１成分形ポリウレタン系シーリング材の硬化過程における引張特性

抄録

 The effect of the hardening process of a moisture-curing, one-component polyurethane sealants on the joint movement followability during curing was examined by experimental and analytical methods. In order to investigate the distribution of the rate of hardening in the depth direction from exposure surface, a bond breaker was applied to the upper or lower half of the adhesive surface between the sealant and the aluminum frame to prevent the adhesion of the specimen. Two types of sealants with different hardening rates were prepared for the experiment. U1 with normal hardening rate, M-U1 with faster hardening rate, respectively. According to the results of the tensile test, the tensile force was shared almost by the upper part of the sealant after 7 days of curing. After 14 days of curing, the upper part has more high strength than the lower part, but the hardening progresses to the lower part, and the elongation and strength was developed. M-U1 had a faster development of strength, and also had a higher strength.

 The adhesive surfaces of the sealant and the aluminum frame were cut at each curing date of 3, 7, and 14 days as test specimens for testing the curing depth of the sealant. The penetration resistance was measured by a needle of 0.75 mm diameter into the cut surface. M-U1 was hardening faster and deeper than U1. A simulation program was proposed to model the penetration and reaction of moisture into the polyurethane and to predict the distribution of hardening rates in the depth direction. The prediction results were a good representation of the results of the penetration test.

 Stress distribution analysis of the sealant under tensile force was performed by FEM using the distribution of hardening degree during curing. The maximum principal stress at the interface between the sealant and the aluminum frame was approximately 2.5 N/mm² for U1. M-U1 is about 1.5 N/mm², which is about 40% smaller than U1. M-U1 had a faster hardening rate and higher strength than U1. However, M-U1 share a wider area of stresses due to the faster progression of hardening in the depth direction. Therefore, even if a tensile force occurs during the curing process, the effect of stress concentration is considered to be controlled. Since the maximum principal stress of M-U1 under a forced displacement of 10% is almost the same as that of U1 at 5%. The internal stress is reduced and the risk of peeling and rupture is considered to be low. From the above results, it can be seen that so as to reduce the influence of external forces during the curing process, it is important to formulate the materials so that curing proceeds uniformly in the depth direction, rather than simply increasing the reaction rate.