JPS6339528B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a technique for reducing the alkali content on the inner surface of a glass tube. The invention also relates to a method of manufacturing a tube fluorescent lamp and a glass tube therefor. Fluorescent lamps generally consist of a sealed glass tube with an electrode at each end and an enclosure containing mercury and an ionizable gas, the inner surface of the glass tube being coated with a fluorescent material.

When glass tubes for such lamps are treated according to the invention, the brightness of the lamp is increased. It has thus been found that the efficiency of the lamp in units of lumens/watt is improved. The glass tube is also treated with acid gas at the time of drawing to reduce the alkali content of its inner surface. This reduction in alkali content results in an increase in lamp brightness.

The drawings schematically depict equipment that can be used to implement the invention.

In the drawing, a tank 1 contains molten glass 2. The molten glass 2 is drawn down around the mandrel 3 to form a soft glass bag 4 and then drawn by a traction device 5 to form a tube 6. This process is known and shown for example in US Pat. No. 2,009,793. The cylindrical container 7 contains acidic gas having the following pH. Examples of acid gases are hydrogen chloride or sulfur dioxide or nitrogen oxide (dinitrogen pentoxide). This gas flows through a pressure regulator 8 and a flowmeter-valve assembly 9, through an acid-resistant line 10, and into a feed line 11. Feed pipe 1
1 is placed inside the mandrel 3 and its lower end projects into the bag 4, where the gas is directed against the inner surface of the softened glass. At the high temperatures of the softened glass, for example about 800 DEG-950 DEG C., the gas reacts with the alkali ions in the glass to form water-soluble salts on the interior surface, which are detached from the glass matrix. This salt may be removed by a conventional cleaning process prior to applying the phosphor coating during the lamp manufacturing process, or by a similar rinsing operation if the glass is used for other purposes.

As a specific example, experiments were conducted using soda lime glass of the type commonly used to make fluorescent lamp tubes. Hydrogen chloride is used as the acidic gas, and this is applied to the feed pipe 11 at a flow rate of about 15/min.
It was introduced into bag 4 through it. Glass tube 6 was cut into 4 foot lengths to produce a fluorescent lamp. After cleaning, the inner surface of the glass tube was analyzed using an Auger electron microscope, and it was found that the amount of sodium on the surface was reduced to 1% by the acid gas treatment. On the untreated glass surface, the sodium content was 5%.

In a 40 watt cool white lamp made from acid-treated glass tubing, the initial brightness was 3206 lumens, an improvement of 26 lumens over the same lamp made from untreated glass tubing. The improvement in brightness over 100 hours was quite large, at 41 lumens.

In a 35 watt lamp with a conductive coating on the glass to improve lamp ignition, the improvement was even greater, with an initial lamp brightness of 48 lumens and a 100 hour improvement of 62 lumens.

[Brief explanation of drawings]

The drawing is a schematic illustration of an example of equipment used to carry out the invention. 1: tank, 2: molten glass, 3: mandrel, 4: bag, 5: traction device, 6: pipe, 7: gas container, 8: pressure regulator, 9: flow meter, 11: feed pipe.

Claims (1)

[Scope of Claims] 1. While drawing hot glass from the glass melt into a tube shape through a bag forming stage where the glass is above its softening temperature, a gas selected from the group of hydrogen chloride, sulfur dioxide and nitrogen oxide is added to the hot bag. forming a water-soluble alkaline salt on the inner surface of the hot glass; cooling and cutting the drawn tube to a predetermined length; and cleaning the cut tube to remove the water-soluble alkaline salt. coating the length of tube with a fluorescent material; and forming the coated length of tube into a fluorescent lamp. Production method. 2 The glass temperature at the point where the gas is introduced is 800
The method according to claim 1, wherein the temperature is ~950°C.