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Paper is defined as a matted or felted sheet usually composed of plant fiber. Paper has been commercially made from such fiber sources as rags (linen), bagasse (sugar cane), cotton, and straw. Modern paper is made almost exclusively from cellulose fiber derived from wood.
International Organization for Standardization states that material weighing more than 250 grams per square meter (51pounds per 1000 square feet) shall be known as paperboard. U.S. practice calls paper that is more than 300 micrometers (0.012 in.) thick paperboard.
Paperboard is a general term of a sheet of fibrous material usually made on a cylinder or fourdrinier machine from wood fibel (pulp), or recycled paper stock (old newspapers, old corrugated), or a combination of these fiber source.
Paperboard differs from paper in that it is heavier, thicker, and rigider. The two general classifications of paperboard are containerboard, which is used principally in making corrugated and solid fiber boxes, and boxboard which is used in the manufacture of folding cartons.
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Kraft paper
Kraft paper is paper produced from the chemical pulp of softwood processed by the kraft process. It is strong and relatively coarse. The grammage is normally from 50~135 g/m’.
Kraft paper is usually a brown colour but can be bleached to produce white paper. It is used for paper grocery bags, multiwall sacks, envelopes and other packaging.
Sack kraft paper
Sack kraft paper (Figure 2-2) or just sack paper is a porous kraft paper with high elasticity and high tear resistance, designed for packaging products with high demands for strength and durability.
Sack paper has the advantages of being soft and strong at the same time. The stretch or elongation increases the energy required to break the material.
They easily carry and protect products up to 50kg, and adapt easily to the nature of their contents and to handling constraints.
At the same time, sacks provide an excellent media for promotional messages and sophisticated printing designs. Sack paper comes in a variety of calipers, basis weights, and treatments.
Fine paper
Fine paper is mainly made from woodchips, which is a by-product of the forest product industry. These materials are pulped and pressed into sheets to make fine paper.
Because it has longer fibers and is brighter than other paper grades, Fine paper is used as writing paper, photo-copier paper and printer paper.
Greaseproof paper
Greaseproof paper (Figure 2-4) is papers that are impermeable to oil or grease and are normally used in cooking and food packaging.
Normally greaseproof paper is produced by refining the paper stock and thus create a sheet with very low porosity. This sheet is supercalendered to further improve the density creating a paper called glassine.
The glassine is treated with starches, alginates or CMC in a size press to fill pores or treat the paper chemically to make it fat repellent. Basis weights are usually 30~50g/㎡.
Glassine paper
Glassine paper is manufactured by a process called supercalendering. After pressing and drying, the paper web is passed through a stack of alternating steel and fiber-covered rolls called supercalender at the end of the paper machine such that the paper fibres flatten out facing in the same direction.
Glassine has a number of uses. It is employed as an interleaving paper in bookbinding, especially for illustrations; the paper can be manufactured with a neutral pH,and can prevent damage from spilling, exposure, or rubbing.
Glassine adhesive tape has been used in book repairing. In chemistry, glassine is used as an inexpensive weighing paper. If is used in food service as a barrier between strips of products (for example: meat, baked goods).
Glassine is resistant to grease and facilitates separation of individual foodstuffs.
Boxboard
Boxboard is a multi-layer rigid paper material that is used to make boxes of various colors, shapes and sizes,including cereal, shoe and candy boxes.
Boxboard usually has six to eight layers. The upper layer is often made of a deinked pulp or other high quality recovered paper.
Inner layers are made with a lower-quality paper stock (e.g., old newsprint and mixed papers with some old corrugated containers added for strength).
Coated paper
Coated paper is a paper which has been coated by a compound to impart certain qualities to the paper, including weight surface gloss, smoothness or reduced ink absorbency.
Kaolinite or calcium carbonate is used to coat paper for high quality printing used in packaging industry and in magazines. The chalk or china clay is bound to the paper with synthetic viscofiers, such as styrene butadiene latexes and natural organic binders such as starch.
The coating formulation may also contain chemical additives such as dispersants, resins, which are to give water resistance and wet strength to the paper, or to protect against ultraviolet radiation.
Other types of paper coatings include polyethylene or polyolefin extrusion coating, silicone, and wax coating to make release liners paper cups and photographic paper.
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