Extrusion coating techniques

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

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. 

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. 

For the deposition of active phase(s), impregnation, adsorption and ion exchange, (co)precipitation, deposition precipitation, and in situ crystallization methods can be used. Moreover, it is possible to mix the active phase in the mixture for extrusion or to deposit the active phase by using a mixed sol containing both the precursors of the oxidic species and the active phase or a slurry with the precursor powder of the active phase. Other coating techniques, e.g., CVD or CVI techniques, can also be used. The dispersion of the active phase depends strongly on the method and conditions used, its precursors form as well as on the history of the active phase. 

Small amounts of synthetic zeolites (based on metal aluminosilicates) can be added to the system to adsorb unwanted organic odour-producing molecules and/or to remove the moisture that contributes to odours (by trapping them in their highly porous crystal structures). This technique is successfully used in extruded polyolefin pipes, injection and extrusion blow-moulded containers, barrier packaging materials, extrusion coatings, and sealant polymers. 

An associated technique is to use the extrusion coating in melt form as an adhesive interply between two substrates to be laminated. This is particularly useful for the lamination of paper to foil. A combination of extrusion lamination and coating can be used for the preparation of more complex structures with single machine pass. 

Extrusion coating R J ASHLEY Techniques and materials used... 

A recent comparison by Sparavigna [4] of ozone with corona and ozone with atmospheric plasma treatment has revealed an interesting opportunity to further optimize the extrusion coating process for flexible packaging structures. In particular, the study involved two experimental runs, which were performed by coating low-density polyethylene onto oriented polypropylene and polyester film. Ordinary heat seal strength techniques were used to quantify the effects of the variables on heat seal strength vs. seal temperature. 

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