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Analysis of the relationship between plastic coloring effect and pigment particle size

Generally, the original pigment (like Pigment red 122, Pigment red 254, Pigment yellow 83)obtained in the pigment production process is called a wet cake, and further commercialization is required, including crushing, drying and other processes. During the drying process, the finer pigment particles agglomerate, making their particle size many times larger than the original particles. Therefore, they cannot be directly used for plastic coloring and must be dispersed. General commercial pigment particles are larger than aggregates and have a particle size of 250 to 750 μm (equivalent to passing through a 40 to 200 mesh sieve)

According to the German Standard Organization nomenclature, the state of pigment particles can be divided into: primary particles, aggregates and aggregates.

1. Primary particles

Existing single crystal particles as the smallest structural unit of the pigment, composed of ideal or actual single crystals,

2. Aggregates

The surface of the primary particles is adsorbed to each other. It is a composition of single crystal particles adjacent to the interface, and its surface area is smaller than the sum of the surface areas of the single crystal particles. The treatment of pigment is to pulverize the pigment aggregates to the size of the agglomerates.

3. Agglomerates

The surface area of a loose combination of primary particles or aggregates, or a mixture of the two on the sides and corners, is approximately equal to the sum of the surface areas.

It can be seen from the structure of the pigment model that there are always particles of different sizes, so for a pigment, the size of a single particle is meaningless, and the number of particles of different sizes should be indicated by its particle size distribution. The size of the pigment particles has a decisive significance for the coloring effect of plastics. Only when the pigment particles are pulverized to the size of an aggregate can the coloring strength, hue, gloss, hiding power, etc. can be improved. The particle size of the pigment after dispersion is appropriate, which can be explained with the following data. The pigment particle size is larger than 30μm, and the surface of the product has spots and streaks; 10 ~ 30μm, the product surface is matte; when the particle size is less than 5μm, it can be used for general products, and for fibers (monofilament diameter 10 ~ 30μm) and super For thin films (thickness less than 10 μm), the pigment particle size should be less than 1 μm.

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