Polyethylene cross-linked foaming method
DATE：2021/11/9 8:57:37 / READ： / SOURCE：This station
Polyethylene cross-linked foaming method
The commonly used cross-linking methods are chemical cross-linking and radiation cross-linking. Chemical cross-linking generally uses organic peroxides as cross-linking agents. Because of its low price and easy operation, radiation cross-linking is widely used in industry. Polyethylene undergoes cross-linking reaction to form network macromolecules under high-speed electron rays or radiation. Radiation cross-linking equipment has a large investment, but the sheet quality is good, and it is generally only used to produce 5-10mm thick cross-linked polyethylene foam sheets. 1Chemical cross-linked foamingWhen the polyethylene resin is mixed with the organic peroxide and heated, the organic peroxide is decomposed into highly chemically active free radicals, and the hydrogen atoms in the polyethylene molecules are taken away to convert some of the carbon atoms in the main chain into active free radicals. The active free radicals on the two macromolecular chains combine with each other to form a cross-linked bond.
The first step of chemical cross-linking and foaming is cross-linking, and the second step is expansion and foaming. The foam molding method of cross-linked polyethylene foam can be divided into one-step method and two-step method.
① The one-step method is to heat the sheet material to a temperature higher than the decomposition temperature of the blowing agent, and then cross-link and foam it.
② The two-step method is to plasticize a certain proportion of polyethylene resin, foaming agent, and chemical cross-linking agent into a sheet, then heat and press to cross-link the blank, and then foam the blank.
2 Radiation crosslinking
After the polyethylene and the chlorodimethylamine equivalent to 10% of the polyethylene mass are uniformly mixed, they are extruded into an expandable sheet with a thickness of 3 mm and a length of 10 cm, and then irradiated with electron rays. The radiation process is carried out in the air at room temperature, and it is cross-linked with radiation measuring 10-100 kGy. Radiation cross-linking can be carried out at high or lower temperature, unlike chemical cross-linking, which needs to be carried out above the melting point of the material.
There are two types of energy used for cross-linking, gamma radiation and electron radiation. The main difference between the two is the speed and the depth of penetration of the material. The 184 types of radiation produced by radioactive isotopes can handle polyethylene with a thickness of 30-60 cm. , But the processing speed is slow, the irradiation time is from a few hours to a day; the electron radiation only penetrates about 1.25cm, but the speed is very fast, up to hundreds of square meters per minute. The viscosity and elasticity of the polyethylene melt after crosslinking are significant To improve, the viscosity and elasticity range suitable for foaming can be adjusted by the addition of chemical crosslinking agent or by controlling a certain radiation dose, so as to maintain the cell structure to prepare foam with high foaming ratio.
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