Common food packaging materials include polyethylene, polypropylene, polystyrene, etc. Different materials have different characteristics, which should be selected according to the characteristics of the food itself.
(1) PE polyethylene: the main component is polyethylene resin, adding a small amount of lubricant, anti-aging agent and other additives. Polyethylene is odorless, nontoxic, and exposed to a milky white waxy solid. According to polymerization method, molecular weight and chain structure, polyethylene can be divided into high-density polyethylene, low-density polyethylene and linear low-density polyethylene.
Low density polyethylene: commonly known as high-pressure polyethylene, because of its low density, the material is the softest, mainly used for plastic bags, food, clothing, medicine, fertilizer, industrial product packaging materials and agricultural film.
High density polyethylene, commonly known as low-pressure polyethylene, has higher heat resistance, oil resistance, steam permeability and environmental stress cracking resistance compared with LDPE and LLDPE. Its electrical insulation, impact resistance and cold resistance are very good. It is mainly used in the production of hollow products (such as milk bottles, detergent bottles), blow molding, injection molding and other fields.
Linear low density polyethylene (LDPE) is a copolymer of ethylene and a small amount of high olefins in the presence of catalyst. LLDPE and LDPE have similar appearance, poor transparency, but good surface gloss. It has the advantages of low temperature toughness, high modulus, bending resistance, stress cracking resistance, and low temperature impact strength.
Mainly used in the production of film, commodity, pipe, wire and cable injection, extrusion, blow molding and other molding methods.
(2) Polypropylene: the main component is polypropylene resin, high gloss, high transparency, poor heat sealing performance than polyethylene, but better than other plastic materials.
1. The barrier performance is better than PE, and the strength, hardness and rigidity are higher than PE;
2. Health and safety are higher than sports
3. Excellent high temperature resistance, which can be used for a long time at the temperature of 100 ~ 200 ℃, but its low temperature resistance is worse than that of PE, and it becomes brittle when it reaches - 17 ℃.
Polypropylene is mainly made of film material for food packaging. Its water resistance and moisture resistance are better than Pt. Its material is transparent and tear resistant, but its printability is worse than Pt and its cost is lower. It can be used for kinking packaging of candy and snacks. It can also be made into heat shrinkable film and used in food heat shrinkable packaging, such as food vacuum packaging bag and other composite packaging bags.
(3) Polystyrene: polymer with styrene monomer as main component. The material is transparent and glossy.
1. The resistance to humidity is worse than that of polyethylene, the chemical stability is general, the hardness is high, but the brittleness is large.
2. Good low temperature resistance, poor high temperature resistance, no higher than 60 ~ 80 ℃.
3. Good safety factor.
It mainly consists of food box, fruit plate, tableware, cold drink cup, etc.
In addition to the common food packaging materials such as PE, PE, PS, PP, PP, polystyrene, melamine and other different types of plastic composite films, multilayer, such as composite bags made of composite film composite materials, etc., these materials can produce different types of bags according to different characteristics and different processing technologies, such as rice self-supporting zipper bags, vacuum bags, dog food and other condiment plastic bags, tea bags.
Color plastic bags are generally used in the process of making colorants. The colorants usually contain benzopyrene, which is a kind of polycyclic aromatic hydrocarbon, which will cause a lot of harm to human health.