Damping coating refers to the coating that can reduce vibration and noise, and has a wide range of uses. The vibration and noise caused by the engines and transmission systems of aviation, aerospace engines, trains and automobiles will directly cause the vibration of the shell, affect the normal operation of instruments and meters, and If the natural frequency of the body is close, it will cause the resonance of the shell. In addition to becoming a secondary vibration source of noise and causing noise pollution in the surrounding space , this resonance will also cause material fatigue, reduce the strength of the material or even break prematurely. Threat to the safety of flight and operation.
Polymer materials have obvious viscoelasticity, which can consume part of the vibration energy and release it in the form , that is, realize the damping function through mechanical loss. The damping performance depends on the loss factor tanδ of the polymer material, and the larger the loss factor value, the better the effect. The loss factor is related to the polymer structure, and changes with the ambient temperature, the frequency of alternating stress, and the prestress, among which the influence of temperature is the greatest. The polymer has the highest loss peak (α peak) in the glass transition region (high elastic state), and the paint film with good damping performance should be in the glass transition region at ambient temperature. Therefore, the selection requires both a suitable glass transition temperature and a high loss factor. The glass transition temperature can be adjusted by adding plasticizer and copolymerization. The glass transition temperatures of several polymers are different from each other, and are incremented or decremented at appropriate intervals, which can have a damping effect in a wide temperature range. The glass transition temperatures of polyvinyl chloride mixture of the three polymers in equal amounts can have three mechanical properties at the frequency of variable stress. The loss peak, that is, greater loss can occur between 87 and 105 °C, and has a strong damping effect. Polymer alloys using effects. Adding flake pigments to the paint can play a reinforcing role and increase the damping effect. It should be noted that when the coating film needs to be heated and cross-linked to cure, the degree of cross-linking should be controlled. If the cross-linking is too high, the polymer cannot enter the viscoelastic state and no loss peak will appear.
Damping coatings are widely used in spacecraft shells, ships, aircraft shells, automobile shells, chassis, car interiors , construction machinery operating rooms, generator and gas turbine enclosures, ship engine room sound insulation, building vibration reduction, and noise reduction. Obvious effect has been achieved. It has been widely used abroad. Our country started relatively late. With the formulation of noise standards and environmental protection laws, the research and development of damping coatings will be further developed.
The vibration and noise reduction effect of damping coatings depends to a large extent on the properties of the base material. Among the researches on many damping materials, polyurethane, epoxy resin, and acrylic base materials are the most common damping materials. Examples are as follows.
(1) IPN polyurethane foam damping material: The semi- compatible polymer made by compounding high Tg and low Tg polymers has a wide range of noise reduction. All foams exhibit superior and low-density foams have better sound absorption effects than high-density foams, which shows that the porous structure is very necessary for sound absorption, because the noise The form contacts the foam structure, where it is converted into heat and dissipated inside the foam structure.
(2) IPN polyurethane% epoxy resin damping material: The glass transition range is a function of the doping amount of epoxy resin. As long as it is a doped system, the glass transition range is wide, indicating that it has good damping ability.
(3) Acrylic LIPN (emulsion interpenetrating network) damping coating: polymer ionomer latex flashes in a wide temperature range and is a new type of damping material with a high damping factor.
