How are Paper Bags Made? (Infographic)
Centuries before, using sacks made of jute, burlap, and jute were the primary methods of holding goods. Although they are sturdy, they are also time-consuming and expensive to produce back in the day. On the other hand, paper bags are portable and much more economical to process.
Kraft paper bags became popular in the 1800s when inventors developed the first technology to mass-produce them. Francis Wolle patented the first paper bag-making machine in 1852. In 1869, Wolle and his brother founded the Union Paper Bag Machine Company with a paper packaging plant that could create 1,000 feet of paper per minute.
Years later, Margaret Knight, a prolific inventor working for the Columbia Paper Bag Company, realized that Wolle’s envelope-like design or today’s pinch-bottom paper bag is not practical and efficient. So she created the square-bottomed packaging and built a machine that paved the way for the widespread commercialization of paper bags.
Since then, paper bags have been a market mainstay. But unlike before, technology has helped producers manufacture paper bags faster and with less waste and cost. Here are how commercial paper bags are processed today.
Preparation of Raw Material
Wood that a pulp mill receives can come in a variety of shapes and sizes. It could come in the form of round-wood bolts (short logs) with the bark still attached or as half-dollar-sized chips from a debarked round wood.
If manufacturers use round wood, a debarking process would be necessary. This is commonly done by tumbling the wood in huge steel drums with wash water. And if the pulping process requires chemical digestion, the debarked wood bolts are processed in a chipper. After that, the chips are sized, cleaned, and stored in preparation for further processing.
Here, the chips are stored in a big pressure cooker (digester) and applied with kraft pulping chemicals. The chips are digested with steam at precise temperatures in order to separate the fibers. This process also partially dissolves lignin and other extractives from the wood. These can weaken and discolor the paper if not removed.
Some digesters constantly run with a steady supply of chips (furnish), while others treat batches at a time. The cooked pulp is discharged into a pressure vessel after the digesting process. The steam and volatile materials are piped away, and the heated pulp is reintroduced into the chemical recovery cycle. Here, the pulp is screened, cleaned, and most of the water is removed in preparation for papermaking.
Because raw pulp still contains a significant amount of lignin and other discoloration, it must be bleached to produce white or light-colored papers, so they undergo bleaching. The order in which they are applied is determined by a variety of criteria. This includes the cost of bleaching chemicals, the type of pulp, and the state of the pulp.
This process also further dignifies the fibers through chlorination and oxidation. At the end of the process, the dissolved lignin is extracted from the surface of the fibers using sodium hydroxide.
The bleached and refined pulp then enters the paper mill and is mixed with water. This pulp solution goes through a series of rotating and stationary blades to make it more refined. The process gives the fibers clean-cut or “fibrillated” ends. Fibrillated fibers bind more tightly with other fibers, making the paper stronger.
Afterward, fillers like calcium carbonate and clay are added to make the paper opaquer and give it better density. To further improve the texture of the paper, manufacturers add dyes and optical brighteners. This final solution enters the paper machine, where the water is squeezed out, and the paper is dried and pressed.
Paper Sheering & Design Printing
The prepared sheets of paper are now stacked one on top of the other before being cut to the customer’s specifications. The shape and design of the paper bag are decided and implemented at this stage.
These papers go through a printing cylinder in a conventional or digital printing press. As it passes through the machine, the client-specified design is stamped into the paper. Typically, the process uses fast-drying solvent or water-based inks to attain quality print at high speed.
Eyelet Punching and Paper Creasing
After the sheering stage, certain details of the customer-specified paper bag handles will be applied to the paper. For example, if the paper bag is going to have rope handles, the material will undergo eyelet punching. The handles are also connected in the same process. If the bag has cut-out holes as handles, that will also be done at this stage.
After that, the paper is pleated to facilitate subsequent folding and sticking of the various sections of the bag. It guarantees that the bags are folded, stuck, and assembled in a consistent manner.
Clients may require their bags to be durable and strong at times. So sheets of paper are pasted together to create a double layer and make the paper bag thicker. After the adhesive is applied between sheets, a machine pushes them together for a clean and long-lasting bond.
Folding, Sticking, and Finishing
The manufacturing process has now reached its conclusion. At this stage, all of the bags’ separately processed pieces, including the front, back, and side flaps, are assembled.
Usually, paper bag manufacturers use a tubing machine. The machine draws in the components, fold them together, and bond them with adhesive. Tuber speed generally runs at 150-250 feet per minute.
In certain procedures, depending on the design, the manufacturer adds another layer of paper for the bottom. This makes the lower part stronger so the paper bag would not easily tear when holding heavy objects.
After that, the application of the finishing touches, such as adding the rope handles, are also completed.
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