Paper coatings

Coated or laminated paper products represent a significant potential market for biodegradable polymers. At present, packaging such as hamburger wrapping and disposable cups, are extrusion coated with low density polyethylene film that is resistant to biodegradation. This also restricts the biodegradation of the paper substrate since it acts as an impervious barrier. 

Loose-fill packaging was one of the first successful areas of application for starch-based biodegradable polymers. Loose-fill starch-based foam is used for packaging consumer products as an alternative to polystyrene and polyethylene. While, biodegradable plastics have made some inroads into these markets, the future prospects for their growth in loose-fill are not so exciting as they are in some other areas of packaging. 

Plastic bags have a high profile in the land waste stream as these materials are not currently accepted in the kerbside collection and recycling systems. Biodegradable plastics present an attractive alternative to polyethylene in these applications. 

In blade coating, as a first step, a layer of coating colour is applied to the paper sheet. The sheet will then pass under a blade, which removes an excess of applied material and thereby creates a very smooth surface. Due to inhomogeneities of the base paper, surface blade coating leads to fluctuations of the coating layer thickness over width and length of the paper sheet. 

As a final step, the paper will be smoothed in the calendering section. Calendering involves subjecting the paper surfaces to high temperatures and pressures in order to create a smooth, glossy surface. A distinction is made between supercalendered and soft-nip calendered papers. In the supercalender, the paper is rim over a large number of nips. 

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  

20 Fine Kaolin clay (high-gloss clay) 

5 resins or ionic compounds (e.g. zirconium acetate) Optical brightener, such as 

Thickeners such as CMC, alginate and phosphated guar gum are used for paper coating. They improve the surface of the paper in the size press, increase strength, reduce porosity and improve resistance to grease and organic solvents. 

HiUni Polymer protective colloid I I Polymer core 

The hydrophilic/hydrophobic balance of the surface can be individually controlled by  

Applied to ink jet papers, a hydrophilic/hydrophobic raster on the paper surface results in a highly accurate fixation of the dye right to the spot at the paper surface. Whereas the hydrophilic areas allow a fast dewatering of the printing ink, mostly to the interior of the paper sheet, the hydrophobic points prevent a spreading parallel to the paper surface. Additional modification of the starch/polymer film by cationic groups results in an additional fixation of the anionic dyes by ionic interaction. Thereby, color density and outline sharpness can be further improved. 

For the reasons given above, coated paper exhibits more uniform ink receptivity and better holdout than uncoated papers. Coating also produces a much smoother paper surface that is particularly a significant factor when printing individual dots, especially when using a rotogravure process (Fig. 4-9). 

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It is used in adhesives, paper coating and sizing, and textile warp size and finishing applications. 

Emulsion polymerization also has the advantages of good heat transfer and low viscosity, which follow from the presence of the aqueous phase. The resulting aqueous dispersion of polymer is called a latex. The polymer can be subsequently separated from the aqueous portion of the latex or the latter can be used directly in eventual appUcations. For example, in coatings applications-such as paints, paper coatings, floor pohshes-soft polymer particles coalesce into a continuous film with the evaporation of water after the latex has been applied to the substrate. 

Most of the acetic acid is produced in the United States, Germany, Great Britain, Japan, France, Canada, and Mexico. Total annual production in these countries is close to four million tons. Uses include the manufacture of vinyl acetate [108-05-4] and acetic anhydride [108-24-7]. Vinyl acetate is used to make latex emulsion resins for paints, adhesives, paper coatings, and textile finishing agents. Acetic anhydride is used in making cellulose acetate fibers, cigarette filter tow, and ceUulosic plastics. 

Other patents (81,82) coveted the preparation of cellulose solutions using NMMO and speculated about their use as dialysis membranes, food casings (sausage skins), fibers, films, paper coatings, and nonwoven binders. NMMO emerged as the best of the amine oxides, and its commercial potential was demonstrated by American Enka (83,84). Others (85) have studied the cellulose-NMMO system in depth one paper indicates that further strength increases can be obtained by adding ammonium chloride or calcium chloride to the dope (86). 

Although the use of simple diluents and adulterants almost certainly predates recorded history, the use of fillers to modify the properties of a composition can be traced as far back as eady Roman times, when artisans used ground marble in lime plaster, frescoes, and po22olanic mortar. The use of fillers in paper and paper coatings made its appearance in the mid-nineteenth century. Functional fillers, which introduce new properties into a composition rather than modify pre-existing properties, were commercially developed eady in the twentieth century when Goodrich added carbon black to mbber and Baekeland formulated phenol— formaldehyde plastics with wood dour. 

Additives. Because of their versatility, imparted via chemical modification, the appHcations of ethyleneimine encompass the entire additive sector. The addition of PEI to PVC plastisols increases the adhesion of the coatings by selective adsorption at the substrate surface (410). PEI derivatives are also used as adhesion promoters in paper coating (411). The adducts formed from fatty alcohol epoxides and PEI are used as dispersants and emulsifiers (412). They are able to control the viscosity of dispersions, and thus faciHtate transport in pipe systems (413). Eatty acid derivatives of PEI are even able to control the viscosity of pigment dispersions (414). The high nitrogen content of PEIs has a flame-retardant effect. This property is used, in combination with phosphoms compounds, for providing wood panels (415), ceUulose (416), or polymer blends (417,418) with a flame-retardant finish. 

The AKDs are used in paper sizing appHcations. Paper sizing chemicals provide paper and paperboard with resistance to wetting by Hquids, especially water repeUency in paper cups, milk cartons, photographic paper, coatings, and packaging paper (139) (see Paper Papermaking additives). 

Traditional appHcations for latices are adhesives, binders for fibers and particulate matter, protective and decorative coatings (qv), dipped goods, foam, paper coatings, backings for carpet and upholstery, modifiers for bitumens and concrete, and thread and textile modifiers. More recent appHcations include biomedical appHcations as protein immobilizers, visual detectors in immunoassays (qv), as release agents, in electronic appHcations as photoresists for circuit boards, in batteries (qv), conductive paint, copy machines, and as key components in molecular electronic devices. 

Thermoplastic pigments for use in paint, screen ink, plastisol, gravure ink, paper coatings, and many other appHcations. d. . ... 

Physical Chemisty of Pigments in Paper Coating, TAPPI Press BookNo. 38, Technical Association of the Pulp and Paper Industry, Atianta, Ga., 1977. 

Binders. Paper-coating biaders are either polymers derived from aatural sources or syathetic polymers. The largest volume, aaturally derived biader is starch (qv) (99). Starch is provided ia derivatized form or unmodified form pead com starch is used predomiaanfly for the latter. Unmodified starch is solubilized by thermal conversion or enzyme conversion. The most common derivatized products are acetylated [9045-28-7] oxidized, and hydroxyethylated starches. 

The other main natural binder is protein that is prepared by extraction from soy meal (100). Casein [9000-71 -0] once a large-volume paper-coating binder, has markedly declined in use because of its high price and susceptibiHty to microbial attack. 

Aqueous dispersions are used in fiber bonding, paper coating, friction and abrasive appHcations, and laminates and wood bonding. PhenoHc dispersions improve the strength of latex-contact adhesive appHcations. Epoxy-modified phenoHc dispersions are prepared by dispersion of the phenoHc epoxy resin. The systems are used for baked primer appHcations and bonding requirements. Minimum baking conditions are 20 min at 150°C (25). 

These pigments are sensitive to heat and bleed ia most paint solvents. They are, however, resistant to acids and bases. Their tinctorial strength is considerably greater than that of inorganic yellows but they are weaker than the diaryUde yellows. They are used extensively ia emulsion paints, paper coating compositions, inks (qv), and, depending on particle size, can ia some cases be used outdoors because of excellent lightfastness ia full shades. 

Pigment Dispersion. AMP is used widely as a pigment dispersant for water-based paints and paper coatings. In small amounts, it efficiently disperses pigments and improves pH stabiUty, viscosity, corrosion inhibition, and odor (13). When AMP is used in conjunction with other surfactants, enhanced performance is obtained with less of these ingredients in the dispersion. 

Reverse cleaners operate on the same principles as forward cleaners (20). Contaminants less dense than water migrate toward the center of the cleaner and exit as a separate (reject) stream from the pulp slurry. Reverse cleaners are used to remove adhesive and plastic particles as well as paper filler particles and lightweight particles formed from paper coatings. 

RCF is sold in a variety of forms, such as loose fiber, blanket, boards, modules, cloth, cements, putties, paper, coatings, felt, vacuum-formed shapes, rope, braid, tape, and textiles. The products are principally used for industrial appHcations as insulation in furnaces, heaters, kiln linings, furnace doors, metal launders, tank car insulation, and other uses up to 1400°C. RCF-consuming industries include ferrous and nonferrous metals, petrochemical, ceramic, glass, chemical, fertiH2er, transportation, constmction, and power generation/incineration. Some newer uses include commercial fire protection and appHcations in aerospace, eg, heat shields and automotive, eg, catalytic converters, metal reinforcement, heat shields, brake pads, and airbags. 

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