Solvent-borne and Water-borne coatings

The VOC emissions from paper, film, and foil coatings occur during coating
application/flash-off and drying/curing of the coatings. Some of the VOC in the coatings evaporates from the web into the coating application area during coating application. Additional VOC evaporates from the web in the flash-off area (prior to entering the dryer). The majority, usually greater than 90 percent, of the VOC in the coatings volatilizes in the drying ovens. The VOC that evaporates from the web in the drying oven(s) are vented through an exhaust stack. The amount of VOC emitted varies depending on the type of coatings being used.

Traditionally, conventional solvent-based coatings (which generally have higher VOC content), have been used in the paper, film, and foil surface coating industry. Due to increased regulation at the federal and State level, the industry has steadily moved toward alternative coating formulations that reduce the amount of air emissions per unit amount of coating solids used. The types of coatings used in the paper, film, and foil surface coating industry include solvent-borne, waterborne, hot-melt adhesives and other 100 percent solids coatings, reactive, and radiation-cure coatings.

Solvent-borne coatings are widely used in the paper, film, and foil surface coating industry. The solvent content of the coating is highly variable in solvent-borne coatings, and depends primarily on the type of coating applicator used (e.g., reverse roll coaters require the use of coatings with lower viscosities than knife coaters, therefore could require a higher solvent content). For solvent-borne coatings, coating formulations typically range from 40 to 80 percent solvents by weight, as supplied by the manufacturer. Users may dilute solvent-borne coatings
with additional solvents. Solvent-borne coatings are typically applied at 60 to 90 percent solvent by weight and sometimes higher. The primary solvents in solvent-borne coatings include methanol, toluene, xylene, methyl ethyl ketone, acetone, ethyl acetate, and ethanol. Knife coaters, reverse roll coaters, and gravure coaters are commonly used to apply solvent-borne coatings.

Waterborne coatings contain water as a significant part of the fluid, although some organic solvents may be used at up to 30 percent of the fluid. Most coating equipment used for solvent-borne coatings can also be used for waterborne coatings. Knife coaters and gravure coaters are particularly well suited to application of waterborne coatings. However, troughs or trays may have to be mixed more often when they contain waterborne coatings than when they contain solvent-borne coatings because waterborne coatings are more susceptible to coagulation or agglomeration of their solids.

Description of VOC Emissions

The paper, film, and foil surface coating process can be described as a web coating
process, which is a process that applies a continuous layer of coating material across essentially the entire width or any portion of the width of a web substrate to: (1) provide a covering, finish, or functional or protective layer to a substrate; (2) saturate a substrate for lamination; or (3) to provide adhesion between two substrates for lamination. The web coating operations and emission control techniques do not vary significantly among the sectors of the paper, film, and foil surface coating industry.

A typical coating line consists of a series of one or more unwind/feed stations; one or more coating applicators; the flash-off area (the area between two or more consecutive coating applicators or between the coating applicator and the drying oven); one or more drying ovens; and one or more rewind/cutting stations.

There are several different types of coating applicators that may be used to apply coatings. The most common types of applicators include: rotogravure, reverse roll, slot die, knife, flexography, Mayer rod, dip and squeeze, and extrusion/calendering. The type of coating applicator used may differ among coating application stations in the same coating line.

Sources of VOC Emissions

The paper, film and foil coatings product category listed under section 183(e) of the CAA includes coatings that are applied to paper, film, or foil surfaces in the manufacturing of several major product types for the following industry sectors: pressure sensitive tape and labels (including fabric coated for use in pressure sensitive tapes and labels); photographic film; industrial and decorative laminates; abrasive products (including fabric coated for use in abrasive products) and flexible packaging (including coating of non-woven polymer substrates for use in flexible packaging). The category also includes coatings applied during miscellaneous coating operations for several products including: corrugated and solid fiber boxes; die-cut paper paperboard, and cardboard; converted paper and paperboard not elsewhere classified; folding paperboard boxes, including sanitary boxes; manifold business forms and related products; plastic asceptic packaging; and carbon paper and inked ribbons.

Coating performed on or in-line with any offset lithographic, screen, letterpress, flexographic, rotogravure, or digital printing press is not part of the paper, film and foil coating category. In addition, size presses and on-machine coaters that function as part of an in-line papermaking system are not part of the paper, film, and foil coating category. The application of inks, coatings and adhesives on or in-line with rotogravure or flexographic printing presses used in the production of flexible packaging is addressed in the CTG for Flexible Package Printing (EPA 453/R-06-003, September 2006). The application of inks, coatings and adhesives on or inline with publication rotogravure printing presses is addressed in the CTG for Graphic Arts: Rotogravure and Flexography (EPA 450/2-78-033). The application of inks, coatings and adhesives on or in-line with offset lithographic or letterpress printing presses is addressed in the CTG for Offset Lithographic Printing and Letterpress Printing (EPA 453/R-06-002, September
2006).