JPS6243301B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a phosphor layer on a tube, which uses a phosphor suspension in water as a solvent to form a good phosphor layer on the inner surface of the bulb of the tube. It is something.

Conventionally, when forming a phosphor layer on the inner surface of a bulb such as a fluorescent lamp or a fluorescent mercury lamp, phosphor powder was mixed into a lacquer obtained by dissolving nitrified cotton in an organic solvent such as butyl acetate. A phosphor suspension in which phosphor is suspended is applied to the inner surface of the bulb and allowed to dry naturally to form a phosphor coating.Next, organic matter such as nitrified cotton remaining in this phosphor coating is removed. Methods such as burning and removing the phosphor were used, but while this method was easy to form a phosphor coating and produced a good phosphor layer, it was highly flammable, toxic, and expensive. It has the disadvantage that organic solvents must be used. In order to solve this drawback, in recent years a phosphor suspension, in which phosphor powder is suspended in a water-soluble lacquer obtained by dissolving a water-soluble organic polymer material such as hydroxyethyl cellulose in water, has been used inside the bulb. A method has been developed to form a phosphor coating film by applying it to the surface and forcing it to dry, and has already entered the stage of practical application. However, the water-soluble lacquer has poor dispersibility of the phosphor compared to the above-mentioned organic solvent lacquer. In order to form a phosphor suspension, it is necessary to subject the phosphor suspension to a mechanical dispersion means such as a ball mill or a colloid mill. For this reason, the phosphor particles are crushed more than necessary, and as a result, the phosphor layer that is finally formed has the disadvantage that the luminous efficiency inevitably decreases compared to when an organic solvent is used. Ta.

The present invention has been made in order to eliminate the above-mentioned drawbacks, and provides a method for forming a good phosphor layer that does not reduce luminous efficiency even when using a water-soluble lacquer compared to when using an organic solvent lacquer. The purpose is to provide

The present invention provides a phosphor suspension obtained by dispersing a phosphor in a water-soluble lacquer in which a non-dissociable water-soluble polymer substance is dissolved in water, and adding an ammonium salt of polycarboxylate as a dispersant. is applied to the inner surface of the tube bulb and forcedly dried under certain conditions to form a phosphor coating film, and this bulb is heated to combine with the organic polymer substance remaining in the phosphor coating film, which is the phosphor material. This method is characterized in that the above-mentioned dispersant is removed by combustion.

Various attempts have been made to improve the dispersibility of the phosphor by adding a dispersant to a phosphor suspension using a water-soluble lacquer. Nonionic surfactants are mainly being studied with solubility in mind. The present inventors further investigated various aspects including ionic surfactants and also taking into account the combination with lacquer materials. As a result, the present inventors used a non-dissociable water-soluble polymer substance as the lacquer material to fluoresce. By making a phosphor suspension and adding polycarboxylic acid ammonium salt, which is a type of anionic surfactant, as a dispersant, a stable phosphor suspension with an extremely good dispersion state can be obtained. I discovered that.

Polycarboxylic acid ammonium salt is Water-soluble polymeric substances with a structure such as the one with a large value of n, that is, those with a high molecular weight (those with a molecular weight of 100,000 or more), have a large thickening effect when dissolved in water, so for example, As shown in Publication No. 47-25686, it is sometimes used as a material for water-soluble lacquer. Also, since it has a hydrophilic group and a lipophilic group in its molecule, it also has properties as a surfactant, especially low molecular weight ones with a small n value (those with a molecular weight of about 500 to 5000).
It is known to work effectively as a dispersant under certain conditions. Moreover, this ammonium polycarboxylate easily thermally decomposes and volatizes when heated, so it is used as a dispersant to be added to the phosphor suspension to form a phosphor layer in the manufacturing process of tubes such as fluorescent lamps. It is suitable as However, since the above ammonium polycarboxylate dissociates into ions when dissolved in water, it tends to become unstable if it coexists with other electrolytes in a dispersion system.
It has the property that the dispersion effect decreases rapidly. Therefore, when used as a dispersant for a phosphor suspension, in order to maximize its dispersion effect, it is necessary to ensure that the water-soluble polymer used as the lacquer material does not react with the ammonium polycarboxylate at all. You need to limit it to things that you won't do. As a result of various studies from the above viewpoints, we found that ammonium polycarboxylate was added to a phosphor suspension using a non-dissociable water-soluble polymer substance such as hydroxyethyl cellulose or polyethylene oxide as a lacquer material. It has been found that a phosphor suspension with the best dispersion state can be obtained when it is added as a dispersant.

Examples will be described below.

1 kg of phosphor powder was suspended in a water-soluble lacquer made by dissolving 30 g of hydroxycellulose in 1.5 ml of pure water, and 0.3 g of polycarboxylic acid ammonium salt (trade name: Dispex A40, manufactured by Allied Colloids Ltd., UK) was added as a dispersion, followed by stirring. The phosphor suspension is poured onto the inner surface of a 40W fluorescent lamp bulb and dried by blowing hot air at 70°C at a speed of approximately 5 m/sec to form a phosphor coating. Next, this valve is passed through a furnace heated to 600°C to burn off the hydroxyethyl cellulose used as a lacquer material and the polycarboxylic acid ammonium salt used as a dispersant remaining in the coating film. After that, we manufactured a 40W fluorescent lamp using the same method as a general fluorescent lamp manufacturing method, and found that the uniformity of the phosphor layer, the brightness at the initial stage of lighting, and the luminous flux maintenance rate were all improved using organic solvents. The result was a product that was completely comparable to conventional lamps of the same type in which a body layer was formed.

In addition, as a result of various studies by changing the amount of polycarboxylic acid ammonium salt added in addition to the above examples,
A suitable addition amount was in the range of 0.001% to 0.1% based on the phosphor. If the amount added is less than 0.001%, the effect of improving the dispersibility of the phosphor will not be sufficient, and therefore the uniformity of the formed phosphor layer will be difficult.
If it exceeds 0.1%, it will be difficult to completely burn and remove it in the firing process, and there is a risk that carbon will remain in the formed phosphor layer.

As described above, according to the present invention, even if a water-soluble lacquer is used, there is no need to apply mechanical dispersion means such as a ball mill to the phosphor suspension as in the conventional method, so phosphor particles are necessary. The phosphor layer is not pulverized more than that, and therefore, it is possible to produce a phosphor layer whose luminous efficiency is not lowered compared to a phosphor layer produced by a conventional method using an organic solvent.

Claims (1)

[Scope of Claims] 1. A phosphor suspension in which a phosphor is suspended in a water-soluble lacquer in which a non-dissociable water-soluble organic polymer substance is dissolved in water, and an ammonium salt of polycarboxylate is added as a dispersant. A method for forming a phosphor layer in a tube, comprising the steps of applying a slurry to the inner surface of a tube bulb and drying it, and heating the bulb to burn off the organic polymer substance and dispersant. . 2. A method for forming a phosphor layer in a tube according to claim 1, characterized in that the amount of polycarboxylic acid ammonium salt added is 0.001% to 0.1% based on the phosphor.