Daylight Fluorescent Pigments: The attractiveness of daylight fluorescent pigments is incomparable with ordinary pigments. It has exceptional brightness, which makes people look particularly eye-catching and dazzling. For example, the spectral reflection curves of two orange pigments (a common pigment, a fluorescent pigment). It was measured with a modified spectrophotometer. The sample was first irradiated with white light and then measured with a photocell. It can be seen that the absorption of both can reach up to 600 nm, and thereafter, the two are rapidly rising. The curve of the fluorescent pigment reaches the highest peak at 625 nm. Here, it is “obvious reflection†and it is about incident light. More than twice. The obviousness of the peak indicates that the fluorescent pigment has a relatively high purity or saturation. The amount of ultraviolet light, blue light, and green light in the light source significantly affects the amount of fluorescence.
The spectrophotometric data can also be converted to tristimulus values ​​(tristimulus values), and then in C. I. E marked on the color map. It can be seen that almost all daylight fluorescent pigments have a relatively high excitation purity and are close to the spectral trajectory at the edges of the graph. Lemon yellow, yellow orange and red orange have more than 90% purity and are close to the spectral trace. Although some common pigments have similar purity, they are relatively dark (low brightness).
This figure can be thought of as a color cone, the bottom of the brightness is low, 90 ~ 100% of the brightness in the upper part. A bright, general orange pigment with a brightness of about 15%, but with a similar hue and purity to a daylight fluorescent pigment, its brightness can be as high as 55%. On the other hand, most daylight fluorescent pigments are in C. I. E color is three-dimensional, so they are called a new area in color.
The characteristic data of some representative fluorescent pigments are shown in the table below.
Items
Data
Density (g/cm3)
1.36
Oil absorption (g/100 g)
47-54
Decomposition point (°C)
180-200
Softening point (°C)
145-155
Refractive rate
1.64
Impermeability (water)
excellent
Impermeability (Ethanol)
Good can
Impermeability (methyl ethyl ketone)
difference
Impermeability (mineral oil)
excellent
Impermeability (linseed oil)
excellent
Impermeability (Toluene)
difference
Impermeability (dioctyl phthalate)
Good can
Alkali resistance
Possible - poor
Acid resistance (oxidant, reducing agent)
Good can
Lightfastness
Possible - poor
Average particle size (microns) standard
3-4 (40-50 maximum)
Average particle size (microns) Medium
2.5 (maximum 10-15)
Average particle size (microns) ultrafine
1.2-1.4 (max 4-5)
Note: Within the average particle size, the data in parentheses is the largest particle data.
Fluorescent dyes only fluoresce in relatively dilute solutions, and after exceeding a suitable concentration, fluorescence extinguishes due to molecular collisions, re-absorption of emitted light, or other processes. If the solution is frozen into a hard glass, no emission deactivation effect is greatly prevented. Therefore, when the solution is changed from a solution state to a plexiglass or a solid state of a plastic, fluorescence is enhanced. Some resins have been found to have no flow effect on the dye molecules. They not only enhance fluorescence but also improve light fastness.
Some of the major daylight fluorescent pigments are prepared by adding a dilute solution of a dye to a triazine-modified sulfonamide resin. This type of resin is a very brittle organic glass, which is formed by the condensation of tosylamine-formaldehyde with a triazine such as melamine or benzoguanamine.
Fluorescent pigments can also be prepared by adding fluorescent dyes to modified glycerine, phthalic acid or vinyl resins.
A few organic compounds also exhibit fluorescent phenomena in the undissolved state, such as some aromatic aldehydes such as aldehyde-linked nitrogen (2-hydroxy-1-naphthaldehyde).
In the characteristic data of fluorescent pigments, the particle size is a very important indicator. Especially for the ink industry, the fluorescence of the pigment is very strong, but when the particles are too large to print, isn't it too?
Since the resin used as a fluorescent pigment at room temperature has a low hardness and toughness, it is not easy to finely pulverize the pigment particles. To improve its hardness and brittleness, it is easy to crush, so low-temperature (cold) smashing is one of the better processes.
The standard particle size is generally 3.5 μm, which can be used in the coating industry. The medium size particle size can be used for gravure printing inks and fabric inks. The ultrafine particle size is mainly used for offset printing, lead printing and flexographic inks. Among them, the smallest particle size can reach 0.25-0.5 microns.