Anti-electromagnetic radiation conductive polymer packaging material

2002/2 China Packaging 81 pointed out the development trend of conductive polymer packaging materials.

With the rapid development of science and technology and electronics industry, more and more electronic devices are used. These electronic devices will radiate a large amount of electromagnetic waves to the outside during operation. At the same time, electronic components are also being developed in the direction of miniaturization and high integration. The sensitivity is getting higher and higher, and they are easily subject to external interference, which makes electromagnetic wave radiation more and more influential to products. This puts forward the packaging of modern high-tech products. Higher requirements, especially military products, such as unpackaged protective measures, under the influence of environmental electromagnetic energy, microelectronic components and electronic devices of the weapon system may cause unimaginable consequences. Therefore, to prevent electromagnetic radiation interference as an important technical indicator of packaging materials, more and more people's attention and attention. Developed countries such as the United States, Japan, and Western Europe have conducted extensive and in-depth research on shielding materials against electromagnetic radiation and have achieved certain research results. The research of electromagnetic wave shielding and packaging materials in China is relatively late, and there is a big gap between the technological level and foreign countries. However, with the development of science and technology and the modernization of weaponry and equipment, the anti-electromagnetic performance requirements for packaging materials are increasing, which will certainly increase. In recent years, the research and development of anti-electromagnetic packaging materials in our country has become more and more popular. Electromagnetic radiation packaging materials mainly include conductive high-molecular materials, surface conductive materials, air-permeable shielding materials, and shielding materials used for gaskets. Packaging material is a new type of functional village material developed in the past ten years. Compared with other materials, it has the advantages of light weight, easy molding, and adjustable resistivity. It has been widely used as a packaging material in electromagnetic shielding.

1 Types of conductive polymer coloring materials 汊 Characteristics 1.1 Composite conductive polymer 1.1.1 Conductive plastics Conductive plastics are divided into structural conductive plastics and composite conductive plastics. Currently, only composite conductive plastics are used in electromagnetic shielding. The field has achieved practical applications, and there are many varieties of commercially available composite conductive plastics that refer to plastics that have been physically modified to have electrical conductivity, typically conductive materials such as carbon black, metal powders or fines, metal fibers, etc. Doped with resin, mixed in an extruder or a mixer, plasticized, granulated by a pelletizer, and pelletized by an injection molding machine and molded. When the metal fiber is used as the conductive filler, due to the poor binding force between the metal fiber and the polymer matrix, the metal fiber is unevenly dispersed in the matrix, and the fiber is easily broken to reduce the aspect ratio. In order to ensure that the conductive fiber still has a large aspect ratio in the formed composite, Bayer has improved the composite process by adding the conductive filler approximately 3D in front of the end of the barrel, where sufficient pressure is available. Material homogenization also reduces the abrasion of conductive fibers caused by strong shearing. Toshiba Chemical Co., Ltd. makes long metal fibers and resins into masterbatch with high packing density and mixes with normal resin particles when molding. It can avoid breaking the fiber as easily as the normal kneading method.

Since the fibers are long, a good shielding effect can be obtained with a small amount of use, and the conductive plastic does not peel off or fall off as a conductive film and affects the shielding effect. Therefore, since the 1980s Has caused widespread concern. Conductive plastics have developed rapidly in the United States, Japan, and other countries, but they have just begun in China. The research direction of this type of material is to improve performance and reduce costs, so in recent years, a lot of research has been done on the filler, molding process, and molding equipment. The electromagnetic shielding properties of some foreign conductive plastics are shown in Table 1. Conductive paint is a functional protective packaging material, which has the characteristics of general coatings and has special conductive functions. Conductive coatings are usually composed of synthetic resins, conductive fillers, solvents, and additives. They are applied to the plastic surface to form a cured film, which produces a conductive effect. Therefore, it can shield electromagnetic waves and is an ideal electromagnetic wave shielding packaging material. .

Conductive fillers are an important part of conductive coatings. The choice of conductive fillers is based on the need to select the appropriate type, shape, and amount of conductive fillers: commonly used conductive materials include metal, carbon, and metal oxide fillers. Composite fillers, etc. At present, most of the metal fillers are silver fillers, nickel powders, and copper powders. The silver-based conductive coatings have good conductivity and resistivity of 10"6. Stable, electromagnetic shielding effect is good, but the price is higher, the application is limited; nickel-based conductive coating resistivity is about the performance of a stable, coating hardness, wear resistance, is a more commonly used class of shielding materials; copper The resistivity of the conductive coating is about 10 Hm, although the conductivity is good, but the oxidation resistance is poor, with the development of antioxidant technology in recent years, its development and application has gradually increased.The current key to the study of the metal filler is how To better solve the oxidation resistance of copper powder and the problem of sedimentation of the metal filler during storage, there are still some technical problems in this area that have not yet been solved.The general characteristics of some conductive coatings for electromagnetic shielding are shown in Table 2. The matrix resin is conductively coated The layer plays a role in the skeleton, therefore, the choice of the matrix resin should consider factors such as the coating method, the drying method, the type of the material to be coated, etc. The matrix resin must be able to make the conductive Coatings have general coating properties, such as film-forming properties, adhesion, durability, etc. The molecular weight of the matrix resin has a great influence on the performance of the conductive coating, if the molecular weight is too small, the strength of the coating skeleton after filming is reduced, thus affecting the coating The other physical properties of the layer, if the molecular weight is too large, the toughness of the coating is reduced, the brittleness is increased, and the thickness of the resin film layer between the metal fine particles is increased, thereby affecting the electrical conductivity of the coating layer. In addition, the matrix resin also has a conductive filler A certain degree of affinity and wettability.Commonly used matrix resins and their properties are shown in Table H. In order to improve the construction performance of conductive coatings, to promote the dispersion of conductive fillers, and to improve the leveling and wettability of coatings, and to increase the reinforcing properties, etc. Some coupling agents should be added to the conductive coating.Experiments show that when the content of the coupling agent is small, it is not enough to form a complete protective film. When the content is too high, the protective film layer is too thick, and the spacing of the conductive particles exceeds the electron emission and tunneling effect. The critical value affects the conduction of the particles.

As a treatment agent for preventing the oxidation of the metal powder in the cold conductive coating, the thickness of the formed film layer should generally be as thin as possible in the case of achieving a protective effect.

Due to the characteristics of light weight, good flexibility, large area film formation and resistivity adjustment over a wide range, structural conductive polymers have shown potential applications in electromagnetic shielding in recent years. At present, more structural conductive polymers are polyaniline (PAn) and poly-p-phenylenevinylene (PPV); S. polyaniline (PAn) polyaniline compared with other conductive polymers, raw materials are readily available, and environmental stability.

Good, with high electrical conductivity and excellent electromagnetic performance, but also has the potential for solution processing, is considered the most promising conductive polymer.

Polyaniline conductive fibers can be divided into polyaniline bulk conductive fibers and composite conductive fibers, due to the poor strength of polyaniline body conductive fibers, brittleness, so there is more prospect before H is polyaniline composite conductive fibers. The preparation of polyaniline composite conductive fibers is an important application research field. Chen Yuchi et al. used an easily processable poly(butyl acrylate)-styrene-Hydroxyethyl acrylate copolymer as a matrix to synthesize PAn in its emulsion by oxidative polymerization method. When the oxidant was increased to PAn, it was oxidized to green protonated “emeraldine”. When the composite membrane has the highest conductivity. Ma Yongmei and others prepared dibutyl naphthalene sulfonic acid or dodecyl benzene sulfonic acid doped polyaniline by precipitation polymerization, and the resulting PAn has conductivity, and is generally soluble in organic solvents. Zhang Qinghua et al. used a concentrated sulfuric acid cold solvent to dissolve a certain proportion of polyaniline and nylon-6 in concentrated sulfuric acid, settled and defoamed, and formulated it into a spinning slurry. A white corrosion-resistant stainless steel wet spinning machine was used to spin polyaniline. / Nylon blended conductive fibers, and the distribution of polyaniline in the blended conductive fibers was studied. The results show that: Polyaniline and nylon-6 are an incompatible blend system, under the action of stress, polyaniline along the fiber direction Orientation, the formation of micro-fiber distribution, the distribution of this withering microfibers to promote the conductive component to form more conductive channels, help to improve the conductivity of the fiber.

Poly(p-phenylene) is a polymer that was first used as a conductive material. It has excellent electrical conductivity only and is an important type of horsepower material after doping with strong oxidants. It is expected to be widely used as an electromagnetic shielding packaging material. application. Burroughes et al. first reported that PPV is conductive. Since then, molecular design and synthesis of PPV molecules have become the most dynamic research areas. The PPV fractional synthesis method is mainly Moni et al's 1131 prepolymer method, Wesseling et al. (abbreviated) 2002/2 Chinese Packaging 83