Performance requirements for nylon colorants
(1) Heat and sunlight resistance
So far there are many organic pigments, inorganic pigments and solvent dyes can be used to color most of the thermoplastic engineering plastics.
Resin processing temperature and requirements for colorants:
Heat resistance, non-migration not acidic and alkaline
As can be seen from the table, the processing temperature of polyamide is very high, the colorants used need to have high heat resistance, as far as organic pigments for plastics are concerned, in addition to its thermal stability requirements, but also need to have good sunlight fastness. Many organic pigments will have obvious negative effect on the performance of polyamide melt, so the organic pigments used for polyamide coloring have certain restrictions.
(2) Chemical stability
The colorant and resin should not have chemical reaction, and should not promote the decomposition of resin. For highly reactive resins such as polyamide resin (PA), its molten state shows reducibility, easy to make colorants change color, therefore, only a few colorants can be chosen.
(3) Migration resistance
There are three main types of migration of colorants.
Solvent extraction, that is, in water and organic solvents leaching color.
Contact migration, resulting in the contamination of adjacent objects.
Surface frosting, when heated, the solubility of colorants in the polymer is larger, while at room temperature, the solubility of colorants is smaller.
Generally speaking, the dispersion of inorganic pigments in the polymer is non-homogeneous, and will not produce frosting; while organic pigments have different degrees of solubility in the polymer and other organic materials, and are more likely to migrate.
(4) Coloring power
The size of coloring power determines the amount of coloring agent to achieve the target color. Generally speaking, the coloring power increases as the particle size of colorant decreases. The coloring power of organic pigment is higher than that of inorganic pigment, and when the color pigment is used with white pigment, the coloring power can be improved significantly.
(5) Dispersibility
The colorant in the polymer can only have good coloring effect if it is evenly dispersed in tiny particle state. Pigment contains many aggregated particles, must use high shear force to break the large aggregates, the formation of small aggregates, so as to meet the requirements.
