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Unit_8_-_Plastic_Packaging (6)

Unit_8_-_Plastic_Packaging (6) - together In contrast if...

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Notice in the photo that the bubble is blow upwards. That is the most common arrangement, although in some cases bubbles are blown downwards or even, rarely, horizontally. In contrast to the cast film/sheet process, blowing cannot be used to make sheet. It is limited to lighter weights, and therefore to film. Also, in order to make blown film, the plastic resin must have good melt strength, the ability to hold together when it is still a liquid. For example, think of the difference between cake decorating frosting and water. You can squeeze the frosting out and shape it as you wish, because even though it is a liquid, it holds
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Unformatted text preview: together. In contrast, if you tried to do that with water, you would just get a puddle. Similarly, we can easily make blown film from HDPE, but if we tried to do it with PET, we would get a mess all over our processing equipment, and no film! PET has very low melt strength. We simply cannot produce a hollow tube of PET and expand it. If we want to make PET film or sheet, we have to use the cast film process. Blown Film Production...
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