Focus on plastic packaging container industry for 15 years.
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Focus on plastic packaging container industry for 15 years.
Author: mgg-Plastic bottle manufacturer
Beautiful fruit plastic solutions Peticle and blow bottle Process To point PET is Polyethylene Terephthalate referred to as PET, the application in the beverage packaging field promotes the rapid development of the beverage packaging industry. At the same time, the development of the beverage packaging industry also provides space for PET applications. Strictly control the PET stack and blowing process is the key to ensuring the appearance of the PET bottle and its economy.
PET's characteristic PET is ethylene glycol and terephthalic acid condensation product is a saturated thermoplastic polymer. The PET molecules have a linear and semi-crystalline state. The simplest process of producing PET is the reaction of benzoic acid and ethylene glycol forming a monomer (esterification), and then the polymerization of the growth chain polymer PET polymerization varies with temperature and pressure.
PET is the same as many plastics, and there are three-state variations during processing, namely glass, high elastic, and viscosity. It involves three temperature transitions: glass transition temperature Tg, crystallization temperature Tc, melting point Tf. The transformation of the radioprotic transition from an amorphous glass-state to the rubber state, which means that the long segment begins to move.
External heating can add molecular (link) degrees of freedom, and can now move in glass solidified molecules. The glass transition depends on the form of PET. When the viscosity of the characteristic (IV) is high, the crystallization of the molecular chain is limited, and the Tg is higher.
As the temperature increases, local spherical crystals are gradually produced, resulting in rearrangement of the partial sub-chain due to molecular energy, ie crystallization. For PET, the maximum crystallinity is about 55%, which is slowly caused by aromatic ring rearrange, so the aromatic ring is hindered from the formation of the crystal zone. If T
The temperature of the melting point TF is meant to all crystalline. PET drying and dryer hydrolyzed solid PET is easily absorbed from air. When stored, PET will moisture so that it is saturated with environmental conditions.
The saturation value can be as high as 0.6% by weight. Typically, PET is shipped at a supplier, with a water content of less than 0.1% by weight. In order to achieve the best product performance, it is necessary to reduce the water content to 0.004%, preferably 30 ppm before melting.
If water is contained in the resin, even if it is low, it will cause a series of reactions: When the temperature is higher than the PET melting point (about 250 ° C), water will quickly cause polymer degradation (due to the degradation of water). This will reduce the molecular weight, reduce apparent viscosity and related physical properties. In fact, hydrolysis begins to occur at lower temperatures (such as 150 ° C), but the speed is low, and its speed rises with temperature. Under drying and molding conditions, the decrease in IV cannot be greater than 0.02 dl / g.
The decrease in viscosity can result in an increase in crystallization speed, unfavorable to the transparency of the bottle blank, and cause a decrease in the mechanical properties of the bottle, the load strength and impact strength decrease. The impact of the heat-degradation temperature on the dry PET is complicated. It not only affects the diffusion speed of the water, but also affects the chemical process of dry, so it will eventually affect the performance of the resin. Considering the potential hydrolysis and heat processes are very necessary, as mentioned earlier, with the decrease in IV, the speed of hydrolysis is accelerated at 150 ° C, because the thermal transformation process is fast than the diffusion process, the temperature is too early when the temperature is adversely of.
Similarly, even if most of the water can be exhausted, too high temperature (such as 180 ° C) will result in thermal degradation and thermal oxidation (in the air drying system), so that the polymer chain breaks, and releases the by-product substance Resulting in a decrease in physical properties. AA ingredients in the by-products, changes in physical properties will be present on the bottle blank, such as the crystallization of haze, IV decline, yellow product yellow. The drying principle and basic properties of the PET dryer are absorbently absorbed by moisture dryers in a desiccant bed, and a hot air blower pressure is pressed into the fight.
The returning fluid is dried through a desiccant. After heating, the desiccant releases water gas, and then absorbs moisture after cooling. Therefore, two separate airways must minimize and have a desiccant. .
