Foaming agent
DATE：2022/3/30 8:58:18 / READ： / SOURCE：This station
Foaming agent
Generally comes from foaming agent, foam process using gas according to the principle of foaming agent gas forming process is different, can be divided into two major categories of physical foaming agent and chemical foaming agent, physical blowing agent in the foaming process, the foaming agent itself without any chemical change, only by physical condition or change the conditions of foaming agent, get a lot of gas to make polymer foam. Foaming process with chemical foaming agent, foaming agent will have chemical changes, foaming agent decomposition of gas to make polymer foaming. In actual production, this two kinds of foaming agent is also sometimes used, for example some physical foaming agent is added when using chemical foaming agent for foam, can not only add amount of friends, but also to the temperature control, because of the decomposition of chemical blowing agent release gases are often exothermic reaction, and carry out a large amount of heat, and physical foaming agent in the gasification process is endothermic reaction, These two processes go hand in hand to facilitate temperature control.There are many types of physical foaming agents and chemical foaming agents, which are described below. Corrugated board equipment www.handern.com
1. Physical foaming agent does not have any chemical change in the process of plastic foaming, but produces a large amount of gas to make plastic foaming through the change of physical state. Physical foaming agents can be divided into three categories, gas, low boiling point liquid and solid hollow ball. At present, low boiling point liquid physical foaming agent is widely used.
The following three types of physical foaming agents are introduced one by one. (1) The chemical activity of inert gas foaming agent is weak, N2 and C0 are commonly used, and other are air, CH and H. Can also act as a foaming agent. The foaming process with inert gas usually requires intense mechanical agitation to mix the gas evenly in the polymer melt or liquid. The mixing process takes place either at high pressure or at atmospheric pressure. Inert gases are usually dissolved in the polymer melt and then cooled to form bubbles. In the latter process, inert gases are often mixed directly with the polymer liquid to form vesicles. These two processes are used in the actual production, the former one is mostly used in the process of extrusion foaming and injection molding of hot plastic, the latter one is mostly used in the process of injection foaming molding of thermosetting plastic, the initial bubble body is often very unstable, so it must be to make the bubble body solidified. Extrusion foam and injection molding foam can use inert gas as foaming agent, but need to set up a special conveying device, will be compressed inert gas, under high pressure, continuous quantitative pressure into the plastic melt, and then through the full screw mixing, so that the inert gas evenly distributed in the melt. When the melt is extruded from the nose, due to the sudden drop of external pressure, the dissolved inert gas in the melt is supersaturated and extremely unstable. It is easy to segregate from the low potential energy point in the melt and form bubbles. PVC sponge board can also use inert gas as foaming agent. The inert gas is pressed into the PVC paste, mixed evenly, and then pressed and heated to make the PVC paste foam, and then shaped into sponge board. When selecting inert gas as foaming agent, special attention should be paid to its penetration rate in the polymer. Generally, it should be selected with low permeability, otherwise it will affect the foaming efficiency. Table 2-9 shows the permeability of several inert gases to various plastic membranes. Corrugated board equipment www.handern.com
(2) Low boiling point liquid is a widely used physical foaming agent at present. Its performance range is very wide. It is best to choose low boiling point liquid in gaseous state at room temperature and pressure, and it is generally required to boil below 110℃ at atmospheric pressure. When the polymer melt is injected under pressure, it is liquid, which is conducive to the uniform mixing of foaming agent and polymer melt, and then through decompression, the foaming agent in the melt is vaporized and bubbles are formed. In addition, can also be low boiling point liquid at room temperature or low temperature into the solid polymer particles, and then heated, small particles of low boiling point liquid gasification, the polymer particles containing a large number of microbubbles, into beads like elastic ball, known as pre-bubble particles. PS with this method made of elastic ball EPS, there are ready-made goods on the market for sale, manufacturers with EPS as raw material, after the second molding foam, you can make high foaming mold products. Low boiling point liquid foaming agent, the first six kinds of inexpensive, low toxicity pentane and butane with high foaming efficiency, the main disadvantage is flammable, often used in PE, PS and PS copolymers and so on in high foaming molding. Dichloromethane is toxic but flame retardant and is used in foam forming of PS, PVC and epoxy resins. When using dichloromethane as foaming agent, safety precautions should be set up to avoid poisoning. The last four low boiling foaming agents are collectively known as freon. Flame retardant, heat is more stable, will not explode, chemically inert non-toxic and has good dielectric properties, can be used for PE, PS and their copolymers, epoxy fat, polyaldehyde resin, polyurethane foam molding, but because they have damage to the atmosphere of the odor layer, so now has been gradually restricted use. Corrugated board equipment www.handern.com
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