ポリサルファイドゴム印象材の粘弾性に関する基礎的研究

抄録

The deformation of a polysulfide rubber base impression material can be considered to appear as an effect of relief of the internal stress occurring during the gelation of the material, or of imperfect recovery from the strain applied to it during and/or after the removal of the impression. However, the mechanism of these phenomena have ever been scarecely elucidated. The author tried to make clear the deformation mechanism of the polysulfide rubber base impession materials used generally for precision impression in recent years. For this purpose, the author rehologically studied into the cause of the stress relaxation behavior from gelation process through relatively stable stage of reaction after gelation. Two stress relaxation tests were conducted : shearing test and tensile test. Principal results of the study are as follows : (1) Stress relaxation of a polysulfide rubber base imprssion material during and/or after gelation can be classified into the physical and the chemical relaxation within a low strain range permitting the fomation of linearity. The former is mainly due to the physical flow of the filler or the unreacted part. The latter is provoked by the network chain exchange reaction relieving the internal stress. (2) Physical relaxation may be explained by a simple Maxwell's relaxation. The chemical relaxation due to the network chain exchange reaction may be considered to follow a primary reaction. (3) In the initial stage of stress relaxation, the combination of physical and chemical relaxation is observed. However, it may be considered that the physical relaxation is completed in a relatively short time and thereafter only the chemical relaxation is observed substantially. (4) Permanent set (P.S%) of materials can be theoretically calculated on the basis of the continuous stress relaxation curve along with the discontinuous stress relaxation curve. The permanent set (P.S%) seems to depend upon both physical and chemical relaxation in the initial tension stage, while mainly upon the chemical relaxation in the later tension stage. This means that a respective increase in physical and chemical relaxation leads to the increase in permanent set. (5) As the gelation progresses, the network chain density increases and the chemical relaxation time is therefore lengthened. As a result, the decrease in fluidity of the contained filler results in the longer physical relaxation time. However, upon substantial completion of the gelation, the network chain density has a practically constant value, and so both physical and chemical relaxation present in a constant time. (6) The increase in temperature of a specimen results in the increase in exchange reaction rate and therefore promotes the relaxation. And then the fluidity of the filler also increases. As a result, the permanent set of the impression material increases.