One of the most common methods of film manufacture is Blown Film (also referred to as Tubular Film) Extrusion. The process involves extrusion of a plastic through a circular die, followed by 'bubble-like' expansion.
Blown Film Extrusion can be used for the manufacture of co-extruded, multi-layer films for high barrier applications such as food packaging.
The Process - Plastic melt is extruded through an annular slit die, usually vertically, to form a thin walled tube. Air is introduced via a hole in the centre of the die to blow up the tube like a balloon. Mounted on top of the die, an air ring blows air onto the hot film to cool it. The tube of film then continues upwards, continually cooling, until it passes through nip rolls where the tube is flattened to create what is known as a 'lay flat' tube of film. This lay-flat or collapsed tube is then taken back down the extrusion 'tower' via more rollers.
The lay-flat film is then either kept as such or the edges of the lay-flat are slit off to produce two flat film sheets and wound up onto reels. If kept as lay-flat, the tube of film is made into bags by sealing across the width of film and cutting or perforating to make each bag.
Materials - Polyethylenes (HDPE, LDPE, LLDPE and PVC) are the most common resins in use, but a wide variety of other materials can be used as blends with these resins or as single layers in a multi-layer film structure.
Extrusion: The "bubble" is around 12 metres high.
Flexography is the major process used to print packaging materials.
Flexographic Printing - Aperio have two types of printing presses used for flexographic printing. These are the stack type and central impression cylinder (CIC). Both types employ a plate cylinder, a metering cylinder known as the anilox roll that applies ink to the plate, and an ink pan. Some presses use a third roller as a fountain roll and, in some cases, a doctor blade for improved ink distribution.
Process Overview - in the typical flexo printing sequence, the substrate is fed into the press from a roll. The image is printed as substrate is pulled through a series of stations, or print units. Each print unit is printing a single colour.
Rotogravure Printing - Aperio offer Rotogravure printing. Rotogravure is an intaglio printing process that is commonly used for printing packaging materials.
Process Overview - Rotogravure uses a depressed or sunken surface for the image. The image areas consist of honey comb shaped cells that are etched or engraved into the surface of a copper plated steel or aluminium cylinder. The un-etched areas of the cylinder represent the non-image or unprinted areas. The surface is normally plated with hard chromium to improve its wearing properties
The cylinder rotates in a bath of ink. As the cylinder turns, the excess ink is wiped off the cylinder by a flexible steel doctor blade. The ink remaining in the recessed cells forms the image by direct transfer to the substrate as it passes between the plate cylinder and the impression cylinder.
Conversion and Slitting
Slitting - is the process, typically after printing, where a large roll of film is broken down into either narrow width and/or small roll diameters.
The material is either cut with razor blades or shear cutting devices into the correct width and then rolled up either on cores using a centre driven shaft or cores that lay on roller ie surface driven.
These machines control the film with web guides and tension control devices to produce flat rolls for the end user. Shown here is a typical centre driven slitter machine in operation.
Conversion Process - The conversion department is just that - it takes reels of either film printed and/or laminated or plain films and converts them into bags or 'reel stock'.
With converting of the 'reel' stock into bags there are several formats as depicted below and these are side weld, bottom seal or pouch type seals:
Side weld: uses a heated point to cut and seal the sides of the bag similar to the 'standard' bag depicted below.
Bottom seal: similar to tube running through a machine and being cut and sealed in one operation; this usually means the cut end is the beginning of the next bag.
Pouch seal: can be a combination of the above but typically are wider seals on three sides of the bag.
Aperio Rapfast is the world's leading producer of food grade PVC cling films.
Aperio Rapfast are PVC film over wrap specialists. Manufacturing processes include extrusion. (...read more)
Aperio Rapfast offer a comprehensive range of films for use with fresh and frozen meat, seafood, poultry, fresh produce, bakery and delicatessen products like cheese and processed meats, together with a full line of films for use in catering, fast food, food service and institutional applications. Zipsafe Slide Cutter is a state of the art adaptation to the existing range of catering film products.
Specialized services such as custom formulation, printing and film for Case Ready meat and poultry applications are also available.
- Catering Films
- Meat Packaging Films
- Produce Films