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 urea-forrnaldehyde, melamine-forrnaldehyde, polyamide, and polyurethane resins [Asano et al. 1983]. Maggio et al. [1978] stated that urea-formaldehyde capsules are more resistant to pressure than those made of gelatin.

Apol and Thoburn [1986] described the process of CCP manufacturing. The plant they investigated made paper from pulp and then applied the appropriate coatings to the paper to make CCP. The paper itself is usually produced in a continuous sheet from a pulp slurry to form a wet web of paper as it exits on a screen, such as in a Fourdrinier paper machine. Apol and Thoburn [1986] describe a process in which the CF and CB coatings are applied to the wet web. The CF coating can also be applied as the paper exits from the paper machine. As the coating is applied, the paper passes through a dryer and is wound on a roll. The CB coating may be applied in a separate plant area to the paper as it passes through a series of dryers and is rewound on a roll.

The CF and CB coatings are prepared in the coater preparation area. The phenolic resins (1- to 10-μm or 1- to 3-μm size range is preferred [Mathiaparanam 1992]) may be prepared by grinding the resins to specific-size particles, or they may be purchased already prepared. The already prepared resin reduces exposure to phenol among workers who handle the coating preparation and is the preferred option for today's technology.

A typical coating composition for the CF component is shown in Table 2–1. The CF is dried in a high-velocity air oven at 93 °C [Kroschwitz and Howe-Grant 1995]. Miller and Phillips [1972] stated that suitable amounts of the various materials per unit of paper are as follows: chromogenic dyes, 0.03 to 0.075 lb/ream (one ream is 500 sheets of 25- × 38-in. paper totaling 3,300 ft2), with the preferred amount being 0.05 lb/ream; solvent, 1 to 3 lb/ream; polymer, 0.5 to 3 lb/ream.

CF, CB, and CFB coated papers are produced in large rolls weighing up to several tons. These are subsequently cut down by machines to a variety of smaller reel and sheet sizes. This cutting means that the contents of the microcapsules will be ruptured and released. Although many of the sheeting, reeling, and packing operations are automated, some of the paper still needs to be hand-sorted. The workers who hand sort these papers are potentially exposed to the components, particularly the contents of the ruptured capsules that have been cut in previous mechanical operations. Some of these workers sort paper at the rate of 90 kg/hr (or more than 2 tons/week [600,000 sheets]) [AEMCP 1985].