Characteristics, uses and categories of polyester film PET

Polyester film is made of polyethylene terephthalate as raw material, which is extruded into thick sheets and then biaxially stretched. It is a colorless, transparent and glossy plastic film (additive particles can be added to make it have color). It has excellent mechanical properties, high rigidity, hardness and toughness, puncture resistance, friction resistance, high temperature and low temperature resistance, chemical resistance, oil resistance, printability, air tightness and fragrance retention. It is one of the commonly used barrier composite film substrates. Polyester film (also known as optical film, polyester film, photosensitive paper, polyester film, benzene tin film, cellophane release film) is a kind of high polymer plastic film, which is increasingly favored by consumers due to its excellent comprehensive performance. It is often used as the outer material of fiber, packaging film, engineering plastics, polyester bottles, cooking packaging, etc.

1. Classification according to material and process of polyester film:

(1) Biaxially oriented polyester film (BOPET for short) is a high-grade film that uses polished material (also known as big polished material, that is, the raw material polyester chips (titanium dioxide content is 0.1%) are dried, melted, extruded, cast and stretched vertically and horizontally. It is widely used). BOPET film has the characteristics of high strength, good rigidity, transparency and high gloss; Odorless, tasteless, colorless, non-toxic, outstanding strength and toughness; Its tensile strength is 3 times that of PC polycarbonate film and PA nylon film, and its impact strength is 3-5 times that of BOPP film. It has excellent wear resistance, folding resistance, pinhole resistance and tear resistance; The heat shrinkability is very small, only 1.25% shrinks after 15 minutes at 120 ℃; With good anti-static property, it is easy to carry out vacuum aluminum plating, and can be coated with PVDC 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, BOPET film cannot be dissolved by most chemicals. However, BOPET will be eroded by strong alkali, which should be noted in actual use. BOPET film has low water absorption and good water resistance, which is suitable for packaging food with high water content.

(2) Uniaxially stretched polyester film (abbreviated as CPET) is a film that uses semi matting material (titanium dioxide is added to the raw material polyester chip) to dry, melt, extrude, cast and longitudinally stretch. It has the lowest grade and price in polyester film and is mainly used for drug tablet packaging. Due to the small amount of use, manufacturers rarely produce on a large scale, accounting for about 5% of the polyester film field, and domestic enterprises also import less. Standard thickness is 150 μ M and other specifications.

2. Classification according to the use of polyester film:

Because of the characteristics of polyester film, it has different uses. Different polyester films have different requirements for raw materials, additives and processing technology, and their thickness and technical indicators are also different. In addition, only BOPET has multiple uses, so all films classified according to their uses are BOPET. It can be divided into the following categories:

(1) PET electrical insulating film

Because of its good electrical, mechanical, thermal and chemical inertness, good insulation performance and high breakdown voltage, it is specially used for electronic and electrical insulation materials. Common standard thickness: 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, etc. Including wire and cable insulation film (thickness: 25-75 μ m) And touch switch insulating film (50-75 μ m）。

(2) PET capacitive film

It has the characteristics of high tensile strength, high dielectric constant, low loss factor, good thickness uniformity, good electrical performance, large electrical resistance, etc., and has been widely used in capacitor dielectric and insulation barrier. Common 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, etc.

(3) PET card protection film

It has good transparency, high stiffness, good thermal stability, excellent winding performance with smooth surface, uniform longitudinal and transverse tensile performance, and excellent performance of waterproof, oil and chemical resistance. It is specially used for the protective packaging of pictures, certificates, documents and office supplies to make them smooth and beautiful after being hot printed as a protective film, and to keep the original clear and not deformed. The common 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, among which 15 μ Above m is mainly used as laser anti-counterfeiting base film or high-grade card protection film.

(4) PET universal film

With excellent strength and dimensional stability, cold resistance and chemical stability, it is widely used in composite packaging, photographic film, metal evaporation, audio and video recording and other substrates. The details are as follows:

① Semi reinforced membrane. The main feature is that the longitudinal tensile strength is large, and it is not easy to break under a large tensile force. It is mainly used for packaging seals of boxed items. The common standard thickness is 20 μ m、28 μ m、30 μ m、36 μ m、50 μ M, etc.

② Bronzing film. It is characterized by good tensile strength and transparency, stable thermal performance and low adhesion with some resins. It is mainly suitable for small size change during high-temperature processing or for use as a transfer carrier. Normal standard thickness is 9 μ m、12 μ m、15 μ m、19 μ m、25 μ m、36 μ M, etc.

③ Print composite packaging film. The main characteristics are good transparency, good penetration resistance, excellent chemical resistance, temperature resistance and moisture resistance. It is applicable to the packaging of frozen food, food, medicine, industrial products and cosmetics. The common standard thickness is 12 μ m、15 μ m、23 μ m、36 μ M, etc.

④ Aluminum coating. The main characteristics are high strength, good temperature resistance and chemical resistance, good processing and aging resistance, and proper corona treatment, which makes the adhesion of aluminum layer and film more firm. After aluminum plating, it can be widely used in tea, milk powder, candy, biscuits and other food packaging bags, as well as decorative films such as flower crafts, Christmas trees and other decorations; At the same time, it is also suitable for printing packaging films such as composite bags or cardboard composite bags. Conventional standard thickness is 12 μ m、16 μ m、25 μ m、36 μ M, etc.

⑤ Magnetic recording film. It has the characteristics of good dimensional stability, uniform thickness and high tensile strength. Base film and special packaging film for magnetic recording materials, including audio and video tape base (common standard thickness is 9-12 μ m) And black film (common standard thickness is 35-36 μ m）。

(5) Nanometer PET film

a. High transparency and glossiness: the particle size of nano particles is between 1~100nm, smaller than the wavelength of visible light, and has less influence on the transparency of the film.

b. High barrier performance and heat resistance: nano materials with special properties and unique processing technology are used to make nano materials uniformly disperse in PET matrix in nano size. During film production, PET films are oriented by stretching, so that PET films have excellent barrier performance. The transmittance of O, CO2, H2O and other substances is doubled, and the heat resistance is also greatly improved. Based on its characteristics, it expands the application field of PET, greatly prolongs the shelf life of the packaged materials, and can also be used in the hot filling or disinfection and sterilization industries.

3. Classification according to the quality of polyester film:

According to the quality of polyester film, different manufacturers 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, Grade A products account for 97-98%, while Grade B products only account for 2-3%. Grade C products, that is, unqualified products, are not sold in the circulation field. The main reason is that the price of raw materials is high. Generally, manufacturers recycle them as raw materials, or sell them as staple fibers to textile mills as textile raw materials. Foreign manufacturers sometimes sell the films in stock every quarter or half a year as Grade B products, which is also a consistent practice of some manufacturers in Southeast Asian countries to reduce inventory.