Paper Industry Basics

PAPER NDUSTRY BASICS Papermaking: Past & Present r Paper identifies a broad range of products which are formed by bonding of many small discrete cellulosic or synthetic fibers into a sheet. The word “paper” is derived from the Egyptian word “papyrus:’ a material which is formed by matting sliced strips of reed together. However, the first production of true paper, a sheet comprised of small individual fibers, is credited to the Chinese in the year 105 A.D. Early papermaking involved the reduc- tion of bark or grass to a fibrous pulp by beating it in a stone mortar. Water was added to create a pulp slurry which was in turn poured into a mould with a porous bottom which allowed the water to drain away. The newly formed sheet was then dried in the sun. Papermaking proceeded in this manner for many centuries. Production, done totally by hand, was very small, but so was demand. However, with Gutenberg’s inven- tion of printing with movable type in 1447, the demand for paper soared. Handforming methods quickly proved inadequate, and a shortage of rags, a prime component of paper at that time, further limited production. name is derived from two brothers named Neither problem was resolved until the Fourdrinier who financed its development. early 19th century. In 1799 the prototype of The fourdrinier, however greatly refined, has today’s fourdrinier machine was invented by not changed in principle since then. a Frenchman named Nicholas Robert. Its Early papermakers had found naturally occurring, relatively pure cellulose fibers in the inner bark of certain trees and in cotton. However, it wasn’t until the 1830’s that 2 T A P P I J 0 U R N A L And water in very large quantities must be available for the manufacture of paper. Energy consumption is enormous in every phase of papermaking from transpor- tation of the raw material to the mill, through the manufacturing phase, and end- ing with transport of the finished product to the consumer. Since the petroleum price increases of the 1970s, most mills have installed additional power boilers to produce energy from woodwaste, spent chemicals, Anselm Payen, a French chemist, identified coal and sources other than oil. cellulose as a separate component of wood. With this discovery, only a few years passed before wood was being pulped for use in papermaking. Thus, the modern papermaking industry was born. Paper is made, to a greater or lesser extent, in nearly every country in the world. The United States, the leader in productive capacity, has the largest concentration of mills, equipment, and buying power in the References world. Pulp and paper is the ninth largest For further reading about the history of pulping and industry in the US. papermaking: Paper is made from hundreds of different Bureau, William E-Milestones in Papermaking. species of hardwood and softwood trees. Pittsburgh, Graphic Arts Pch. Foundation, 1981. Many factors, such as age and climate, affect Hunter, Dard-Papermaking through Eighteen the nature and composition of wood species. Centuries. New York, W.E. Rudge, 1930. Mod fiber is the primary raw material; Hunter, Dard-Papermaking: The History and Qch- but other fibers, including synthetics, are used niques of an Ancient Craft, 1st Ed., New York, A.A. in some grades. Many different chemicals Knopf, 1943. are used for both the pulping and manufacturing processes and as additives required as dyes and fillers and strengthening agents. 3 PAPER INDUSTRY BASICS The Process kld in pul$.ng. The more refined the pulp must be, the more involved and costly the method of pulping. For example, kraft paper and linerboard do not require nearly the amount of chemicals as that required for white text paper, nor do they require refining and washing. Mechanical pulping involves grinding a whole log to a pulpy mass by abrasion. With the refiner mechanical method, wood chips are steam-softened or partially decomposed with chemical solutions. In the chemical process, chips are loaded into a digester and “cooked” in a liquor with chemicals to remove lignin and other nod- brous impurities. The wood fibers separate when the cooked chips are “blown” from the digester. The unwanted nonfibrous resi- due is then drained off. After a series of washing and bleaching stages, the fibers are passed through refiners which fiay them for better bonding in the forming process. The greater the quantity of slurry released from the headbox, the thicker will PAPER FORMATION be the resulting paper. As the wire moves Whatever pulping method is used, the next along, water drains through the wire mesh step is to form the slurry into the desired allowing the fibers to mat and interlace and type of paper. After all bleaching, washing form the sheet of paper. and refining is accomplished, and required Another important factor in paper chemicals are added, the slurry is pumped formation is the speed of the fourdrinier into a headbox. From the headbox the slurry machine. A mill measures its success in is introduced onto the wire mesh of the terms of saleable output. The faster the fourdrinier machine. paper is produced, the more profitable the mill will be. 4 TAPPI JOURNAL 7W.nWire Formers The twin wire machine is a recent innovation which is gaining popularity. The traditional fourdrinier is essentially a two-dimensional unit measured in width and length. The twin wire machine, on the other hand, &three dimensional. Twin wire machines can be either vertical or horizontal in design. In the vertical twin wire machine, the pulp sluny emerges under pressure fiom the headbox into a vertical upward flow. Two separate loops of wire mesh come together at a forming nip, and the sluny enters at that point. Drainage begins immediately with water leaving the wires in both directions. After the paper web has completed the short forming distance; it travels along the second wire and, as with the fourdrhier, is picked up by a felt and carried into the press section for further dewatering. The operating speed of the twin wire machine is well in excess of the fourdrinier. In tissue production, speeds of 6,000 feet per minute have been reached, with an even higher potential. Mills strive to attain maximum speed Drying possible while preserving the quality of the As the paper web is carried on a moving felt sheet. Linerboard, for example, requires into the press section, it is compressed and strength characteristics that must be main- more water is squeezed out. Then it enters a tained. In contrast, newsprint permits long series of dryers. It continues through higher speed formation since the quality and this section of steamheated cylinders to the strength criteria are less critical. calender stacks where it is pressed and After the paper travels the fid length of smoothed. The finished paper is then wound the fourdrinier, it leaves the wire and enters onto a large roll. the press section for further dewatering. The fourdrinier wire, in the meantime, continues its loop. 5 PAPER INDUSTRY BASICS I FINISHING & CONVERTING r The finished roll of paper must be processed smooth it before winding it onto a roll. The I further into different sizes and forms to fill smoother the paper desired, the more rollers L the requirements of various end users. the paper passes through. Smoother finish ~ paper will have less bulk for its basis weight Coating than a vellum finish product. Not all papers are coated, but there is a great Winding and Sheeting I demand for paper with a smooth printing surface. Most printing processes produce Winding the paper onto a roll is just about better results on coated papers; and for four the last step of the manufacturing process color work, coated stock is essential. after it has been coated and calendered or Coatings add opacity and brightness a otherwise processed. The width of the reel reflective whiteness to the paper. In printing will correspond to the width of the four- papers, coated stock comes in three principal drinier. This reel will then typically pass forms: glossy, dull and matte. Glossy stock through a rewinder and slit into smaller rolls. is just that, shiny, and is what many people These rolls may go directly to the end think of when the term “coated” is used. user, or they may be converted into sheets. However, dull coated is ideal for books where Paper merchants stock many types of paper the elimination of light glare is important. in standard sheet sizes for the large printing Matte coated is similar to dull but also has a market. “tooth” in it. Matte is a popular artists’ paper. Although some lower grade publication stocks are coated in an added process in the dryer section, higher grades are usually manufactured as a separate operation off the machine. Air knife and blade are the two popular methods of applying coatings. In the air knife process, a jet of air serves as a blade to remove the excess of freshly-applied coating material. In blade coating, a flexible blade is set at an angle to accomplish this. Coatings can be applied on one or both sides of the paper. Calendering Calendering involves passing the paper through a series of polished steel rollers to 6 TAPPI JOURNAL End Products Hundreds of different types of paper are groundwood fhnish with a small additional used today for commercial, industrial and amount of chemical pulp to provide neces- domestic applications. They range from the sary strength. A growing percentage of hest printing papers to panelboard. Nearly newsprint is produced using recycled paper. 78-don tons of paper and paperboard ~ ~ were produced in the United States in the P"GA"G past year.

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