Plastic Film - an overview

23 Jul.,2022

1.3.1 Films Films are materials with a nominal thickness not exceeding 250 μm. They are the largest

 

pvc protective film

automotive masking film

1.3.1 Films

Films are materials with a nominal thickness not exceeding 250   μm. They are the largest group of products made of plastic and are mainly used in the packaging market (Rosato, 2000). Monofilms are homogeneous films made of one material. Beyond these, multilayer films, described in Section 1.3.2, are commonly applied in the market.

Plastic film is most often manufactured as follows:

blow molding of a sleeve: the molten material is extruded through a circular aperture, and air pressure gives it the form of a sleeve;

casting, or flat slotted extrusion: molten material is extruded through a flat die and cast on a cooled cylinder.

To manufacture a film for printing purposes, the following are primarily used:

plastics such as

polyethylene (PE),

polypropylene (PP),

polyethylene terephthalate (PET),

polyvinyl chloride (PVC),

polyamide (PA),

polystyrene (PS),

PC,

biodegradable plastics such as

polylactide (PLA),

cellulose,

products based on starch.

To improve the properties of films, they are often subjected to monoaxial or biaxial orientation. Orientation of a film is its stretching in a certain way, which depends on the manufacturing process and the type of polymer. Biaxially oriented PP films are most commonly used as substrates and packaging materials. Also, polyester films are often subjected to orientation. This method improves their barrier properties to water vapor and gases and strength—tear resistance and tensile strength (Emblem & Emblem, 2012).

Films, if they are not dyed in mass, are originally transparent substrates. Often onto transparency film addition to multicolored printing also underprint is performed. If the entire surface of the film is to be printed in color and is intended to be a nontransparent material, films are originally dyed in mass with white color.

A special version of films are metalized films. They are applied in laminate manufacture, improving the barrier properties of films to gas and water vapor, and in providing a barrier to UV radiation. Most commonly, metallization involves the application of a thin layer of aluminum on the material. It is made primarily for PET and PP films and biodegradable PLA. Metalized films are a special group of substrates, which requires the use of different control devices for checking the quality of the print. This is due to silver, high-gloss film, which requires a spherical geometry for measuring color.

Thermoshrink films are also worth mentioning. They are produced from monoaxially oriented films of polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyethylene terephthalate glycol-modified (PETG), and oriented polystyrene (OPS). They are used for packaging of individual products (e.g., laminating books) or bulk packaging (e.g., six bottles of water wrapped in film), and for labeling the so-called shrink sleeve labels, for instance, labeling of plastic bottles and cups for dairy products. Heat-shrinkable films are printed with flexography; then a heat shrink sleeve is prepared, which is cut into individual labels. In the next stage, labels are placed on the product, on which they are to be shrunk. High-temperature leads to adoption of the shape of the packaging on which the labels are placed (Abdel-Bary, 2003; Elsayed, 2003; Emblem & Emblem, 2012).

Most films before the printing process require the preparation of their surface. Especially films having the widest application in the packaging industry—PP, PE films before printing must undergo activation in order to raise their very low surface free energy values. The most extensive industrial use is corona activation, often performed immediately before printing with a printing press. The film can also be activated by the manufacturer and delivered as already prepared for printing, but it should be remembered that the stability of the activation is limited. After some time, the energy raised in this way will decrease—initially, rapidly and then more slowly. Printing on films is performed by flexography or gravure.