Foam molding methods are generally as follows:
1. Paste technology. That is, the monomer or amide paste is amidated by heat, and the gas foaming occurs in the condensation fruit foam box, but a foaming agent is added.
2. Pulp technology. That is, when the high viscosity slurry of imidized powder is heated, the solvent is controlled to evaporate and foam, but a foaming agent is added.
3. Powder process. That is, the reactant is first made into a powder precursor, and the powder is pulverized and sieved, and the particle diameter is 600 μm or less. The powder contains a chemical foaming agent, which is heated and activated to foam.
4. Solvent swelling process. That is, the first solvent swells the PI sheet first, and then the second solvent is used to replace the first solvent, and then the foam is heated. For example, polyetherimide tablets are swelled with acetone, and then a mixed solvent consisting of ethanol, trichloroethane, and water is used to replace acetone, followed by heating and foaming.
5, closed mold powder process. The above process is difficult to prepare rhenium-density foam. To increase the density of the foam, it is necessary to put the reactants in a closed mold to heat and foam. The materials are mostly amic acid powder or amide ester powder.
6. Kneading process. The material of the fruit foam box is placed in a kneader to be hot-melted and foamed. The material needs to be thermoplastic, so use a more responsible kneader.
It should be lived that the paste process in the above foaming method is the simplest. Due to the high viscosity of the resin during imidization, it can effectively save the condensed volatiles. The paste process used to prepare thermoplastic fruit foam boxes is limited, because the thermoplastic foam will crack and collapse when the temperature rise exceeds 200 ° C.
The first four processes do not require pressure and are suitable for preparing low-density foams, films, sheets, foam coatings, and foam adhesives; the latter two methods are suitable for preparing high-density foams.
Many factors have an adverse effect on the foam structure and density control of the fruit foam box. The main unpredictable factor is that the gas at the high temperature foaming reaction has an excessively high pressure, which deforms the foam structure and causes uneven density. When preparing the foam of the product, the mold can be preheated as required. The mold materials can be aluminum, steel, and fluoroplastic coated inside.