Page 148 - Handbook of Plastics Technologies

THERMOSETS

3.18 CHAPTER 3

FIGURE 3.12 Hexamethoxymethyl melamine.

methylol melamine reacts with them (Fig. 3.13) to produce cross-linked thermoset coat-
ings of excellent appearance and durability.
3.1.2.3.3 Laminates. While phenol-formaldehyde-kraft-paper laminates are used for
counters, cabinets, walls, and panels in public transportation, the dark brown-black color
requires a decorative overlay to make it attractive. Colored and printed paper is impreg-
nated with melamine-formaldehyde resin and applied as the surface layer to these lami-
nates, providing decoration along with resistance to scratches, heat, ultraviolet, water,
solvents, and stains. The laminating resin is made with melamine/formaldehyde ratios of
1/2 to 3 and press-cured at 125 to 150°C. This uses 14 percent of the melamine-formalde-
hyde market.

3.1.2.3.4 Moldings. Melamine-formaldehyde resin (M/F = 1/2) is reinforced with al-
pha-cellulose cotton fiber, catalyzed with phthalic anhydride, and molded at 145 to 165°C
and 4000 to 8000 psi (Table 3.14). Moldings have the highest hardness and scratch resis-

FIGURE 3.13 Melamine-formaldehyde cure of coatings.

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