Plastic packaging and plastic packaging products have become more and more popular in the market. Especially compound plastic soft packaging, they have been widely used in food, medicine, chemical industry and other fields. Among them, the proportion of food packaging is the largest, such as beverage packaging, quick frozen food packaging, steamed food packaging, fast food packaging, etc., which bring great convenience to people's lives Li.

1. Biaxial tensile polypropylene film (BOPP)

BOPP is a multilayer ataxic film, which is made by the co extrusion of polypropylene particles into sheet, and then stretched in both directions. Due to the orientation of tensile molecules, the film has good physical stability, mechanical strength, air tightness, high transparency and glossiness, toughness and wear resistance. It is the most widely used printing film at present. The thickness is 20-40 μ m and the most widely used is 20 μ M. The main disadvantage of biaxial tensile polypropylene film is poor thermal sealing. Therefore, it is generally used as outer film of composite film. For example, moisture resistance, transparency, strength, stiffness and printing property are ideal after compounding with polyethylene film, which is suitable for dry food. Because the surface of biaxial tensile polypropylene film is non-polar, high crystallinity and low surface free energy, its printing performance is poor, and the adhesion of ink and adhesive is poor. Surface treatment is required before printing and compounding.

2. LDPE film

Low density polyethylene film is generally made by blow molding and casting. The thickness of the film is uniform, but it is rarely used because of its high price. Blow molding polyethylene film is made of PE particles of blowing grade by blow molding machine, and its cost is low, so it is widely used.

Low density polyethylene film is a kind of translucent, glossy and soft film, which has excellent chemical stability, heat sealing, water resistance and moisture resistance, and is cold resistant and can be boiled in water. The main disadvantage is that the oxygen barrier is poor, which is often used in the inner layer film of composite soft packaging materials, and is also the most widely used and most widely used plastic packaging film, accounting for more than 40% of the consumption of plastic packaging film.

Because polyethylene molecules do not contain polar groups, and high crystallinity and low surface free energy, the printing performance of the film is poor and the adhesion of ink and adhesive is poor, so surface treatment is required before printing and compounding.

3. Polyester film (PET)

According to the raw materials and drawing process used in the production of polyester film, it can be divided into the following two types:

① Biaxial stretch polyester film (BOPET) is a kind of high-grade film which uses light material (also known as big light material, that is, the titanium dioxide content of raw material polyester slice is 0.1%, which is dried, melted, extruded, cast and stretched horizontally and horizontally, and is widely used). BOPET film has the characteristics of high strength, good rigidity, transparency and high gloss; it has strong toughness without smell, tastelessness, colorless, non-toxic and outstanding; its tensile strength is 3 times of PC film and nylon film, and impact strength is 3-5 times of BOPP film, with excellent wear resistance, folding resistance, needle hole resistance and tear resistance, etc.; the thermal shrinkage is very small, at 120 ℃, and only 1.25% after 15 minutes; It has good antistatic property, easy to vacuum aluminum plating, can coating PVDC, so as to improve its heat sealing, barrier and printing adhesion; BOPET also has good heat resistance, excellent cooking resistance, low temperature freezing resistance, good oil resistance and chemical resistance. Except nitrobenzene, chloroform and benzyl alcohol, most chemicals can not dissolve BOPET film. However, BOPET will be eroded by strong alkali, and attention should be paid to it when using. BOPET film has low water absorption, good water resistance, and is suitable for packaging food with high water content.

② The one-way stretch polyester film (CPET) is a kind of film which uses semi extinction material (titanium dioxide is added to the raw material polyester slice), which is dried, melted, extruded, cast and longitudinally stretched. It has the lowest grade and price in the polyester film, and is mainly used for drug tablet packaging. Because of the small use, the manufacturers are less mass production, accounting for about 5% of the polyester film field, and Chinese enterprises are less imported, and the standard thickness is 150 μ M.

4. Nylon film (PA)

Nylon film is a very tough film, with good transparency, good luster, high tensile strength and tensile strength. It also has good heat resistance, cold resistance, oil resistance and organic solvent resistance, good wear resistance and puncture resistance, and is relatively soft and oxygen resistant. However, it has poor water vapor barrier, high moisture absorption, moisture permeability and poor heat sealing, It is suitable for packing hard goods, such as greasy food, meat products, fried food, vacuum packaging food, cooking food, etc.

5. Flow extended polypropylene film (CPP)

The flow drawn polypropylene film is a kind of polypropylene film produced by the casting process. It can be divided into general CPP (GCPP) film, aluminum plated CPP (mCPP) film and cooking grade CPP (export CPP) film. It has excellent transparency, uniform thickness and even longitudinal and horizontal properties, which is generally used as the inner layer material of composite film. The thickness of ordinary CPP film is generally between 25-50 μ M. after the composite with OPP, the film has better transparency, bright surface and strong hand feeling. This material is used in general gift packaging bags. The film has good thermal sealing property. The thickness of CPP film of cooking grade is generally 60-80 μ m, which can withstand high temperature cooking at 121 ℃ and 30 min. it has good oil resistance and air tightness, and has high heat sealing strength. Generally, CPP film of cooking grade is used in the inner layer of meat packaging.

6. Aluminum coated film

Aluminum coating has both the characteristics of plastic film and metal. The aluminum coating on the surface of the film is used to prevent ultraviolet rays and light. It not only prolongs the shelf life of the content, but also improves the brightness of the film. It replaces the aluminum foil to a certain extent, and also has the advantages of low price, beautiful appearance and good barrier performance. Therefore, the aluminum coating should be widely used in the composite packaging, mainly used in the drying and expanding food packaging such as biscuits, and some medicine and chemical products On the outer package of makeup. At present, the most widely used aluminum coating films are polyester aluminum coating (VMPET) and CPP aluminum coating (VMCPP).