Grades, of paper

Rigid paperboard containers are made of paper greater than 0.254 mm (0.010 in) in caUper and include folding cartons, cormgated ftberboard cases, and spiral wound composite cans. Many paperboard cartons require the use of inner liners or overwraps, made of protective grades of paper, plastic, or aluminum foil laminations. 

Continuous paper machines have undergone extensive mechanical developments since the 1950s, although the principles employed have changed Utde. Cylinder machines stUl are operated and involve multiples of five to seven cylinders they are used to produce heavy multi-ply boards. Fourdriniers are common in the industry and can be used to produce virtually any grade of paper or paperboard. They vary from 1 to 10 meters in width and, including the press and dryer sections, may be more than 200 m long. 

In addition, many grades of paper and paperboard are used in direct or indirect contact with foods. Thus, many mills only use paper chemicals that have been cleared for use by the U.S. Pood and Dmg Administration (PDA) (3), so that it is not necessary to segregate machine broke (off-grade paper and edge clippings that are reclaimed for their fiber value) and white water. Most of the chemicals discussed in this article are approved by the PDA for use in paper and paperboard that are intended for appHcations in food processing and packaging. However, there are various restrictions on both the specific functional uses and amounts of paper chemical additives which can be used, so the PDA status should be confirmed by the suppHer before use. 

These rosin-based sizes, whether paste, Hquid, or emulsions, can be used to size all grades of paper that are produced at acid pH. The latter include bleached or unbleached kraft Hnerboard and bag paper, bleached printing and writing grades, and cylinder board. In addition, polyaluminum compounds have been used in place of alum, most notably, polyaluminum chloride (48), which can reduce barium deposits where these have been a problem. The barium chloride by-product is more water-soluble than barium sulfate. Other polyaluminum compounds such as polyhydroxylated forms of alum and polyaluminum siHcosulfate have been evaluated as alum replacements. 

In recent years, synthetic polymeric pigments have been promoted as fillers for paper. Pigments that ate based on polystyrene [9003-53-6] latexes and on highly cross-linked urea—formaldehyde resins have been evaluated for this appHcation. These synthetic pigments are less dense than mineral fillers and could be used to produce lightweight grades of paper, but their use has been limited in the United States. 

Spray appHcations to the surface of the sheet have been useful, especially for appHcation of creping aids and release agents in towel and tissue miUs. The spray appHcation of functional chemicals has not been used widely. Generally, the uniformity of appHcation is mote difficult to control when functional chemicals are sprayed than when they are appHed by a size press. Eunctional chemicals also can be appHed to heavier grades of paper or paperboard at the calender stack. 

Curl Control. Many grades of paper tend to cud, especially as humidity varies, because of the stresses produced duting the dryiag process. This is especially troublesome when only one side of the paper receives a surface treatment. Judicious appHcation of water to the opposite side of the dry sheet followed by redryiag may correct the curling. Water may be appHed by surface appHcation at the size press, water box, or calender stack or it may be sprayed on. Small amounts of water can be appHed to the paper surface as a foam with exceUent results. 

In the manufacture of a laminate for electrical insulation, paper, which is the best dielectric, is normally selected as the base reinforcement. An electrical grade of paper is in fact a better dielectric than the resin and thus in eonditions... 

Recently, a synthesis of PE on the waste of the cellulose and woodworking industry has been reported [288]. Good quality structural and cladding materials can be obtained by pressing these compositions, or special grades of paper and cardboard after appropriate processing. 

Other sources of fibers include cotton rags and linters, flax, hemp, bagasse, tobacco, and synthetic fibers such as polypropylene. These substances are not used widely, however, as they are typically for low-volume, specialty grades of paper. 

Consider a typical linear programming example in which N grades of paper are produced on a paper machine. Due to raw materials restrictions not more than a, tons of grade i can be produced in a week. Let... 

It is important that high quality grades of paper, such as those used for printing, writing and artwork, should have as uniform a fibre... 

Internal sizing may be carried out over a wide pH range, but it is popular now to use neutral or slightly alkaline systems. When successfully performed, it retards the rate of penetration of a fluid through capillaries formed both within and between fibres. The fluid involved is, for most commercial grades of paper, water but resistance to non-aqueous fluids may also be important in some applications. This discussion will concern itself only with sizing against aqueous systems. 

In grades of paper where a high density, clear, tough, well-sealed film on the surface is required, alginates may be used, sometimes in... 

Before discussing specialty starches for size press applications, it should be noted that the largest volume of starch applied at the size press is either enzyme converted or ammonium persulfate hydrolyzed native corn starch. These are economic considerations and the properties resulting from these treatments do not compare to the properties provided by specialty starches. It is also fair to state that all grades of paper do not require a specialty starch and it is only through the need for improved paper performance that specialty starches are required. 

Although the Fourdrinier machine is used for making almost all grades of paper and board, other designs are sometimes more advantageous. The cylinder machine, invented at about the same time as the Fourdrinier, consists of a rotating cylindrical mold covered with a wire screen and partially submerged in a vat. The stock flows into the vat, and a mat is formed on the cylinder under a hydraulic head difference between the stock level in the vat and the white-water level inside the cylinder. The... 

Mechanical and ultra-high yield pulps are used primarily for low-value, short-life grades of paper such as newsprint and advertising, catalog, and directory papers. Their use in more valuable paper products is severely restricted by the rapid yellowing which occurs upon exposure to daylight, a phenomenon which is attributed to the photooxidation of lignin. 

Prints to be toned should be darker and softer than normal prints. Use approximately 25% overexposure on the next softer grade of paper. Development of the print should be carried out in a standard developer, such as Kodak D-72, with particular attention given to avoid underdevelopment or forcing the print with overdevelopment. Prints should be fixed as usual, thoroughly washed, and completely dried before toning. 

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