November 2014 Archives

Luminous paints are well-known for their application to alarm-clock dial plates."Phosphorescence" refers to the phenomenon whereby a material that is excited by some form of energy continues to produce light even after the excitation ceases.
The term "phosphor" refers to a material that is capable of exhibiting luminescence. Luminous paints are made by using phosphors with an exceptionally long afterglow time.

The cadmium sulfide type (CaS/Bi - using bismuth as an activator agent to cadmium sulfide; CaS+SrS/Bi) and the zinc sulfide type (ZnS/Cu, ZnS+CdS/Cu - using copper as an activator agent) are available as a phosphor. The luminescent color varies from blue to red (including blue, pale blue, green, yellow, orange, and reddish orange).

To use luminous paints, the phosphor is mixed with the vehicle at the point of use.Since these inorganic phosphors are crystallized, adding pressure or mixing by a roll mill will crush crystals and result in a degradation of the light luminance.Zinc/copper sulfide and cadmium sulfide/bismuth have an exceptionally long afterglow time and are used as a phosphor.

Phosphors used for luminous paints are shown in [Table 1].

[Table 1] Phosphor used for luminous paints

Luminous paints are excited by cathode rays, long/short wave ultraviolet, and X rays, and others. Based on the afterglow time dependence, they are classified into very short, short, long, and very long types.
Classification and application of luminous paints are shown in [Table 2].

[Table 2] Classification and application of luminous paints

Fluorescent paints are frequently used for accident prevention signs, advertising boards capturing consumers' attention, and posters, etc.

Luminescence or florescence refers to the phenomenon where absorbed energy is converted into another form of energy to emit light including visible radiation when a material receives light energy from the outside.
Fluorescence is a form of light emission that occurs only while the external energy is being absorbed. When the external energy disappears, the light also goes out.

The fluorescent material used for fluorescent paint is an organic substance called daylight fluorescent pigment that is made by dyeing synthetic resin with fluorescent paint.
The fluorescent dye emits fluorescence light when the concentration of dye solution is low. As the concentration increases, the fluorescence intensity increases as well. However, the intensity will decline once it has reached at a certain concentration level.

Synthetic resins that are used as a carrier of the fluorescent dye are as follows: polymethacrylic acid ester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, alkyd resin, aromatic sulfonamide resin, urea resin, benzoguanamine resin, polyamide resin, styrene resin, and their copolymers.
Examples of fluorescent dye are Brilliant Sulphoflavin FF and Fluorol Green Gold.

Fluorescent paint types are shown in [Table 1].
In recent years, the fluorescent dyes that are made up of glass powders (La₂O₃、ZnO、B₂O₃) and water-soluble binder (polyethylene oxide, hydroxyl cellulose, carboxymethyl cellulose, etc.) are available.

[Table 1] Type and Application of Fluorescent Paints