The history of plastic containers is not long, but it h […]
The history of plastic containers is not long, but it has the characteristics of simple processing, beautiful appearance and low price, so it develops rapidly. Since the early 20th century, synthetic fiber resin materials have been used in the food packaging industry, such as polyvinyl chloride, polystyrene, polyamide, polyvinylidene chloride, polyethylene, polyester, polypropylene, etc., and they have been used with paper. Composite materials composed of aluminum foil, etc., which are gradually used in flexible packaging plastic bags and semi-rigid, rigid plastic cups, bottles, and shallow plates. At present, plastic containers account for 15-20% of the entire packaging container in economically developed countries such as Europe, America and Japan.
Plastic containers are made of synthetic resin as the basic raw material, and there are many types, mainly in the following three types.
1 single-layer plastic film bag: commonly used plastics are high-pressure polyethylene (ie low-density polyethylene), low-pressure polyethylene (ie high-density polyethylene), polypropylene, polyvinylidene chloride and so on. High-pressure polyethylene film has good water-blocking property, softness and low-temperature resistance, and has large oxygen and carbon dioxide gas permeability. Therefore, it is suitable for packaging solid foods, liquid foods and frozen foods that are easy to absorb moisture. Fresh vegetables, fruits and other packaging can maintain its "physiological respiration" process, and keep the moisture from shrinking and deteriorating. However, high-pressure polyethylene has poor heat resistance, cannot withstand heat sterilization temperature, and is not resistant to oil and has low strength, so it has certain limitations in application. Low-pressure polyethylene can withstand heat sterilization temperatures above 100 °C and is resistant to grease, so the application range is larger than that of high-pressure polyethylene. Polypropylene film has excellent gas and water vapor barrier properties, grease resistance, high transparency, smooth surface, heat sterilization temperature above 100 °C, and can be made into a thin directional packaging film with high strength, but low temperature resistance. It is less suitable, so it can be used for packaging other foods other than frozen food. Polyvinylidene chloride is generally made into a biaxially oriented film with large heat shrinkage and excellent gas barrier properties. It has high transparency, good elasticity, high strength and grease resistance. It is suitable for vacuum packaging and heat shrink packaging. And frozen food packaging.