[Abstract] The causes of static electricity, the damage of electrostatic accumulation and discharge to sensitive products are briefly described, and the electrostatic sensitivities of some electronic and military products are introduced. The principle of anti-static packaging was analyzed in detail. Through the analysis of the status quo of anti-static packaging technology, the author believes that decisive measures should be taken to enforce the electrostatic protection technology. It is recommended to strengthen the testing and research on electrostatic hazards, deepen the understanding of electrostatic hazards, and formulate corresponding technical standards as soon as possible from the combination of theory and practice.
Keywords: electrostatic sensitivity anti-static packaging
1 Electrostatic accumulation and electrostatic discharge
When the two substances rub against each other, the one that easily loses electrons is positively charged, and the one that easily receives electrons is negatively charged. The two independent positive and negative charges are the static electricity (ie, static charge) that people usually refer to. In addition to friction, induction of an electric field or an electromagnetic field is also an important cause of static electricity generation.
Static electricity can accumulate, that is, the more electrons are lost, the more positive charges are accumulated; the more electrons are obtained, the more negative charges accumulated.
Accumulation of static electricity can generate extremely high voltages to a very alarming degree. The electrostatic voltage generated by some common activities in daily life is shown in Table 1.
The measured static voltage of some plastics after the experiment is shown in Table 2.
Table 1 The electrostatic voltage generated in daily life
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Generation Method Electrostatic Voltage (V)
----------------------
10%~20%(RH) 65%~90%(RH)
-------------------------------------------------- ---------- Walk on the carpet 3500 1500
-------------------------------------------------- ---------
Walking on Polyolefin Rug 1200 250
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Work on the work bench 6000 100
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Tear envelope 7000 600
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Pick up polyethylene bag 20000 1200 from workbench
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Sitting on a working chair filled with polyurethane foam 18000 1500
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Table 2 The electrostatic voltage brought by some plastics after friction
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Plastic Type Electrostatic Voltage (kV)
Hard PVC 2-4
Soft PVC 1-3
HDPE 1-2
LDPE 0.4-0.8
PP 2-4
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Note: The friction plates are stainless steel, measured at 200C, 65% RH.
Accumulated static electricity encounters suitable conditions (such as when two objects come close to each other), generates an electrostatic discharge (Electrostatic Discharge), and instantly releases a huge amount of energy. In everyday life, when we take off our chemical fiber clothes, we will hear a "click" noise. If you see darkness, you will see a bright flash. This is the phenomenon of electrostatic discharge generated by chemical fiber in friction. The lightning in the natural phenomenon is essentially the discharge phenomenon that the static electricity generated by the water molecules in the mutual friction accumulates under certain conditions.
TPU (Thermoplastic polyurethanes) is a thermoplastic polyurethane elastomer rubber. (60HA-85HD), wear-resistant, oil-resistant, transparent, good elasticity, in the daily necessities, sporting goods, toys, decorative materials and other fields have been widely used in the field of polyester and polyester, Halogen-free flame retardant TPU can also replace the soft PVC to meet more and more areas of environmental requirements.
The so-called elastomer refers to the glass transition temperature is lower than the room temperature, elongation at break> 50%, external recovery after recovery is better polymer materials. Polyurethane elastomers are a special category of elastomers. The polyurethane elastomers have a wide range of hardness and a wide range of properties. Therefore, polyurethane elastomers are a kind of polymer material between rubber and plastic.Can be heated plasticized, chemical structure is not or rarely cross-linked, the molecules are basically linear, but there is a certain physical cross-linking. This type of polyurethane is called TPU.
The main features of TPU are:
Hardness
range: by changing the TPU reaction components of the ratio, you can
get different hardness of the product, and with the increase in
hardness, its products still maintain good flexibility and wear
resistance.
High mechanical strength: TPU products carrying capacity, impact resistance and shock absorption performance.
Cold
resistance highlights: TPU glass transition temperature is relatively
low, at minus 35 degrees still maintain good flexibility, flexibility
and other physical properties.
Good processing
performance: TPU can be a common thermoplastic materials processing
methods, such as injection molding, extrusion, rolling and so on. At the same time, TPU and some polymer materials can be co-processing performance of complementary polymer alloy.
Oil, water, resistant to mold.
Good recycling efficiency.
TPU is a
thermoplastic polyurethane, polyester and polyether type, it is a wide
range of hardness (60A-85D), wear, oil, transparent, good elasticity, in
daily necessities, sporting goods, toys, decorative materials and other
fields are widely Application, halogen-free flame
retardant TPU can also replace the soft PVC to meet the environmental
requirements of more and more areas.
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