How to choose colorant for nylon?
Colorants are divided into two categories: pigments and dyes, of which pigments are divided into inorganic and organic pigments. Because the characteristics of nylon have special requirements for colorants, 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 coefficient of friction, wear resistance, self-lubricating, shock absorption and noise dissipation; oil resistance, weak acid resistance, alkali resistance and general solvent resistance; good electrical insulation, self-extinguishing; non-toxic, odorless, good weather resistance; but poor dyeing.
(2) The main applications of nylon
One of the main uses of polyamide is for synthetic fibers, and its most outstanding advantage is that its abrasion resistance is higher than all other fibers. Because polyamide is non-toxic, it can be used as medical suture.
Because of its safety, light weight, excellent mechanical strength, wear resistance and good corrosion resistance, polyamide is increasingly used to replace copper and other metals in machinery, chemicals, instruments, automobiles and other industries to manufacture bearings, gears, pump leaves and other parts.
In industry, nylon is used in large quantities to manufacture cord, industrial cloth, cable, conveyor belt, tent, fishing net, etc.
In the defense industry as a parachute and other military fabrics preferred materials.
2. Colorant classification and performance comparison
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:
Organic pigments are characterized by the presence of color-emitting groups, which can be excited from the ground state to the excited state by selecting the absorption of visible light, thus making the molecules produce complementary tones.
Pigments whose main component is inorganic. Almost all inorganic pigments, which are compounds, are often complex mixtures
Compounds whose dyes absorb and transmit certain wavelengths of light, without scattering any of them. Are transparent
3. What are the properties required of colorants for nylon?
(1) Heat and sunlight resistance:
So far there are many organic pigments, inorganic pigments and solvent dyes can be used for most of the thermoplastic engineering plastics coloring.
Resin processing temperature and colorant requirements:
Resin
Processing temperature ( ℃ )
As can be seen from the table, the processing temperature of polyamide is very high, and the coloring agent used needs to have high heat resistance, and as far as the organic pigments for plastics are concerned, besides having certain requirements for their thermal stability, they 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:
Colorant and resin both should not occur chemical reaction, should not promote the decomposition of resin. For highly reactive resin such as polyamide resin (PA), its molten state shows reducibility, easy to make colorant change color, therefore, only a few colorants can be chosen.
(3) Migration resistance:
Migration of colorants are mainly three types.
(1) solvent extraction, that is, in water and organic solvents, color bleeding.
(2) contact migration, causing contamination of adjacent objects.
(3) Surface frosting, when heated, the solubility of the colorant in the polymer is larger, while at room temperature, the solubility of the colorant is smaller.
Generally speaking, the dispersion of inorganic pigments in the polymer is non-homogeneous, which will not produce the phenomenon of spraying frost; while organic pigments have different degrees of solubility in the polymer and other organic materials, which are more likely to migrate.
(4) Coloring power:
The size of coloring power determines the amount of colorant used to achieve the target color. Generally speaking, the coloring power increases with the decrease of colorant particle size. The coloring power of organic pigment is higher than that of inorganic pigment, when color pigment and white pigment are used, the coloring power can be improved significantly.
(5) Dispersibility:
Colorant in the polymer only in tiny particles state uniform dispersion, in order to have good coloring effect. Pigment contains a lot of aggregated particles, must use high shear force to break the large aggregates, the formation of small aggregates, so as to meet the requirements.
4. How to choose colorant for nylon?
Combined with the characteristics of colorants for nylon and the performance comparison table of several colorants:
Inorganic pigments are superior to organic pigments in terms of light resistance, weather resistance, migration resistance, chemical resistance, etc. They are generally suitable for plastics, but the color intensity and brightness are much worse. When good color is required, organic pigments are preferred. In addition, inorganic pigments have high reflection index and are often used in opaque products.
Organic pigments show high color intensity and vividness compared with inorganic pigments, and PA processing temperature is high, which requires high heat stability of pigments.
At present, organic pigments suitable for nylon, especially light-colored varieties, are still lacking and need to be studied in depth, so we can only choose dyes to match brighter colors.
Dyes, colorants that can be dissolved in water, oil or organic solvents, dyes are generally organic compounds. The advantages of dyes are bright colors, eye-catching colors, and a complete color spectrum, but the disadvantage is that heat resistance, weather resistance, and solvent resistance are poor, and easy to decompose and change colors during the processing temperature of plastics or higher temperatures. Although the temperature resistance of dyes is relatively poor, the color will eventually stabilize after high temperature in nylon, and can still achieve a certain degree of brightness. In addition, high temperature resistant dyes have been developed to meet the demand.
Dyes are the main coloring agent for textiles such as fibers and fabrics, and are less used in plastics, mainly in optical plastic products, which can make transparent plastics keep better transparency.
