Heat shrinkable Polyimide Film demand is stable at room temperature, heating (glass transition temperature and above) contractions, and occurred in a direction more than 50% shrink is better. Heat shrinkable plastic film packaging features are: body-transparent, reflecting the product image; Jinshu packaging, anti-casual good; rain, moisture, mildew; no recovery, there has been some anti-counterfeiting features. Heat shrinkable plastic film commonly used in convenience food, beverage, electronics, metal products, such as packaging, shrink labels in particular, its most important applications.
In addition to shrinking plastic film used for shrink labels, in recent years have begun packaging for household goods. Because both can avoid the impact of packaged goods, rain, moisture, rust, and it also enabled packaging products to the fine print to win customers, while it is a good show a good image of the manufacturer. Currently, more and more use of printed shrink film packaging manufacturers to replace the traditional transparent film. Printed shrink film can be improved because of the appearance of product quality, beneficial products, advertising, trademark brand in the minds of consumers can make a profound impression.
Heat shrinkable Polyimide Film generally more amorphous plastics processing system may, for example, polystyrene, polyvinyl chloride, PVDC and so on. Polystyrene (PS) shrink film strength is low, the impact of intolerance, it is rarely used; and polyvinyl chloride (PVC) is not conducive to recycling, do not meet environmental requirements. In other countries, particularly in Europe, polyvinyl chloride (PVC) plastic film has been banned in the packaging field, especially in the use of food packaging.
Polyester (PET) is a new type of heat shrinkable film heat shrink packaging material. Because of its ease of recycling, non-toxic, tasteless, good mechanical properties, in particular, is in line with environmental protection and other characteristics of the developed countries, polyester (PET) has become replaced by polyvinyl chloride (PVC) shrink film of the ideal substitute.
Heat shrinkable Polyimide Film Copolymerization
Polyester (PET) film is a crystalline material, ordinary polyester film can only get through the special treatment below 30% shrinkage. To obtain a high shrinkage polyester film, then they must be modified. In other words, in order to prepare high shrinkage polyester film, the need for ordinary polyester or polyethylene terephthalate for copolymerization. Copolymer modified PET films with the highest shrinkage rate of up to 70% or more.
Ordinary polyester is normally provided by terephthalic acid (PTA) and ethylene glycol (EG) after esterification and condensation reactions in the system, are crystalline polymers (strictly speaking, is the coexistence of crystalline and amorphous polymers) . The so-called copolymerization is in addition to terephthalic acid (PTA) and ethylene glycol (EG) two main components, the re-introduction of the third or fourth component in copolymer is intended to enable the formation of asymmetric molecular structure the formation of amorphous PET copolymer.
The introduction of the third or even fourth monomer can be a dicarboxylic acid or diol. Among them, the dicarboxylic acids are isophthalic acid, malonic acid, succinic acid, adipic acid, sebacic acid; diols are neopentyl glycol, propylene glycol, diethylene glycol, cyclohexane 1.4 Second, such as methanol. If the dicarboxylic acid (Acidic) when the copolymerization, the copolymer obtained in the PET, called APET; terms of binary alcohol (Glycolic) when the copolymerization, the copolymer obtained in the PET, is called PETG.
The introduction of the third monomer, the most commonly used dicarboxylic acids are isophthalic acid (IPA). The addition of IPA can change the symmetry of the tight structure of polyester, destroyed the regularity of the macromolecular chains, thus reducing the force between molecules, the molecular structure of polyester become more supple. Meanwhile, the introduction of IPA, the nucleation crystallization of polyester hard, and with the increase in the amount of IPA introduced, APET crystalline copolymer by the transition to non-crystalline polymers, as the crystallization of such modified PET APET reduced ability to larger amorphous region, it can be used to make high shrinkage film. Recommended the addition of IPA content of 20% or so.
The introduction of the third monomer can also be a diol. The most commonly used diols 1.4 Cyclohexanedimethanol (CHDM). Process the polyester copolymer added to change CHDM polyester tg, tm and the crystallization rate will have a huge impact. With the increasing CHDM content, decrease the melting point of PETG copolyester, glass transition temperature increases, the copolymer becomes amorphous structure. However, 1.4 Cyclohexanedimethanol (CHDM) shall control the added amount of the appropriate range, is generally recommended dosage of CHDM is 30 ~ 40%. The use of glycol modified PETG film not only for the preparation of high shrinkage, can also be used to produce heat sealing film, high transparent membrane, etc., use very extensive.
The shrinkage of heat shrinkable film
BOPET film production process by example, the production process is to first dry the PET copolymer resin, and then to the extruder in the melt extrusion, through the die / cooling drum cast film, cast film will then be heated to the glass transition temperature above the melting temperature below a suitable temperature range, and in the external force, to a certain multiple of one-way or two-way stretch, usually required 3.5 to 4.0 times the horizontal stretch. PET molecular chains by stretching the force along the direction of orientation, and then to cool shape, so that the molecular structure of PET has been oriented “freeze” the stereotypes. The high-elastic deformation under external force has the shrinking of the “memory effect”, when the call this a “memory effect” of the film and then heated to a temperature above the stretching, the molecular orientation is frozen structure began to relaxation, At the macro performance of PET film on the occurrence of contraction. It is worth mentioning that this heat shrinkable PET film is mainly amorphous part of the orientation contribution. This is why the copolymer film modified amorphous PET (APET or PETG) than the average crystalline PET film shrinkage is much greater reason. Therefore, the orientation of the films by increasing the amorphous region can be greatly improved to achieve the purpose of film shrinkage. As mentioned earlier, the general shrinkage polyester film in the 30% rate, while the copolymer modified polyester shrinkage of up to 70%.
With the continuous development of plastic packaging industry and the continuous improvement of living standards, juice, soft drinks and other beverages are mostly integrated performance, have better barrier properties, non-toxic, odorless plastic PET bottles for packaging, the amount is considerable. According to statistics, the amount of the national PET beverage bottles at least 25 million tons, a complete set of PET shrink label film is the amount of up to 2 to 3 tons. In addition, since China’s accession to WTO, foreign trade is continuously expanding, in order to improve the image and value of exports, but also must use more high-grade polyester heat shrink film and other packaging materials. In short, the application of heat shrinkable PET film is very promising!
