Polyethylene, which we use for our films, is an extraordinarily versatile polymer, and maybe the most-used plastic in the world. Each year, more than 80 million tons of polyethylene (PE) are produced globally. 

High-density polyethylene (abbreviated to HDPE) is a thermo-plastic polymer produced from oil. Compared to low-density polyethylene (LDPE), the molecular chain of HDPE creates lkess branching; the result is higher resistance to traction, and greater intra-molecular force created to the less dense types of polyethylene, which gives the material a greater specific force. 

Low-density polyethylene (abbreviated to LDPE)  is a thermo-plastic polymer produced from oil. It was the first type of polyethylene created, by Imperial Chemical Industries in London in 1933, thanks to a high-pressure procedure with free-radical polymerisation.

Extrusion is an industrial productive process of plastic deformation that creates small pieces of a fixed cross-section. It essentially involves the compression of the material in a paste state, forced through a die of the shape of the piece required. If the latter is hollow, a core that reproduces the profile of the internal cavity will be present. Once out of the die, the material is cooled. In the case of plastic materials, these are introduced into the mould as pellets or dust: the heat generated by attrition with the sides of the extruder and by electric resistance creates the “fusion” (for crystalline polymers) or “softening” (in the case of amorphous or semi-cystalline polymers).

Films are measured in microns, equivalent to one thousandth of a millimetre. This means that 1000 microns equal 1 millimetre, and 0.001 millimetre equals 1 micron. Our film thicknesses range from 7 microns for the bitumen membranes, to 25 microns for the food packaging industry, and 6 microns for the coupling sector for food paper, while multi-layer co-extrusions can reach 300-500 microns.

This is the ratio between weight and volume, and expresses the “specific weight” of a given material. From everyday life, we know that iron is heavier than wood, which in turn is heavier than cork. The same principle applies to film: some materials are “naturally” heavier than other. It is however much more difficult to recognise such differences in density because there are are so much smaller, and because the materials we manage are normally in the form of a sheet with a very limited weight. It is therefore difficult to appreciate the differences.

Density is measured in terms of grams per cubic centimeter. In the film sector, density  values are around 1, similar therefore to water. The following is a brief list of typical densities of various films:

  • Cellophane 1.45g/cm3
  • Polyethylene (high- and low-density) 0.90g/cm3
  • Bioriented polyproplene 0.91g/cm3
  • Polyster 1.40g/cm3
  • Polyamide (nylon) 1.15 g/cm3
  • PVC 1.35 g/cm3

This is the weight of the surface of a given film, measured in grams per square metre. If a film has a surface weight of 23 grams/m², this means that a square meter of that film measures 23 grams. It is easy to calculate the surface weight of a monofilm, by multiplying the thickness of the film by the density of the material. For example, a bioriented polyproplene of 20 microns thickness with a density of 0.91 will have a surface weight of 18.2 grams per m² (20 microns x 0.91g/cm3 = 18.2g /m²). There are specific scales used to measure the surface weight of a film. In this case, all you need is to extract a piece of the surface of a given film (a 10x10cm square) and place it on the scales. These scales are particularly needed in cases of multi-material films (coupled or co-extrused) or sheets.

Yield is the number of square meters of film obtained from one kilo of product. It is calculated by dividing 1000 by the title. In the example above, the bioriented polyproplene of 20 microns, which has a surface weight of 18.2g/m², will have a yield of 54.94 square metres per kilo of film (1000g/18.2g/m² = 54.94m2/kg)

The monofilm is a film made of a single sheet.

Coupled films are made by glueing together two or more different films. Coupled generally refers to two films, triplex to three, while four different films is extremely rare. The advantage of this process is that it allows for very different films to be placed together (which for technological reasons, it is not possible with co-extrusion), thereby creating a new film with generally better overall characteristics than the sum of the characteristics of each component.

The size of the coil is called the band.

Metalization is a process in which metal is coated to one side of the film, usually aluminium. The rollsare introduced into a vacuum chamber, the coil is unwound and re-wound, and a jet of vapourised metal is sprayed onto the side of the film. This aluminium coating deposited onto the film creates an excellent barrier against humidity, oxygenisation and also light. Metalization also gives the metal visual effect that clients often request to improve the aesthetic aspect of their products. This layer is extremely thin, usually considerably less than 1 micron, and not measurable by the micrometer. For this reason, other measuring systems are employed to measure the thickness of the layer, such as the electrical conductivity of the surface compared to the optical density. Nearly all types of film can be metalized. This process does not change the density of the film, but does make the film unsuitable for direct contact with food products.

This is a film made of two films or a monofilm bound together at their extremes.

This is a film made of two films or a monofilm bound together at their extremes.

This process involves putting two different films together. If carried out properly, this is a straightforward process. It is best if the films used for the application are not generic types of film, but have been specifically designed for the combined product.

This process involves passing the film across a bed of needles, to create small craters in its surface.

This international standard defines the standards for a quality management system for a company; these are general standards and can be implemented by firms of any type or sector. The latest revision of the standard was in 2015 (ISO 9001:2015). It is the essential standard for any company that wants to conduct cyclical quality control, starting from the needs (explicit or otherwise) of the clients and ending with monitoring of the entire production process. Clients and satisfying their needs are the core of ISO 9001; each activity, application and monitoring process of the company’s work and procedures are designed to offer the maximum satisfaction to the end user.

This procedure increases the surface tension of plastic materials to order to prepare them for further working (printing, coupling, adhesives etc). The process consists of giving a calibrated electric shock to the material for a calculated period of time to create a form of “oxidisation”and make it receptive to further working. It is a safe, efficient and economically advantageous process compared to others, completely invisible to the naked eye and without damaging or altering the technical properties of the surface treated (it does not look any different, and its elasticity and resistance to traction are unchanged, as are its thickness or other technical parameters). It can be applied onto many different base materials, plastic or otherwise (paper, metalized surfaces), although the results obtained do vary. It can also be applied to conductors and non-conductors, even if its main use is to improved the adhesive quality of Polyethylene and Polypropylene, the two types of plastic film with the lowest surface energy.