[in Japanese]

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Synopsis: Studies suggest that a fuel efficient tire can reduce as much as about 57kg of CO₂ emission compared with a conventional tire. One of the representing technologies for realizing such fuel efficient tires is silica compounding technology. The critical benefit of silica compound is to improve a balance of rolling resistance and wet skid resistance of a tire, which are usually in trade-off relationship. In order to maximize such benefit, one needs to disperse silica in rubbery matrix well enough. Numerous methods have been developed for this purpose. In addition to the use of ordinary silane coupling agents, critical improvements were achieved by molecular designs of dispersion aid chemicals and tailormade polymers for better silica dispersion and silica-polymer reinforcement. On the other hand, technologies for material characterization and property prediction at nano-scale are advancing thanks to rapid progresses of analytical and simulation tools that can handle nano-scale phenomena. We are about to capture hierarchical nature of nanostructure of a compound in quantitative manner, and deepening our understanding about the mechanism behind the hysteresis loss of rubber compounds. By utilizing these designed materials and analytical/modeling technologies, tires that deliver the maximum balance of wet skid resistance and low rolling resistance have been developed and put in the today’s market.

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Synopsis: The fuel consumption efficiency of tires has become more significant in the tire industry from the viewpoint of energy saving and resource saving. Rolling resistance of tires is related to the hysteresis loss of tire tread compounds. Silicafilled rubber compounds show low hysteresis loss in comparison with carbon black-filled rubber compounds, and silica has been widely used as notable filler for high performance tires with good wet grip and low rolling resistance. However, silica is more difficult to disperse well in rubber than carbon black because of interparticle flocculation caused by the interaction of silanol groups covering its surface. Living anionic polymerization is useful technique to resolve this problem, new functionalized SBR which can strongly interact with silica has been proposed in order to reduce rolling resistance. Following the development of new functionalization technology, further reduction of hysteresis loss has been achieved by development of new polymers for silica compound systems. This paper reviews some details of functionalization technology for solution SBR, such as chain-end functionalized SBR, both chain-end functionalized SBR, multi-functional SBR.

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Synopsis: Crosslinking junctions are well-known to be one of the important factors governing mechanical properties of vulcanized rubbers. It is, therefore, necessary to develop a positive method to analyze the crosslinking junctions through solid state NMR spectroscopy, since the vulcanized rubbers are insoluble in most deuteriated solvents. Here, outcomes in the last three-decades were summarized for study on the structural analysis of the crosslinking junctions of vulcanized natural rubber, which was performed by solid state NMR spectroscopy. First, assignments of some signals in ¹³C-NMR spectrum for vulcanized natural rubber were described in conjunction with values of chemical shift estimated for plausible crosslinking junctions by empirical method. Problems on the assignments were explained with respect to the vulcanization mechanism. Secondly, the positive structural analysis of the crosslinking junctions of the vulcanized natural rubber are described with field gradient fast magic angle solid state NMR spectroscopy, which was developed by a novel innovative technology. Finally, relationship between the assigned signals and mechanical properties were discussed in regard to newly proposed vulcanization mechanism.

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Synopsis: Use of transmission electron microscopy (TEM) combined with computerized tomography (abbreviated as 3D-TEM in this review, which is sometimes called electron tomography) enabled us to reconstruct three-dimensional (3D) images of nano-filler aggregates, agglomerates and network in rubbery matrix. The 3D-TEM results on dispersion of carbon black (CB) and silica in natural rubber (NR) were presented in this review. The network structure formed by agglomeration of CB aggregates was elucidated by combining the 3D images and physical properties of the vulcanizates. On the other hand, the relationship between optical transparency and filler loading was found to differ markedly between hydrophobic silicafilled and hydrophilic silica-filled peroxide cross-linked NR. The optical transparency of the former NR showed virtually no change when the hydrophobic silica filler loading was increased. In contrast, the latter NR exhibited an optical anomaly in which optical transparency initially decreased with increasing hydrophilic silica filler loading and then began to increase again. Then, the observed silica networks were analyzed using 3D-TEM. As a result, a light scattering equation was formulated using the product of the density and squared length of the isolated chains, and the equation was used to reveal the differences in optical transparency between the two types of silica-filled NR samples.

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Synopsis: Rubber production is a typical network polymer through vulcanization process using vulcanizing agent such as sulfur. It is well known technique for rubber reinforcing method to be combined rubber with phenolic resin which is also network polymer, and it is taking a large role in a rubber industry. The rubber reinforcing using phenolic resin is to be mixed rubber compound with phenolic resin served with a hardener such as hexamethylenetetramine, to be cured during vulcanization process, and to be built the network structure in addition to rubber’s network structure. And its reinforcing rubber is obtained the high hardness, the high elastic modulus, and the high strength in its properties. It can say it is important to discuss the compatibility, the dispersing quality, and the network structure between phenolic resin and rubber. Here we show that the rubber reinforcing with phenolic resin in automobile tires which is the major in rubber product’s using. We interpret the recent development state of phenolic resin and peripheral material such as a hardener for demand characteristics in the tire industry, the study of reinforcing mechanism by phenolic resin through the basic experiment to confirm the network structure and dispersing quality in rubber compound using a variety of phenolic resin and hardener, the recycle technology, which is challenges for network polymer, and the movement in the future.

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