Views: 74 Author: Site Editor Publish Time: 2022-03-29 Origin: Site
PET bottles have strong applicability and are widely used in daily necessities, daily chemical packaging and other fields. The preform is the intermediate semi-finished product of the subsequent two-way stretch blow molding. Some factors of the preform affect the quality of the injection molded product. Below, I will share with you the precautions for the PET preform. Under a certain temperature and pressure, the mold is filled with raw materials and processed by the injection molding machine to form a bottle blank with a certain thickness and height corresponding to the mold. PET preforms are reprocessed by blow molding to form plastic bottles, including bottles used for packaging cosmetics, medicines, health care, beverages, mineral water, reagents, etc. This bottle making method is called a two-step method, that is, the preform is formed through injection molding. A method of forming PET plastic bottles through blow molding.
The transparency is as high as 90% or more, the surface gloss is excellent, and the glass-like appearance is excellent; the fragrance retention is excellent, the air tightness is good; the chemical resistance is excellent, and it is resistant to almost all organic drugs, led by acid; good hygiene; Toxic gas is generated; the strength characteristics are excellent, and various characteristics can be further improved by biaxial stretching.
Because PET has a certain degree of water absorption, it will absorb a lot of water during transportation, storage, and use. High content of water will be exacerbated in the production: -AA (Acetaldehyde) increase in acetaldehyde. The impact on the bottle's odor leads to a change in flavor (but has little impact on the human body) and a decrease in -IV (IntrinsicViscosity) viscosity. It has an impact on the pressure resistance of the bottle and is easy to break. (The essence is caused by the hydrolytic degradation of PET). At the same time, it prepares for high temperature for PET into the injection molding machine for shearing and plasticizing.
Dry setting temperature 165℃-175℃, residence time 4-6 hours, discharge port temperature above 160℃, dew point below -30℃,
Dry air flow rate 3.7m⊃3; /h per kg/h.
The ideal moisture content after drying is about 0.001-0.004%. Excessive drying will also aggravate: -AA (Acetaldehyde) increase, -IV (IntrinsicViscosity) viscosity decrease (essentially caused by PET oxidative degradation).
(1) Treatment of plastics
Because PET macromolecules contain fat base and have certain hydrophilicity, the pellets are more sensitive to water at high temperature. When the moisture content exceeds the limit, the molecular weight of PET decreases during processing, and the product becomes colored and brittle. Therefore, the materials must be dried before processing, and the drying temperature is 150°C for more than 4 hours; generally 170°C for 3-4 hours. The air shot method can be used to check whether the material is completely dry. Generally, the proportion of recycled PET preforms should not exceed 25%, and the recycled materials should be thoroughly dried.
(2) Selection of injection molding machine
Because PET has a short stabilization time after melting point and high melting point, it is necessary to choose an injection system with more temperature control sections and less self-friction heat generation during plasticization, and the actual weight of the product (water cut material) cannot be less than the machine injection 2/3 of the amount.