There are many varieties of plastic films, which can be applied in agriculture, daily necessities, pharmaceuticals, construction, water treatment, solar power generation, battery separators, bulletproof glass, etc. according to their different characteristics.
Film forming
There are many plastic film forming methods, among which three processes of casting, extrusion and blow molding are common:
Casting method: A non-stretched, non-oriented flat extruded film is produced by a melt flow quenching process. The film produced by this process does not have a distinct orientation structure.
Extrusion method: Common ones are uniaxial stretching and biaxial stretching. The basic principle of biaxial stretching: the high polymer raw material is first heated and melted into a thick sheet by an extruder, and then carried out in the longitudinal and transverse directions by a stretching machine in a suitable temperature range above the glass transition temperature and below the melting point. Stretching a certain number of times, the molecular chains are oriented and arranged in an order parallel to the plane of the film, and then heat-set in a tensioned state to fix the oriented macromolecular structure, and finally form a film by cooling and subsequent treatment. .
Blow molding method: usually produced by extrusion blow molding, plasticizing and extruding materials, forming tube blank inflation molding, and then cooling, drawing and coiling. The blown film is oriented. The blow molding process is simple and is the most commonly used film forming process. Multiple film properties
HDPE
The HDPE film is called a geomembrane or a barrier film. Its melting point is about 110 ° C -130 ° C, the relative density of 0.918-0.965 kg / cm3. It is a kind of thermoplastic resin with high crystallinity and non-polarity. The original HDPE has a milky white appearance and a semi-transparent shape in a slight cross section. It has good resistance to high and low temperature and impact resistance, even at low temperatures of -40F. Its chemical stability, rigidity, toughness, mechanical strength and tear strength are excellent, and as the density increases, mechanical properties, barrier properties, tensile strength and heat resistance will increase accordingly, and it can withstand acid, alkali, and Corrosion by organic solvents, etc. Identification method: Most of them are opaque, feel like wax, and there is rustling when the plastic bag is rubbed or rubbed.
LDPE
LDPE film has low density, softness, low temperature resistance and impact resistance. It has good chemical stability. Under normal circumstances, it is resistant to acid (except strong oxidizing acid), alkali and salt corrosion, and has good electrical insulation. Most of LDPE is used in plastic bags, and the material symbol is - No. 4. Its products are widely used in civil engineering and agricultural fields, such as geomembrane, agricultural film (shed film, plastic film, bitter cover film, green film, etc.). Its recycled materials, trims, etc. can be re-made into flexible plastic re-products such as trash cans, tool boxes, bicycle mats, and garbage trucks. Identification method: The plastic bag made of LDPE is softer, and it will not emit rustling when it is smashed. The outer packaging plastic film is soft and easy to tear is LDPE, and the brittle and hard is PVC or PP film.
PP
Ordinary PP film is blow molded, which is simple in process and low in cost, but its optical performance is slightly lower than CPP and BOPP. PP is characterized by high temperature resistance (about -20 ° C ~ 120 ° C), and melting point of up to 167 ° C, suitable for filling soy milk, rice pulp and other products that require steam sterilization. Its hardness is higher than that of PE, which is used to make container caps. The symbol of the material is No. 5. Identification method: Generally speaking, PP has a high hardness and a shiny surface, which does not produce a pungent odor when burned, while PE has a heavier candle smell.
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