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市販の微小片表層の三層構造パーティクルボードを対象に，吸脱湿に伴う両方向膨張収縮に対する構成層間の相互拘束作用，およびボード端部固定状態での面方向に作用する膨張応力の発現挙動について実験を行った結果，以下のことが明らかとなった．（1）三層構造パーティクルボードの吸脱湿に伴う面方向寸法変化は，表層と心層では大きな差があるため，各層間に膨張収縮に対する相互拘束作用が鋭敏に発現し，その拘束の程度は各層間...の含水率の差に大きく左右される．（2）吸湿に伴いボードの面方向に作用する膨張応力は，初期に急増し，含水率12～14％で最大値に達した後，徐々に綬和する挙動を示し，この応力発生には表層が強く関与している．（3）ボード構成各層間の相互拘束作用が大きくなるように設計することにより，含水率変化に伴うボード全体としての寸法変化，および両端固定状態における吸湿によるボードの膨張応力を抑制できる．（4）ボードの層構造設計においては，相互拘束係数とボード全体の曲げ弾性係数との兼ね合いにより，表・心各層での弾性係数比，および層構成比に適性値が存在する．
The dimensional change in the plane of the flat-pressed particleboard is very small compared with that in the thickness. However, the boards are generally used as a large member in plane, so the amount of dimensional change in the plane occurs to a great extent. Recently, the particleboards have been widely used while exposed to the severe air condition, so the serious problems due to the dimensional change in the plane have often arisen. This paper is concerned with the fundamental mechanism of the hygroscopic swelling and shrinkage in the plane of the flat-pressed three-layer particleboards. The results were summarized as follows ; 1) Both changes of dimension and MOE parallel to the plane of board increased more in the face than the core. Therefore, the interactive restraint between both faces and core in board generated sensitively with the change of humidity condition, and furthermore it depended remarkably on the difference of moisture content between face and core. 2) During exposure to humid air, the swelling stress parallel to the plane increased rapidly in the early stage, and after becoming the maximum, it decreased with the increase of moisture content of board in latter stage. Especially, this behavior of swelling stress generation was affected by the thickness ratio of face to core. 3) By designing the layer construction of board so as to increase the interactive restraint between both faces and core, the development of the dimensional change and swelling stress parallel to the plane of board can be effectively controlled. 4) In designing the layer construction of board, both the optimum ratios of MOE and thickness of face to core should be applicable not only to the increase of MOE, but to the dimensional stabilization of the whole board.続きを見る
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