Polyethylene blown film

Rokudai, M., Mihara, S., and Fujiki, T., Influence of Shearing History on the Rheo-iogical Properties and Processability of Branched Polymers. II. Optical Properties of Low-Density Polyethylene Blown Films, /. Appl. Polym. Set, 23, 3289 (1979)... 

US patent 4790815 (1988) to Baxter, Heat sterilizable plastic container with non-stick internal surfaces, describes the need to prevent sticking when two layers of plasticised PVC are left in contact during sterilisation. A texture of crosshatched lines is given to one surface of the film in the calendaring process, as a result of the surface of one steel roll being textured. If polyethylene blown film is used, texturing is achieved by the use of embossing rollers, but the polymer is less likely to block than plasticised PVC. 

Dart impact resistance of polyethylene blown film was improved by addition of nucleation agent. The nncleating agent was Hyperform HPN-20E (34% zinc stearate and 66% 1,2-cyclohexanedicarboxylic acid, calcium salt). ... 

Bafna, A., Beaucage. G., MirabeDa, F., SkiUas, G., and Sukumaran, S. (2001) Optical properties and orientation in polyethylene blown films. Journal of... 

ONLINE ORIENTATION DURING POLYETHYLENE BLOWN FILM EXTRUSION USING POLARIZED RAMAN SPECTROSCOPY... 

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. 

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. 

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. 

Poly(vinyl alcohol) is employed for a variety of purposes. Film cast from aqueous alcohol solution is an important release agent in the manufacture of reinforced plastics. Incompletely hydrolysed grades have been developed for water-soluble packages for bath salts, bleaches, insecticides and disinfectants. Techniques for making tubular blown film, similar to that used with polyethylene, have been developed for this purpose. Moulded and extruded products which combine oil resistance with toughness and flexibility are produced in the United States but have never become popular in Europe. 

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. 

Polyethylene is used in extrusion and injection molding processes. When used to manufacture blown films a standard polyethylene will have a melt index of approximately 1 g/10 min, while that used for injection molding typically has a melt index of 5 to 20 g/10 min. Why are the polymers used for these two processes so different ... 

As cast or blown films we encounter polyethylene in packaging films, bags, cling film, greenhouse skins, diaper back sheets, and high altitude scientific balloons. In these applications... 

High density extruded planks, 23 404 High density lipoproteins (HDLs), 5 135-137 10 829 niacin and, 25 798 High density polyethylene (HDPE), 10 596-595 11 225 16 21 17 724 20 149-179 24 267, 268. See also HDPE entries analysis of, 19 566 as barrier polymer, 3 377 bimodal reactor technology for, 20 170 blow molding of, 20 171-172 blown film applications, 20 173-174 catalysts used for, 20 152-155 chemical resistance of, 20 166 commercial applications of,... 

Beagan, C.M., McNally, G.M., and Murphy, W. R., Metallocene Catalysed Polyethylene in Blown Film Applications-A Comparison Between Monoextruded Blended Films and Coextruded Films, SPEANTEC Tech. Papers, 44, 128 (1998)... 

S.S. Cherukupalli and A.A. Ogale, Online measurements of crystaUinity using Raman spectroscopy during blown film extrusion of a linear low-density polyethylene, Polym. Eng. Sci, 44, 1484—1490 (2004). 

Blown film extrusion is perhaps the most widely used extrusion technique, by production volume. Billions of pounds of polyethylene are processed annually by this method to make products such as grocery sacks and trash can liners. In a blown film system (Figure 14-30), the melt is generally extruded vertically upward through an annular die. The thin tube is filled with air as it travels up to a collapsing frame that flattens it before it enters the nip rollers, which pull the film away from the die. The flattened tube then travels over a series of idle rollers to a slitter,... 

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