2874 Chapter 23 



A top coat is then applied to grooved and embossed panels by precision roll 

 coater and to decorative boards by curtain coater, following which solvents are 

 evaporated and surfaces heated to about 500°F. Boards are then cooled, graded, 

 stacked, and packaged. 



Thickness of finish coats are about as follows: 



Product and coat Thickness of dry coat 



Mil 

 '/4-inch interior paneling 



Fill 0.3 



Ground .8 



Top .6 



Total 1.7 



Tile board 



Fill .3 



Ground 1.1 



Top .8 - 1.0 



Total 2.2-2.4 



Speeds of finishing lines similar to that shown in figure 23-97 are usually 

 limited by the dryers; excessive dryer temperatures embrittle coatings. Typically 

 V4-inch-thick interior paneling is finished at 150 to 200 feet per minute. Tile 

 boards, which have heavier top coats to resist high humidities, run slower — 

 e.g., at about 120 fpm. 



Siding. — Figure 23-101 shows a finishing line for siding, which typically 

 operates at about 150 fpm. All coats on siding may be thermal set acrylic latex. 

 The thickness of the coats (2.0-2.2 mills when dry, total) depends on the length 

 of time for which the siding is guaranteed. Only about 30 percent of all hard- 

 board siding is completely prefinished; 70 percent is only primed. Primed siding 

 provides flexibility in color selection of final coats applied after installation, and 

 also removes the burden of providing performance guarantees on the finished 

 product. 



Sanding the bottom surface of siding hardboard to reduce thickness variation 

 is particularly important for two-tone embossed products, where high spots are 

 coated with precision roll coaters. 



Single-color regular embossed siding is coated with direct-roll coaters 

 equipped with pile rolls. Lightly embossed boards and flat boards are curtain 

 coated. The solvent is removed in a dryer and the resin cured in an oven yielding 

 a board surface temperature of about 300°F. Curing is followed by 1 minute of 

 air cooling, grading, and packing. 



Vinyl and paper overlays. — In typical overlay finishing lines a latex glue is 

 applied to the hardboard substrate by a direct roll coater. The glue is dried by 

 infra-red energy and the overlay then applied by a heated-roll press. Excess 

 overlay is trimmed by knives or abrasive wheels. 



In a method used by Abitibi Corporation, a printed paper is applied to the wet 

 mat of SIS board prior to pressing with embossed caul plates. After fabrication 

 an accent coat is applied by pile coater to the surface of the paper overlay, after 

 which a direct roll coater picks surplus paint off all high spots. This leaves the 



