Nylon colorants Performance requirements
(1) Heat and light resistance
So far, many organic pigments, inorganic pigments and solvent dyes can be used for coloring most thermoplastic engineering plastics.
Resin processing temperature and colorant requirements:
Heat-resistant, non-migrating and non-acidic
As can be seen from the table, the processing temperature of polyamide is very high, and the colorants used need to have high heat resistance. As for organic pigments for plastics, in addition to certain requirements for their thermal stability, they also need to have Better light fastness. Many organic pigments have significant negative effects on the performance of polyamide melts, so there are certain restrictions on the organic pigments used for polyamide coloring.
(2) Chemical stability
The colorant and the resin should not react chemically or promote the decomposition of the resin. For highly reactive resins such as polyamide resin (PA), its molten state shows reducing properties, which easily causes the colorant to change color. Therefore, there are only a few colorants to choose from.
(3) Migration resistance
There are three main types of colorant migration:
Solvent extraction, i.e. color bleeding in water and organic solvents;
Contact migration, causing contamination of adjacent objects;
When the surface is frosted, the solubility of the colorant in the polymer is greater when heated, but the solubility of the colorant is smaller at room temperature.
Generally speaking, the dispersion of inorganic pigments in polymers is heterogeneous and will not cause blooming; while organic pigments are dissolved to varying degrees in polymers and other organic matter and are relatively prone to migration.
(4) Coloring Power
Tinting power determines the amount of colorant used to achieve the target color. Generally speaking, tinting power increases as the colorant particle size decreases. The tinting power of organic pigments is higher than that of inorganic pigments. When color pigments and white pigments are used together, the tinting power can be significantly improved.
(5) Dispersion
Only when the colorant is uniformly dispersed in the state of tiny particles in the polymer can a good coloring effect be achieved. Pigments contain many aggregated particles, and high shear force must be used to break large aggregates into small aggregates to meet the requirements.
