Various Film Molding Methods And Characteristics

There are many varieties of plastic films, which can be used in agriculture, daily necessities, pharmaceuticals, construction and water treatment, solar power generation, battery diaphragm, bullet-proof glass and many other fields according to their different characteristics.

Film Molding Methods

There are many plastic film molding methods, of which casting, extrusion and blow molding are the three most common:

Cast: A non-stretching, non-oriented, flat-extruded film is produced by the melt salivation quenching process. The film produced by this process does not have an obvious orientation structure.

Extrusion method: common unidirectional stretching and bi-directional stretching method.

The basic principle of bi-directional stretching: polymer raw materials are first heated through the extruder to melt and extrude into a thick sheet, and then in the glass transition temperature above the melting point of the appropriate temperature range, through the stretching machine successively along the longitudinal and transverse stretching a certain number of times, so that the molecular chain in the plane parallel to the film is oriented and orderly arrangement, and then in the state of tightening the heat-setting, so that the orientation of the structure of the macromolecule is fixed, and finally by cooling and subsequent processing of the film. Finally, the film is formed by cooling and subsequent processing.

Blow molding method: usually extrusion blow molding method of manufacturing, material plasticization extrusion, forming a billet blow molding, then cooling, hauling, winding. Blown film is oriented. Blow molding film forming process is simple, is the most commonly used film forming process.

Multiple film properties

-hdpe-

HDPE film is known as geomembrane or impermeable membrane. It has a melting point of 110°C-130°C and a relative density of 0.918-0.965kg/cm3. It is a highly crystalline, non-polar thermoplastic resin with a milky-white color in its raw state and a certain degree of semi-transparency in the micro-thin section. It has good high and low temperature resistance and impact resistance, even at low temperatures of -40F. Its chemical stability, rigidity, toughness, mechanical strength, tear strength properties are excellent, and with the rise in density, mechanical properties, barrier properties, tensile strength and heat resistance will increase accordingly, can be resistant to acids, alkalis, organic solvents and other corrosion.

Recognition method: mostly semi-transparent, feel like wax, plastic bags rubbing or friction with rustling sound.

-LDPE-

LDPE film has low density, soft, low temperature resistance, impact resistance and good chemical stability, generally resistant to acid (except strong oxidizing acid), alkali, salt corrosion, with good electrical insulation.LDPE is mostly used in plastic bags, marked with the material symbol -- 4, and its products are mostly used in the field of civil engineering and agriculture, such as geomembranes, agricultural films (shed film, ground film, bitter cover film, green storage film, etc.). Its products are mostly used in civil engineering and agricultural fields, such as geomembranes and agricultural films (shed film, ground film, bitter cover film, green storage film, etc.). Its recycled materials, edges and corners can be made into garbage cans, toolboxes, bicycle mats, garbage trucks and other flexible plastic reproductions.

Identification method: LDPE made of plastic bags are softer, rubbing more will not send out rustling sound, packaging plastic film soft and easy to tear is LDPE, more brittle and hard is PVC or PP film.

-PP-

Ordinary PP film using blow molding, simple process, low cost, but the optical properties are slightly lower than CPP and BOPP. PP's most important feature is high temperature (about -20 ° C ~ 120 ° C), and the melting point of up to 167 ° C, suitable for filling soya bean paste, rice milk, and other products that need to be sterilized by steam. Its hardness is higher than PE, used in the manufacture of containers and caps mostly, labeled material symbol for the 5th.

Identification method: generally speaking, PP hardness is higher, and the surface is more glossy, burning does not produce irritating odor, while PE has a heavy candle flavor.

-PVA-

Polyvinyl Alcohol (PVA) high barrier composite film is a film with extremely high barrier properties formed by using Polyethylene plastic as the substrate and coating the modified polyvinyl alcohol water-soluble liquid on the substrate. As the polyvinyl alcohol high barrier composite film has good barrier properties and meets the environmental requirements, so the market prospect of this packaging material is very bright, and there is a broad market space in the food industry.

-CPP-

Cast Polypropylene film (CPP) is a non-stretching, non-directional, flat-extruded film produced by melt calendering quenching. It is characterized by high production speed, high yield, good film transparency, gloss, barrier, flexibility, thickness uniformity, can withstand high-temperature cooking (cooking temperature of 120 ℃ or more) and low-temperature heat sealing (heat sealing temperature of less than 125 ℃), the balance of the various properties is excellent. Follow-up work such as printing, composite convenient, widely used in textiles, flowers, food, daily necessities of packaging, do composite packaging of the inner layer of the substrate, can extend the shelf life of food, increase the degree of aesthetics.

-BOPP-

Bi-oriented polypropylene film (BOPP) is a transparent flexible packaging materials developed in the 1960s, is a specialized production line will be mixed with polypropylene raw materials and functional additives, melt blending, made of sheet, and then made into film by stretching. This film not only has the original low density of PP resin, corrosion resistance, heat resistance, and the advantages of good film optical properties, high mechanical strength, raw materials from a variety of sources, with excellent printing performance, can be composite with paper, PET and other substrates, with high clarity and gloss, excellent ink absorption and coating adhesion, high tensile strength, excellent grease barrier properties, low static electricity characteristics. It is widely used in the field of printing and laminating, and is also used as packaging material in tobacco and other areas.

-PET-

Polyester film (PET) is a thermoplastic engineering plastic. Extrusion is used to form a thick sheet, and then the film material made by bi-directional stretching. Polyester film is characterized by excellent mechanical properties, rigidity, hardness and toughness, puncture resistance, friction resistance, high and low temperature resistance, chemical resistance, oil resistance, airtightness and aroma retention is good, is commonly used as one of the permeability barrier composite film substrate, but corona resistance is poorer, the price is higher. Film thickness is generally 0.12mm, commonly used as the outer material of food packaging, printing is better. In the plastic products labeled material symbol for the No. 1. Its recycled materials can be made again: monofilament → wigs, zipper serrations; sheet → packaging boxes (egg cartons, stationery L clip); polyester cotton → filler cotton, non-woven fabrics, polyester fabrics.

-PA-

Nylon plastic film (polyamide PA) is currently industrially produced in many varieties, of which the main varieties used to produce film are nylon 6, nylon 12, nylon 66 and so on. Nylon film is a very tough film with good transparency and good gloss. Tensile strength, tensile strength, high and low temperature resistance, oil resistance, organic solvent resistance, abrasion resistance and puncture resistance are very good, and the film is relatively soft, excellent oxygen barrier, but the barrier to water vapor is poor, moisture absorption, moisture permeability is greater, and heat sealing is poor. It is suitable for packing hard goods, such as greasy food, meat products, fried food, vacuum-packed food, and steamed food.

-PVC-

PVC film has similar advantages with PET, which is transparent, airtight and acid and alkaline resistant, and PVC bottles were used in the packaging of mineral water in the early days. However, PVC is not suitable for filling food-grade substances due to the release of carcinogens during the manufacturing process because of incomplete polymerization of some monomers, and has been changed to PET bottles, which is labeled with the material symbol of No. 3. Recycled materials can be remanufactured into: water pipe elbows, artificial leather, wire covering, fire-resistant building materials.

-PS-

PS film has low water absorption but good dimensional stability and can be processed by injection molding, compression molding, extrusion, and thermoforming. Generally, PS films are categorized into foamed and unfoamed according to whether they have undergone foaming process or not. Unfoamed PS is mainly used in building materials, toys, stationery, etc. It can also be commonly used to make containers filled with fermented dairy products (e.g., Nutrifresh, Healthy, DuoDuo, etc., or lactic acid products), etc. In recent years, it has also been used in large quantities to make non-washable tableware, and is labeled with the material symbol of No. 6. Recycled materials can be recycled into: camera shells can be photographed, coat hangers and other hard, fragile, inelastic plastic reproductions.

-Aluminized-

Aluminized film has the characteristics of both plastic film and metal. The role of the film surface aluminizing is to shield the light, anti-ultraviolet radiation, not only to extend the shelf life of the contents, but also to improve the brightness of the film, to a certain extent, instead of aluminum foil, but also inexpensive, beautiful and better barrier properties. Therefore, the application of aluminized film in composite packaging is very wide, mainly used in cookies and other dry, puffed food packaging, as well as some pharmaceuticals, cosmetics on the outer packaging.