How to choose colorants for nylon?

How to choose colorants for nylon?
Colorants are divided into two categories: pigments and dyes, of which pigments are divided into inorganic pigments and organic pigments. Due to the characteristics of nylon colorants have special requirements, today we mainly look at how to choose colorants for nylon.

1.About Nylon
(1) What are the characteristics of nylon?
Nylon has high mechanical strength, high softening point, heat resistance, low friction coefficient, wear resistance, self-lubricating, vibration absorption and muffling; oil resistance, weak acid resistance, alkali resistance and general solvents; good electrical insulation, self-extinguishing; non-toxic, odorless, weathering good; but poor dyeing.
(2) The main applications of nylon
One of the main uses of polyamide is used for synthetic fibers, its most prominent advantage is that the abrasion resistance is higher than all other fibers. Because polyamide is non-toxic, can be used as medical sutures.
As polyamide has a safe, lightweight, excellent mechanical strength, abrasion resistance and good corrosion resistance, so more and more used in place of copper and other metals, in machinery, chemical industry, instrumentation, automotive and other industries in the manufacture of bearings, gears, pumps and other parts.

In industry, nylon is used in large quantities to manufacture cord, industrial cloth, cable, conveyor belts, tents, fishing nets and so on.
In the defense industry as a parachute and other military fabrics preferred material.
2. Classification and performance comparison of colorants
Colorants are divided into two categories: pigments and dyes, of which pigments are divided into inorganic pigments and organic pigments. The performance comparison between them can be seen in the following table:

3. What are the properties of colorants for nylon?
(1) Heat and sunlight resistance:
So far there are many organic pigments, inorganic pigments and solvent dyes can be used in most thermoplastic engineering plastics coloring.
Resin processing temperature and colorant requirements:
Heat resistant, non-migrating not acidic or alkaline
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 far as organic pigments for plastics are concerned, in addition to certain requirements on their thermal stability, they also need to have good fastness to sunlight. Many organic pigments on the performance of polyamide melt will have a significant negative effect, so the organic pigments used for polyamide coloring have certain limitations.

(2) Chemical stability:
Colorants and resins should not be chemically reactive, should not promote the decomposition of the resin. For highly active resins such as polyamide resin (PA), its molten state shows reductivity, which tends to make the colorant change its color, so only a few colorants are available.
(3) Migration resistance:
There are three main types of migration of colorants.
(1) solvent extraction, that is, in water and organic solvents bleed color.
(2) contact migration, resulting in contamination of adjacent objects.
(3) Surface frosting, when heated, the solubility of colorant in polymer is larger, while at room temperature, the solubility of colorant is smaller.
Generally speaking, the dispersion of inorganic pigment in polymer is non-homogeneous, and will not produce frost phenomenon; while organic pigment has different degree of solubility in polymer and other organic matter, and it is easier to migrate.
(4) Color strength:
The size of the tinting power determines the amount of colorant used to achieve the target color. Generally speaking, the coloring power increases as the particle size of the colorant decreases. The coloring power of organic pigment is higher than that of inorganic pigment, and when color pigment and white pigment are used together, the coloring power can be improved significantly.
(5) Dispersibility:
Only when the colorant is uniformly dispersed in the polymer in the state of tiny particles, it can have good coloring effect. The pigment contains a lot of aggregated particles, it must be broken by high shear force to form small aggregates, so as to meet the requirement.
4. How to choose colorants for nylon?
Combined with the characteristics of colorants for nylon and the performance comparison table of several kinds of colorants:
Inorganic pigments are superior to organic pigments in terms of light resistance, weather resistance, migration resistance, chemical resistance, etc. They are generally applicable to plastics, but the color strength and brightness are much worse. However, the color strength and brightness are much worse. When good color is required, organic pigments are preferred. Besides, inorganic pigments have high reflective index and are often used in opaque products.
Compared with inorganic pigments, organic pigments show high color strength and vividness.PA processing temperature is high, the requirement of heat-resistant stability of pigments is also high, at the same time, PA resin shows strong reducibility when it is melted, which makes a lot of organic pigments for plastics unsuitable for use in nylon.

At present, organic pigments suitable for nylon, especially light-colored varieties, there is still a certain lack of in-depth study, so to match the more vibrant colors can only choose dyes.
Dyes are colorants that can be dissolved in water, oil or organic solvents, and they are generally organic compounds. The advantage of dyes is bright, eye-catching colors, full color spectrum, but the disadvantage is heat resistance, weather resistance, solvent resistance is poor, in the plastic processing temperature or higher temperature use of the process is easy to decomposition and discoloration. Although the temperature resistance of dyes is relatively poor, but in nylon after high temperature color will eventually stabilize, or can achieve a certain degree of brightness. In addition, dyes that are resistant to high temperatures are now being developed to meet demand.
Dyestuffs are the main coloring agents for textiles such as fibers and fabrics, and are less used in plastics, mainly in optical plastic products, which can make transparent plastics maintain good transparency.