Paper sheets

Fig. 7. The vat machine. A, last cylinder taking up slurry from the surrounding vat B, extractor C, perforated cylinder containing D, a stationary water extractor E, press F, supply of slurry x, paper on its way to the dryers jy, multiple wet paper sheet coming from preceding cylinders (15).

It is also important to study the interactions of papermaking additives (4) in the paper machine water system some additives act synergisticaHy, so that the performance of each is enhanced by the presence of the other. However, some additives have a negative impact on the performance of other additives, or on other desirable paper properties. Thus, optimization of the addition points and usage rates of the entire additive system is necessary in order to maximize performance of the chemical additives and the paper sheet properties, and to minimize cost and negative interactions both on the paper machine and in the white-water system. This is especially tme as unanticipated additives enter the wet end of the paper machine from recycled furnishes, including coated broke (5). 

These cylinder units are applicable to almost any form of sheet material that is not injuriously affected by contact with steam-heated metal surfaces. They are used chiefly when the sheet possesses certain properties such as a tendency to shrink or lacks the mechanical strength necessary for most types of continuous-sheeting air diyers. Applications are to diy films of various sorts, paper pulp in sheet form, paper sheets, paperboard, textile piece goods and fibers, etc. In some cases, imparting a special finish to the surface of the sheet may be an objective. 

The value of the coefficient of heat transfer from steam to sheet is determined by the conditions prevailiug on the inside and on the surface of the dryers. Low coefficients may be caused by (1) poor removal of air or other noncoudeusables from the steam in the cyhn-ders, (2) poor removal of condensate, (3) accumulation of oil or rust on the interior of the drums, and (4) accumulation of a fiber lint on the outer surface of the drums. In a test reported by Lewis et al. [Pulp Pap. Mag. Can., 22 (Februaiy 1927)] on a sulfite-paper diyer, in which the actual sheet temperatures were measured, a value of 187 W/(m °C) [33 Btu/(h ft" °F)j was obtained for the coefficient of heat flow between the steam and the paper sheet. 

Hot melts are sometimes applied on top of a water-based primer, as mentioned above. The primer penetrates the paper and stiffens the ends of the paper sheets prior to their being attaehed to the eover with a hot melt overlayer. In some eases a pre-primer is employed whieh aetually penetrates eaeh sheet and stiffens the eore of the paper as well. 

In the pulp and paper industry, anionic and cationic acrylamide polymers are used as chemical additives or processing aids. The positive effect is achieved due to a fuller retention of the filler (basically kaoline) in the paper pulp, so that the structure of the paper sheet surface layer improves. Copolymers of acrylamide with vi-nylamine not only attach better qualities to the surface layer of.paper, they also add to the tensile properties of paper in the wet state. Paper reinforcement with anionic polymers is due to the formation of complexes between the polymer additive and ions of Cr and Cu incorporated in the paper pulp. The direct effect of acrylamide polymers on strength increases and improved surface properties of paper sheets is accompanied by a fuller extraction of metallic ions (iron and cobalt, in addition to those mentioned above), which improves effluent water quality. 

Pressure-sensitive recording materials are obtained by dissolving a triphenylmethane leuco dye in a solvent composed of paraffin oils. The microcapsules are formed from a water-soluble106 or water-dispersible material.107,108 Leuco dyes dissolved in sunflower oil are microencapsulated in a solution containing a melamine-HCHO precondensate and coated on the back side of a paper sheet. Contact of the microcapsule-coated sheet with an acid-coated receptor sheet allows the color formation to occur. 

The paper making process, in very simplistic terms, involves the use of pulp, additives and water to make a final paper sheet. The type of paper being made will influence the levels of all of these components, for example high quality paper will utilise high levels of pulp fibre and additives, whereas tissue paper will use very little. Diagram 1 below illustrates the process. 

The pulp and paper additives enter the process first through a dump chest in their concentrated form. Adjustments are then made to the concentration in the stock chest just prior to transfer onto the Fourdrinier wire where the paper sheet is produced. Surface additives are sprayed after sheet formation and the final sheet is dried at high temperatures in dryers. The water from the wire is removed into underground tanks and in most cases, recirculated and reused. 

The development of these biofilms within the system and on the wire can lead to major production problems due to these being transferred onto the paper sheets. Once these are an integral part of the sheet, the drying stage causes shrinkage and holes or tears can occur. This causes considerable down time and loss of income. 

In some cases, bacterial spores can also be passed onto the paper sheet and these can withstand the short exposure to high temperature drying. Hence these spores can remain on the paper sheet and if used in food contact applications, could lead to this paper being rejected under quality control procedures. 

In some situations, if good plant hygiene is not maintained, fungal spores can also become established in and around the Fourdrinier wire. These can develop into large surface colonies which can become dislodged and transfer onto the paper sheet during formation. Again, this can lead to paper sheet failure. 

Wet end operations formation of paper sheet from wet pulp... 

PAPER SHEETING EXAMINATION-TREATMENT TABLES 125 LG 17.75 W12S 6530010923914 PG 22.63 ... 

Obtain a paper chromatography developing chamber (similar to that shown in Figure 11.12). Pour 70% isopropyl alcohol (the mobile phase) into the chamber to a depth of 2 cm. Then, place the paper sheet in the chamber as shown in Figure 11.12. Cover the chamber. 

Scanning electron microscope picture of typical carbon fiber paper sheets used in fuel cells (a) Toray TGPH-060 CFP with no PTFE (reference bar indicates 500 pm) (b) close-up view of the TGPH-060 CFP with no PTFE (reference bar indicates 100 pm) (c) Toray TGPlT-060 CFP with 20% PTFE (reference bar indicates 500 pm) (d) close-up view of the TGPH-060 CFP with 20% PTFE (reference bar indicates 100 pm). 

Thin zeolite sheets offer improved mass transfer for possible rapid cycle adsorption processes. One of the first studies of zeolite as fillers in paper-making was issued to NCR in 1955, although at that time the term zeolite was more often used to describe any ion exchanger whether or not it was actually a crystalline microporous zeolite [95]. A later patent described the incorporation of micropo-rous zeolite powders in paper sheets [96]. More recently a number of patents described zeolite-containing papers in adsorption processes [97-99]. 

The common factor in nanotechnology is the lateral dimension, being in the nanometer (10 9 = m, that is 1 billionth of a meter or l/1000th of the thickness of a paper sheet ) range of the structures studied. Atomic or molecular distances, sizes of... 

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