Fluorescent pigment properties, uses and production processes
Fluorescent pigments are a class of organic pigments that fluoresce after photoexcitation. The source used for excitation can be either ultraviolet light or daylight. This pigment glows and cannot last in the dark. Fluorescent insoluble or poorly soluble solvent pigments containing oxides, sulfides, silicates, and tungstates such as calcium, barium, magnesium, and cadmium, plus a small amount of flux and trace activator The formulated mixture is calcined. The color of the fluorescence depends on the nature of the activator and the composition of the luminescent pigment. For example, cadmium sulfide is added to the zinc sulfide fluorescent pigment, and the blue color is transferred to the red portion by using silver as an activator. Transfer from green to red with copper as the activator. Commonly used in the manufacture of fluorescent coatings and plastics. Fluorescent pigments that are excited by sunlight are commonly known as phosphors, which are pigments made by dissolving a water-soluble fluorescent dye in a resin. Such dyes are mainly basic dyes such as alkaline yellow O (C.I. basic yellow 2), alkaline rose essence (C.I. alkaline purple 10), and the like, and individual acid dyes can also be used for this purpose. The specific method is as follows: the dye is dissolved in a mixture of melamine-p-toluenesulfonamide-formaldehyde, the dye is contained in the resin after being polymerized into a resin, and the dried resin is ground into a fine powder to obtain a fluorescent pigment of daylight type. . Its characteristic is that the color light is unusually bright, but the light fastness and heat fastness are poor. Fluorescent pigments excited by ultraviolet light are mostly water-insoluble organic compounds, such as dispersed fluorescent yellow FFL (CI dispersed yellow 124), dispersed fluorescent yellow D (CI dispersed yellow 11), dispersed fluorescent yellow S (CI solvent yellow 98), dispersed fluorescence Red S (CI Disperse Red 303), etc. The color of such fluorescent pigments is not very bright, and only when dissolved in a substrate at a low concentration, it exhibits dazzling fluorescence. According to the principle of fluorescence emission, the fluorescent pigment visible to the naked eye has a chromatogram of yellow, orange and red. The blue and green fluorescent pigments sold on the market are actually compounded after the addition of the fluorescent whitening agent to the blue and green pigments. Fluorescent pigments are mainly used in plastics, inks, coatings, and stationery to improve decorative effects, and have recently been used to make solar energy gathering materials.
Fluorescence is a process of photoluminescence. In this process, short-wavelength electromagnetic waves in the ultraviolet or visible light band are absorbed and released as long-wavelength electromagnetic waves. The latter usually falls within the visible range and superimposes with conventionally reflected light, thus revealing a dazzling fluorescent color.
(1) Generally, fluorescent pigment molecules contain a group that emits fluorescence, such as a carbonyl group, a nitrogen-nitrogen double bond, a carbon-nitrogen double bond, and the like.
(2) The molecule contains a color-assisting group. The coercive group red shifts the spectrum and increases the fluorescence efficiency, such as primary amino groups, secondary amine groups, hydroxyl groups, ether bonds, amide groups, and the like.
(3) A conjugated π bond containing a rigid planar structure in the molecule. The greater the in-molecular conjugate system, the stronger the planarity and the higher the fluorescence intensity. Some factors that increase the degree of conjugation increase the fluorescence efficiency and shift the fluorescence wavelength toward the long wavelength.
Anti-fluorescent pigment fading and fading additive
The auxiliaries for preventing fading of fluorescent pigments mainly include wetting and dispersing agents, light stabilizers, antioxidants and the like.
(1) Wetting and dispersing agent improves the surface characteristics of fluorescent pigments, improves the compatibility of fluorescent pigments with binders, and improves the processing properties of fluorescent pigments.
(2) Light stabilizers provide long-lasting stability against fading of fluorescent pigments.
(3) Antioxidants are generally reducing substances that prevent the absorption of oxygen by fluorescent pigments.