Processing and application of the hottest shrink p

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Processing and application of heat shrinkable polyester film

the characteristics of heat shrinkable plastic film packaging are that it is transparent, has good dispersion resistance, is rainproof, moisture-proof, mildew proof, has certain anti-counterfeiting functions, etc. as a kind of heat shrinkable plastic film, heat shrinkable polyester film has a good development momentum because of its characteristics of easy recycling, non-toxic and tasteless

the requirement of heat shrinkable plastic film is to be stable at room temperature and shrink when heated (above the glass transition temperature). Ideally, the film can shrink by more than 50% in one direction. Heat shrinkable plastic films are often used in the packaging of convenience food, beverages, electronic appliances, metal products, etc., especially shrink labels. In recent years, heat shrinkable plastic films have also been used for the outer packaging of daily-use goods. Because this kind of film can not only protect the packaging items from impact, rain, moisture and rust, but also make the products win the favor of consumers with a beautifully printed appearance, and at the same time, it can well display the good image of the manufacturer. At present, more and more packaging manufacturers use printing shrink film to replace the traditional transparent film to improve the appearance of products and make the trademark brand have a deep impression on consumers

heat shrinkable plastic films are generally processed from amorphous plastics, such as polystyrene, polyvinyl chloride, PVDC, etc. Polystyrene shrink film has low strength and is not resistant to impact, so it is rarely used. PVC is not conducive to recycling and does not meet the requirements of environmental protection. In foreign countries, especially in Europe, PVC plastic film has been prohibited from being used in the field of packaging, especially in food packaging

polyester (PET) heat shrinkable film is a new type of heat shrinkable packaging material. Because it is easy to recycle, non-toxic, tasteless, good mechanical properties, especially in line with environmental protection requirements, polyester has become an ideal material to replace PVC heat shrinkable film in developed countries

copolymerization modification of heat shrinkable polyester film

polyester film is a crystalline material. After special processing, ordinary polyester film can only obtain a heat shrinkage of less than 30%. In order to obtain polyester film with high thermal shrinkage, it must be modified. In other words, in order to prepare polyester film with high thermal shrinkage, common polyester needs to be copolymerized. The highest thermal shrinkage of polyester film modified by copolymerization can be as high as 70%

ordinary polyester is generally prepared by esterification and polycondensation of terephthalic acid (PTA) and ethylene glycol (eg), which is a crystalline polymer. The so-called copolymerization modification is to introduce the third or even the fourth component to participate in copolymerization in addition to the two main components of terephthalic acid and ethylene glycol. The purpose is that the remaining funds will be invested in the production intelligent upgrading and transformation and the construction project of technology research and development center, so as to generate asymmetric molecular structure and form amorphous pet copolymer. The introduced third or even fourth monomer can be dibasic acid or diol. Among them, dicarboxylic acids include isophthalic acid, malonic acid, succinic acid, adipic acid, sebacic acid, etc; Diols include neopentyl glycol, propylene glycol, diethylene glycol, 1.4-cyclohexane dimethanol, etc. If dicarboxylic acid is copolymerized, the pet copolymer is called APET. If dicarboxylic alcohol is copolymerized, the pet copolymer is called PETG

among the introduced third monomers, the most commonly used dicarboxylic acid is isophthalic acid (IPA). The addition of IPA can change the symmetry of polyester. Although ordinary iron instruments can not eliminate the vibration tight structure and destroy the regularity of macromolecular chain, so as to reduce the force between macromolecules and make the polyester molecular structure more flexible. At the same time, due to the introduction of IPA, it is difficult for polyester to nucleate and crystallize, and with the increase of the amount of IPA, APET copolymer transits from partially crystalline to amorphous polymer. Because the crystallization ability of this modified polyester APET decreases and the amorphous region becomes larger, it can be used to manufacture high shrinkage films. The recommended dosage of IPA is about 20%

the third monomer introduced can also be diol. The most commonly used diol is 1.4-cyclohexanedimethanol (CHDM). In the process of polyester copolymerization, the addition of CHDM will have a great impact on the change of T, t and crystallization rate of polyester. With the increase of CHDM content, the melting point of copolyester PETG decreased, the glass transition temperature increased, and the copolymer became amorphous. However, the addition amount of CHDM must be controlled within an appropriate range. Generally, it is recommended that the addition amount of CHDM be 30% - 40%. This kind of PETG modified with diol can be used not only to prepare high shrinkage film, but also to produce heat sealing film and high packaging machine 'target'=_ Blank> transparent diaphragms are widely used

production process of heat shrinkable polyester film

the production process conditions of heat shrinkable polyester film are briefly introduced as follows

1. Drying treatment

because polyester macromolecular chain contains ester group, it has hygroscopic tendency. Under the condition of heating, even if there is a small amount of water, it is very easy to hydrolyze. As a result, a large number of bubbles will be produced in the process of molding, affecting normal production. At the same time, due to hydrolysis and degradation, the molecular weight decreased and the quality of pet deteriorated. Therefore, materials must be dried before melt extrusion processing. It is recommended to use vacuum drum drying. The drying temperature is 70~c ~ 75 ℃, and the drying time is 6h

2. Melt extrusion

copolyester after drying can be added to the single screw extruder for melt extrusion. The temperature of each section is set as 180 ℃ - 240 ℃ - 26o ℃ - 270 ℃ - 275 ℃, and the melt temperature is about 270 ℃. If the exhaust twin-screw extruder is used for melt extrusion, the vacuum drum drying system can be omitted. Because the exhaust twin-screw extruder is generally equipped with two exhaust ports, which are respectively connected with two vacuum pumping systems. The water contained in PET resin and the low molecular weight produced in the process of melt extrusion can be pumped away by vacuum pump, which achieves the same effect, and can greatly save investment and operation cost

3. Cast sheet

the melt extruded by melting enters the clothes hanger die head through the melt metering pump, filter and melt pipe, and then is cast from the die lip to the cooling drum to form a cast sheet. The cooling water temperature of the cooling drum is controlled by Lixin at about 30 ℃

4. Unidirectional stretching

high heat shrinkable polyester, especially communication giants, are competing to invest in films, which often require unidirectional shrinkage, especially transverse heat shrinkage. The preheating temperature of transverse stretching is 90V ~ 1O0 ℃, the stretching temperature is 105 ℃ ~ 110 ℃, and the stretching ratio is 3 ~ 3.5 times. The chain clamp must be strengthened with air cooling, and the clamp temperature should be controlled below 110 ℃ to prevent the copolymer resin from sticking to the clamp. The stretched PET film is immediately cooled without heat setting treatment

5. Winding and slitting

the PET film after unidirectional stretching is cut, inspected and packaged according to the specifications required by the user, which is the finished product of heat shrinkable film

according to statistics, at present, the consumption of PET beverage bottles nationwide is at least 250000 tons, and the consumption of pet heat shrinkable label film can reach 20000 ~ 30000 tons. In addition, since China joined the WTO, foreign trade has been expanding. In order to improve the image and value of export commodities, it is also necessary to use high-grade packaging materials such as polyester heat shrinkable film. In a word, the application prospect of heat shrinkable PET film is very promising

source: modern plastics

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