Coated materials

There are three basic forms of abrasives grit (loose, granular, or powdered particles) bonded materials (particles are bonded iato wheels, segments, or stick shapes) and coated materials (particles are bonded to paper, plastic, cloth, or metal). 

Cellulose nitrate also has widespread use as an adhesive and coating material. Whereas stabilizers are added to products, eg, sodium carbonate as a neutralizer, many conservators are hesitant to use cellulose nitrate materials because of the inherent instabiUty and the dangers to the object from nitric acid, formed when the nitric oxide combines with moisture. 

The remaining tailings left over from the clay fractionation step is either flocculated with alum, high molecular weight polymers, or a weak (pH 3.0) solution of sulfuric acid, and stored in settling ponds as waste, or may be filtered and sold to the brick industry as a coating material. It also may be dried and sold as a filler in plastics and textured paint (qv). 

Most organic compounds, including aromatic hydrocarbons, alcohols, esters, ketones, ethers, and carboxyUc acids are miscible with nitroparaffins, whereas alkanes and cycloalkanes have limited solubiUty. The lower nitroparaffins are excellent solvents for coating materials, waxes, resins, gums, and dyes. 

In knife-over-roll or blade coating, the coating material is placed on the fabric surface behind a knife, or doctor blade, and metered according to the gap set between the blade and the fabric surface. This method is used to apply thick coatings of highly viscous materials such as pastes, plastisols, or foams. 

Various types of surface coating materials can be used with sohd fiber paperboard to achieve desired package properties. The coatings and treatments described for cormgated paperboard apply to sohd fiber paperboard as weU. Various solvent and aqueous-based polymeric emulsion coatings are also commonly used (see Emulsions). 

When selecting a particular paster adhesive, coating material, and coating process for sohd fiber packaging, the fact that sohd fiberboard lacks the open-flute stmcture (to facihtate exit of moisture from internal phes of paperboard) should be considered. It is generally desirable to minimize the amount of process water added with the adhesive or coating with sohd fiber products. Moisture trapped in the filler phes can result in pin holes or bhsters in the coating and/or warp of the sheet (15). 

UCAR Alcohols for Coatings Applications, Brochure F-48588, Solvents and Coatings Materials Division, Union Carbide Chemicals and Plastics Corp., Danbury, Conn., Sept. 1984. 

No. 2 Heavy Melting Steel. Supphed ia more than one grade form based on length and width requirements and a minimum thickness of about 0.3 cm (1/8 ia.), this scrap is lower quaUty than No. 1 heavy melting. There is the possible iaclusion of a wide variety of items such as alloy steels and coated materials. 

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