A plastic additive is a chemical that is dispersed in the molecular structure of plastics and does not seriously affect the molecular structure of plastics, but can improve its properties or reduce costs. The addition of additives can improve the processing, physical and chemical properties of the base material and increase the physical and chemical characteristics of the substrate.
(1) The unsaturated double bond in antioxidant plastics is caused by the invasion of oxygen atoms, heat and light, which leads to the free radicals resulting in a chain reaction, which causes the molecular chain to break or form a chain cross-linking, and the strength of the plastic finished product decreases or becomes brittle. The function of antioxidants is to delay the decomposition of plastics by oxidation and prolong the life of plastic products.
(2) Antistatic agent's main function is to give the plastic to produce conductivity, so that it avoids friction caused by electrostatic accumulation. The commonly used antistatic agent has four grade ammonium salt, ethyl oxidizing amine type, fatty acid ester and sulfonated wax class and so on.
(3) Foaming agent plastic used in three main types of blowing agent: ① nitrogen, carbon dioxide and air, directly into the plastic melts to make foam; ② volatile liquid such as butane, pentane, petroleum ether, two chloride methane, etc., in the heat after the expansion of the volatile, and make plastic foam, common polystyrene foam that belongs to this type ③ Chemical foaming agents, which are generally solid powders that decompose and emit gas (usually nitrogen or carbon dioxide) when heated, making the plastic cell-like structure and reducing weight. This kind of foaming agent is the organic azo compound, such as azo-dimethyl amide, Azo-N-nitrile. Foaming plastics mainly include: ABS, PS, PVC, PU, EVA, PE, pp and so on.
(4) Flame retardant when the addition of refractory plastics exposed to flame, can suppress the spread of flame, prevent the formation of smoke, when the flame is removed when the burning will stop. The principle of flame retardant used in plastics can be roughly divided into three kinds:
The ① reactive combustible agent can react with oxygen to form inert gas, enveloped in the burning substance around, reducing the oxygen content of combustion, in order to achieve the end of combustion. When burning can produce co, CO2, NH3 and halogen compounds, such as PVC, PU foam, polyester or epoxy resins are selected this method.
The ② refractory is a compound containing halogen, phosphorus, nitrogen, or boron, which, when burned, decomposes an inert substance that covers the surface of the plastic burner and forms a barrier to insulate the oxygen from the outside world and to achieve the purpose of flame-resistance.
③ containing water oxides such as alumina refractory burning, can release moisture, absorb the heat of the combustion process, so that the temperature around the combustion to suppress the spread of flame to prevent the formation of smoke.
(5) Lubricant lubricant can be divided into internal lubricant and external lubricant, the main function of the internal lubricant is to improve the internal fluidity of the resin, reduce the internal friction between the resin molecular chain, such as fatty acid lipids (stearic acid monostearate); The external lubricant reduces the adhesion of the resin to the processing machinery and enhances the smoothness and easy demoulding of the product surface.
(6) Impact-resistant modifier resistant to impact modifier is usually a special resin to mix the way to add, and improve the impact resistance of plastics. Impact modifiers often affect the heat resistance, fluidity or processability of plastics, and must be carefully chosen.
(7) Plasticizer Most of the resin has plasticity, but the size of plasticity is not the same, in order to make the resin easy to plasticizing and give the product softness, generally in the resin to add some low-molecular-weight substances, these low-molecular-weight materials called plasticizers. Plasticizer is liquid or low melting point material, and resin should have better miscibility. Commonly used plasticizers have phthalate esters, aliphatic two acid ester, phosphate ester, chlorinated paraffin and so on.
(8) Coloring agent is to beautify and decorate the plastic and add in the material containing pigment additive called colorant.
(9) Fillers are added to the plastic compound to reduce costs, and sometimes to improve the physical properties of plastics
The relatively inert substance, such as hardness, stiffness, and impact strength, is called filler. The most commonly used fillers are clay, silicate, talc, carbonate and so on.