In the early 1990s, the Chinese pesticide industry began a boom in plastics. In less than a decade, plastic bottles have dominated the packaging of pesticides with their irreplaceable advantages. It can be said that in addition to some low-grade pesticide products or small enterprises are still using glass bottles, people have rarely used it to package pesticides.
However, in addition to the advantages of light weight, beautiful appearance, easy processing, and easy to break, and the comprehensive cost is competitive, there are also some headaches that are easily deformed. This article intends to make an in-depth discussion on the causes of this deficiency and how to solve it, and play a role in inspiring and brainstorming. The cause of deformation of pesticide plastic packaging bottles
The deformation of pesticide plastic packaging bottles occurs mostly in the packaging of emulsifiable pesticides, and their deformation can be divided into three categories according to their causes:
First, deformation due to hot filling:
In the peak season of pesticide sales or in some special cases, the temperature of pesticides poured into plastic bottles will be much higher than the ambient temperature. In general, pesticides are immediately sealed and tightly closed after filling. In order to avoid spilling or spilling the bottle when filling the pesticide, the internal volume of the bottle is at least 10% more than the volume required to fill the liquid. That is to say, more than 10% of the remaining air in the bottle after hot filling is the same as the pesticide. When the pesticide and internal air are lowered to ambient temperature after a period of time, the bottle will be under negative pressure due to thermal expansion and contraction and liquefaction of the liquid vapor. When the negative pressure exceeds the strength of the bottle wall, it will cause the plastic bottle wall to collapse and deform.
Second, due to mutual dissolution, weight loss and deformation.
This deformation is derived from the principle of close compatibility of the polarities of the chemical. When the polarity of the plastic bottle material is similar to the polarity of the organic solvent of the emulsified pesticide, the mutual solubility occurs. As time goes on, mutual solubility will develop into infiltration. The organic solvent will permeate out of the molecular gap of the bottle material. A bottle of 100 ml pesticide will turn into 90 ml, 80 ml or even less after a certain time. Therefore, the lid of the pesticide bottle is sealed, and the weight loss caused by such leakage inevitably generates a negative pressure, which eventually deforms the bottle.
Generally, when high density polyethylene bottles (PE) are used to package aliphatics, or esters and ketones, or aromatic solvents; when polyester bottles (PET) are packaged with dimethylformamide (DMF); This phenomenon occurs when the inner layer of the co-extruded bottle is a polyvinyl alcohol (EVOH) packaged aromatic or ester and ketone solvent. Third, deformation due to negative pressure caused by oxidation.
The composition of pesticides is very complicated. Some special solvents, or emulsifiers, or unknown impurities in the raw materials often oxidize with oxygen in the air left in the bottle, which leads to negative pressure. Deformation.
We have done many rapid aging tests to confirm this phenomenon. For example, we put 1.8% avermectin test pesticide into a plastic bottle, close the lid and open a small hole in the lid to connect with a U-tube with some water. Then, we put the bottle of pesticide and its connected U-tube into the oven at 50 ° ± 2 ° C for 5 days, and record the change of the liquid level of the U-tube every day.
During the period of temperature rise and after a period of time, a positive pressure is generated in the bottle due to the expansion of the liquid and air in the pesticide bottle. The liquid level in which the U-shaped tube communicates with the inside of the bottle is lower than the liquid level that is open to the outside atmosphere. However, as time goes by, the liquid level difference gradually becomes smaller, and it is flush at 30 hours. Then, the liquid level with the atmosphere begins to fall below the level of the liquid that communicates with the inside of the bottle, which indicates that a negative pressure has 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 to a negative pressure value of -12.9 kPa (Kpa). At this time, the oxygen content in the bottle is also about 20% from the original one. 21% fell to 5% to 7%. Several ways to solve the deformation
In view of the common phenomenon of plastic bottle deformation, it is necessary for plastic bottle manufacturers to work together with pesticide manufacturers to explore and work hard to solve this problem.
First, overcome the method of deformation caused by hot filling. It is very simple and straightforward, filling it as much as possible at room temperature. In order to achieve this goal, pesticide manufacturers should overcome or reduce the temperature of the reactor by taking or extending the circulation pipeline or adding a cooling device. If these methods are not possible, the pesticide should be sealed in the plastic bottle and then sealed until it is cooled to room temperature.
Second, the solution to the deformation caused by mutual dissolution and weight loss. The main method is to select different plastic bottles with targeted barrier materials according to different solvents in the emulsifiable pesticides, and confirm them by compatibility test before selection.
In general, liquid pesticides and suspensions of liquid pesticides are less deformed, and ordinary plastic bottles are fully capable.
Epoxy pesticides are highly corrosive because of their solvents. Therefore, in the "Pesticide Emulsion Packaging" which was recently promulgated in China and implemented on March 1, 2001, it is particularly clear that glass bottles, high-density polyethylene fluorinated bottles and Equivalent bottles (bags) of other materials are used for packaging.
It should be said that polyester bottles (PET) also have a good barrier effect on some solvents used in emulsifiable pesticides, but PET is easy to absorb the moisture in the environment, which leads to the inherent deficiency of pesticide moisture exceeding, decomposing and even failing. Restricted use.
In terms of barrier effect, glass bottles, aluminum bottles, multi-layer co-extruded bottles (inner layer of nylon or polyvinyl alcohol) and fluorinated bottles all perform well. However, relatively speaking, glass bottles are becoming less and less used due to their vulnerability to the fatal weakness of pollution. Aluminum bottles are more expensive. In terms of cost performance, multi-layer bottles are inferior to fluorinated bottles; in terms of effect, multi-layer bottles of 100 ml and below are superior to fluorinated bottles, but the larger the specification, the stronger the competitiveness of fluorinated bottles.
Since the inner layer of the multi-layer bottle is made of nylon or polyvinyl alcohol, it depends on the type of solvent in the pesticide. The inner wall of the fluorinated bottle is a fluoroplastic layer such as polytetraethylene (plastic king). The composition is very complicated, so the two kinds of barrier bottles are selected. The compatibility test of the product must be carried out to confirm the barrier effect. Third, the solution to the deformation caused by the oxidation of negative pressure.
For pesticide manufacturers, it may be considered to replace the solvent or emulsifier and control the impurity content of the raw material to increase the purity and reduce the possibility of oxidation. At the same time, it can emulate an international company to fill nitrogen during pesticide filling to reduce the oxygen content of the retained air, achieving the dual purpose of stabilizing pesticide components and avoiding oxidation reactions.
In the case of plastic bottle manufacturers, the weight of the bottle can be increased to increase the deformation resistance of the bottle with the permission of the equipment and mold. When the increase in weight has reached the limit and the problem remains unresolved, consideration should be given to developing a new bottle with ribs to solve the problem, but this method requires the development of new molds and takes a certain amount of time. The manufacturer must have considerable investment and Take on no small risk (when the bottle shape is not acceptable to the user).
However, in addition to the advantages of light weight, beautiful appearance, easy processing, and easy to break, and the comprehensive cost is competitive, there are also some headaches that are easily deformed. This article intends to make an in-depth discussion on the causes of this deficiency and how to solve it, and play a role in inspiring and brainstorming. The cause of deformation of pesticide plastic packaging bottles
The deformation of pesticide plastic packaging bottles occurs mostly in the packaging of emulsifiable pesticides, and their deformation can be divided into three categories according to their causes:
First, deformation due to hot filling:
In the peak season of pesticide sales or in some special cases, the temperature of pesticides poured into plastic bottles will be much higher than the ambient temperature. In general, pesticides are immediately sealed and tightly closed after filling. In order to avoid spilling or spilling the bottle when filling the pesticide, the internal volume of the bottle is at least 10% more than the volume required to fill the liquid. That is to say, more than 10% of the remaining air in the bottle after hot filling is the same as the pesticide. When the pesticide and internal air are lowered to ambient temperature after a period of time, the bottle will be under negative pressure due to thermal expansion and contraction and liquefaction of the liquid vapor. When the negative pressure exceeds the strength of the bottle wall, it will cause the plastic bottle wall to collapse and deform.
Second, due to mutual dissolution, weight loss and deformation.
This deformation is derived from the principle of close compatibility of the polarities of the chemical. When the polarity of the plastic bottle material is similar to the polarity of the organic solvent of the emulsified pesticide, the mutual solubility occurs. As time goes on, mutual solubility will develop into infiltration. The organic solvent will permeate out of the molecular gap of the bottle material. A bottle of 100 ml pesticide will turn into 90 ml, 80 ml or even less after a certain time. Therefore, the lid of the pesticide bottle is sealed, and the weight loss caused by such leakage inevitably generates a negative pressure, which eventually deforms the bottle.
Generally, when high density polyethylene bottles (PE) are used to package aliphatics, or esters and ketones, or aromatic solvents; when polyester bottles (PET) are packaged with dimethylformamide (DMF); This phenomenon occurs when the inner layer of the co-extruded bottle is a polyvinyl alcohol (EVOH) packaged aromatic or ester and ketone solvent. Third, deformation due to negative pressure caused by oxidation.
The composition of pesticides is very complicated. Some special solvents, or emulsifiers, or unknown impurities in the raw materials often oxidize with oxygen in the air left in the bottle, which leads to negative pressure. Deformation.
We have done many rapid aging tests to confirm this phenomenon. For example, we put 1.8% avermectin test pesticide into a plastic bottle, close the lid and open a small hole in the lid to connect with a U-tube with some water. Then, we put the bottle of pesticide and its connected U-tube into the oven at 50 ° ± 2 ° C for 5 days, and record the change of the liquid level of the U-tube every day.
During the period of temperature rise and after a period of time, a positive pressure is generated in the bottle due to the expansion of the liquid and air in the pesticide bottle. The liquid level in which the U-shaped tube communicates with the inside of the bottle is lower than the liquid level that is open to the outside atmosphere. However, as time goes by, the liquid level difference gradually becomes smaller, and it is flush at 30 hours. Then, the liquid level with the atmosphere begins to fall below the level of the liquid that communicates with the inside of the bottle, which indicates that a negative pressure has 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 to a negative pressure value of -12.9 kPa (Kpa). At this time, the oxygen content in the bottle is also about 20% from the original one. 21% fell to 5% to 7%. Several ways to solve the deformation
In view of the common phenomenon of plastic bottle deformation, it is necessary for plastic bottle manufacturers to work together with pesticide manufacturers to explore and work hard to solve this problem.
First, overcome the method of deformation caused by hot filling. It is very simple and straightforward, filling it as much as possible at room temperature. In order to achieve this goal, pesticide manufacturers should overcome or reduce the temperature of the reactor by taking or extending the circulation pipeline or adding a cooling device. If these methods are not possible, the pesticide should be sealed in the plastic bottle and then sealed until it is cooled to room temperature.
Second, the solution to the deformation caused by mutual dissolution and weight loss. The main method is to select different plastic bottles with targeted barrier materials according to different solvents in the emulsifiable pesticides, and confirm them by compatibility test before selection.
In general, liquid pesticides and suspensions of liquid pesticides are less deformed, and ordinary plastic bottles are fully capable.
Epoxy pesticides are highly corrosive because of their solvents. Therefore, in the "Pesticide Emulsion Packaging" which was recently promulgated in China and implemented on March 1, 2001, it is particularly clear that glass bottles, high-density polyethylene fluorinated bottles and Equivalent bottles (bags) of other materials are used for packaging.
It should be said that polyester bottles (PET) also have a good barrier effect on some solvents used in emulsifiable pesticides, but PET is easy to absorb the moisture in the environment, which leads to the inherent deficiency of pesticide moisture exceeding, decomposing and even failing. Restricted use.
In terms of barrier effect, glass bottles, aluminum bottles, multi-layer co-extruded bottles (inner layer of nylon or polyvinyl alcohol) and fluorinated bottles all perform well. However, relatively speaking, glass bottles are becoming less and less used due to their vulnerability to the fatal weakness of pollution. Aluminum bottles are more expensive. In terms of cost performance, multi-layer bottles are inferior to fluorinated bottles; in terms of effect, multi-layer bottles of 100 ml and below are superior to fluorinated bottles, but the larger the specification, the stronger the competitiveness of fluorinated bottles.
Since the inner layer of the multi-layer bottle is made of nylon or polyvinyl alcohol, it depends on the type of solvent in the pesticide. The inner wall of the fluorinated bottle is a fluoroplastic layer such as polytetraethylene (plastic king). The composition is very complicated, so the two kinds of barrier bottles are selected. The compatibility test of the product must be carried out to confirm the barrier effect. Third, the solution to the deformation caused by the oxidation of negative pressure.
For pesticide manufacturers, it may be considered to replace the solvent or emulsifier and control the impurity content of the raw material to increase the purity and reduce the possibility of oxidation. At the same time, it can emulate an international company to fill nitrogen during pesticide filling to reduce the oxygen content of the retained air, achieving the dual purpose of stabilizing pesticide components and avoiding oxidation reactions.
In the case of plastic bottle manufacturers, the weight of the bottle can be increased to increase the deformation resistance of the bottle with the permission of the equipment and mold. When the increase in weight has reached the limit and the problem remains unresolved, consideration should be given to developing a new bottle with ribs to solve the problem, but this method requires the development of new molds and takes a certain amount of time. The manufacturer must have considerable investment and Take on no small risk (when the bottle shape is not acceptable to the user).
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