Optical characteristics analysis of luminescent pigments for inks

Daylight fluorescent pigments: The attractiveness of daylight fluorescent pigments is unmatched by ordinary pigments. It has exceptional brightness, which makes people look particularly eye-catching and glaring. For example, the spectral reflectance curves of two orange pigments (a common pigment, a fluorescent pigment). It is measured by a modified spectrophotometer. The sample is first irradiated with white light and then measured by a photocell. It can be seen that the absorption of both can reach 600nm, and then the two rise rapidly. The curve of the fluorescent pigment reaches the highest peak at 625nm. Here, it is "obvious reflection", which is about incident light. More than twice as much. The apparent nature 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 will significantly affect the amount of fluorescence.

Spectrophotometric data can also be converted to tristimulus values (tristimulus values) and then at C. I. It is indicated on the E chromaticity diagram. It can be seen that almost all of the fluorescent pigments have a relatively high excitation purity and are close to the spectral trajectory at the edge of the image. Lemon yellow, yellow orange and red orange have a purity of more than 90% and are close to the spectral trajectory. Although some general pigments have similar purity, they are darker (lower brightness).

This figure can be thought of as a color cone with a low brightness at the bottom and 90 to 100% brightness at the top. A bright, generally orange pigment with a brightness of about 15%, but a daylight fluorescent pigment with a similar hue and purity, can be as bright as 55%. On the other hand, most of the fluorescent pigments are in C. I. E colors are outside the stereo, so they are called a new field in color.

The characteristic data of some representative fluorescent pigments are shown in the table below.

Project data

Density (g/cm3) 1.36

Oil absorption (g / 100g) 47-54

Decomposition point (°C) 180-200

Softening point (°C) 145-155

Refractive (shot) rate 1.64

Impermeability (water)

Impermeability (ethanol) Good - can

Impermeability (methyl ethyl ketone)

Impermeability (mineral oil)

Impermeability (linseed oil)

Impermeability (toluene) difference

Impermeability (dioctyl phthalate) good - can

Alkali resistance

Acid resistance (oxidant, reducing agent) Good - can

Lightfastness

Average particle size (micron) standard 3-4 (maximum 40-50)

Average particle size (micron) medium 2.5 (maximum 10-15)

Average particle size (micron) superfine 1.2-1.4 (maximum 4-5)

Note: Within the average particle size item, the data in parentheses is the largest particle data.

Fluorescent dyes only fluoresce in relatively dilute solutions. After a suitable concentration, the fluorescence is extinguished due to molecular collisions, reabsorption of emitted light or other processes. If the solution is frozen into a hard glass, the no-deactivation and deactivation effect is greatly prevented. Therefore, when changing from a solution state to a plexiglass or a plastic solid state, the fluorescence is enhanced. Some resins have been found to have a non-flowing effect on dye molecules, which not only enhance fluorescence, but also improve light fastness.

Some of the major daylight fluorescent pigments are prepared by adding a dilute solution of the dye to a triazine-modified sulfonamide resin. This type of resin is a very brittle organic glass which is formed by the condensation of toluenesulfonamide-formaldehyde with a triazine such as melamine or benzoguanamine.

Fluorescent pigments can also be prepared by adding a fluorescent dye to a modified glycerin, phthalic acid resin or vinyl resin.

A few organic compounds also exhibit fluorescence when they are in an undissolved state, such as the aldehyde nitrogen (2-hydroxy-1-naphthaldehyde) of some aromatic aldehydes.

In the characteristic data of fluorescent pigments, particle size is a very important indicator. Especially for the ink industry, although the fluorescence of the pigment is very strong, when the particles are too large to be printed, is it not awkward?

Since the resin used as a fluorescent pigment at normal temperature is low in hardness and tough, it is difficult to pulverize the pigment particles to be fine. In order to improve its hardness and brittleness, it is easy to pulverize, so low temperature (cold) pulverization is one of the better processes.

The standard system has a particle size of typically 3.5 microns and is used in the coatings industry. Medium particle sizes can be used for gravure inks and fabric inks, while ultrafine cell sizes are used primarily for offset, offset and flexographic inks. Among them, the smallest particle size can reach 0.25-0.5 microns.