Base papers requirements, coating

Formation This property refers to small-scale basis weight variations in paper. There are areas that are denser and less absorbent to the coating than other areas. To reach uniform coating penetration, base paper requires even formation, otherwise mottling may occur in printing. 

Sihcone products dominate the pressure-sensitive adhesive release paper market, but other materials such as Quilon (E.I. du Pont de Nemours Co., Inc.), a Werner-type chromium complex, stearato chromic chloride [12768-56-8] are also used. Various base papers are used, including polyethylene-coated kraft as well as polymer substrates such as polyethylene or polyester film. Sihcone coatings that cross-link to form a film and also bond to the cellulose are used in various forms, such as solvent and solventless dispersions and emulsions. Technical requirements for the coated papers include good release, no contamination of the adhesive being protected, no blocking in roUs, good solvent holdout with respect to adhesives appHed from solvent, and good thermal and dimensional stabiUty (see Silicon COMPOUNDS, silicones). 

Other water-soluble polymers which do not tend to suffer from problems of retrogradation are sometimes used when different properties are required. Soluble cellulose derivatives, particularly car-boxymethyl cellulose, which is prepared by reaction of high purity cellulose with chloroacetic acid in the presence of alkali (equation 8.1), is popular for surface sizing base papers which are subsequently to be coated, because it assists in water removal when the coating mix is applied. 

In the manufacture of paper, starch-based adhesives are used either to strengthen the paper base or for coating the surface of the paper. Raw starch is unsuitable for either purpose. To achieve sufficient adhesive power with raw starch would require the application of a solution that was far too thick for practical use. Instead, chemically modified starch, with a much lower viscosity in solution, is used. As an economical alternative to modifying the starch with aggressive oxidizing agents, the starch can be treated with enzymes ( df-amylases) to obtain the same thinning effect... 

Specifically, diazo paper was used at that time to generate patterns from which garments would be cut in the clothing industry. These patterns were called markers, and Stem s company was called Photomarker. In addition to coating an inexpensive diazopaper, this company also sold exposure machines, all based on diazo-chemistry. Why go to UVI Diazo papers required moist development, and this caused considerable dimensional stability problems with the 6-foot-wide, 18+-foot-long markers. A dry process would minimize this problem. 

Smoothness Smooth base paper gives a uniform and closed coated surface. The various coating processes have slightly different smoothness requirements. Air knife coaters require a relatively smooth surface because, in that method, coating... 

The main constituents of a coating colour formulation are the inorganic pigments, which serve to cover the surface of the base paper and thus to improve its optical and printing properties. Coating pigments therefore have to fulfil the following requirements ... 

Microfilm blowback Enlargement on coated papers was termed blowback . Up to this time, this was done with silver based paper products that required development. 3M... 

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