Best Gold Pearlescent Pigment Solutions

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Jiangsu Pritty Pearlescent Pigment
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223800 Suqian, China



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Plastic Injection Molding

Injection molding is the second most used manufacturing process for producing shapes by injecting molten or viscous material under pressure into a specially designed mold. Most people are familiar with plastic injection molding however a wide range of materials can be used with the injection molding process such as metals, glasses, elastomers, confections (candy), and most commonly used thermoplastic and thermosetting polymers.


A brief overview of the the plastic injection molding process, plastic material in the form of beads, what are called “nurdles” (often called “resin” in the industry) is gravity fed from an overhead hopper into a barrel containing a rotating screw which forces the material into a heated zone of the barrel where it’s melted, mixed and forced under high pressure into a mold cavity filling it completely. When the plastic has cooled sufficiently and hardens, retaining the shape of the cavity, and the mold is opened and the molded shape is ejected.


Additives such as colourants, UV inhibitors and effect pigments are often used and can be mixed into the beads prior to arriving at the hopper which then is called a “Masterbatch”. It’s important to understand effect pigments differ substantially from organic pigments as effect pigments are comprised of non-homogenous individually structured platelets within a set range of sizes which give the pearlescent effect as opposed to organic pigments which are a homogenous mass which retains its colour no matter how finely its ground. Therefore when using effect pigments care must be taken with the mixing and the extrusion process such as screw speed and filters to not damage the effect pigment platelets from exerting excessive shear force which will dramatically reduce the pearlescent lustre effect.



Plastic injection molding has much in common with plastic extrusion process from the point of view of how the plastic is fed into the machine but differs as injection molding is not a continuous process while plastic extrusion is a continuous process. Additionally the plastic extrusion process will have the tendency to align the effect pigment all in the same plane as the molten mass is flowing in one direction thus giving optimal optical iridescence effects. However with injection molding the flow of the molten mass filling the mold cavity does not flow in only one direction and therefore this may cause the orientation of effect pigment platelets to change from their desired ideal alignment. This will cause what are called in the industry “flow lines” and “weld lines” where the edges of molten mass in filling the mold cavity meet together. The solution is a well-engineered mold taking into consideration the flow characteristics of the molten mass to minimise flow lines as well directing the weld lines to an unseen part of the molded shape by for example the position of the injection gate(s).

Ideally for the use of effect pigments circular, centralized and edge minimized injected molded shapes are well suited for Effect pigments. However in instances where this is not possible Pritty recommends our Diamond Effect pigment family in low concentrations as it gives a strong sparkling effect while minimizing any visual perception of irregularities caused by platelet orientation.