To manufacture bags, industry uses a process known as Blown Film Extrusion. This process is used to manufacture not only garbage bags but also items such as; vapor barrier, bread bags, grocery bags, or any one of thousands of different items that you would see packaged for resale.
The plastic is fed in pellet form into the machine hopper (this machine is known as an Extruder), the plastic is conveyed forward by a rotating screw inside a heated barrel and softened by both friction and heat. The softened plastic is then forced upwards through a circular die in a shape of a hollow tube.
This is a continuous process where the tube is expanded with air above the die, and collapsed by the take-off or nip rollers, the volume of air inside the bubble, the speed of the nip rollers and the extruders output rate all play a role in determining the thickness and size of the film.
The tube or “web” of film is then continuously rolled up by take-off rollers, or the web of film may be fed directly into a bag-machine in an in-line process. The tube is heat-sealed across its width to form the bottom of the bag and cut across further up the tube to form the opening.
The extrusion of Cast Films by the flat die technique is becoming more and more important in view of its superior performance: throughput of more than 1 ton per hour against a few hundred kilogram’s per hour for the circular die technique, and better control of the distribution of layer thickness in the transverse direction.
As in the case of bi-oriented films, the technique of multi-layer co-extrusion allows for 3, 5 or 7 layers within complex structures.
The material temperature recommended for manufacturing is situated between 230 and 280°C when using a flat die and between 180 and 210°C for a circular die, with water-cooling of the tubular film ; higher temperatures must be avoided as they may cause degradation of the additives.
Cast polypropylene films are used for the packaging of foodstuffs, textiles, the production of stationery, simulated leather goods, as well as for the manufacture of complex films by lamination or co-extrusion coating.
Injection molding is a manufacturing technique for making parts from thermoplastic material. Molten plastic is injected at high pressure into a mold, which is the inverse of the product’s shape. The mold is made by a mold maker (or toolmaker) from metal, usually either steel or aluminum, and precision-machined to form the features of the desired part. Injection molding is widely used for manufacturing a variety of parts, from the smallest component to entire body panels of cars. Injection Molding is the most common method of production, with some commonly made items including bottle caps and outdoor furniture.
The most commonly used thermoplastic materials are polystyrene (low cost, lacking the strength and longevity of other materials), ABS or acrylonitrile butadiene styrene (a co-polymer or mixture of compounds used for everything from toy parts to electronics housings), nylon (chemically resistant, heat resistant, tough and flexible – used for combs), polypropylene (tough and flexible – used for containers), polyethylene, and polyvinyl chloride or PVC (more common in extrusions as used for pipes, window frames, or as the insulation on wiring where it is rendered flexible by the inclusion of a high proportion of plasticiser).
The Extrusion blow molding process begins with the conventional extrusion of a parison or tube, using a die similar to that used for making plastic pipe. To manufacture Plastic Bottles, industry uses a process known as Blow Molding. This process is used to manufacture hollow plastic bottles such as; milk jugs, shampoo bottles, bleach bottles, or any one of countless products you might see on store shelves. The plastic is fed in pellet form into the machines hopper, (this machine is known as a Blow Molder), the plastic is conveyed forward by a screw inside a heated barrel being softened by both friction and heat. The softened plastic is then forced downwards through a circular die forming a hollow plastic tube called a “parison”.
The parison is then clamped inside a hollow mold and inflated from with-in. The air pressure forces the parison to inflate against the mold surface, the plastic cools in the shape of the interior of the mold cavity. The mold then opens and the plastic bottle is ejected. The bottle may they be conveyed on to trimming, printing and filling stations.
Other processes for Blow Molding include Stretch Blow and Injection Blow.
Extrusion blow molding: Can be used to process many different plastics, including HDPE, PP, PET and LDPE.
Thermoforming describes the process of heating a thermoplastic sheet to its softening point, stretching it over or into a single-sided mold, and holding it in place while it cools and solidifies into the desired shape. The thermoplastic sheet is clamped into a holding device and heated by an oven using either convection or radiant heat until it is softened. The sheet is then held horizontally over a mold and pressed into or stretched over the mold using vacuum pressure, air pressure, or mechanical force. The softened sheet conforms to the shape of the mold and is held in place until it cools. The excess material is then trimmed away and the formed part is released. Excess material can be reground, mixed with unused plastic, and reformed into thermoplastic sheets
Thermoforming is commonly used for food packaging, but has many applications from plastic toys to aircraft windscreens to cafeteria trays. Thin-gauge (less than 0.060 inches) sheets are mostly used for rigid or disposable packaging, while thick-gauge (greater than 0.120 inches) sheets are typically used for cosmetic permanent surfaces on automobiles, shower enclosures, and electronic equipment. A variety of thermoplastic materials can be used in this process, including the following:
As mentioned above, there are different methods of forcing the thermoplastic sheet to conform to the mold. These types of thermoforming include the following:
Non-woven fabrics are produced by depositing extruded, spun filaments onto a collecting belt in a uniform random manner followed by bonding the fibers. The fibers are separated during the web laying process by air jets or electrostatic charges. The collecting surface is usually perforated to prevent the air stream from deflecting and carrying the fibers in an uncontrolled manner. Non-woven products are employed in carpet backing, geotextiles, and disposable medical/hygiene products. Since the fabric production is combined with fiber production, the process is generally more economical than when using staple fiber to make non-woven fabrics