Resin: This is a short term for Polyethylene (PE) resin. The three types of PE resins are LDPE, LLDPE and HMW-HDPE (see below). Other plastic resins include vinyl, polypropylene, styrene and nylon.
Types of Resin
Virgin Resin: This is a term that refers to pure and clean (no recycled material is included) resins.
Refers to the usage of high-quality, "fresh from the reactor", resin.
Refers to the combination of two or more types of resin.
Refers to resin that has been used at least once before. Can be post-industrial (scrap) or post-consumer (recycling). Property of resin is decreased each time it is reused.
Polymer resin is pelletized - Polymer bags begin as resin pellets. Resin can be completely new virgin resin, or recycled resin.
Containers of polymer resin pellets.
Resin pellets are melted and blown - The resin is then heated to a liquid state and blown with a stream of hot air through a ring die to create a tube of polymer film.
Resin is melted and blown into film.
Film is extruded - The continuous tube of film is cooled and flattened through a series of rollers.
Film extruded by rollers
Cutting and folding - The film tube is cut and folded in various shapes. The film is then spooled onto rolls in predetermined lengths.
Film is folded along more rollers
Conversion - Rolls of film are converted into individual or blocks of bags by cutting and/or sealing. Measured stacks of bags are configured for specific applications and packaged for shipping.
Cut and sealed bags can be put on wickets for use.
One of the most common plastics processing techniques covering a vast range of applications in whichresinsare melted, heated and pumped for processing. Extrusion machines accomplish these tasks by means of one or more internal screws. In extrusion, the material to be processed is sheared between the root of the screw and the wall of the barrel that surrounds it. This process produces frictional energy that heats and melts the substance as it is conveyed down the barrel. Melted extrudate from the machine is further processed after the extrusion phase, which typically produces pellets, sheet, cast film, blown film, fibers, coatings, pipes, profiles or molded parts. (Modern Plastics Encyclopedia 1995).
Co-extrusion: The simultaneous extrusion of two or more different thermoplastic resins into a sandwich-like film with clearly distinguishable individual layers. This involves a process where parts are blow-molded with walls containing two or more layers of different material. Coextrusion offers wide latitude for material selection and also allows the use of recycled materials. A material with good barrier properties, for example, can be used for the inside and outside surfaces of a blow molded bottle, while recycled material can be used for the internal layer. (Modern Plastics Encyclopedia 1995). (Co-Extruded Bags)
There are many shapes and folding patterns available for poly rolls or "film" that serve as end products or precursors to making various bag configurations. A few examples are shown here.