PET plastic profiles
Polyethylene terephthalate mainly includes polyethylene terephthalate PET and polyethylene terephthalate PBT. Polyethylene terephthalate is also called polyester resin, commonly known as polyester resin condensation of ethylene glycol with ethylene glycol, PBT with thermoplastic or saturated polyester. Polyester is thermoplastic linear saturated polyester represented by PET, including PET, PBT, PEN, PCT and their copolymers. PET is the earliest developed, most produced and most widely used polyester product. PET recycled plastic can be used in food packaging and can be recycled infinitely. This is an environmentally friendly technology that China is reaching. Due to the plastic packaging of petroleum, in order to save resources, many developed countries have developed plastic packaging recycling technology. In early 1991, it was necessary to recycle PET plastic sheets for food packaging.
Second, the development status of PET plastics in Korea
At present, pet plastic packaging containers in our country are mainly limited to biaxial oriented polyester blowing bottles. Therefore, the following mainly introduces the development status of Korea’s PET plastics from the development of PET bottles in Korea, and cites examples of two groups leading the PET bottle production industry. Biaxial oriented PET bottle blow molding in our country started relatively late in the plastic packaging industry, but since the introduction of injection stretch blow molding PET bottle production line in Japan in the 1980s, it has achieved good results in cola beverage packaging. Introduced foreign advanced injection stretch blow molding pet bottle blowing machine production equipment, and developed a two-stage PET stretch blow molding machine with independent intellectual property rights based on foreign advanced technology digestion, suitable for Chinese national conditions and simple structure used with general injection molding machines to manufacture PET preforms and biaxial oriented PET bottles.
1. Equipment
With the continuous development of science and technology and the continuous expansion of production scale, the automation degree of PET blow molding machine is getting higher and higher. The production capacity of the equipment has continued to increase from the previous tens of thousands of bottles per hour to the current tens of thousands of bottles per hour. The previous operation has greatly reduced the difficulty of the process and increased the stability of the process. Now the manual button type is developed for full computer control. Although the manufacturers are different, the equipment principles are generally similar, including five parts: blank system, heating system, blow molding system, control system and auxiliary equipment.
2. Blow molding process
The process of blowing a PET bottle important factor influencing the process of blowing a PET bottle are bottle preparation, heating, pre-blowing, mold and environment.
Preform
Preparation of blow molded bottles. First, in the case of PET injection molding preform, the proportion of secondary recycled material should not be too high (less than 5%), the number of recycling should not exceed twice, and the molecular weight and viscosity should not be too low (molecular weight 31000-50000, intrinsic Viscosity 0.78-0.85 cm3/g). The infusion bottle must be stored on top for 48 hours before use. After heating, the preform is not used up and must be stored on top for 48 hours before being reheated for use. Preforms should not be stored for more than 6 months. The quality of the preform is highly dependent on the quality of the PET material. Materials that are easy to install and form should be used and a reasonable preform forming process should be used. Experiments have shown that imported raw materials for PET materials with the same viscosity are easier to blow molding than domestic materials, and the production date and blow molding process may be different even for the same batch of bottles.
Heating
The heating furnace is heated by the heating furnace, and the temperature is manually set. The far-infrared lamp tube heats the far-infrared preform in the oven, and the oven and the bottom of the pot are thermally circulated, and the temperature in the oven is uniform. While the oven is advancing, the bottle body rotates at the same time, so that the bottle body wall is heated evenly. Lights lined up from top to bottom in an oven usually have two more in a “zone” shape and fewer in the middle oven heat due to tube openings, overall temperature settings, oven power and heating rather than normal controls. The opening of the tube must be adjusted with a pre-blowing bottle. Oven better service, height adjustment, cooling plate is important. Improper adjustment, blow molding, the bottle in the mouth of the bottle is easy to expand and become larger), stiffness (the neck material does not open) and other defects
Environment
The quality of the production environment has a greater influence on the process adjustment, and certain conditions can maintain the stability of the process and the stability of the product. PET bottles are blow molded at room temperature and humidity. 3 Other requirements must meet pressure test and pressure test requirements at the same time. The pressure test is to prevent contact between the bottom of the PET bottle blowing machine and the lubricant (alkaline) during the breakdown and leakage of molecular chains and internal quality control. Pressure testing is to prevent gas bottles from being filled with certain pressure bursts and quality control. To meet these two requirements, the thickness of the center point must be controlled within a certain range. In general, the center point is thinner, the stress test is better, and the pressure difference is strong. The center point is thick, the pressure resistance is good, and the differential pressure is strong. Of course, the stress test result is also closely related to the accumulation of the transition region around the central point, and should be adjusted according to actual experience.
