Processing and molding of PET bottles for gunpowde

2022-08-17
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Processing and molding of medical PET bottles (Part 1)

polyester plastic (PET) bottles are one of the most important packaging containers at present. Their molecular structure is completely the same as that of ordinary polyethylene. They are also used to package alcoholic beverages, tea beverages, fruit juices, mineral water, edible oil, condiments, cosmetics, pesticides, detergents and other liquids. As a drug packaging container, polyester bottles have many advantages. First, polyester bottles are light in weight, easy to form and firm in body. Their strength and elasticity are significantly higher than those made of other plastic materials. They can withstand considerable impact without damage. They are most suitable for making drug packaging bottles with thin wall, light weight and high strength. PET bottle source has developed rapidly with an irresistible momentum since it came out in China in the early 1980s. In a short period of more than 20 years, it has developed into the world's most important form of liquid and solid packaging. In the field of drug packaging, when the volume of the medicine is the same, the weight of the PET bottle is only about 1/10 of that of the glass bottle. The capacity of the PET bottle with the same outer diameter is 1.5 times that of the glass bottle. Transparent or opaque brown bottle bodies can be made from PET raw materials. Medical PET bottles have good gas barrier property. Among the commonly used plastics, PET bottles have the best performance of blocking water vapor and oxygen, which can fully meet the special storage requirements of drug packaging. Pet has excellent chemical resistance and can be used for the packaging of all items except strong alkali and some organic solvents. The recycling rate of PET resin is higher than that of other plastics. When it is burned as waste, it is flammable due to its low combustion heat card value and does not produce harmful gases. The food packaging made of pet meets the requirements of food hygiene, because PET resin is not only a harmless resin, but also a pure resin without any additives. It has passed the inspection of quite strict food hygiene laws including the United States, Europe and Japan, and is recognized as a qualified and safe packaging material for drugs and food. Polyester resin is a polymer containing ester groups on the main chain of molecules. When polyester is applied, it usually refers to linear polyester: polyethylene terephthalate. It is transparent, has high tensile strength, good heat and low temperature resistance, non-toxic, light weight, good chemical stability, good barrier to oxygen, steam and odor. These advantages make it a leader in plastics. At present, the world's output is growing at a double-digit rate. The pharmaceutical plastic bottle made of polyester as the main raw material is one of the most ideal varieties at present in terms of appearance, gloss, physical and chemical properties and quality assurance

main processing technology of pharmaceutical polyester bottles

1. Characteristics of pharmaceutical polyester raw materials

the PET raw material used for bottle body blow molding is saturated linear thermoplastic polyester. The main application performance indicators are: the intrinsic viscosity (IV) should be controlled at ml/g, so that the blow molding bottle has high mechanical strength and transparency. It is used to stretch the bottle body with large volume (greater than 2 liters). The intrinsic viscosity of polyester raw material is ml/g. Injection blow molding pharmaceutical small volumetric flasks should preferably be produced with higher intrinsic viscosity index. Whether the variety of raw materials is selected correctly or not is related to the selection of molding process parameters in the production process and the quality of the bottle after molding. Therefore, when producing pharmaceutical PET bottles, the process data such as the intrinsic viscosity, crystallization temperature, cooling rate and orientation effect of raw materials are particularly important, because polyester material is a crystallizable polymer, and its crystallization rate is very small, only 6um/min (max). That is, by controlling the crystallization temperature and cooling rate, the polyester bottle can become amorphous or crystalline, and the type and quantity of crystals can be changed. The crystallinity of polyester is generally about 30%. At a temperature slightly higher than the glass transition temperature or slightly lower than the melting point, the crystallization rate of polyester is very small, and the crystallization takes a long time. At a temperature of about 175 ℃, the crystallization time is much shorter. In short, polyester crystallizes only by heating. The crystallization process is slow, and it is possible to form spherulites with large grains, which will refract light, making the product white and brittle. In addition, the crystallization rate of polyester decreases with the increase of its IV. Orientation can make polyester molecules orderly arrange and promote crystallization. The formed crystal is called strain induced crystal. Its grain size is very small and will not refract light, so oriented polyester products are transparent. If the polyester sample with partially crystallized orientation is heat set to further crystallize, the sample is still transparent. Therefore, crystallization and orientation are the key factors that affect the performance of stretch blow molded polyester bottles in the molding process. If you want to produce the bottle into hot filling and can be used for bar disinfection treatment, you also need to heat set the partially crystallized polyester to further crystallize it to improve the heat resistance. Therefore, the process characteristics, molecular crystallization and orientation of polyester raw materials are the key factors of quality characteristics in the processing process

2. Dehumidification and drying of polyester materials

due to the hydrolysis of the water contained in polyester during processing, it has also made great contributions to the national economy and national defense construction. In the process, it reacts with polyester melt and is consumed rapidly, that is, water in process products show bubbles. Hydrolysis will reduce the intrinsic viscosity of polyester melt, and also affect the mechanical strength and performance of products. Polyester raw materials are hygroscopic polymers, so they should be strictly dried before processing, so that the residual moisture content is less than 0.005%. Polyester raw materials should be dried by dehumidification drying system. As the dry hot air provided by the drying device enters the raw material from the bottom of the hopper, it absorbs the moisture contained in the raw material and returns to the drying device. In order to prolong the service life of the originally flammable polyurethane foam in the dehumidification bed of the drying device into a fire-resistant material with high oxygen index, low flame propagation, low smoke, low toxicity, good flammability and strong fire-resistant flame penetration, and maintain its efficiency, it is necessary to make the wet air from the hopper pass through the post cooling device (which can be cooled by circulating water), so that the air temperature is lower than 65 ℃. The post cooling device should be thermostatically controlled to prevent the air with too high temperature from entering the dehumidification bed. The cooled air passes through the filter to remove particles in the air. Then the air is removed by the dehumidification bed, and finally heated by the heater and then returned to the drying hopper again. Generally, the conditions for drying raw materials in the dryer are as follows: the drying temperature should not bear the fatal test caused by severe inflation, taking 140 ℃ -180 ℃, air dew point -40 ℃, air volume 0.06 cubic meters/min (kg.h), and drying time 4H. Attention should be paid to mastering these conditions; (1) When the value of air volume is higher than 0.06 cubic meter/min (kg.h), the operation range can be widened, the drying temperature can be reduced, and the energy consumption will be too high. (2) It is very important to ensure that the dry dew point is as low as possible, but there will be no problem if the dew point is as low as -10 ℃, but the air dew point should also be strictly monitored. If it is found to be too high, it should be reduced in time. (3) Drying temperature is a key parameter. The best drying temperature can be determined by drying at various temperatures and measuring the intrinsic viscosity of the parison, generally 150 ℃ -163 ℃. The drying temperature should be reduced to about 120 ℃ during shutdown. (4) Lengthening the drying time will reduce the intrinsic viscosity of polyester raw materials. A reasonable grasp of the drying temperature has become a key parameter. A small increase in temperature will lead to a large reduction in the intrinsic viscosity of polyester. Therefore, the drying time should be as short as possible to broaden the operation range. In the drying process, due to the high drying temperature of polyester, the hopper of the equipment should have good heat insulation performance and use glass fiber as the heat insulation layer. It should avoid the contact between the dry polyester raw material and the outside air, because the polyester raw material will quickly absorb the wet steam in the air. For example, the moisture content of completely dry polyester raw materials will reach 0.005% after contacting with air with a relative humidity of 35%-40% for 12 minutes

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