Polypropylene blown film

Polypropylene blown film which has excellent optical and mechanical properties was obtained using nucleating agents. The polypropylene composition contains a clarifier selected from the group of aromatic phosphoric acid ester metal salts and almniniitm-hydroxy-bis[2,2 -methylene-bis(4,6-di-t-butylphenyl)phosphate] in the qirantities from 0.01 to 5 wt%. ... 

The film tube is collapsed within a V-shaped frame of rollers and is nipped at the end of the frame to trap the air within the bubble. The nip roUs also draw the film away from the die. The draw rate is controlled to balance the physical properties with the transverse properties achieved by the blow draw ratio. The tube may be wound as such or may be sHt and wound as a single-film layer onto one or more roUs. The tube may also be direcdy processed into bags. The blown film method is used principally to produce polyethylene film. It has occasionally been used for polypropylene, poly(ethylene terephthalate), vinyls, nylon, and other polymers. 

The double-bubble process may be used to produce biaxiaHy oriented film, primarily polypropylene. In this process the first bubble formation is similar to the conventional blown film, except that the bubble is not coUapsed. Rather it is reheated to the orientation temperature and blown and drawn further in a second stage. It is then coUapsed, sUt, and wound. This process is generally limited to a final film thickness of less than 24 p.m. 

Extmsion of polyethylene and some polypropylenes is usually through a circular die into a tubular form, which is cut and collapsed into flat film. Extmsion through a linear slot onto chilled rollers is called casting and is often used for polypropylene, polyester, and other resins. Cast, as well as some blown, films may be further heated and stretched in the machine or in transverse directions to orient the polymer within the film and improve physical properties such as tensile strength, stiffness, and low temperature resistance. 

Many polymers, including polyethylene, polypropylene, and nylons, do not dissolve in suitable casting solvents. In the laboratory, membranes can be made from such polymers by melt pressing, in which the polymer is sandwiched at high pressure between two heated plates. A pressure of 13.8—34.5 MPa (2000—5000 psi) is appHed for 0.5 to 5 minutes, at a plate temperature just above the melting point of the polymer. Melt forming is commonly used to make dense films for packaging appHcations, either by extmsion as a sheet from a die or as blown film. 

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. 

An important application for polypropylene is film tape. This is made by slitting unoriented film (cast or blown) into tapes 2 or 3.5 mm wide and stretching under heat about seven-fold. With cast film the orientation is more completely monoaxial and there is a tendency for the film to split along its length (fibrillate). Tubular film does not self-split so easily and also has a somewhat softer feel. Such tapes may be woven into sacks and these have... 

Polypropylene film is found in a variety of applications. Films are thin plastic sheets with thicknesses less than 250 pm. Applications for these films include candy mappers, plastic label material, electrical capacitors (which requires very pure polymer), and fiber glass insulation backing. There are two general categories of polypropylene films unoriented and oriented. Films are manufactured through either a cast or a blown film extrusion process. Oriented films exhibit improved strength relative to unoriented films. This means that they can be... 

Flexible film applications are much more demanding regarding the stiffness/ toughness ratio of the Ecoflex /PLA compound. Usually, polypropylene with a stiffness of 1,600 MPa is the stiffest product to be used in blown film extrusion. But,... 

AFM Imaging of Processed Polymers (1) Blown Films of High Melt Strength Polypropylene (hmsPP)... 

In the intermittent contact mode phase images shown in Fig. 3.74 a clear contrast between the constituent phases can be observed both for the compression-molded hmsPP (panel a), as well as for the blown film (in the machine and transverse direction in panels band c, respectively). The soft EPR phase appears with dark phase contrast indicating that a substantial amount of energy is dissipated in this phase compared to the PP phase. The EPR particles measure 1 pm or smaller in diameter dispersed in the polypropylene matrix. The horizontal lines and the occasional vertical streaks in the images are artifacts of microtoming. 

Fig. 3.74 Intermittent contact mode AFM phase images obtained with an amplitude setpoint ratio of 0.5 on (a) compression molded high melt strength polypropylene and microtomed sections of hmsPP blown film in the (b) machine direction (MD), and (c) the transverse direction (TD). Reproduced with permission from [152]. Copyright 2002. Elsevier...

Most blown film operations extrude the resin in an upward direction. However, blown polypropylene film is generally extruded downwards and water or mandrel quenched. The extruded tube is then reheated, to a point still below its melt temperature, before it is blown. The collapsed bubble can be fed over a series of heated rollers to reheat it and relieve thermal stresses if a heat-stabilized film is wanted or it can be heated and reinflated in what is known as the double bubble process, which will be discussed in Section 7.3.7. In either case, the film is restrained until cooling is complete, to keep it from shrinking. 

Biaxial orientation effects are important in the manufacture of films and sheet. Biaxially stretched polypropylene, poly(ethyleneterephthalate) (e.g., Melinex) and poly(vinylidene chloride) (Saran) produced by flat-film extrusion and tentering are strong films of high clarity. In biaxial orientation, molecules are randomly oriented in two dimensions just as fibers would be in a random mat the orientation-induced crystallization produces structures which do not interfere with the light waves. With polyethylene, biaxial orientation often can be achieved in blown-film extrusion. 

Film Processing Methods Extrusion, coextrusion, and Saran F- lacquer solution films. Multilayer Extrusion Saran resins are used in combination with a myriad of other polymers in flexible and rigid multilayer products. Multilayer cast and blown film coextrusion processes for Saran can be used with all polyethylenes, polypropylenes, and nylons. 

Adflex Q 301F TPO resin. Designed for impact modification of polypropylene, as well as monolayer and multilayer air-quenched blown films. i63]... 

From the chlorinated paraffins, solid products containing 70 per cent of chlorine are used for relatively low-temperature processing such as blown films. Dechlorane Plus is also a low-temperature additive of limited utility. Hexabromocyclododecane is suggested for polypropylene. 

Fig. 18.3 PP with 65 wt% elastomer (from the LHS) morphology in pellets, in blown film, and in blown film in PP copolymerized with 3 mol% C2 - effect of compatibilization (Montell Impact Copolymer Polypropylene, commercial information 2012)...

Sumita M, Tsukumo Y, Miyasaka K et al (1983) Tensile yield stress of polypropylene composites filled with ultrafine particles. J Mater Sci 18 1758—1764 Thellen C, Orroth C, Froio D et al (2005) Influence of montmorillonite layered silicate on plasticized poly(l-lactide) blown films. Polymer 46 1716-11727 Uyama H, Kuwabara M, Tsujimoto T et al (2003) Green nanocomposites from renewable resources plant oil-clay hybrid materials. Chem Mater 15 2492-2494 Wang SF, Shen L, Zhang WD et al (2005a) Preparation and mechanical properties of chitosan/ carhon nanotuhes composites. Biomactomolecules 6 3067—3072... 

Blown film is manufactured from metallocene-catalyzed polypropylene containing a-nucleating agent. The a-nucleating agent is a phosphate ester salt or a carboxylate salt added in quantity of 10 to 5000 ppm. The blown film has improved film forming properties and good optical and mechanical properties. ... 

An extraded air cooled blown film has been produced from polypropylene with nucleating agent based polymeric amide. ... 

An extrusion system used extensively for thin films of polyethylene and polypropylene is the blown film process. In this process the polymer is extruded as a relatively thick tubular extrusion and is then blown up by internal air pressure to form a thin-walled tube. The tube is then sUt to form a sheet of film up to 10 ft in width or is left as a flattened tube known commercially as lay-fiat tubing. To improve gauge uniformity in this process, the circular extrusion die, the air cooling ring, or both are frequently rotated. Although low-density polyethylene and polypropylene are the materials most used for this process, polyvinyl chloride, polyamides (nylon), and some polystyrenes have all been used. (See also blown film lay-flat tubing.)... 

Bheda, J.H. and SpruieU, J.E. (1986) The effect of process and polymer variables on the light transmission properties of polypropylene tubular blown film. Polymer Engng Sci., 26, 736. 

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