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Plastic Pigments pearlescent pigment

Pearlescent Pigments in Plastic
Pearlescent pigments can be used in nearly all thermoplastics and most processes.Their effects are most 
intense in transparent resins like PS, PP, PE, PVC, acrylic,styrene-block copolymers, and silicone. It is 
also possible to attain pearlescence and luster in polymers having little or no transparency as with nylon, 
ABS&HIPS,but only with higher pigment loadings. Pearlescent pigments combined with dark absorption 
pigments in opaque polymers can yield a strong reflection color and produce pearl effects of great 
richness and depth. Highly filled plastics are not good candidates for pearlescent pigments because 
opaque fillers scatter light, eliminating the pearlescent effect.  Most users limit fillers to less than 1% in 
systems containing pearl pigments. Pearlescent pigments can be used in many thermosetting plastics,
including unsaturated polyester, acrylic,urethane,andepoxy as well as cast polyester cultured marble and 
onyx components for countertops, floors, furniture, and fireplace elements. Pearlescent pigments can also 
be added to cast acrylic sheet and alloyed or blended materials such as rubber-toughened polycarbonate, 
nylon/ABS, and PC/ABS. 

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Compounding Pearlescent Pigments in plastics
Pearlescent pigments can be master batched containing 25% pearlescent pigments (up to 50%)in most
resins by drum tumbling or mixing in twinshell, ribbon, or highspeed blenders. Pearlescent pigments are 
never ground or subjected to extended cycles or heavy shear because these can shear off the metal 
oxidecladding and damage the platelets.Banburytype or continuous mixers are most often used to create 
pearlescent masterbatches,although tworoll mills,calenders,vertical intensive mixers, and double planetary 
mixers are also suitable as long as you avoid excessive shear. Pearlescent pigments are usually 
incorporated in powdered polymers such as PVC  and PE by simple blending. Blending usually begins 
with organic pigments,followed by inorganic pigments, and lastly the  pearlescent pigments. 

Questions to note in the experiment

(1) in the mixing process, the pearlescent pigment should avoid the effect of high shear for a long time, so as to avoid damaging the flake crystal structure of pearlescent pigment and affecting the pearlescent effect of the product.

1.The transparency of the colored plastic resin is better (or highlights);

2. As far as possible, use pigments with good transparency to mix with pearlescent pigments;

3. As far as possible to reduce the damage of the processing process to the pearlescent pigment film;

4. The pearlescent pigment is fully dispersed and the pigment slice is parallel to the orientation of the plastic surface.

5. The properties and processing methods of plastic resin will also affect the gloss performance of the final product.

(2)Polyolefin is stabilized with phenolic antioxidants before processing.Special attention should be paid to the fact that when pearly pigments containing TiO2 (ordinary grade) are mixed with polyethylene hydrocarbons, the phenolic groups of antioxidants will interact with TiO2, resulting in yellowing.The company recommends the use of AY series (yellowing resistance) pearlescent pigments, AY series pearlescent pigments after special processing, to overcome the ordinary pearlescent pigments in the use of yellowing phenomenon.

(3)PVC  pearl pigment can be used for both hard PVC, but also can be used for soft PVC, PVC plastic material the higher the transparency, the greater the brightness.In the selection of stabilizer should ensure that the color and stability of the treatment still remain transparent, so as to better reflect the pearlescent effect.However, iron particles in some PVC formulations are likely to cause a decline in stability, because the use of iron mica type pearlite pigment, must be first stability test.

(4)Before processing to dry plastic (PMM, PC, PA) and other pearlescent pigments generally have low water content adsorption water.Hygroscopic plastics must be dried before use, so that the resin, pearlescent pigment with its masterbatch, the raw material and the final masterbatch drying is very important.In practice, the degassing port of twin screw extruder can be used as the outlet of moisture.

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Solution

1. improve the mixing effect of screw, so as to improve the pearl pigment dispersion uniformity;

2. using a larger L/D and add filter net, can improve the pearl masterbatch coloring effect;

3. Within the allowable range, increase the processing temperature and reduce the damage to the crystal structure of pearlescent pigment flakes;

4. in order to get a better pearlescent color, mold surface finish and mold gate design is very important.The smoother the mold, the more uniform alignment and smooth uniform pearlescent color.Single sprue is better than multiple sprue, the location of the sprue should usually be at the original thick location away from the flow barrier, and the space distance between the end of the sprue and the runner system should be as small as possible.