Introduction to the production principle of the net sleeve machine

The net sleeve machine is a kind of polymer material formed by a large number of gas micropores dispersed in solid plastic (polyethylene), with shock absorption and buffering functions, mainly used in fruits Packaging and transportation industry.

Physical indicators of foam mesh

One: how to "foam"? two: how to make "tubular mesh"?

  Foaming principle: The foaming method of plastic can be divided into two categories: physical foaming method and chemical foaming method according to the different foaming agents used. Here is a brief introduction to the foaming agent.

foaming agent

Blowing agents can be roughly divided into physical blowing agents and chemical blowing agents. The requirements for the physical foaming agent are: non-toxic, odorless, non-corrosive, non-flammable, good in thermal stability, no chemical reaction in the gaseous state, and the diffusion rate in the plastic melt in the gaseous state is lower than that in the air. diffusion rate. Commonly used rational foaming agents are air, nitrogen, carbon dioxide, hydrocarbons, Freon, etc.; chemical foaming agent is a substance that can release gases such as nitrogen, carbon dioxide, etc. when heated. The requirements for chemical foaming agents are: its points Explain that the gas released should be non-toxic, non-corrosive, non-flammable, and have no effect on the molding and physical and chemical properties of the product. The speed of the released gas should be controlled, and the foaming agent should have good dispersibility in the plastic. Widely used inorganic foaming agents such as sodium bicarbonate and ammonium carbonate, organic   foaming agents such as amides and azobis.

Physical foaming

Simply speaking, it is to use physical methods to foam plastic. There are generally three methods:

(1) First dissolve the inert gas in the plastic melt or paste under pressure, and then release the gas through decompression, so as to form pores in the plastic. bubble;

(2) Foaming by vaporizing the low-boiling liquid dissolved in the polymer melt;

(3) Add hollow spheres to plastic to form foam and foam, etc. The cost of the physical foaming agent used in the physical foaming method is relatively low, especially the cost of carbon dioxide and nitrogen is low, and it is flame-retardant and pollution-free, so the application value is high; and the physical foaming agent has no residue after foaming, It has little effect on the properties of foamed plastics.

Chemical foaming

Chemical foaming method is to use chemical methods to generate gas to foam plastic: heating the chemical foaming agent added to plastic to decompose it and release gas to foam; In addition, it is also foamed by using the gas released by the chemical reaction between the various plastic components. The process of foaming plastic with chemical foaming agent is basically the same as the general foaming process. Heating, mixing, plasticizing and most of the foaming and expansion of plastics are done in the extruder. In a word, no matter what kind of plastic raw material is selected, and no matter what kind of foaming method is adopted, the foaming process generally goes through the stages of forming a bubble nucleus, expanding the bubble nucleus, and curing and shaping the bubble body.

Foaming method--no matter what method is used for foaming, the basic process is: ②Introducing gas into liquid or molten plastic to generate micropores;   ②Grow the micropores to a certain volume; ③Fix the micropore structure by physical or chemical methods. According to the way of introducing gas, the foaming methods include mechanical method, physical method and chemical method. The mechanical method introduces a large amount of air or other gas into the liquid plastic by means of vigorous stirring. In industry, this method is mainly used to produce urea-formaldehyde foam, which can be used as thermal insulation material or set material in movies (such as artificial snowflakes).

Physical methods often dissolve low-boiling hydrocarbons or halogenated hydrocarbons into plastics. When heated, the plastics soften, and the dissolved liquids volatilize, expand and foam. Such as polystyrene foam, during the suspension polymerization of styrene,   pentane is first dissolved in the monomer, or the polystyrene resin that has been polymerized into beads is treated with pentane under heat and pressure   manufacture.

Process preparation and method Preparation method: Extrusion Extrusion, also known as extrusion molding or extrusion, is made by heating, The method of pressurizing the material continuously through the die in a flowing state.