Tell about the types and functions of plastic packaging materials

1, polyethylene (PE)

Polyethylene is a high molecular polymer of ethylene and is a thermoplastic. According to its industrial production method, there are high pressure, medium pressure and low pressure polymerization methods. The molecular structure is also very different depending on the production method, and the product performance varies with the molecular structure.

Polyethylene is a milky white waxy solid, lighter than water, softer, water resistant, low temperature resistant, odorless, non-toxic, poor heat resistance, poor airtightness of film, sensitive to ultraviolet light. It is easy to oxidize, aging, and has a large change in heat shrinkage and poor printing performance. By its density. Can be divided into high density, medium density, low density polyethylene, and linear low density polyethylene.

2, polypropylene (PP)

Polypropylene is a by-product propylene which is produced by petroleum refining, and is obtained by subjecting a refined propylene monomer to polymerization under the catalyst of a catalyst and then separating from the polymer. The molecular weight is 100,000 to 500,000, the density is very small, and it is the smallest among the known plastics; it is non-toxic, tasteless, high in transparency, mechanical properties, surface strength, anti-friction and moisture resistance are good; impact resistance value above room temperature Large, but low temperature impact resistance; it is easy to carry static electricity, poor printing performance. Polypropylene has a wide range of raw materials, low prices and wide adaptability to performance. Widely used in the food industry. It is widely used in the manufacture of film and composite film. It has good transparency and surface gloss and can withstand temperatures of 120 degrees. It can be made into a package and blown into a plastic bottle.

3. Polystyrene (PS)

Polystyrene is obtained by alkylation of ethylene and benzene under the catalysis of anhydrous tri-alumina to form ethylbenzene, which is then dehydrogenated to obtain styrene. The styrene monomer is heated and polymerized into a polystyrene in an aqueous suspension of an appropriate amount of an initiator (benzoyl peroxide) and a dispersant (polyvinyl alcohol). Polystyrene is a colorless, transparent, non-ductile thermoplastic; non-toxic, odorless, good coloring, moisture permeability greater than polyethylene, low hygroscopicity, dimensional stability, good gloss; good processing performance, cost Low; mechanical properties increase with increasing molecular weight; low heat resistance, can not be used in boiling water; low temperature resistance, can withstand -40 ° C low temperature; good indoor aging resistance; for alcohol organic solvents, mineral oil It has good tolerance and good acid and alkali resistance.

Polystyrene is widely used in the food industry due to its superior performance, low price and wide application. It can be made into films and containers. The shrinkage rate can reach 60-70%. It is a good material for making shrink packaging and has good insulation properties. Can produce a variety of telecommunications parts; can also make a variety of machine parts, toys and so on.

4, polyvinyl chloride (PVC)

Polyoxyethylene is a vinyl chloride which is subjected to suspension polymerization or emulsion polymerization to form polyvinyl chloride. It has light brown color, transparency and good toughness, and has a density of 1.4g/cm. It has good chemical stability and is not easily corroded by acid and alkali. It has good air tightness, water resistance and heat sealing performance, good printing performance and energy consumption. Less, cheaper; mechanical strength, wear resistance, pressure resistance are better than polyethylene and polypropylene. The main disadvantage is that the thermal stability is poor, it is easily decomposed by heat, and hydrogen chloride gas is released. Due to the variety and quantity of additives, such as plasticizers and stabilizers, PVC can be made into different products, which can produce hard products such as hard pipes and building materials; artificial leather and plastic flooring can be manufactured. Its main function on the packaging is to make a film, which is divided into soft film, hard film and shrink film. The soft film has a soft texture and good heat sealability, and is suitable for high-frequency sealing; the tensile strength is small, the tear strength is high; the sliding property is poor, and the processing property is also poor. The tensile strength and tear strength of the hard film are large, the texture is hard, the elongation is small; the moisture permeability is small, the gas barrier property is good, the slidability is good; the printing adaptability is good, but the appropriate ink solvent is selected; It has poor temperature resistance and becomes brittle at low temperatures. The shrink film has good transparency, small gas permeability, shrinkage upon heating, wide shrinkage temperature range, and large shrinkage, and is a good heat shrinkable packaging material.

5, polyester (PET)

Polyester is a polycondensation product of terephthalic acid and ethylene glycol. Compared with other plastics, polyester has excellent barrier properties, such as carbon dioxide, oxygen, water and fragrance. It has excellent mechanical properties and high strength, pressure resistance and impact resistance. Good chemical stability, acid and alkali corrosion resistance; high transparency, good optical properties; non-toxic, odorless, in line with food hygiene standards; ester structure in its structure, so printing performance is good. Polyester is a unique and versatile packaging material. It can be made into a film, made into a packaging container such as a bottle, a can, a cup, etc., and can also be used as a dual-purpose baking tray.

6, phenolic plastic (PF)

The phenolic resin is formed by polycondensation of phenols (mainly phenol) and aldehydes (mainly formaldehyde). Depending on whether the catalyst is acidic or basic, the ratio of phenol to formaldehyde is different. A thermoplastic resin or a thermosetting resin can be obtained. Both can be converted to each other under suitable conditions. In practice, thermosetting resins are often used. Phenolic resin has good mechanical strength and good thermal strength; moisture resistance and corrosion resistance are good; easy to process and low in price.

After the phenolic resin is processed by adding different fillers, curing agents, etc., different phenolic plastics can be obtained. Various flaky fillers are added to the thermosetting resin, and laminated to obtain a variety of properties of the laminate; phenolic foam can be obtained by adding a foaming agent; when the phenolic plastic is used for packaging, the phenolic resin is mixed with the filler and cured. Agents, colorants, etc. are made into molding powders, which are then molded into caps, machine parts, daily necessities, and some packaging containers.

7. Polyamide (PA)

Polyamide, commonly known as "nylon", can be obtained by polycondensation of a dibasic acid and a binary. Polyamide is non-toxic, colorless and transparent; good wear resistance. Strong impact toughness, excellent mechanical properties; good light resistance, light aging, good oil resistance, good chemical stability, but not resistant to alcohols, formic acid and phenol; good air tightness; adaptability to temperature, can be -40 Use within ~100 degrees; good printability and decoration; high hygroscopicity.

Polyamides are used in a wide range of applications, such as bearings, gears, and automotive parts. Its application on packaging is mainly flexible packaging, which is made into a film for food packaging and can also be used to make straps and ropes, which is more robust than polypropylene strapping.

8, urea-formaldehyde plastic (UF)

"Electric jade" is made from urea and formaldehyde as raw materials, which is obtained by polycondensation reaction, and then processed into a compression molding powder (electric jade powder) by adding filler, coloring agent, lubricant, plasticizer, etc., and then heated and molded. It has a large surface hardness, a certain mechanical strength, is not easy to deform, but has high brittleness; it is odorless, tasteless, strong in coloring power, bright in color; good in heat resistance, not easy to burn; acid, alkali and water resistance Poor, water absorption. Urea-formaldehyde plastic can produce a variety of products, such as daily necessities, electrical components, etc. It can be made into a beautiful packaging box, packaging tray, bottle cap, etc.; because formaldehyde has certain toxicity, it is not suitable For food packaging.

9, melamine plastic (ME)

The melamine plastic is the same as the urea-formaldehyde plastic. It is a thermosetting plastic which is obtained by polycondensation reaction of melamine and formaldehyde to obtain a resin as a main component, and is added with a filler, a lubricant, a coloring agent, a hardener, and the like.

The melamine plastic is non-toxic, odorless, tasteless and has good hygienic properties; it has high mechanical strength, good surface hardness and is not easy to be deformed; the surface is smooth and feels like porcelain; it has strong impact resistance and pollution resistance; and good chemical stability. Melamine plastics can be used to make packaging containers in a variety of colors including food packaging.

10, polyvinyl alcohol (PVA)

Polyvinyl alcohol is a hydrolysis product of polyvinyl acetate. It is transparent, non-toxic, tasteless; has excellent gas barrier properties, water resistance and oil resistance; good chemical stability; good printability, no static electricity; good mechanical properties.

Polyvinyl alcohol uses its film on packaging and can be used for food packaging. It can prevent food from oxidative discoloration, odor and deterioration, and maintain the freshness of food. It can also package other products, such as chemical products.

11, polycarbonate (Pc)

Polycarbonate is a general term for a resin having a carbonate structure in a molecular chain, and generally refers to a bisphenol A type polycarbonate. It is colorless and transparent, has good gloss; excellent heat resistance and cold resistance, and can be used for pressure sterilization; high mechanical strength. It can be juxtaposed with polyester and nylon; it has excellent impact toughness, and the product is not easily broken by impact; it has low water absorption and permeability; it has good chemical corrosion resistance, can prevent ultraviolet rays from being transmitted through non-toxic and odorless; Molding methods are available. The molded product is highly accurate. However, the heat sealing performance is poor. Polycarbonate is a kind of engineering plastic with excellent comprehensive performance. It can make various gears, machine parts, etc. It can be used to package foods and other articles. When it needs to be sealed, it can be made into composite film to improve heat sealing performance. Can also be made into a variety of packaging containers.

12. Polyvinylidene chloride (PVDC)

Polyvinylidene chloride is a homopolymer of meta-dioxyethylene. It is non-toxic, odorless, and transparent; it has high mechanical strength. Good toughness; oil and organic solvent; good heat shrinkage and self-adhesiveness, easy adhesion between films; excellent air tightness and moisture resistance. However, it has poor machinability, poor thermal stability, is not easily heat-sealed, and is easily decomposed by ultraviolet rays. The application of polyvinylidene chloride on packaging is mainly to make food packaging film, which can be used as a sealed package to effectively prevent moisture absorption of food. Oxidation of oils and fats makes the food quality long-term; it can be used as a sterilized food packaging because it can be heat-sterilized; it can also be used as a packaging material for household daily use.

13, polyurethane (PVP)

Polyurethane, also known as polyurethane, is prepared by reacting isocyanate with a hydroxy compound. The main characteristics of polyurethane are good wear resistance, excellent low temperature resistance, outstanding oil resistance and chemical resistance. Polyurethane is mainly processed into foamed plastic, and the foam and plastic materials can be obtained by changing the raw materials and the ratio. Soft products have good toughness, good elasticity and oil resistance. They are the main varieties of polyurethane foams and are widely used in packaging to make cushioning materials such as gaskets. Hard products are heat-resistant, cold-resistant, and have excellent shock resistance. They are widely used in the packaging of precision instruments and meters. The production of polyurethane foam is simple. The utility model has the advantages of convenient operation, low cost, good shockproof performance, and can be obtained at normal temperature, and can be obtained by in-situ foaming, which brings great convenience to packaging.