Production process
The plant processes granules produced at the Silvano D’Orba facility, which are used to produce bags (household waste collection bags, garment packaging and storage bags) and industrial-use stretch film for pallet wrapping.
The Tagliolo Monferrato plant uses virgin granules to produce bags intended for the food product line, which account for 20% of overall production.
There is also a product line of biodegradable bags suitable for wet waste.
ReLife Plastic Packaging uses blown film extrusion technology with single, double, triple and up to seven-layer blown film structures.
The plant is comprised of:
The plant houses 14 extruders in total (2 dedicated to the food line and hence compartmentalised), which can each produce approximately 300 kg of reels/hour.
Blown film extrusion is the method used for polyethylene intended for the production of flexible packaging or refuse bags.
Blown film extruder operation
The process consists of forcing the molten polymer of material, which has been melted by the heat of the extruder line, towards a rotating die head and then nip rollers which, with the aid of compressed air blown into the molten plastic, help to form a “bubble”. The size of the “bubble” dictates several product characteristics, which vary based on the intended use.
The material is initially loaded and mixed in silos to create a blend (for products not part of the Food line, post-consumer granules constitute between 50% and 100% of the mix). The plant has single, double, triple and up to seven-layer blown film extruders, depending on the performance required at output, and customer requirements.
Extruder
The extruder resembles a massive mixing machine which, thanks to a rotating worm gear driven by a motor, brings the plastic granules at a temperature to 160-170°C to the extrusion head. The extrusion head then shapes the plastic material into a cylindrical tube. The tube is subsequently blown into a bubble and cooled by air which is blown inside. Visually, it appears to be a large elongated cylinder in which, thanks to the stretching of the polymer chains and the cooling produced by the introduction of air, the film is endowed with good mechanical and optical properties. The taller the blown tube (bubble), the better the exchange of insufflated air, resulting in optimal distribution of thickness. The end result consists of mother reels of semi-finished product weighing approximately 2000 kg.
The extrusion stage can also include flexo printing for customisation of the film. Following extrusion and (where applicable) printing, the reels proceed to the subsequent welding stage, after an intermediate 72 hour film stabilisation period.
Welding
The welding stage transforms the mother reels into finished products of various colours and thicknesses. The end products are freezer bags in virgin polyethylene, garment bags and refuse bags in virgin and recycled polyethylene. The welding stage involves the use of 25 welding units. The tube is blown into a bubble, after which hot slit knives weld the bottom of the bags at the required length, and the sides too. It is then made into pre-cut rolls, affixed with a band of anonymous or customised gummed paper.
During this stage:
- gussets are created, facilitating filling of the bag during use.
- a bag tie is added
Three types of refuse bags are produced:
01Standard bags
• Bags with side and bottom welds (open top)
02Bags with handles
Handle bags, also called T-shirt bags
03Drawstring bags
Bags with a drawstring tie around the top opening
The welding machines can produce two or three rolls simultaneously, and up to 7 bundles of bags for Food line products. The rolls are then manually packed into cartons, palletised and stored in dedicated areas, ready to be shipped to customers.
Laboratory tests
At the end of the process, quality testing is conducted in accordance with UNI EN 13592.
1 VISUAL CHECK
2 DIMENSIONAL CHECK
3 Wet waste / LEAK TEST
4 VERTICAL IMPACT TEST
5 JERK TEST
6 OPACITY
7 THICKNESS
Visual inspection of the bag to verify uniformity of colour and material, print quality (where applicable), the presence of a tie or drawstrings.
This verifies the average length and width of the bag measured at both ends with a millimetre scale ruler.
The bag is placed on a special container and filled with water, then left hanging for a few minutes to check for leaks.
The bag is filled with weights that vary depending on the litreage, and then dropped from a height of 1.20 m, after which it is inspected thoroughly for holes or tears.
This test is carried out on bags with tie handles, using the same criteria and procedures as the previous test; in this case, however, the bag is hung from a hook by its handles and then dropped.
This test measures how much light passes through the bag. A strip of material at the mid-circumference point of the bag is passed in between a lamp and a lens; a display reads the measured amount of light that passes through the bag.
A strip of material at the mid-circumference point of the bag is passed under a digital micrometer and the thickness of the bag is accurately measured at a distance of 3 cm.
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