Comparison of three film forming processes of casting, extrusion and blow molding

Process principle comparison

Casting film

It is a non-stretched, non-oriented flat extruded film produced by melt flow quenching. There is no obvious orientation structure.

Extrusion film formation

Common ones are uniaxial stretching and biaxial stretching, and biaxial stretching is a production method of considerable interest in recent years. The basic principle of the biaxial stretching technology is that the high polymer raw material is first heated and melted into a thick sheet by an extruder, and then is subjected to a certain temperature range below the melting point above the glass transition temperature, and is then carried out in the longitudinal direction and the transverse direction by a stretching machine. The stretching of the multiples causes the molecular chains to be oriented and arranged in an order parallel to the plane of the film, and then heat-set in a tensioned state to fix the oriented macromolecular structure, and finally to form a film by cooling and subsequent treatment.

Blow molding

It is usually manufactured by extrusion blow molding, plasticizing and extruding materials, forming tube blank inflation molding, and then cooling, drawing and coiling. The blown film is oriented.

Different from the above three processes, the conductivity of the film is significantly different; while the stretched film has higher barrier properties than the unstretched film, lower permeability to gas, and improved optical properties, transparency and surface gloss. The dimensional temperature is good, and the thickness is uniform.

Application area comparison

Take CPP, BOPP and ordinary PP film as examples for comparison

CPP

The product has the characteristics of transparency, softness, barrier property and mechanical adaptability. It is resistant to high temperature cooking (cooking temperature above 120 °C) and low temperature heat sealing (heat sealing temperature is less than 125 °C). It is mainly used as an inner layer substrate for composite packaging of food, candy, native products, cooked foods (suitable for sterilization packaging), frozen products, seasonings, soups, etc., which can extend the shelf life of food and increase the aesthetics. It can also be used for the surface layer and compartment of stationery products, as well as auxiliary films, such as photo sheets and labels for photos and collections.

BOPP

Excellent printing performance, can be combined with paper, PET and other substrates, with high definition and gloss, excellent ink absorption and coating adhesion, high tensile strength, excellent grease barrier properties, low electrostatic properties Wait. It is widely used in the field of printing and compounding, and as a packaging material in tobacco and other aspects.

Ordinary PP

Due to the simple process and low cost, the optical performance is slightly lower than CPP and BOPP. Mainly used for the outer packaging of snacks, bread, textiles, folders, record covers, sports shoes, etc.

Among them, BOPP and CPP have improved composite performance and wider application. After compounding, they have moisture-proof, transparent and stiff, and can be used for packaging of dry foods such as peanuts, fast food, chocolate, and cakes. In recent years, the types and types of plastic films in China have gradually increased, and each has its own strengths. With the continuous improvement of technical processes, the packaging film has broad prospects.