The main component of luminescent pigments is aluminate. It is a new type of long afterglow luminescent material. Compared with traditional ZnS luminescent materials, their afterglow time after short-term illumination is more than ten times longer. Additionally, they have excellent lightfastness and durability. It is non-toxic and non-radioactive. No toxic chemicals are introduced or produced during the production process. The main component of the luminescent pigments provided is aluminate, and the afterglow time is more than 12 hours. When applied to plastics, luminescent pigments impart self-luminous properties. It can be used both as an indicator in the dark and for decorative purposes.
1. Method of adding luminous pigments to plastic
There are two different ways to add luminous pigments to plastic.
One method is to directly mix luminescent pigments with resin to process the product. However, this method cannot ensure that the luminescent pigment is evenly dispersed in the product and may affect its performance. To ensure uniform dispersion, the pigment particles need to be thoroughly wetted. This can be achieved by adding low-viscosity additives or increasing processing temperatures. The method typically involves dry blending luminescent pigments with powders and granules in a mixer at room temperature. There is an option to add a dispersant if desired. These premixes are then fed directly into an injection molding machine or extruder. This method is suitable for thick-walled products with low-performance requirements. Yet, it may not be suitable for thin-walled products because it cannot achieve high quality.
Another method is to use a luminescent masterbatch. Although the method is technically similar to adding luminescent pigments directly. The advantage lies in the optimal dispersion of the luminescent pigments. Besides, by adding appropriate additives to the luminescent masterbatch, the decrease in mechanical properties caused by the addition of luminescent pigments to the final product can be reduced.
2. There are several advantages to using luminescent masterbatch
- Luminous pigments are evenly dispersed in the resin.
- No dust is generated during production operations. Protect the environment and workers.
- Reduce manufacturer’s equipment wear and energy consumption, save labor, time and energy.
- Conducive to automated production.
3. Causes and solutions for luminous pigments turning black
3.1 Reasons
Improper handling of luminescent pigments during processing may cause the material to darken. It results in a decrease in the luminous intensity of the product. Most of the processing steps in plastic processing are done in machinery. So becoming black is inevitable. Yet, appropriate measures can be taken to reduce it. Reduces the amount of darkening by minimizing shear and friction. By studying changes in luminous intensity under different processing equipment, processes and formulations, optimal conditions can be determined. This significantly improves the appearance and luminous intensity of the product.
3.2 Solutions
3.2.1 Change the screw structure
Change part of the screw meshing section into a threaded section. This increases the brightness of the luminescent plastic particles. And improve the appearance and color of luminous plastic particles.
Reduce the aspect ratio of the screw. The aspect ratio has changed from the original 28/1 to the current 2/1. This can reduce the friction time of materials in the cylinder to achieve the purpose of improving brightness.
3.2.2 Change process conditions
Properly increase the temperature of the second section of the screw. The material will quickly enter a viscous flow state after entering the cylinder. Wrap the luminous pigment to reduce friction on the screw and prevent blackening.
By reducing the screw speed, the problem of insufficient plasticization of the material caused by reducing the aspect ratio can be overcome. It can also reduce the friction of materials in the cylinder and prevent blackening.
3.2.3 Selection of raw materials
Choose luminescent pigments with larger diameters, but the mechanical properties of the product will decrease. So, mechanical properties and brightness should be considered comprehensively when selecting luminescent pigments.
Try to choose a transparent resin to reduce the hiding of the luminous pigments.
When producing a plastic luminescent masterbatch, matrix resin with a large melt index is also selected. Not only is it beneficial to the dispersion of pigments, but it also melts quickly. Let the luminous pigment be encapsulated by the resin as early as possible.
