Polyethylene foam molding method

DATE：2021/11/3 8:57:38 / READ： / SOURCE：This station

Polyethylene foam molding method

       There are many production methods for polyethylene foam, which are mainly divided into extrusion method, molding method and expandable bead method. The United States has used the extrusion method to produce non-crosslinked polyethylene foams since 1958. At present, half of the polyethylene foams in the United States are still produced by this method. Japan is a major producer of various cross-linked polyethylene foams. Our country mainly adopts extrusion method and mould pressing method to produce polyethylene foam plastic products.

      Extrusion
      The extrusion method is to extrude the molten polyethylene material containing foaming agent from the die of the extruder. When the molten material drops from high pressure to normal pressure, the gas dissolved in the molten material expands and foams.
      The addition of foaming agent has the following three forms.
     ① Add thermal decomposition foaming agent to the resin.
     ②Inject low-boiling liquid foaming agent under pressure in the melting section in the middle of the extruder
     ③ Prepare expandable beads containing volatile foaming agent by dipping method and then extrude and foam.
     The first is called the chemical foaming method, which is mostly used for low-foaming products, such as the preparation of wire and cable insulation. The third type requires the preparation of expandable beads before extrusion. The following focuses on the second foaming method, also known as the physical foaming method

      The extrusion foaming method has a simple process, as long as the volatile foaming agent with a boiling point of 30-20°C is injected into the melting section in the middle of the extruder, the extrusion foaming can be achieved. Similar to extruded polystyrene foam, in order to make the bubbles fine and uniform, a small amount of nucleating agent can be added, such as adding 0.01% to 1% of organic acid, carbonate or acid carbonate, powdered dioxide The extrusion temperature of silicon, etc. is selected between 5°C lower than the melting temperature to the softening temperature, and the appropriate extrusion temperature can be selected to produce a polyethylene foam with a foaming ratio of 20 times.
     Extrusion foaming process
     In production, the uniformly mixed raw materials are fed into the extruder from the hopper, and are compacted by the screw rotation, and melted and plasticized in the barrel. The foaming agent is injected into the molten material with a metering pump from the injection port in the middle of the extruder. The mechanical stirring is completely mixed with the materials. The molten material with uniform temperature is extruded from the die of the machine head, and after blow molding, a polyethylene foam sheet with a beautiful pearl-like luster on the surface and a uniform internal cell structure is obtained. Some pigments can also be added to make a variety of colorful colors. Of colored polyethylene foam sheets. In addition to sheets, the types of polyethylene foam made by this method include plates, tubes, bars, etc.

Author：admin

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