Page 146 - Handbook of Plastics Technologies

THERMOSETS

3.16 CHAPTER 3

FIGURE 3.9 Urea-formaldehyde chemistry.

FIGURE 3.10 Etherification of methylol ureas.

3.1.2.2.3 Coatings. Urea-formaldehyde resins (5 percent) are used to treat paper to
give it wet strength. They are also used (2 percent) to treat cotton and wool cloth to pro-
duce permanent press and increase strength, shrink resistance, and wrinkle resistance.
3.1.2.2.4 Molding Powders. Urea-formaldehyde resins are compounded with alpha-
cellulose cotton fiber reinforcement to produce molding powders (4 percent) for compres-
sion, transfer, and injection molding. Typical molding conditions are 127 to 182°C and
2000 to 8000 psi. They are superior to phenolics in white color, electrical resistance, and
low cost, but are limited by moisture sensitivity (Table 3.13). They are used primarily in
electrical wiring devices such as wall outlets, receptacles, electric blanket controls, circuit
breakers, and knob handles. Smaller amounts are used in bottle caps, housewares, buttons,
and sanitary ware.

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