Most items at your favorite supermarket, discount store, or shopping mall were safely delivered in boxes made of corrugated cardboard, và many are displayed in the same boxes, which were manufactured so they could be opened and used for this purpose. Other items may arrive sầu in their own corrugated or uncorrugated paperboard boxes. Because corrugated cardboard is such a versatile packaging material, millions of tons are used each year to lớn protect & display products. During 1992, more than 25 million tons of corrugated cardboard were produced in the United States. Another 6 million tons of uncorrugated boxboard or paperboard were also produced for use in folding cartons.
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Corrugated cardboard is a stiff, strong, and light-weight material made up of three layers of brown kraft paper. In 1884, Swedish chemist, Carl F. Dahl, developed a process for pulping wood chips into a strong paper that resists tearing, splitting, và bursting. He named it the kraft process because it produces a strong paper that resists tearing, splitting, and bursting.
From the paper mill, rolls of kraft paper are transported to lớn a corrugating, or converting, plant. At the plant, layers of kraft paper are crimped và glued to lớn size corrugated cardboard, which is then cut, printed, folded, and glued to lớn make boxes. At the beginning of this process, kraft rolls from the paper mill are loaded inlớn a huge machine called a corrugator. A typical corrugator is as long as a football field—300 feet (91.44 meters). Some rolls of kraft paper are used as the corrugating medium, và others are used as liners, the layers of kraft paper glued on each side of the medium. After the corrugator has heated, glued, & pressed the kraft paper lớn khung corrugated cardboard, the continuous sheet of cardboard is cut into wide box blanks that then go lớn other machines for printing, cutting, and gluing. Finally, batches of finished boxes are banded together for shipping to the food processor, toy maker, automobile parts distributor, or any of the thousands of businesses that depover on corrugated cardboard packaging.
Raw Materials
Fast-growing pine trees provide the primary raw material used lớn make corrugated cardboard. The largest packaging companies own thousands of acres of lvà where trees are matured, harvested, & replaced with seedlings. After the trees are harvested, they are stripped of their limbs; only the trunks will be shipped by truông xã to a pulp mill. The largest packaging companies also own the mills where trees are converted lớn kraft paper. At the mill, the harvested tree trunks are subjected khổng lồ the kraft process, also known as the sulfate process because of the chemicals used khổng lồ break down wood chips into fibrous pulp. After pulping và other processing, the fibers are sent directly lớn the paper machine where they are formed, pressed, dried, & rolled inlớn the wide, heavy rolls of kraft paper sent khổng lồ corrugating plants to be made inkhổng lồ cardboard.
At the corrugating plant, only a few other raw materials are needed to make a finished box. Com starch glue is used khổng lồ bond the corrugated medium to lớn the liner sheets. Because so much glue is used, rail cars or large tanker trucks deliver it as a dry powder that will be stored in huge silos at the corrugating plant until it is needed. Drawn from the silo, the dry com starch is mixed with water và other chemicals and pumped into the corrugator lớn be spread on the corrugated medium as the layers of liner are added. Other raw materials are used to finish the corrugated cardboard after production. Waxes made from paraffin or vegetable oils can be applied khổng lồ make a water- or grease-resistant container for food products. Brightly colored inks are also applied lớn create bold graphic designs for self-supporting displays featuring hàng hóa name, information, và company name và logo. Teams of salespeople and designers work together to create the manufacturing & printing patterns, called dies, that are used to cut and print a specific box kiến thiết. The dies are created in a pattern shop and transferred to lớn the rotary die-cutting equipment & printers that finish the box blanks.
Design
Kraft paper has been manufactured since 1906. Since then, pulp processing, paper making, & corrugating operations have been developed to lớn a high state of efficiency và productivity. Today, in the corrugated cardboard industry, designers are creating innovative sầu containers that require four-color printing and complex die-cutting. These innovative sầu containers are designed with sophisticated software such as computer- aided design (CAD) programs, allowing a packaging designer lớn brainstorm different package designs before manufacturing begins. A designer using a CAD program can gọi up & modify different designs that have sầu been stored in a computer design library. Thus, existing packages can generate new designs. Many retail stores use such light, svào, and colorful containers directly, as point-of-purchase displays.
The Manufacturing Process
Pulping the pine chips
1 Manufacturing a corrugated cardboard box begins with the pulping of wood chips in the kraft (sulfate) process. First, tree trunks are stripped of bark và torn inlớn small chips. Next, these chips are placed in a large, high-pressure tank called a batch digester, where they are cooked in a solution, or liquor, made of sodium hydroxide (NaOH) & several other ionic compounds such as sulfates, sulfides, và sulfites. These strongly alkaline chemicals dissolve sầu the lignin, the glue-lượt thích substance that holds the individual wood fibers together in a tree trunk.
2 When the pressure is released after several hours, the wood chips explode lượt thích popcorn inkhổng lồ fluffy masses of fiber.
Making kraft paper
3 After additional cleaning and refining steps, a consistent slurry of wood pulp is pumped lớn the paper-making machine, also known as a Fourdrinier machine. Gigantic, square structures up lớn 600 feet long (182.88 meters), these machines contain a wire mesh in which the paper is initially formed. Next, the paper is fed into lớn massive, steam-heated rollers and wide felt blankets that remove sầu the water. At the kết thúc, the finished medium, or liner, is rolled for shipment.
Shipping & storing the kraft paper
4 Rolls of kraft paper for corrugating are available in many sizes to lớn fit the production equipment at different corrugating plants. The most comtháng roll sizes are 67 inches (170.18 centimeters) wide và 87 inches (220.98 centimeters) wide. An 87- inch roll of heavier paper can weigh up khổng lồ 6,0 pounds (2,724 kilograms). As many as 22 rolls of 87-inch paper can be loaded inlớn one railroad boxoto for shipment to a corrugating plant.
5 At the plant, the kraft paper is separated into lớn different grades, which will be used for the medium & the liner. These different grades of corrugated cardboard can be made by combining different grades of kraft paper. A knowledgeable packaging specialist works with a customer to lớn determine the strength required for the corrugated cardboard container being planned. Then, when a plant receives an order for containers, a hàng hóa engineer specifies the combination of medium and liner to produce a cardboard to match the customer’s requirement.
Corrugating the cardboard
6 Using powerful fork-lifts, skilled equipment operators select, move, & load rolls of kraft paper at one end of the corrugator.
(Corrugated cardboard manufacture includes two key steps: making kraft paper và corrugating the cardboard. Kraft paper involves pulping wood chips & then feeding the resulting paper substance through massive steam rollers that remove the water. Corrugating is also done in a machine that utilizes heavy rollers. One roll of cardboard is corrugated & then glued between two other layers (liners) by the same machine. The glue is then cured by passing the cardboard over heated rolls.)
7 One roll of medium is loaded to lớn run through the corrugating rolls, và a roll of liner is fed inlớn the corrugator to be joined with the corrugated medium. Liner from another roll travels up over the corrugating rolls along a flat structure called the bridge. This liner will be glued khổng lồ the corrugated medium later in the process.
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8 For a large production run, additional rolls are loaded inlớn automatic splicers. Sensitive sầu detectors check the rolls of paper feeding into lớn the corrugator. When a roll is nearly empty, the corrugator control system starts a splicer, and paper from the new roll is joined lớn the kết thúc of the paper going through the machine. Thus, production of corrugated cardboard is continuous, & no production tốc độ is lost.
9 The medium lớn be corrugated is fed into the giant, electrically driven rollers of the corrugator, first through the preheating rollers và then inkhổng lồ the corrugating rolls. Steam at 175 to lớn 180 pounds of pressure per square inch (psi) is forced through both sets of rollers, and, as the paper passes through them, temperatures reach 350 to lớn 365 degrees Fahrenheit (177 khổng lồ 185 degrees Celsius).The corrugating rolls are covered with flutes—horizontal, parallel ridges like the teeth of massively wide gears. When the hot paper passes between the corrugating rolls, the flutes trap and bkết thúc it, forming the middle part of a sheet of corrugated cardboard. Each corrugating machine has interchangeable corrugating rolls featuring different flute sizes. Installing a different flute kích thước in the corrugator changes the width of the corrugated medium.
(A finished piece of corrugated cardboard consists of a single corrugated layer sandwiched between two liner layers.)
The medium travels next khổng lồ a phối of rollers called the single-facer glue station. Here, one layer of liner is glued khổng lồ the medium. Starch glue is carefully applied to lớn the corrugated edges of the medium, và the first layer of liner is added. From the single- facer, the medium và liner go to lớn the double- backer glue station where the other layer of liner from the bridge is added following the same procedure. Continuing through the corrugator, the cardboard passes over steam heated plates that cure the glue.
Forming the blanks into boxes
lO At the end of corrugator, a slitter Lm scorer trims the cardboard and cuts it inkhổng lồ large sheets called box blanks. Box blanks pop out of the slitter-scorer like wide slices of toast & slide inkhổng lồ an automatic stacker that loads them onto lớn a large, rolling platkhung. From here, they will be transported to lớn the other machines that will convert them inkhổng lồ finished containers. Skilled production workers use a computer terminal & printer lớn prepare a job ticket for each staông chồng of box blanks produced by the corrugator. With the job ticket, workers can route the staông xã lớn the right fabrication machines, called flexos (the name is short for flexographic machine). A flexo is a wide, flat machine that processes box blanks.
Printing dies & die-cutting patterns are prepared in a pattern cửa hàng on large, flexible sheets of rubber or tin. The dies and patterns are loaded onlớn the large rollers in the flexo, & the box blanks are automatically fed through it. As each blank passes through the rollers of the flexo, it is trimmed, printed, cut, scored, and, in a printer-folder- gluer, folded and glued to form a box. From the flexo, the finished boxes are automatically stacked và sent lớn a banding machine to lớn be wrapped for shipping. Other equipment in a corrugating plant includes stand-alone die-cutters, die-cutters with print stations, and machines known as curtain coaters that apply a wax coating to lớn fruit, vegetable, & meat containers. Box blanks requiring only simple, one-color printing and die-cutting can be run through a stand-alone die-cutter, print station, and curtain coater lớn produce water- or grease-resistant containers.
Quality Control
Quality control begins with the suppliers of the kraft paper used khổng lồ make corrugated cardboard. Kraft paper must be smooth và strong. After the paper passes through the corrugator và is made inkhổng lồ box blanks, individual blanks are pulled from a staông xã và tested. The Cobb thử nghiệm measures moisture in the liner & medium. Glue strength, bursting strength, compression, and highly accurate dimensional tests determine the quality of the manufacturing process. A warp test determines the flatness of the box blank, insuring that each blank will travel smoothly through the flexo machines. As skilled workers run batches of box blanks through the flexo machines, individual boxes are pulled and inspected. Trimming, cutting, and scoring must be correct. No damage to the cardboard is allowed. Also, the different layers of colored ink used in color printing must be perfectly aligned.
The Future
Future corrugated containers will be manufactured using kraft paper produced from recycled packaging rather than trees. Recycling và other environmentally friendly processes will continue to grow in importance in the future of corrugated cardboard. Today, inks based on soybean oil and biodegradable waxes and other coatings are beginning lớn be used in container manufacturing. Leading packaging companies are already operating paper mills that make fresh, clean kraft paper by de-inking và pulping used containers.
Where To Learn More
Books
Bessen, A. Howard. Design & Production of Corrugated Packaging & Displays. Jelmar Publishing Company, Inc., 1991.
The Corrugated & Paperboard Container Industry: An Analysis of Current Markets &
Prospects for Future Growth. Business Trover Analysts, Inc., 1991.
Maltenfort, George G. Corrugated Shipping Containers: An Engineering Approach. Jelmar Publishing Company, Inc., 1988.
Rohde, Elliot S. Producing Corrugated Containers Profitably. Jelmar Publishing Company, Inc., 1993.
Kline, James E. Paper And Paperboard: Manufacturing và Converting Fundamen¬tals, 1991.
Periodicals
Carey, Kevin. “The Science of Diecutter Makeready.” Boxboard Containers. March, 1993.