686 PACKAGING, RECYCLING AND PRINTING / Packaging Grades H C OH 3 Cl O N H C CH N 3 3 NH HN N H C 3 CH3 N O Cl HO CH3 Pigment Yellow 13 Figure 11 Structure of pigment yellow 13. See also: Papermaking: Paper Grades; The History of O H Paper and Papermaking; World Paper Industry Overview. H3C C N Further Reading Adams JM and Dolin PA (2002) Printing Technology. N C CH3 Clifton Park, NY: Delmar. H O DeJidas LP and Destree TM (1999) Sheetfed Offset Press Operating. Pittsburgh: GATF Press. Figure 12 Structure of quinacridone magenta pigment. Dennis EA, Odesina O, and Wilson DG (1997) Litho- graphic Technology. Albany, NY: Delmar. Eldred NR and Scarlett T (2001) What the Printer Should Know about Ink. Pittsburgh: GATF Press. CH3 FFTA (1999) Flexography: Principles and Practices, 5th edn. Ronkonkoma, NY: FTA/FFTA. Gray T (ed.) (2003) Gravure Process and Technology. Rochester, NY: GEF/GAA. Kipphan H (ed.) (2001) Handbook of Print Media. Berlin, Germany: Springer-Verlag. Levy U and Biscoe G (1998) Nonimpact Electronic − Printing. Charlottesville, VA: Interquest. SO 3 Thompson B (1998) Printing Materials. Leatherhead, UK: PIRA. + Wilson LA (1998) What the Printer Should know about Ca2 N Paper. Pittsburgh: GATF Press. N OH Packaging Grades G J F Ring, University of Wisconsin–Stevens Point, Stevens Point, WI, USA − CO 2 & 2004, Elsevier Ltd. All Rights Reserved. Pigment Red 57:1 Figure 13 Structure of pigment red 57. Introduction obtained by varying the pH, temperature, and time Nasiri Khosrau of Persia (now Iran) recorded the first of heating during oxidation. These were used by use of paper as a packaging material in 1035 AD printers for all printing inks through the mid nine- when he observed vendors in Cairo (Egypt) wrapping teenth century, before the discovery of synthetic vegetables, spices, and dry goods in paper. Today, organic dyes. paper continues to be an important material used to PACKAGING, RECYCLING AND PRINTING / Packaging Grades 687 transport, distribute, and market virtually every together to form a block bottom that is ideal for commodity and manufactured item. Paper competes packaging flour, rice, sugar, and other dry food items. very successfully with metals, glass, plastics, wood, The satchel-bottom bags, when filled, can stand and textiles, because it has many desirable properties upright. Finally, self-opening bags have gussets to including being biodegradable, recyclable, and re- form square bags and specially folded bottoms that newable. Paper functions in many diverse packaging form flat-bottom squares or rectangles. These bags applications from heavyweight shipping containers are folded flat but are designed to open with a snap to lightweight wrapping papers. This article will of the wrist and stand by themselves for filling. concentrate on lightweight specialty papers such as Grocery bags and sandwich lunch bags are examples retail paper bags, food wrapping, gift wrapping, of self-opening bags. spiral-wound paper tubes, label stock, and other Wet strength is an important paper additive for specialty items. The cut sheet size for wrapping retail bags. Grocery bags in particular must be able papers is 24 in. by 36 in., giving a total ream area of to maintain a substantial portion of their strength 3000 ft2. Types of paper used to manufacture boxes when brought into contact with wet food and other and containers are discussed elsewhere (see Paper- products. making: Paperboard Grades). Multiwall Paper Sacks Retail Paper Bags Multiwall paper sacks are designed to be exception- Retail bags are closed-bottom, flexible-walled con- ally strong and carry heavy and bulky materials for tainers that are capable of carrying many types of dry the building, food, and chemical industries. In goods within them. Paper bags are manufactured essence, multiwall sacks are two or more separate from kraft paper due to the requirement for high sacks nested together to form a stronger and tougher À strength. The paper may be bleached or unbleached sack. Five or six total plies of paper (60–110 g m 2) depending upon the use. The grammage range for may be necessary. For paper sacks, kraft paper is À lightweight bags is 40–60 g m 2. For heavier weight used; however, stretch and porosity as well as bags such as grocery bags that are required to carry strength are critical performance criteria. as much as 12 kg the grammage range extends to Stretch or extensibility is important because multi- À 110 g m 2. wall sacks are required to withstand numerous Historically, bags were fabricated from textiles or impacts during shipping and warehousing without animal skins with sewn bottoms. During the early rupturing and spilling their contents. Sack paper’s nineteenth century, powdered goods such as flour or ability to absorb shock during impact is measured by medicines were sold in hand-rolled paper sacks called tensile energy absorption (TEA), which is a paper ‘pokes.’ These early paper bags were actually property that combines both strength and stretch. inverted cones that required only folding to close TEA can be thought of as a measure of ‘work to the bottom. By 1877, paper bags were produced by burst.’ Special extensible sack paper that has been machines that cut, folded, and either glued or sewed produced through the ‘clupak’ process greatly the sides from rolls of paper. Today, paper bags come enhances TEA and permits the use of lower À in four basic shapes: flat, square, satchel-bottom, and grammage ranges (50–100 g m 2) thus saving about self-opening. 20% fiber by weight. The clupak process, invented Flat paper bags are made from kraft paper that has by Sanford Cluett, produces extensible paper that is been glued with a starch-based adhesive to form a difficult to tear by passing wet paper through a steel tube with its bottom folded and glued. This type of and rubber nip that causes fiber crimping in the bag is commonly used for candy, greeting cards and machine direction. Additional extensibility in the many retail items that are small and lightweight. The machine direction is produced on the paper machine square-bottom bag is similar to the flat bag except through using slack draws in the dryer section. Slack that the paper tube is first folded inwards along the draws prevent the sheet from developing dried-in sides to form an expanding gusset before the bottom drains leading to limited stretch. is folded. When the square bag is opened or filled, the Porosity is important for multiwall paper sacks bag has a square or rectangular cross section. In this because air needs to escape through the wall of the manner, the square bag can hold thicker and heavier bag to permit rapid filling. Sack filling machines are items such as books and newspapers. The satchel- able to fill a 25–50 kg sack in 1 second at bottom bag also forms a square shape when opened temperatures that can exceed 1001C. Sewn-bottom but the bottom is folded into triangles and glued and pasted bottom open-mouthed sacks are used for 688 PACKAGING, RECYCLING AND PRINTING / Packaging Grades low pressure gravity-filling systems. Valve sacks function of the roughness of the paper. Rough paper are required when materials must be filled under surfaces produce matte or dull appearing metal pressure. layers, while smooth paper surfaces produce glossy Multilayer sacks may be constructed with plastic metal layers. High-gloss metal layers are manufac- liners to prevent moisture contamination. Plastic tured via indirect or transfer metallizing. In transfer linings are important for foods and chemicals where metallizing a polypropylene web is initial metallized. the ingredients have to maintain a certain moisture Because the metal does not bond to the polypropy- level. Wet-strength resins are also used to control lene, the entire metal layer can be transferred to the moisture penetration through the paper. surface of an adhesive-coated paper sheet. The transferred metal layer has the surface smoothness of the polypropylene sheet. Thus, a high gloss Food Wrapping Paper metallized sheet is produced regardless of the original Paper intended for the wrapping and serving of surface of the paper. Before printing, metallized food must be manufactured from ingredients paper is coated with a special primer layer to that do not adulterate food. This requirement enhance adherence of the printing inks. Metallized necessitates the use of virgin chemically processed paper is used as packaging materials for a number of pulps along with paper additives and coatings that food products that include chocolate bars, oily snack are recognized as safe to human consumption. These foods, candies, and chewing gums. papers must have some form of wet strength Foil-backed paper is produced by laminating and grease resistance as well as have reasonable aluminum foil to paper with an aqueous adhesive. printing properties. The basis weight range for The resultant sheet is attractive, easily printed upon, À food wrapping paper is 28–65 g m 2. General and has similar barrier properties to metallized categories of food wrapping paper include: grease- paper. However, additional properties such as proof, metallized, and foil-backed papers. Special dead fold and heat retention capabilities that make fruit wrapping papers impregnated with preserva- it ideal for wrapping fast-food items such as tives can also be found. hamburgers and other hot sandwiches. Dead fold is Greaseproof papers are papers that resist the a direct property of the aluminum foil. Aluminum penetration of grease and oils, and are also called metal is very malleable and can be greatly deformed moisture resistant papers. Vegetable parchment is a without cracking or losing its barrier capability. nonporous, homogeneous sheet of cellulose formed When fully annealed, aluminum maintains no from sulfuric acid treating pulp.