To observe the variation of mechanical strength of rigid polyurethane foam, the compressive modulus and compressive strength of polyurethane foam were examined in the range, 0.04∼0.25, of density (g/cm³). The mixing ratio of two species of diisocyanate(MDI/TDI), were 10/0, 8/2, 5/5, 2/8 and 0/10. And three species of polyol which had different hydroxy values were used. Experimental results were introduced to representative empirical equation ; (Properties)=A(Density)^α, then coefficients A and α were calcuated from the equation. 1) When the mixing ratio of MDI and TDI was changed, the compressive properties (compressive modulus and compressive strength) of the foam were reduced as TDI were increased. 2)We obtained the following ranges of coefficients according to the variation of density and of MDI/TDI mixing ratio. ⅰ) In case of compressive modulus, A=16,000∼6,000, α=1.4∼1.6. ⅱ) In case of compressive strength, A=500∼250, α=1.5∼1.6. 3) From the optical microscopic studies of cell structure, it became known that when TDI fraction was increased, the fraction of open cell and the irregularity of formed cell structure were increased more than when only MDI was used.

2종의 isocyanate 혼합물을 사용한 경질 polyurethane foam의 기계적 강도를 고찰하기 위하여, 2종의 isocyanate 혼합비(MDI/TDI)를 10/0, 8/2, 5/5, 2/8 및 0/10으로 변화시켜, 0.04∼0.25(g/cm²)의 밀도범위에서 압축탄성율과 압축강도 변화를 측정하였다. 폴리올은 히드록시 값이 서로 다른 3종에 대하여 실험하였다. 측정된 실험값들은 탄성율과 강도에 관한 대표적인 실험식 (property)=A(density)^α 로부터 계수 A와 α를 산출하면, MDI/TDI혼합비에 따라, ⅰ) 압축탄성율은 A=16,000∼6,000, α=1.4∼1.6이고, ii) 압축강도는A=500∼260, α=1.5∼1.6의 값을 갖음을 알 수 있었다. isocyanate 혼합비에 따른cell구조를 광학현미경으로 관찰하면 MDI만으로 제조된 foam은 측정전밀도범위에서 주로 독립 cell를 형성하나, TDI 혼합비율이 커짐에 따라 cell 모양이 불규칙해지고 연속 cell형성이 증가되어 강도의 저하를 일으킴을 알 수 있었다.