Plastic bags are a common packaging bag in daily life. The types of plastic bags are: high-pressure polyethylene plastic bags, low-pressure polyethylene plastic bags, and polyvinyl chloride plastic bags. The raw materials for making plastic bags include polyethylene, PVC-polyvinyl chloride, shrink film, etc. Among them, polyethylene is recognized as the best material for contact with food in the world, and it is also the most used and most important material for plastic packaging printing.

Basic introduction

Plastic bags: the most commonly used packaging bags in daily life.

Raw materials for plastic bags:

Polyethylene, referred to as PE. It is a high-molecular organic compound formed by the addition polymerization of ethylene. Polyethylene is recognized as the best material for contact with food in the world. It is non-toxic, tasteless, and odorless, and meets the sanitation standards for food packaging. Polyethylene film is light and transparent, and has the properties of moisture resistance, oxidation resistance, acid resistance, alkali resistance, general air tightness, and excellent heat sealing. It is known as the "plastic flower". It is the most used and most important material for plastic packaging printing.

PVC--Polyvinyl chloride

PVC, referred to as PVC, is the main type of vinyl polymer and the second largest plastic variety in the world after polyethylene. Its production in China ranks first among plastics.

Shrinkfilm--Shrink film

Shrink film is a thermoplastic film that is stretched and oriented during the production process and shrinks when it is treated with hot air or infrared rays during use. After heat treatment, the film is tightly wrapped around the packaged object, and the shrinkage force reaches its maximum value during the cooling stage and can be stored for a long time.

LDPE--Low-density polyethylene

Low-density polyethylene, referred to as LDPE, is the largest variety used in the plastic packaging and printing industries of various countries. The specific gravity is 0.92-0.93 and can float on water. It has a low crystallinity (60%) and undergoes bulk polymerization at a pressure of 1000-3000kg/C©O, so it is also called high-pressure polyethylene. At 23 degrees Celsius, the density is around 0.92. The calendering formability is poor, and it is suitable for blow molding to be processed into tubular film. It is suitable for food packaging, fiber product packaging, and daily chemical product packaging.

HDPE--High Density Polyethylene

High-density polyethylene, referred to as HDPE. The density is 0.941-0.965g/cubic centimeter. It is polymerized at low pressure, so it is also called low-pressure polyethylene. It is milky white, indicating that the gloss is poor. The film can be processed by blow molding and T-die extrusion process. It is heat-resistant and steam-resistant, cold-resistant and freezing-resistant, and has good moisture-proof, gas-proof and insulation properties. It is not easy to break, and its strength is twice that of LDPE. It is very easy to open. It has strong paper-like properties and is known as "paper-like plastic film".

BOPP--Biaxially Stretch Polypropylene Film

Biaxially Stretch Polypropylene Film, also known as Biaxially Stretch Polypropylene Film, English abbreviation code BOPP, is characterized by stretching molecular orientation, mechanical strength, folding strength, air density, and moisture barrier properties are better than ordinary plastic films. Compared with cellophane per unit area, the unit price is lower than that of cellophane. Because this film has excellent transparency and the color reproduced after printing is particularly bright and beautiful, it is an important base material for plastic composite flexible packaging.

Identification of toxicity of plastic bags

Commonly used food plastic product bags: Most of them are made of polyethylene film, which is non-toxic, so they can be used to hold food. There is also a film made of polyvinyl chloride, which itself is also non-toxic, but the additives added according to the purpose of the film are often harmful to the human body and have certain toxicity. Therefore, this type of film and plastic bags made of this film are not suitable for holding food. If you want to distinguish polyvinyl chloride plastic bags and polyethylene plastic bags, you can use the following simple method to identify them.

Polyethylene film (non-toxic)

The film is milky white and translucent (especially obvious when observed by stacking several layers), feels smooth, as if there is a wax layer on the surface, shakes hard, makes a crisp sound, is flammable when exposed to fire, has a yellow flame, and has mucus dripping when burning, and has the smell of burning candles.

Polyvinyl chloride film (generally toxic), if not pigmented, is transparent, feels a little sticky, makes a muffled sound when shaken, does not burn easily when exposed to fire, goes out immediately away from flame, and has a green flame.

Types of plastic bags:

(1) High-pressure polyethylene plastic bags

(2) Low-pressure polyethylene plastic bags

(3) Polypropylene plastic bags

(4) Polyvinyl chloride plastic bags

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