2. Experimental
2.1. Materials
Among the various floorings, we chose laminate flooring and
engineered flooring. Currently, these are extensively used in new
apartment interiors and in the remodeling market in Korea. Lami-nate flooring is composed of waterproof, high-density fiberboard
(HDF) as the core material, with overlay paper, deco paper and
valance paper. The wood fiber, for HDF, distributed from Dong-wha Enterprise was made from Korean pine (Pinus densiflora) with
a moisture content of 4%. Urea–melamine–formaldehyde (UMF)
resin was used to manufacture HDF. The molar ratios of the resin
was 0.95 (F/M + U). Before the HDF was manufactured, 3 parts (to
resin) of 25% ammonium chloride as a hardener and 13 parts of
44% wax solution for water-proofing were added. The wood fiber
distributed from Dongwha Enterprise was made from Korean pine
(P. densiflora) with a moisture content of 4%. The MDF was manufac-tured using the above adhesives, in order to have a specific gravity of
0.8. The mixture was then hot pressed, to form composite boards, at
a peak pressure of 40 kgf/cm
2
and a temperature of 180
◦
C. The main
pressing time was 4 min and the pressure was then released in two
steps of 1 min each. Overlay paper, deco paper and valance paper
were impregnated with melamine-papers pressed at about 200◦
C
and called low pressure melamine (LPM) as shown inFig. 1a. The
resin for impregnation is shown inTable 1. Finally, the edges of the
product are machined to produce a tongue and groove profile. In the
case of engineered flooring, 0.5 mm-thick fancy veneer of maple is
glued to a 7.2 mm-thick plywood sheet and pressed at about 160
◦
C.
A UV-curable coating is coated on this fancy veneer as shown in
Fig. 1b. The UV-curable urethane acrylate system consisted of three
main components; urethane diacrylate oligomers, reactive diluent
monomer and photoinitiator. The manufacturing step of laminate
flooring for this research was divided into two steps; HDF only and
HDF with LPMs. In the case of engineered flooring, the manufactur-ing steps were divided into three steps; plywood only, fancy veneer
bonded on plywood and UV coated on fancy veneer with plywood.