Packaging has been the need of human kind from early time for storing, transporting, preserve foods, goods, products … The earliest time, people made the packages from animal skins, large leaves, vegetables to keep their food clean and fresh. In the war time, iron, steel could have invented to keep food safe for soldiers. In daily life, lots of materials were put in use: paper, glass, wood to corn, aluminum … With the dramatic innovation of technology, the interaction between people from different areas, different countries increase and demand of trading rises day by day , packaging in a most convenience way is necessary and vital. Plastic bag has been invented to meet that demand as an excellent solution. So how plastic bags are produced?
Plastic comes as a by-product of oil refining, and uses only 4% of the total world's oil production. It is a 'biogeochemical' manipulation of certain properties of oil, into polymers, that behave 'plastically.' Plastic polymers are manufactured into 5 main types, of which, plastic bags are made of the type known as Polyethylene. From polyethylene, resins are produced and come straight into plastic bag's production.
With special types such as food plastic bags, shopper plastic bags, luxurious plastic bags for many brand names as soft loop plastic handle bags, plastic handle bags, plastic plastic handle bags, % virgin resins are used to make the best quality bags: strong, smooth and nice appearance. Customers also require other film colors of plastic bags (blue, green, orange, yellow, red …) to make the bags look different and impressive. That is why manufacturers will add masterbatches (color resins) to change from transparent to the specific colors. If customers need the bags at cheaper prices, manufacturers will put few percent of additive materials such as CaCO3 (calcium carbonate) or or recycle materials to reduce bag cost. At this case, sometimes manufacturers will add an additive called impact modifier to make bags strong. When customers require plastic bags which can be destroyed easily in lands, suppliers must mix biodegradable additives as EPI or DW2 with quantity 1 or 2% when extruding.
The 1st process is blowing film or called extruding film. All the materials will be put into extruding machine to make big plastic film roll. In this steps, workers or technicians must control the bag rolls into smooth appearance.
The second step is printing process which is mainly used for shopping bags which many companies could customize the printing image with their logo, brand name, information about products … When getting orders with printing image, manufactures will create printing plates (printing cylinders) to put into printing machines. Images are analyzed into different colors; each color will be controlled by one worker if the bags need print many colors or printing images are difficult.
The third step is cutting and sealing process. The plastic rolls are put into cutting workshop to make it into different shapes and different handles. There are a lot of cutting machines available served for different handles: T-shirt, die cut, soft loop, patch handle, rigid, flat merchandise, etc
For the special kinds such as drawstring plastic handle bags, rigid plastic handle bags, soft loop plastic handle bags, they are usually required some manual steps which can not be implemented by automatic machine. In manual workshop, workers have to sew the handles into the bags, putting the cardboard into gussets (customized to customer's requirement), punching the hole …