From synthesis to application: a comprehensive introduction to foam
First, how is foam made?
Foam plastic is a kind of polymer material formed by dispersing a large amount of gas micropores in solid plastics. It has the characteristics of light weight, heat insulation, sound absorption, corrosion resistance, shock absorption, etc., and its dielectric properties are superior to matrix resins. Compared with pure plastics, foams have low density, light weight, high specific strength (the strength increases with increasing density) and the ability to absorb impact loads, and have excellent cushioning, sound absorption and sound absorption properties, thermal conductivity. Low, good thermal insulation, and excellent electrical insulation, corrosion resistance and mold resistance. The flexible foam has excellent properties such as elasticity.
Almost all kinds of plastics can be made into foam, and foam molding has become an important field in plastic processing. There are two types of cells: closed pores and open pores. The pores in the closed-cell type are isolated from each other and have a floating property; the pores in the open-hole type are connected to each other without floating. It can be made of resin such as polystyrene, polyvinyl chloride or polyurethane.
No matter what method is used, the basic process is foaming:
1 introducing a gas into a liquid or molten plastic to produce micropores;
2 to make the micropores grow to a certain volume;
3 Fix the microporous structure by physical or chemical means.
Second, what are the foaming methods?
According to the manner in which the gas is introduced, the foaming methods are mechanical, physical, and chemical.
1. Mechanical method:
A large amount of air or other gas is introduced into the liquid plastic by means of vigorous stirring. This method is mainly used in the industry to produce urea-formaldehyde foam, which can be used as a thermal insulation material or a set material in a movie (such as artificial snowflake).
2, physical law:
1) Dissolve low-boiling hydrocarbons or halogenated hydrocarbons into plastics:
The plastic softens when heated, and the dissolved liquid volatilizes and expands. For example: polystyrene foam, in the suspension polymerization of styrene, first dissolve pentane into the monomer, or treat the polystyrene resin which has been polymerized into beads by pentane under heat and pressure. So-called expandable polystyrene beads. The beads are pre-expanded in hot water or steam, and then placed in a mold to pass steam, so that the pre-expanded particles are secondarily expanded and sintered to each other, and after cooling, a product having the same shape as that of the mold cavity is obtained. They are widely used as shock-proof materials in insulation and packaging.
2) Extrusion molding can also be used:
At this time, the expandable beads can be used to be foamed and extruded into a sheet at one time; ordinary polystyrene pellets can also be used, and a halogenated hydrocarbon is added to the appropriate portion of the extruder to make it melt with the plastic. Mix evenly and expand and foam when the material leaves the machine head. The extrusion method is commonly used for making sheets or sheets, and the sheets can be formed into food packaging boxes and trays by vacuum forming. Polyethylene can also be obtained in a similar manner to produce an extruded foamed article.
3) Physical methods for introducing gas include dissolution method, hollow microsphere method, etc.:
In the dissolution method, a soluble substance such as salt, starch or the like is mixed with a resin to form a product, and then the product is repeatedly treated in water to dissolve the soluble substance, thereby obtaining an open-cell type foam product, which is often used as a filter material.
The hollow microsphere method is to mix the hollow glass microspheres with high melting temperature with the plastic melt, and a special closed-cell foam can be obtained under the molding conditions that the glass beads are not broken.
Imported EPS foam molding machine adopts re-resource technology