When the one-dimensional linear scale of a solid or liquid is much smaller than the other two-dimensional linear scale, we call such a solid or liquid a membrane.Generally, films can be divided into two types, one is the film with thickness greater than 1 μ m, called thick film;The other is the film with a thickness of less than 1 μ m, which is called the film.[1]
application
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Semiconductor functional devices andOptical coatingIt is the main application of thin film technology.
A well-known application of surface technology is household mirrors: in order to form a reflective surface, a layer of metal is often plated on the back of the mirror. Silver plating is widely used in the production of mirrors, while extremely thin coatings below one nanometer are often used to make double-sided mirrors.
When optical thin film materials (such as antireflection film and antireflection film) are compounded by several thin layers with different thicknesses and reflectivity, their optical properties can be enhanced.Periodically arranged thin films composed of different metal thin layers with similar structures will form the so-called superlattice structure.In the superlattice structure, the movement of electrons is limited in two-dimensional space and cannot move in three-dimensional space, which results in the quantum well effect.
Thin film technology has a wide range of applications.For a long time, ferromagnetic thin films have been used in computer storage devices, pharmaceuticals, and thin film batteries,Dye sensitized solar cellEtc.
Ceramic filmIt is also widely used.Because of the relatively high hardness of ceramic materials, such films can be used to protect substrates from corrosion, oxidation and wear.The ceramic film on the tool has a particularly significant function, and the service life of the tool with ceramic film can be effectively improved by several orders of magnitude.
At present, research on a new type of inorganic oxide material called multi-component amorphous heavy metal cationic oxide is ongoing, which is expected to be used to manufacture stable, environmentally friendly and low-cost transparent transistors.
Plastic film material
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Plastic packagingPlastic packaging products are taking more and more shares in the market, especially composite plastic flexible packaging, which has been widely used in food, medicine, chemical industry and other fields, among which food packaging accounts for the largest proportion, such as beverage packaging, frozen food packaging, steamed and boiled food packaging, fast food packaging, etc. These products have brought great convenience to people's lives.Here, we briefly introduce several plastic film packaging materials that are most widely used in the industry.[2]
Biaxially oriented polypropylene film is obtained by co extrusion of polypropylene particles into sheets, and then stretching in both vertical and horizontal directions.Due to tensile molecular orientation, this film has good physical stability, mechanical strength, air tightness, high transparency and gloss, and is tough and wear-resistant. It is currently the most widely used printing film.Generally, the thickness is 20-40μ m. The most widely used is 20μ m 。Its main disadvantage is poor heat sealing performance, so it is generally used asComposite filmThe outer layer of the film, such as polyethylene film composite moisture resistance, transparency, strength, stiffness and printability are ideal, suitable for containing dry food.As the surface of biaxially oriented polypropylene film is non-polar, with high crystallinity and low surface free energy, its printing performance is poor, and its adhesion to ink and adhesive is poor, so surface treatment is required before printing and laminating.
Low density polyethylene film is generally made by blow molding and tape casting. The tape casting polyethylene film has uniform thickness, but it is seldom used because of its high price.Blown polyethylene film is blown by blow molding grade PE particles through a blow molding machine, with low cost, so it is most widely used.Low density polyethylene film is a translucent, shiny, soft film with excellentchemical stability, heat sealing, water resistance and moisture-proof, freezing resistance, water boiling, its main disadvantage is poor oxygen barrier, commonly used inComposite flexible packagingThe inner layer film of the material is also one of the most widely used and used at presentPlastic packaging film, accounting for more than 40% of the consumption of plastic packaging film.
Because polyethylene molecule does not contain polar groups, that is, its surface is non-polar, with high crystallinity and low surface free energy, the printing performance of the film is poor, and the adhesion to ink and adhesive is poor. Therefore, surface treatment is required before printing and laminating.
Polyester film is based onPolyethylene terephthalateAs the raw material, the thick sheet is made by extrusion method, and then the film material is made by biaxial stretching.It is a colorless, transparent and shiny film with excellent mechanical properties, high rigidity, hardness and toughness, puncture resistance, friction resistance, high temperature and low temperature resistance, good chemical resistance, oil resistance, air tightness and fragrance retention. It is one of the commonly used barrier composite film substrates, but the price of polyester film is high, and the general thickness is 12μm. It is often used as the outer material of cooking packaging, and has good printability.
Nylon film (PA)
Nylon film is a very tough film with good transparency, good gloss, high tensile strength, high tensile strength, good heat resistance, cold resistance, oil resistance and organic solvent resistance, good abrasion resistance, puncture resistance, and soft, excellent oxygen resistance, but poor water vapor barrier, high moisture absorption, moisture permeability, and poor heat sealing,It is suitable for packaging hard goods, mostly used for the packaging of greasy food, meat products, fried food, vacuum packaged food, cooking food, etc.
Tape cast polypropylene film is a polypropylene film produced by tape casting process. It can also be divided into ordinary CPP and cooking grade CPP. It has excellent transparency, uniform thickness, and uniform performance in both vertical and horizontal directions. It is generally used asComposite filmThe inner layer material of.
The thickness of ordinary CPP film is generally 25-50μM, after compounded with OPP, it has good transparency, bright surface and firm hand feel, which is used for general gift packaging bags.At the same time, the film also has good heat sealing property.The thickness of cooking grade CPP film is generally 60~80μ It can withstand high temperature cooking at 121 ℃ for 30 minutes. It has good oil resistance, air tightness, and high heat sealing strength. Generally, the inner layer of meat packaging uses cooking grade CPP film.
At present, the most widely used aluminized films are polyester aluminized film (VMPET) and CPP aluminized film (VMCPP).The aluminized film not only has the characteristics of plastic film, but also has the characteristics of metal. The role of aluminized film surface is to block light and prevent ultraviolet radiation, which not only extends the shelf life of the contents, but also improves the brightness and appearance of the film. To some extent, it replaces the aluminum foil, which is cheap, beautiful and has good barrier performance. Therefore,The application of aluminized film in composite packaging is very extensive. At present, it is mainly used in the packaging of biscuits and other dry and puffed food, as well as the packaging of other medicines and cosmetics.
