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Pesticide plastic packaging bottle deformation causes and solutions, plastic bottle blowing machine-machinery professional production

by:Yosion Machinery     2021-07-15
In the early 1990s, there was an upsurge of replacing glass with plastic in the pesticide industry in China. In less than ten years, plastic bottles have occupied the leading position in pesticide packaging with their irreplaceable advantages. It can be said that, with the exception of some low-grade pesticide products or small businesses still using glass bottles, people seldom use them to package pesticides anymore. However, in addition to the advantages of light weight, beautiful appearance, easy processing, not easy to break, and competitive overall cost, plastic bottles also have the headache of being deformed. This article intends to make an in-depth discussion on the cause of this problem and how to solve it, and play a role in attracting ideas and brainstorming. Deformation of pesticide plastic packaging bottles mostly occurs in the packaging of emulsifiable concentrate pesticides. The deformation can be divided into three categories according to its causes: 1. Deformation due to hot filling. Pesticides filled in plastic bottles during the pesticide sales season or in some special circumstances The temperature will be much higher than the ambient temperature. Generally, pesticides will be sealed immediately after filling. In order to prevent pesticides from splashing or overflowing the mouth of the bottle during filling, the internal volume of the bottle is generally at least 10% larger than the volume of the liquid to be filled. In other words, the temperature of more than 10% of the remaining air in the bottle after hot filling is the same as that of the pesticide. After a period of time, when the pesticide and internal air drop to the ambient temperature, the bottle will cause negative pressure due to thermal expansion and contraction and the liquefaction of liquid vapor. When the negative pressure exceeds the strength of the bottle wall, it will cause the plastic bottle wall to sink and deform. 2. Deformation due to mutual dissolution and weightlessness. This deformation is derived from the principle of similar polarity of chemical substances. When the polarity of the material of the plastic packaging bottle is similar to the polarity of the organic solvent of the emulsifiable concentrate and pesticide it is packed, there will be mutual miscibility between each other. Over time, mutual dissolution will develop into osmosis. Organic solvents will permeate and escape from the molecular gaps in the material of the packaging bottle. A 100ml bottle of pesticide will become 90ml, 80ml or even less after a certain period of time. Therefore, the lid of the pesticide bottle is sealed, and the weight loss caused by this leakage will inevitably produce negative pressure, which will eventually deform the bottle. Generally, when high-density polyethylene bottles (PE) are used to package aliphatic, or esters and ketones, or aromatic solvents; when polyester bottles (PET) are used to package dimethylformamide (DMF); when more This phenomenon occurs when the inner layer of the co-extruded bottle is polyvinyl alcohol (EVOH) for packaging aromatic or ester and ketone solvents. 3. Deformation due to negative pressure generated by oxidation. The composition of pesticides is very complicated. Some special solvents, emulsifiers, or unknown impurities in the raw materials often oxidize with the oxygen in the air in the bottle, which will lead to negative pressure. Deformed. We have done many rapid aging tests to confirm this phenomenon. For example, we put 1.8% abamectin test pesticide into a plastic bottle, close the lid and make a small hole in the lid to connect it with a U-shaped tube with some water. Then, we put the bottle of pesticide and the U-shaped tube connected to it in an oven at 50°±2°C for 5 days and record the change of the liquid level of the U-shaped tube every day. At the beginning of the temperature rise and for a period of time thereafter, due to the thermal expansion of the liquid and air in the pesticide bottle, a positive pressure is generated in the bottle. The liquid level of the U-shaped tube communicating with the bottle is lower than the liquid level communicating with the outside atmosphere. However, as time goes by, the liquid level difference gradually becomes smaller, and it is level at 30 hours. Then, the liquid level communicating with the atmosphere began to be lower than the liquid level communicating with the bottle, which indicated that negative pressure had begun to appear in the bottle. When the test pesticide is taken out for five days and returned to room temperature, the measured liquid level difference is converted into a negative pressure value of -12.9 kilopascals (Kpa). At this time, the oxygen content in the bottle is also about 20% from the original value~ 21% dropped to 5%~7%. Several methods to solve the deformation In view of the fact that plastic bottle deformation is a common phenomenon, it is necessary for plastic bottle manufacturers to cooperate with pesticide manufacturers to discuss and work hard to solve this problem. 1. The method to overcome the deformation caused by hot filling. It is very simple and straightforward, filling at room temperature as much as possible. In order to achieve this goal, pesticide manufacturers should adopt or extend the circulation transmission pipeline or increase the cooling device to overcome when the temperature of the reactor cannot be lowered. If none of these methods can be achieved, the pesticide should be filled into the plastic bottle and then sealed and capped after it has cooled to normal temperature.
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