Kraft papers, grades

Table 21.3 presents an overview of wood pulping types by the method of fiber separation, resultant fiber quality, and percent of 1998 U.S. pulp production.1112 Many mills perform multiple pulping processes at the same site, most frequently nondeink secondary fiber pulping and paper-grade kraft... 

In case that corrugated base papers are not any more produced from recycled paper, as it is typical for testliner and medium in Germany, virgin fibres would have to be used. The corresponding paper grades as kraftliner would be produced from kraft pulp and fluting from semi-chemical pulp. For the simplified calculation of the required wood demand for the fibres, an average process yield of 60% (kraft pulp = 50%, semi-chemical pulp = 70%) is used. The substitution of the... 

Bleached paper grade kraft and soda (bleach plant effluent - existing BAT and pretreatment for existing 5.06 g/kkg 2.01 g/kkg ... 

In the production of corrugating medium, linerboard and other unbleached (Kraft) paperboard grades, starch is added as a slurry spray to the fiber mat on the paper-maker s wire.205 This procedure provides better starch retention in the sheet than the addition of dispersed starch to the stock. According to the position of the spray boom, starch can be forced into the sheet for strength gain or held on the surface for improved surface quality. 

Materials and Regents. Paper samples employed in this study were 8- X 10-in. sheets cut from a continuous portion of a single roll or JCPA-60 bleached kraft paper. This paper had been manufactured from a pulp mixture consisting of 70 bleached southern kraft and 30 bleached hardwood kraft. The paper contained 13 clay materials, which are composed mainly of titanium dioxide. It also contained 212 ppm of iron and 66 ppm of copper and had a pH of 5.4. All chemicals employed were analytical reagent grade. Water used for the washing of paper samples and the preparation of solutions had a minimum resistivity of 15 Mil. 

Electrical grade polymer films have now largely replaced the Kraft paper that was previously used in capacitor applications. Polypropylene and poly(ethylene terephthalate) are both used in capacitors as free films or metallized with a thin layer of aluminum. Other, newer materials for capacitor applications are made by metallizing polysulfone and polycarbonate films. 

While mechanical pulps are used mostly in low-quality paper grades and assortments, e.g. for newsprint or packing papers, Kraft pulps are the strongest pulps used in all-quality papers and paperboards where high strength properties are required. 

Retrofitting of the existing double-disc refiner used to refine unbleached long-fibre Pinus radiata kraft pulp to make flat sack kraft paper by an HC refining system followed by LC refining enabled the mill to manufacture premium-grade semi-extensible sack kraft papers... 

Packaging paper grades range from simple wrapping paper (WP, made from mixed recovered paper) to kraft paper, and are predominantly supplied in roUs. 

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. 

The furnish of a paper machine varies widely, depending on the grade of paper being made. Newsprint usually consists of about 80 percent groundwood and 20 percent chemical fiber (sulfite or semibleached kraft). Bag papers and linerboard are usually 100 percent unbleached softwood kraft. Printing papers are made from bleached pulps and contain both hardwoods and softwoods. By selecting the proper pulps and refining conditions, a wide variety of paper qualities can be achieved. 

Before the pulp can be made into paper, it is necessary to mechanically beat or refine it. It is also usually bleached with chlorine and calcium hypochlorite. Unbleached kraft pulp is used for grocery bags and heavy wrapping paper. Other materials may also be added to the pulp depending on the type of paper to be made. For book paper, fillers such as white clay and titanium oxide may be added to provide opaqueness and extra whiteness. Size may be added for stiffness and smoothness. Dyes are added for tinted papers. The specific combination of pulp and additives used to produce a particular type of paper is called the furnish for that paper. With better grades of paper, care is taken to produce a furnish that is chemically neutral (pH 7 on the acid-base scale). For a paper to have long life, it must be acid-free. 

The number of dryers and the auxiliary equipment used in a dryer section depend on the particular grade to be produced and the speed of the machine. Up to 70 cylinders may be used in a Kraft dryer section 50-55 would be adequate for a typical newsprint or fine paper dryer section. On the other hand, although the breaker stack and size press are necessary for Kraft bag and the hot press, size press, and intercalender dryers for linerboard, none of these is used for corrugating medium [4],... 

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