According to its performance, the plastic can be divided into two kinds: thermoplastic plastics (can be repeatedly melt-processability and can maintain the basic characteristics) and thermosetting plastic (can only be melt molding for one time). According to the uses it can be divided into general-purpose plastics which is wide used and cheap with better overall performance, such as PE, PP, PVC, PS, and amino plastics with good physical and mechanical strength. The other one is engineering plastics which can replace the metal used in construction, such as: ABS, nylon, polyester, POM, TPX-1, and a class of engineering plastics with particularly excellent in a performance, like special plastic with particularly good radiation resistance and high temperature resistance, such as poly (aryl sulfone), liquid crystal polymers and so on. According to the thermoplastic resin molecular crystal size, the plastic can be divided into thermoplastic amorphous polymer and crystalline polymers.
According to the Flexible Packaging Materials, plastic bags can be divided into OPP, CPP, PP, PE, PVA, EVA, composite bags, co-extruded bags and so on.
OPP plastic bag:
Characteristics: Hard, pulling without change. Non-stretch (two-way stretch) monolithic folded, side seal welding, the longest length can't exceed 640m/m.
Monolithic: 1.28M, width: 0.6m.
Advantages: good transparency.
Disadvantages: on both sides of the seal is easy to tear.
PP plastic bags: Polypropylene
Features: its hardness is only under OPP's, and can be stretched (two-way stretch) after pulling into a triangle, bottom seal or side seal (envelope bag), tube material. Transparency is worse than the OPP.
PE plastic bags: Polyethylene
Features: with formalin, the transparency is poorer.
HDPE: High Density Polyethylene, brittle touching feel, most used to make vest bag.
LDPE: Low DENSITY POLYETHYLENE, soft touching feel.
PVA plastic bag: Vinylon
Characteristics: environmentally friendly materials, on the water will melt. Right now domestic market can not produce its raw materials, which are mainly imported from Japan with expensive price. Used more often in a foreign countries.
Advantages: soft, pollution-free, good transparency.
CPP plastic bags:
Features: non-toxic, no formalin, composite, better transparency than PE, poorer hardness, soft texture. It has the transparency of PP and the softness of PE.
Features: firm side sealing strength, printability, ink will not fall off.
Characteristics: nice transparency, soft texture, printable.
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