Packaging sealing and heat sealing materials are as follows;
1. Packaging sealing method
The methods of sealing package include hot sealing, cold sealing, adhesive sealing, etc. Heat sealing refers to the use of the thermoplastic inner layer component in the multilayer composite film structure, which softens the sealing when heating, and solidifies when the heat source is removed. Heat sealing plastics, coatings and hot melts are commonly used heat sealing materials. Cold sealing refers to that it can be sealed by pressing without heating. The most common cold sealing coating is the edge coating applied on the edge of packaging bag. Adhesive sealing is rarely used in multi-layer material packaging, only used for packaging materials containing paper.
2. Heat sealing material
(1) Polyethylene (PE) is a kind of milky white, translucent and opaque waxy solid. It is almost tasteless, nontoxic and lighter than water. PE macromolecular chain has good flexibility and is easy to crystallize. It is a tough material at room temperature. As a packaging material, the main disadvantage of PE is poor air tightness, high permeability to gas and organic vapor, low strength and heat resistance; it is easy to be degraded by light, heat and pole, so antioxidant and light and heat stabilizer are often added to PE products to prevent aging; PE has poor environmental stress cracking resistance, and is not resistant to the corrosion of concentrated h2s04, HNO3 and its oxidant, and will be eroded by some aliphatic hydrocarbons or chlorinated hydrocarbons when heated; the printing performance of PE is poor, and the surface is non-polar, so corona treatment must be carried out before printing and dry bonding to improve the affinity and dry connection of printing ink.
PE used for heat sealing packaging mainly includes:
① low density polyethylene (LDPE), also known as high pressure polyethylene;
② high density polyethylene (HI) PE, also known as low pressure polyethylene;
③ medium density polyethylene (nu) PE:); linear low density polyethylene (LLDPE);
④ metallocene catalyzed polyethylene.
(2) The properties of cast polypropylene film (CPP) used for heat sealing material are slightly different from that of biaxially oriented polypropylene due to its different production process. The advantages and disadvantages of CPP are shown in the relevant contents of “polypropylene”.
(3) PVC (abbreviated as PVC) is a colorless, transparent and tough resin with strong molecular polarity and strong intermolecular force, so it has good hardness and rigid plastic bottle.
PVC is cheaper and more versatile. It can be made into rigid packaging containers, transparent bubbles and flexible packaging films and foam plastic cushioning materials. Because of its toxicity and decomposition corrosion, its consumption is decreasing and gradually replaced by other materials.
(4) EVA (ethylene vinyl acetate copolymer) poly (ethylene vinyl acetate) (EVA) poly (ethylene vinyl acetate) (EVA) poly (ethylene vinyl acetate) (EVA) poly (ethylene vinyl acetate) (EVA) poly (ethylene vinyl acetate) (EVA) poly (ethylene vinyl acetate) (EVA) poly (ethylene vinyl acetate) (eva-eva) poly (ethylene vinyl acetate) (EVA) poly (ethylene vinyl acetate) (EVA. EVA is a translucent or slightly milky white solid prepared by copolymerization of ethylene and vinylacetic acid vinegar. Its properties change with the content of the two monomers. Therefore, when selecting the model of EVA, it should be determined according to the use, and can be used as plastic, hot melt adhesive and coating.
EVA is widely used as the inner layer of composite film because of its good elasticity and low heat sealing strength. It is used in adhesives, coatings, coatings, cable insulation and color carrier with its good adhesion (good or certain drillability with many polar and non-polar materials).
(5) PVDC (polyvinylidene chloride) PVDC generally refers to the copolymer of vinylidene chloride. The polymer obtained by polymerization has high crystallinity, high softening point (185-200′c) and close to the decomposition temperature (210-2250). It has poor compatibility with general tackifier, so it is difficult to be molded.
PVDC is a strong and transparent material with high crystallinity and yellowish green. It has very low transmission rate to water swallow gas, gas and smell, and has excellent moisture resistance, air tightness and fragrance retention. It is an excellent high limit barrier material. It is resistant to acid, alkali and various solvents, oil resistant, refractory and self extinguishing.