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

1. Biaxially stretched polyester film (BOPET) is a kind of high-grade film with light material (also known as big light material, i.e. the titanium dioxide content of the raw material polyester chip is 0.1%, which has been dried, melted, extruded, cast and stretched vertically and horizontally, and is widely used). BOPET film has the characteristics of high strength, good rigidity, transparency, high gloss, odorless, tasteless, colorless, nontoxic, outstanding strength and toughness; its tensile strength is 3 times of PC film and nylon film, its impact strength is 3-5 times of BOPP film, and it has excellent wear resistance, folding resistance, needle hole resistance and tear resistance; its thermal shrinkage is very small, only 1.25% after 15 minutes at 120 ℃; It has good antistatic property, is easy to carry out vacuum aluminizing, can coat 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. Apart from nitrobenzene, chloroform and benzyl alcohol, most of the BOPET films can not be dissolved by chemicals. However, BOPET will be eroded by strong alkali, so attention should be paid when using. BOPET film has low water absorption, good water resistance and is suitable for packing foods with high water content.

2. Unidirectional stretched polyester film (CPET) is a kind of film which is made of semi extinction material (titanium dioxide is added to polyester chip), dried, melted, extruded, cast and longitudinally stretched. It has the lowest grade and price in polyester film, and is mainly used for drug tablet packaging. Due to less use and less large-scale production by manufacturers, which accounts for about 5% of the polyester film field, Chinese enterprises also import less, and the standard thickness is 150 μ M. Due to the characteristics of polyester film, it has different uses.

Polyester film with different uses has different requirements for raw materials, additives and processing technology, and its thickness and technical indicators are also different; in addition, only BOPET has multiple uses, so the films classified according to use are BOPET. It can be divided into the following categories:

1. Electrical insulating film. Due to its good electrical, mechanical, thermal and chemical inertness, good insulation performance and high resistance voltage, it is specially used for electronic and electrical insulation materials. The commonly used standard thickness is 25 μ m, 36 μ m, 40 μ m, 48 μ m, 50 μ m, 70 μ m, 75 μ m, 80 μ m, 100 μ m and 125 μ m (μ m). It includes the insulation film of wire and cable (25-75 μ m in thickness) and the insulation film of touch switch (50-75 μ m).

2. Capacitor film. It has the characteristics of high tensile strength, high dielectric constant, low loss factor, good thickness uniformity, good electrical performance, high electrical resistance, etc. it has been widely used in capacitor medium and insulation layer. The commonly used standard thickness is 3.5 μ m, 3.8 μ m, 4 μ m, 4.3 μ m, 4.8 μ m, 5 μ m, 6 μ m, 8 μ m, 9 μ m, 9.8 μ m, 10 μ m, 12 μ M.

3. Protective film. It has good transparency, high stiffness, good thermal stability, excellent winding performance with flat surface, uniform longitudinal and transverse tensile performance, and has excellent performance of water-proof, oil-proof and chemical resistant. It is specially used for the protective packaging of pictures, certificates, documents and office supplies, so that it is smooth and beautiful after being used as the protective film, and can keep the original clear and deformation free. The commonly used standard thickness is 10.75 μ m, 12 μ m, 15 μ m, 25 μ m, 28 μ m, 30 μ m, 36 μ m, 45 μ m, 55 μ m, 65 μ m, 70 μ m, of which the above 15 μ m is mainly used as laser anti-counterfeiting base film or high-grade card protection film.

4. General purpose membrane. With excellent strength and dimensional stability, cold resistance and chemical stability, it is widely used in composite packaging, photographic film, metal evaporation, recording and video recording and other substrates.

5. Nano PET film

High transparency and glossiness: the particle size of nanoparticles is between 1-100nm, which is smaller than the wavelength of visible light, and has little effect on the transparency of the film.

High barrier and heat resistance: nano materials with special properties and unique processing technology are used to make nano materials disperse uniformly in pet matrix with nano size, and pet is made by stretching orientation in the film production process The film has excellent barrier performance, the transmittance of O, CO2 and H2O has been reduced by many times, and the heat resistance has been greatly improved. It can expand the application field of pet, greatly extend the shelf life of the packed products, and also can be used in the occasions requiring hot filling or sterilization. According to the quality of polyester film, different manufacturers can have different classification names. Chinese manufacturers are generally divided into superior products, first-class products and qualified products, while foreign manufacturers are generally divided into A-class products, B-class products and C-class products. Among the products sold by general manufacturers, class a products account for 97-98%, class B products only account for 2-3%, and class C products are unqualified products, which are not sold in the circulation field. The main reason is the high price of raw materials. Generally, manufacturers use them as raw materials again, or sell them as staple fibers to textile mills for textile raw materials. Foreign manufacturers sometimes sell the stock films of each quarter or half a year as class B products, which is the consistent practice of some manufacturers in Southeast Asian countries, with the purpose of reducing inventory.