Coating extrusion

We use extrusion coating to apply thin layers of polymer to the surface of non-polymeric substrates such as cardboard or aluminum foil. Extrusion coated materials are extensively used in food packaging. Products include the coated cardboard used to make milk cartons and the coated aluminum foil used to seal dairy product tubs. The process of extrusion coating has much in common with film casting. 

The coating of polymer that we put on paperboard serves two purposes when we convert it into juice and milk cartons. It prevents the contents from leaking out and it acts as an adhesive so that we can heat-seal the coated paperboard to itself to form a container. Low density polyethylene is the polymer of choice for this application it has sufficient melt strength to 

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The Extrusion Coating of Wire, 2nd ed., technical service note, Wilmington, Del., 1969. 

The development of the all-polyethylene sack has somewhat reduced the relative importance of extrusion coating. At one time paper-polyethylene laminates were widely used for sacks but their use has declined. However, techniques have been developed for coating a wide range of substrates to provide a useful range of materials of interest to the packaging industry. 

C. Dry Bonding Without Adhesives and Extrusion Coating Techniques... 

Extrusion coating is ideal for rods, tube and wire. The article is passed through a paint reservoir and then out via a die, which leaves only the correct thickness of paint in place. There are further techniques suitable for flat articles in sheet or web form. Knife coating is ideal for very thin coats, especially on continuous paper or plastic webs. The knife is either a metal doctor blade or a curtain of high velocity air (an air knife) directed onto the surface and it removes surplus material applied previously. 

Note Values are typical for injection molding and most extrusion operations. Extrusion coating is done at higher temperatures (i.e., about 600 F for LDPE). 

Formation of carbonyl groups which may occur when polyethylene is overheated, such as in an extrusion coating operation. Here a proper balance between extrudate temperature and exposure time to air is required. 

Waghorn, P. E., The Control of Oxidation and Odour in Extrusion Coating, ... 

Extrusion Clothing fabrics Packaging films Extrusion coating films for food packaging Insulator films Photographic film base ... 

Low cycle fatigue testing, 13 489, 491-493 Low density copolymer resins, for extrusion coating, 20 235t... 

Figure 5.14 displays the principle of a wire extrusion-coating line. 

Matsuoka, T. and Takahashi, H., Finite Element Analysis of Polymer Melt Flow in Profile Extrusion Coating Die, Int. Polym. Proc., 3,183 (1991)... 

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