Plastic

The basic raw material of pearlescent pigments is natural mica. Mica is carefully ground into fine powders of different particle sizes, and then coated with titanium dioxide to form coatings of different thicknesses, and then fired at a high temperature above 700 degrees Celsius and special treatments to make translucent, very stable, almost It is a chemically inert pearlescent pigment. They are not affected by temperature during application. Its flaky structure will not precipitate, bloom or melt in the resin.

Pearlescent pigments are non-toxic and do not contain metal components. They completely rely on chemical principles to form different colors. By controlling the particle size of the mica and the thickness of the coating layer, a series of white, metallic and golden pearlescent pigments with different particle size ranges can be obtained.

1. Features

       Compared with other pigments, pearlescent pigments have an incomparable soft pearl luster. The special surface structure, high refractive index and good transparency enable it to create the same effect as pearl luster in a transparent medium.

The excellent chemical, thermal and mechanical properties of pearlescent pigments provide it with the possibility of being widely used in paints, inks, plastics and various fields. They provide a whole new color quality for these products. Pearlescent powder is non-toxic and harmless to the human body. Therefore, it can be used for food packaging and children's toys. Dilute acids and alkalis cannot attack pearlescent pigments. Pearlescent pigments are harmless to the environment, because they are practically insoluble in water and do not contain any heavy metals, which are of a grade that is harmless to water quality. Pearlescent products cannot burn, spontaneously combust, do not conduct electricity, and can withstand high temperatures of 800°C. Pearlescent products can also be used in reactive coatings for radiation curing systems (electron beam curing, light curing). The chemical structure of pearlescent products makes them have excellent dispersion properties and can be applied to water-based coatings.

2. Material selection

       Since the pearlescent pigment itself is translucent and needs to rely on the reflection of external light to achieve a good pearlescent effect, when choosing plastics, materials with better transparency should be used as much as possible. The following plastics are more commonly used, and their common point is that they are relatively transparent. After adding pearlescent pigments, light can pass through the surface plastic to reach the surface of the pearlescent pigment chip and cause reflection and refraction. Polyethylene HDPE, LDPE, polypropylene PP, acrylic PMMA, saturated polyester PET, polycarbonate PC, polyvinyl chloride PVC, unsaturated polyester AK, epoxy resin EPT, polyurethane PU-like, low-transparency or opaque plastics such as ABS, etc., the pearlescent effect is not obvious, but this does not mean that these plastics cannot use pearlescent pigments, but the amount of pearlescent pigments is relatively large.

       In terms of the choice of mixed pigments, pearlescent pigments cannot be mixed with conventional opaque pigments (such as chromium, cadmium pigments, and titanium dioxide). Pearlescent pigments can be used for transparent and translucent plastic resins. The use of pearlescent pigments will bring a charming color visual effect. Pearlescent pigments are widely used in cosmetic containers, various packaging, toys, decorative materials, various films and other plastic products.

3. Coloring of plastic resin by pearlescent pigment

       There are many ways to color thermoplastic resins. Among them, the pearlescent masterbatch is excellent. Although direct coloring is simple, the quality is difficult to guarantee.

1. Direct coloring of resin powder

       When the powder is colored, it is only necessary to directly add the pigment to the kneader and mix evenly. This type of kneader has two types: drum type and high-speed type. When using a high-speed kneader, add ordinary pigments and other additives to the resin powder and mix evenly. Add pearlescent powder before the end of the mixing. This is because the lamellae structure of pearlescent pigments is easily damaged under the action of high shearing force. , Affect the pearlescent effect.

2. Directly color the resin pellets

       Pearlescent pigments cannot be directly added to the resin pellets, but a liquid coupling agent must be used to fix them on the surface of the resin particles to produce a physical or chemical combination. Such coupling agents include various softeners and refined mineral oils. In addition, the wettability of the interface can be improved by adding emulsifiers or high-boiling solvents. Under normal circumstances, the amount of coupling agent added is 0.2-0.5% of the amount of resin. If the pearlescent pigment is more uniformly dispersed in the resin, 1% of low molecular weight polyethylene powder can be added to the pigment and resin mixture.

       With this method, the larger additive amount is 2%. If this amount is exceeded, the excess pigment can only be scattered because there is no space on the resin surface to continue to adsorb.

3. Liquid solidification and mixing

       Pearlescent pigments can also be pre-mixed with solvents, additives, and organic pigments to make liquid pigments, that is, pearlescent paste. For pulping with organic pigments, the organic pigments should be ground to the specified fineness before mixing with pearlescent pigments. Pearlescent paste should pay attention to the precipitation of pearlescent pigments, use appropriate anti-settling additives, and stir evenly before application to ensure the uniformity of the concentration of pearlescent pigments in the paste.

4. Coloring with pearlescent masterbatch

       The masterbatch method has a good coloring effect. Ordinary coarse and fine resin powders can be used to prepare color masterbatches. Because pearlescent powder will reduce the melt index after adding, generally use higher melt index, stronger fluidity, and similar polymers with lower molecular weight than the colored resin as pigments. Carrier. There are two methods for the preparation of masterbatch: continuous and intermittent. The general industrial production is continuous production with double screw extruder.

Four, application precautions

      Because pearlescent pigments have different characteristics from ordinary pigment processing and use. Generally, to get an excellent pearlescent effect, the following conditions must be paid attention to:

① The transparency of the colored plastic resin is better (or high brightness)

② Try to mix the pigments with good transparency and pearlescent pigments as much as possible

③ Minimize the damage to the pearlescent pigment flakes during processing

④ The pearlescent pigments are fully dispersed and the pigment flakes are oriented parallel to the plastic surface.

In addition to the above conditions, the characteristics and processing methods of the plastic resin will also affect the gloss performance of the product