Film Blowing and Casting

Blowing and casting are the main processes used industrially for making films from thermoplastic polymers. Blown films are mostly used for food and rubbish bags. A blown film is extruded as a tube and the tube is filled with air to expand it to the desired size [88]. The film is then cooled, flattened and extruded again over an isolated bubble of air. Typical film thicknesses are 0.007-0.125 mm. High melt viscosity resin is required for processing a blown film so that the melt can be pulled upward from the die [88]. 

A cast film is prepared by drawing a molten web of polymer from the die onto a roll for controlled cooling. The cast film process is used to make a film with gloss and sparkle. In this process the melt temperature is higher than in the blown film process, since a higher melt temperature imparts better optical properties [88]. 

For efficient film processing, a thermoplastic must crystallise quickly, i.e., in a few seconds. Cargill patented four methods to increase the rate of PLA crystallisation [99]  

As mentioned in Section 6.1.5, EPG patented an extrusion process and a formulation technology to produce thermoplastic PVA pellets suitable to be converted into films and sheets [75]. Dual extrusion is also possible using this technology allowing films to be produced which combine layers of PVA film with different water solubility characteristics [100]. 

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LLDPE is now beginning to compete with I. DPR in film blowing and casting applications because of its superior resistance to puncture by hard particles. It also has better qualities of toughness and lower brittle temprantuies than LDPE, and is now used to replace blends of HDPE and LDPE. 

There are two main processes used commercially for making film from thermoplastics, blowing and casting. 

Union Carbide, Daicel and Interox are the three producers of poly-s-caprolactone world wide. High molecular weight poly-s-caprolactone may be processed by a variety of techniques, including film blowing and slot casting. Main application in the field of biodegradable plastics is in combination with thermoplastic starch in films, sheets and injection molded parts. 

Blow and cast film extrusion are the common methods in film production. Blow film extrusion is a major method for producing bags from LDPE, LLDPE, and FIDPE. 

Packaging films (extruded, blown, and cast) are used in pressure-sensitive tapes and electrical applications and as replacements for cellophane and glassine films in liners for cereal boxes, wraps for snack foods, cigarettes, bread, and cheese. Blow-molded containers are used in applications where the higher use temperature of polypropene is needed (compared to HDPE), such as in packaging of syrups that are hot-filled. 

Batch injection molding machine thermoplastics commodity resins, polyolefins (LDPE, HDPE, PP), styrenics (PS, PMMA. polycarbonates, ABS, PET), and engineered resins for higher impact strength. Continuous extruder thermoplastics. Casting PP fine film 10 to 50 pm cast film 100 to 400 pm thermoformable sheet 200 to 2500 pm. Film blow LDPE, HDPE, PP. Pug mill clay materials for bricks, tiles, and ceramics. 

Plaswite . [Cabot Plastics Ltd.] Uta-nium dioxide masterbaich in polyethylene, polypropylene, or pdys nene carriers some widi lidiopone or caldum carbonate as extenders white master-batch for blown and cast film, inj. mold-it, blow mdding of drug, cosmetic, arid food coniainas. 

Ultrathene . [Quantum SI] EVA copolymer for adhesives, coatings, blown and cast film, inj. molding, blow molding, flexible tubing, profiles, sheet. 

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