Introduction to the properties of coated composites

1. Electromagnetic functional coating

 

The anti-corrosion coating is a protective coating applied to the surface of the substrate (metal, cement or wood, etc.) according to the principle of electrochemical corrosion. In addition to the technical properties of general paints (such as dryness, viscosity, fineness, impact, adhesion and flexibility, etc.), the coating also needs to meet the special requirements of anti-corrosion. The anti-corrosion function of the coating lies in the shielding effect, resistance effect, wet adhesion, chemical passivation and cathodic protection of the coating. The general anti-corrosion coating is divided into three layers, namely the bottom layer, the middle layer and the surface layer. The bottom layer prevents the formation and development of rust by adding anti-rust agent (zinc-rich material), and the intermediate layer and surface layer give the substrate appearance characteristics. The coating thickness is about 200um.

 

2. Electrical insulating coating

 

Electrical insulating coatings are mainly used in wires and electrical equipment to insulate and protect. They are divided into surface coating type and insulating void filling type. The coating surface layer mainly uses coating materials, mainly polyurethane system, epoxy system and PI. The insulation grade of the insulating coating with PI as the main material can reach F grade and H grade. Filled insulation type uses insulating material to fill the material, E grade or below requirements, coated with polyester film and then wrapped, F grade or above, wrapped with PI film or PI coated silicone pressure-sensitive adhesive.

 

3. Electromagnetic wave shielding coating and conductive coating

 

Electromagnetic waves and electrostatic interference will cause confusion on the TV screen, noise on the radio, computer errors, and even major accidents such as robot killing; electromagnetic radiation from strong electromagnetic wave emission sources will also cause great harm to the environment and operators, so it is necessary to carry out appropriate measures. Electromagnetic shielding and electrostatic shielding. Through the electromagnetic wave shielding material, the electromagnetic wave is reflected, which can effectively avoid the interference of the electromagnetic wave. In the past, electronic and electrical equipment were generally shielded by metal casings, but now with the extensive use of plastic materials, the problem of electromagnetic interference has become increasingly prominent. Filling the material with conductive components and applying a conductive coating on the surface of the material are the main solutions to avoid electromagnetic wave interference. After the material is filled with conductive components, the mechanical properties of the material are often affected. Therefore, it is the most effective method to apply a conductive coating on the surface of the material. The existing conductive coating methods are divided into two types: direct coating of conductive paint and bonding of conductive tape. The former is a coating mixed with conductive powder (such as metal powder, metal oxide, graphite carbon and various organic or inorganic powders coated with metal or carbon) on the surface of the material. Conductive tapes are mainly made of metal foil-backed conductive adhesives and adhesives modified with conductive particles. Such as 3M's conductive tape (5000, 6000, 7000 series). Due to its easy construction and stability, conductive tape has gradually begun to be popularized and applied in the electronics industry, but the adhesive strength and stability of the tape still need to be improved.

 

4. Electromagnetic wave absorption coating

 

Electromagnetic wave absorbing coating material is a material that prevents electromagnetic interference by absorbing electromagnetic wave radiation energy and attenuating electromagnetic wave. The electromagnetic waves reflected by high-rise buildings will interfere with the received signal of TV broadcasting, resulting in the so-called ghost image; when the ship is near a large bridge, the ship's radar will also generate ghost images, which will affect the navigation safety of the ship at night or in dense fog. ; Radar on aircraft flight timing can cause the same problem. In order to prevent high-rise buildings, bridges, ships, airplanes, etc. from reflecting electromagnetic waves, electromagnetic wave absorbing coatings can be applied on them. The existing technology is to use electromagnetic wave absorbing paint for spraying. Electromagnetic absorption materials are iron series (iron powder, ferrite, polycrystalline iron fiber, etc.), carbon series (graphite, acetylene carbon black, carbon fiber tube, carbon nanotube, etc.), ceramic series, plasma and chiral wave absorbing materials Wait. The absorbing coating needs to cooperate with the EMI coating to achieve the desired effect.

 

5. Stealth coating

 

Stealth technology is mainly used in the military field, which refers to controlling and reducing the identifiable characteristic signal of the target in a certain detection environment, making it difficult to be found, identified and attacked within a certain range. At this stage, it mainly focuses on radar and infrared detection technology. The stealth technology for radar has matured after more than 60 years of development from World War II to the present. Infrared detection technology and laser detection technology will be the future development direction. Similar to electromagnetic wave absorption coating, the forming process of stealth coating is mainly coating type and structure type. In order to achieve better wave absorption effect, both are often used in one product. Camouflage is the easy way to stealth technology in visible light, the technology used to stealth lamps during World War II, and now, thin fluorescent panels, light-emitting polymer panels, and shimmering skins have made aircraft invisible.

 

6. Magnetic coating

 

It is widely used in audio tapes, video tapes, computer floppy disks, various credit cards, train tickets and regular tickets. In addition, there are also paints for electrophotographic scribing and coatings for printed circuits and integrated circuits. The former is a precoat primer made of epoxy resin and photoconductive zinc oxide; the latter is a UV-cured electrophoretic photoresist for printed circuit boards using electrophoretic coating technology and photosensitive resin technology.