There are many ways of forming polyethylene foam, which are mainly extruded, moulded and granular. China mainly uses extrusion and molding to produce polyethylene foam.The extrusion method is to extrude the polyethylene containing Foaming Nucleating Agent from the die of the extruder head. When the melting material is reduced from high pressure to normal pressure, the gas dissolved in the melting material expands and foams
There are three ways to add foaming agent:
① Add thermal decomposition foaming agent into the resin;
Secondly, a low boiling point liquid foaming agent was injected into the middle melting section of the extruder;
(3) the beads containing volatile foaming agent were prepared by swabbing and then extruded for foaming.
Chemical foaming is used for the preparation of many low foaming products, such as wire and cable insulation.The third is to prepare the expandable beads before extrusion.
The following focuses on the second foaming method, also known as physical foaming method
- Polyethylene foaming agent sodium bicarbonate citric acid melt flow rate 1g / 10min, density 920kg / m3, melting temperature 114c, softening temperature 90C, relative density 144, boiling point 36C, industrial pole 100 10 ~ 200.1 ~ 0.30.1 ~ 0.3
- extrusion foaming process is simple. As long as the volatile foaming agent -30~20C is injected into the melting section of the extruder, it can be extruded and foaming. It is similar to extruded polystyrene foam. In order to make the bubbles fine and uniform in structure, a small amount of nucleating agents can be added, such as 0.01%~1% organic acid, carbonate or acid carbonate, and powdered silica. When the extrusion temperature is between 5C lower than the melting temperature and the softening point, and the extrusion temperature is suitable, the polyethylene foam plastic with 20 times foam ratio can be produced
- In the production of extrusion foaming process, the raw materials with uniform mixing are first fed into the extruder from the hopper, then the screw rotates and compacts, and then melt and plasticize in the barrel. The foaming agent is injected into the molten materials from the injection port in the middle of the extruder with a metering pump, and then the materials are completely mixed by mechanical mixing. The melting materials with uniform temperature are extruded from the desert port of the extruder head, and the surface is Pearl like and beautiful after blowing foaming Polyethylene foamed sheet with uniform glossy interior and uniform pore structure, and some pigments can be added to produce polyvinyl foam sheets with various colors. The polyethylene foams obtained from this method include sheet, tube, bar and so on.
