Plastic films made of polyvinyl chloride, polyethylene, polypropylene, polystyrene and other resins are used for packaging and for film coating. Plastic packaging film products market share was growing, especially the composite plastic packaging, has been widely used in food, medicine, chemical and other fields, especially in food packaging accounted for the largest proportion, such as beverage packaging, frozen food packaging, food packaging, food packaging, food cooking. These products have brought great convenience to people's life.
PVA coating high barrier film is the application of PVA coated with nano inorganic particles on polyethylene film
Biaxially oriented polypropylene film is made from polypropylene particles by coextrusion and then stretched in two directions. Due to stretching of molecular orientation, physical stability, so this kind of film mechanical strength, good air tightness of transparency and gloss, high tenacity, wear-resisting, is currently the most widely used printing film, generally use the thickness of 20 ~ 40 m, the most widely used is 20 m. The main drawback is the biaxially oriented polypropylene film heat sealing is poor, so generally used as an outer film composite film, such as polyethylene film and composite moisture resistance, transparency, strength, stiffness and printability were ideal, suitable for holding dry food. Because the surface of biaxially oriented polypropylene film for nonpolar, high crystallinity and low surface free energy, therefore, the poor performance of printing, ink and adhesive adhesion, surface treatment and compound before printing.
LDPE films are usually made by two processes: blow molding and tape casting. Cast polyethylene film is uniform in thickness, but it is widely used because of its high price and low cost. Low density polyethylene film is a translucent, glossy, soft texture film, with excellent chemical stability, heat sealing, water resistance and moisture resistance, freezing resistance, can be boiled. The main drawback is that the oxygen barrier property is poor, the inner membrane is commonly used in soft packing materials, and is currently the most widely used, one of the largest amount of plastic packaging film, accounting for more than 40% of the consumption of plastic packaging film.Polyester film is made from poly (ethylene terephthalate) by extrusion method and then stretched by biaxial stretching. It is a colorless and transparent film, gloss, excellent mechanical performance, rigidity, hardness and high toughness, puncture resistance, friction resistance, high temperature resistance and low temperature resistance, chemical resistance, oil resistance, air tightness and fragrance is good, is one of the commonly used barrier composite film substrate. But the price of polyester film is high, the general thickness is 12 m, commonly used as cooking and packaging of the outer layer material, printability is better.
Nylon film is a very tough film, good transparency, good gloss, tensile strength, high tensile strength, but also has good heat resistance, cold resistance, oil resistance and organic solvent resistance, wear resistance, puncture resistance and excellent, relatively soft, excellent oxygen barrier, but the water vapor barrier is poor, moisture absorption, moisture permeability is larger, the heat sealing is poor, suitable for packaging rigid items, such as greasy food, meat, fried food, vacuum packing food, cooking food etc..
Polypropylene film of polypropylene film production by casting process, can be divided into ordinary CPP and CPP two kinds of cooking, excellent transparency, uniform thickness, and the horizontal and vertical uniform performance, generally used as inner material composite films. The thickness of ordinary CPP film is generally between 25~50 m, and the transparency of OPP film is better, the surface is bright, the handle is strong, and the general gift packaging bag is made of this material. The film also has good thermal sealing property. Cooking CPP film thickness is generally between 60 ~ 80 m, high temperature cooking ability of 121 C and 30 min, oil resistance, good air tightness, and high heat sealing strength, meat packing inner general CPP film is adopted in cooking class.
The most widely used aluminized films are polyester aluminum plated film (VMPET) and CPP aluminum plated film (VMCPP). Aluminum plating film has both the characteristics of plastic film and the characteristics of metal. The surface of aluminum film is light and ultraviolet radiation, can prolong the shelf life of contents, but also improves the brightness of the film, from a certain extent, instead of aluminum foil, also is cheap, beautiful and good barrier properties, therefore, in the film composite packaging is widely used in the.
Plastic film is the most widely used in the field of packaging. Plastic films can be used in food packaging, electrical product packaging, daily necessities packaging, clothing packaging and so on. They have one thing in common, that is, the plastic film should be printed in color, and as food packaging, multi layer composite or vacuum aluminum plating and other process operations. Therefore, the requirements of surface free plastic film can be wet, high tension to a large, firm adhesion in favor of printing ink, adhesive or aluminized layer and plastic film; in the production of plastic film coiling and high-speed packaging process requires the film surface friction properties of preventing film adhesion or used in appliances, slipping; electronic products require packaging, the film has certain anti-static properties and so on.
The surface tension of the plastic film depends on the free energy of the plastic film surface, and the surface energy of the film depends on the molecular structure of the film itself. Most of the plastic film such as polyolefin films (LDPE, HDPE, LLDPE, PP) is a non polar polymer, the surface free energy of small, wet surface tension is low, generally about 30 dyne / cm. In theory, if the surface tension of objects less than 33 dynes / cm, ordinary ink or adhesive can not be firmly attached, so must the surface treatment. Polyester (PET, PBT, PEN, PETG) is a polar polymer, the surface free energy is higher, the surface tension in the wet 40 dyne / cm. But for high speed color printing or increasing the bonding force between the vacuum aluminizing layer and the BOPET film surface, the surface treatment of the BOPET film is needed to further improve its surface wet tension.
The surface treatment methods of plastic film are corona treatment, chemical treatment, mechanical polishing, coating, etc. the most commonly used method is corona treatment.
The basic principle of corona treatment method is: through the metal electrode and the corona roller (usually high temperature and ozone resistance, and high silicon rubber insulation) is applied between high frequency and high voltage power supply, causing the discharge, so that the air ionization and the formation of a large number of ozone. At the same time, high energy electrospark impact on the surface of the film. Under the combined action, the surface of the plastic film is activated and the surface energy is increased. The corona treatment can make the wet tension of polyolefin film increased to 38 dyne / cm; the polyester film surface tension to wet 52-56 dyne / cm above. The surface tension of corona treated plastic film is related to the voltage applied on the electrode, the distance between the electrode and the corona treatment roller and so on. Of course, corona treatment should be moderate, not the higher the corona treatment intensity. It is worth noting here is between the plastic film and the corona treatment and should be avoided with air, otherwise it may make the reverse of the film is also a corona treatment. Negative corona results are: 1 may produce ink printing anti sticking phenomenon; 2 in aluminum plating will occur aluminum layer transfer, in the coating will occur coating adhesive layer transfer. The main measure to prevent the corona on the back of the film is to adjust the pressure of the rubber pressing roller in front of the corona treatment roll. The pressure at both ends of the pressing roller should be consistent and the pressure should be appropriate. In addition, the corona roller and the press roller must be strictly static and dynamic balance test, radial runout is less than 0.05 mm, the purpose is to ensure the smooth plastic film into the corona roller, to prevent air into, so as to avoid negative corona phenomenon.