Abstract
Flake type wood particles were oriented through a 5cm deep frame orienter, in which many vertical plates were set in parallel each other at regular intervals. The effects of flake length, plate spacing and free fall distance from the bottom of plates to the top of the particle mat on the degree of alinement, and the effects of face flake length on physical and mechanical properties of 15mm thick three layer boards were investigated. The particles were prepared from thinnings of Sugi (Cryptomeria japonica). All boards had random orientation in the core; half of the boards had random faces, the rest had faces comprised of oriented flakes. The solid content of adhesive (melamine-urea resin) added was 11% for face particles and 7% for core in oven-dry state. Weighing ratio of face to core particles was 1:3:1 in dry state. Press time was 15 minutes at 150°C and the pressure was 35kg/cm2.
The average alinement angle increased with increasing free fall distance and plate spacing, and with decreasing flake length. Provided that all other conditions remain unchanged (e.g. slenderness ratio of particle, resin content and board density), the bending strength of boards may increase 1.6 to 2.2 times as much by orienting the face flackes. MOR and MOE values parallel to the orientation of alined boards showed continuous increase up to the particle length-thickness ratio 150, and reached a plateau which is very close to that of solid wood. The average retention of MOR after 2hr hot water (70°C) immersion of oriented boards was 74%. As for the internal bond strength and thickness swelling, there was no difference between the oriented and the random boards.
