1、 Coloring:
Plastic coloring can also give plastics a variety of functions, such as improving the light resistance and weather resistance of plastics; Give plastics some special functions, such as conductivity and antistatic; Different colored agricultural land films have the functions of weeding or avoiding insects and raising seedlings. That is, through color matching and coloring, it can also meet the requirements of some applications.
2、 Colorant:
Colorants are mainly divided into pigments and dyes. Pigment is a colorant that cannot be dissolved in ordinary solvents. Therefore, in order to obtain ideal coloring performance, it is necessary to evenly disperse the pigment in plastic by mechanical method. According to the structure, it can be divided into organic pigments and inorganic pigments. Inorganic pigments have excellent thermal stability and light stability, low price, but relatively poor coloring power and high relative density; Organic pigments have high coloring power, bright color, complete chromatography and low relative density. Their disadvantages are that they are inferior to inorganic pigments in heat resistance, weather resistance and covering power. Dyes are organic compounds that can be used in most solvents and dyed plastics. They have the advantages of low density, high coloring power and good transparency, but their general molecular structure is small and easy to migrate during coloring.
White pigments mainly include titanium dioxide, zinc oxide and lithopone. Titanium dioxide can be divided into rutile and anatase. Rutile titanium dioxide has high refractive index, high hiding power, stability and good weather resistance.
Carbon black is a commonly used black pigment. It is cheap, and it also has the function of ultraviolet protection (anti-aging) and conduction of plastics. Different production processes can get different kinds of carbon black with a wide range of sizes, and the properties differ greatly. Carbon black can be divided into pigmented carbon black and rubber reinforcing carbon black according to its use. Pigmented carbon black can be divided into high pigmented carbon black, medium pigmented carbon black and low pigmented carbon black according to its coloring ability. Carbon black particles are easy to aggregate. To improve the coloring power of carbon black, we should solve the dispersion of carbon black.
Pearlescent pigment, also known as mica titanium pearlescent pigment, is a kind of mica wafer coated with titanium dioxide. According to different hues, it can be divided into silver white pearlescent pigments, rainbow pearlescent pigments and color pearlescent pigments.
3、 Color matching and coloring process:
Coloring can be done by adding toner directly to resin and masterbatch.
After the toner is directly mixed with plastic resin, it is sent to the next product forming process, which has short process and low cost, but the working environment is poor, the coloring force is poor, the coloring uniformity and quality stability are poor.
The color masterbatch method is a granular material with a certain concentration of colorant prepared from colorant, carrier resin, dispersant and other additives. When the product is formed, a certain amount of color masterbatch is added according to the coloring requirements to make the product contain the required coloring dose and meet the coloring requirements.
Color masterbatch can be classified according to the resin to be colored, such as ABS Color Masterbatch, PC Color Masterbatch, PP Color Masterbatch, etc; It can also be classified according to the coloring resin plus process, including injection molding, film blowing and extrusion masterbatch. Because the pigment is pretreated first, the color masterbatch has high coloring power, the dosage can be reduced, the quality is stable, the transportation, storage and use are convenient, and the environmental pollution is greatly reduced.
The dispersant removes surface air by wetting and penetrating the pigment, disperses the condensate and aggregate into fine, stable and uniform particles, and will no longer agglomerate in the processing process. The common dispersant is low molecular weight polyethylene wax, and EVA wax or oxidized polyethylene wax is used for organic pigment and carbon black that are difficult to disperse, The synthesis of low molecular weight polyethylene wax is very different from that of polyethylene cracking. Other additives include coupling agents, antioxidants, light stabilizers, antistatic agents, fillers, etc. the amount of additives depends on the requirements and varieties, which is called multi-functional masterbatch. For example, adding brighteners is conducive to demoulding of molded products and improving the surface brightness of products.
The performance indexes of Color Masterbatch include color difference, whiteness, yellowness, yellowness, thermal stability, oxygen index, melt flow rate, etc.