6.5×
Since it is adjusted to 10 ^-3 cm ³ /g or less, a uniform phosphor coating can be formed. Moreover, the solvent can also be obtained at low cost. Furthermore, it has many advantages such as shortened lamp manufacturing time and miniaturization of manufacturing equipment.

[Brief explanation of drawings]

FIG. 1 shows a perspective view of a saddle-shaped bulb used in an embodiment of the present invention, and FIG. 2 is a characteristic diagram showing the formation of a phosphor film when the present invention is applied to a saddle-shaped bulb. .

Claims (1)

[Claims] 1. Applying a phosphor suspension to the inner wall surface of a curved tube-shaped bulb to form a phosphor coating, drying the phosphor coating, and baking the dried phosphor coating. The phosphor suspension is prepared by mixing two or more organic solvents with different evaporation rates so that the evaporation rate is 3.5 per minute in an atmosphere of 20°C.
A method for forming a phosphor coating, characterized by using a mixed solvent adjusted to have a concentration of ^{10 -3} g/cm ² or more and 6.5 x 10 ^-3 g/cm ² or less.