Blown-film process

Melt Extrusion. By far the most important method for producing film and sheeting materials reties on one or another of the various melt extmsion techniques (5). The main variations of melt extmsion are the slot (or flat) die-cast film process, the blown films process, and the flat die sheeting-stack process. These may be combined with one or more steps such as coextmsion wherein multilayer film or sheet is formed, biaxial orientation, and in-line coating (6). 

One of the requirements of this process is that the melt maintain good contact with the chill roU, ie, air must not pass between the film and the roU. Otherwise, air insulates the plastic and causes it to cool at a rate different from the rest of the plastic and this spoils the appearance of an otherwise satisfactory product. The melt should not emit volatiles, which condense on the chill roU, reduce heat transfer, and mar the film s appearance. The cast film process allows the use of a higher melt temperature than is characteristic of the blown film process. The higher temperature imparts better optical properties. 

Film manufacture also requires special considerations in the case of polypropylene in order to ensure small crystal structures and hence high clarity. Chill-roll casting processes may be used and these give films of high clarity and minimal thickness variations at high rates of production. Blown film processes can, however, give superior mechanical properties and in addition equipment costs are lower, and in consequence the process is more economic for lower tonnage production. 

Current usage is almost entirely associated with the good adhesion to aluminium. Specific applications include the bonding of aluminium foil to plastics films, as the adhesive layer between aluminium foil and polyethylene in multilayer extrusion-laminated non-lead toothpaste tubes and in coated aluminium foil pouches. Grades have more recently become available for manufacture by blown film processes designed for use in skin packaging applications. Such materials are said to comply with FDA regulations. 

R. Halle, Structure, properties and blown film processing of a new family of linear ethylene polymers, SME Blown Film Technology Seminar, Oct 1993, USA. 

E-plastomers, particularly the high- and medium-density materials, have found extensive use in films [17]. They are valued for their excellent seal character which allows the formation of mechanically strong seals at relatively low temperatures compared to traditional low-density polyethylene (LDPE). In addition, these E-plastomers can be obtained in a range of crystallinities and softness. These higher-density materials are typically made in the blown-film process and are used for protective film covers and disposable bags. 

The mechanisms described above tell us how heat travels in systems, but we are also interested in its rate of transfer. The most common way to describe the heat transfer rate is through the use of thermal conductivity coefficients, which define how quickly heat will travel per unit length (or area for convection processes). Every material has a characteristic thermal conductivity coefficient. Metals have high thermal conductivities, while polymers generally exhibit low thermal conductivities. One interesting application of thermal conductivity is the utilization of calcium carbonate in blown film processing. Calcium carbonate is added to a polyethylene resin to increase the heat transfer rate from the melt to the air surrounding the bubble. Without the calcium carbonate, the resin cools much more slowly and production rates are decreased. 

During blown film processing, orientation is imparted to the film by both pulling the melt into the nip rollers and by increasing the circumference of the bubble with air. By managing... 

The LDPE blown film process is successful with a thermoplastic, since the cooling of the melt bubble is extremely fast (a few seconds), so there is little time... 

Fig. 16 Blown film processing of Bionoiie Table 3 Mechanical properties of petroleum-based and bio-based materials...

After a long development time, we started manufacture of the compound by carrying out a mull extrusion. The conditions for mull extrusion are especially important to produce good quality compound. The film processing is only possible when the selection of extrusion conditions is appropriate. The properties of the manufactured film are also affected by these conditions. The conditions of blown film processing for this starch compound are shown in Table 4. 

Polymerization of Bionolle 3001 (polybutylene succinate/adipate) using bio-based and petro-based succinic acid was examined. As for polymerization conditions and processability, there was no significant difference between these two types of resin. Mechanical properties of blown films processed from both resins were almost the same. The quality of bio-based succinic acid turned out to be good enough as a polymer grade. 

Film. The blown film process is most commonly used in the production of PB film from resins with melt indexes from 0.3 io 10 g/10 min at a melt temperature of200-215DC using conventional equipment. Mechanical properties of blown PB film depend on the degree of orientation and other processing parameters. PB film can be sealed ai 100 220 (1. Another technique for the PB film production consists of film casting from the melt on polished chilled rolls and co-extrusion or lamination with other films. 

PB film is usually made by the blown film process, but also can be cast oil drill lolls. Film applications include food and meat packaging, compression wraps, and hot-fill containers. The material can be formulated to provide a wide range of seal strengths for peelable or easy-opening packaging. 

C. J. S. Petrie, A Comparison of Theoretical Predications with Published Experimental Measurements on the Blown Film Process, AIChE J., 21, 275-282 (1975). 

The blown film process involves extruding a relatively thick tube that is then expanded or blown by the usual internal air pressure or the water quench process to produce a relatively thin film (Figure 5.6). The tube can be collapsed to form double-layer layflat film or can be slit to make one or two single-layer film webs. The water quench process is the generally preferred method of producing blown PP type film. 

Figure 5.19 Example of upward extruded blown film process for biaxially orienting film...

The lay-flat film is then either kept as such or the edges of the lay-flat are slit off to produce two flat film sheets and wound up onto reels. If kept as lay-flat, the tube of film is made into bags by sealing across the width of film and cutting or perforating to make each bag. This is done either in line with the blown film process or at a later stage. 

The process for making a cast film involves drawing a molten web of resin from a die onto a roll for controlled cooling. The cast film process is used to make a film with gloss and sparkle. The melt temperature in the cast film process is higher than in the blown film process. The higher the melt temperature the better are the optical properties of the film. 

OPS is commercially available in 0.13-0.76 mm gauge. The tenter frame process for manufacturing OPS is the most common process used today. A typical tenter frame process is shown in Figure 11.1. Tentered OPS is distinguished from polystyrene blown films (which are also biaxially oriented) in that the tenter frame process can produce heavier gauge films than the blown-film process. Blown films (0.025-0.13 mm) are used primarily in window envelopes, lamination, and printed applications tentered OPS is typically used in thermoformed trays, lids, and containers for rigid food packaging applications. 

PE films are usually produced by the blown film extmsion method. The alternative method is sheet extrusion followed by passing through chilled rollers. Blown film is more economic biaxial orientation is introduced by the draw-off and blow ratios. Bubble stability is critical to the blown film process. Bubble stabihty is provided by the melt strength and rheological characteristics of the PE. Long... 

An alternative way of producing a film is by the blown film process. An annular die is used from which the material emerges as a thin-walled tube, which is immediately blown up by internal pressure to a much larger diameter (Fig. 23.9). 

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