According to the theory of adhesion, factors that influence adhesion are intermolecular force, chemicalbonding, molecular diffusion, mechanical bonding and so on. However, it is not easy to clarify what kind offactor contributes to adhesion in practical materials. XPS, TOF-SIMS and FT-IR are effective for the analysisof surface composition and chemical structure. Depth profiling techniques that have improved recentlyare making it possible to evaluate the molecular diffusion and the chemical bonding at adhesion interface.Furthermore, it is becoming possible to analyze the adhesive interface from the cross section by AFM-IR andAFM-Raman that can perform vibration spectroscopy with spatial resolution exceeding the diffraction limit oflight. In this article, we will explain analysis methods currently being used to evaluate adhesion interface andits progress. Especially, we explain details of quantification of interfacial functional group by XPS with thechemical modification, and push-in testing for evaluating the mechanical properties of fiber / resin interface inFRP.

Buried interface such as adhesive layer between rubber and brass plated steel cord often has difficulties interms of direct observation. Because the interface layer is strongly adhered each other, and composed of somelayers, such as cupper sulfide, zinc oxide and zinc sulfide. Many studies have been carried out to observe andclarify the adhesion mechanism between rubber and steel cords.In this paper, some studies focusing on the buried interfaces of rubber/brass systems are introduced.Synchrotron PES（ Photoelectron Spectroscopy） analysis can access the formation process of the adhesiveinterlayer during vulcanization by using so-called a paper filter method. The paper filter method can preparequasi-adhesive layer on the brass plate which is easily taken out. In another technique HAXPES（ Hard X-rayPhotoelectron Spectroscopy） can directly observe the buried interfaces. Furthermore, studies on TEM orSEM observation are also introduced. FIB can prepare cross-section specimens of the adhesive layer for TEMor SEM observation. Recently a 3D-observation method using FIB-SEM is developed and applied to observerubber/brass adhesive layer. Direct analysis using TEM or SEM is one of the powerful tools to clarify theadhesive mechanism.

Features of dissimilar materials bonding are surface bonding and several type of adhesives can be used. Bycontrolling thermal expansion coefficient of an adhesive to get middle of dissimilar materials, residual stresscan be reduced, in case of internal stress caused by thermal movement the difference of thermal expansioncoefficient between a metal and a plastic．Also it is possible to reduce a stress which is caused by thermalmovement, by adjusting the elastic modulus of adhesive. We introduce structural and elastic adhesives usedfor dissimilar materials bonding and their characteristics and applications. We also would like to introduce ourSTPE base adhesives which newly developed for the purpose of dissimilar materials bonding. It is known that asea-island structure can be obtained by curing a STPE and an epoxy resin in mixture. The sea-island structureis that the epoxy resin is dispersed in the elastic matrix of STPE. New polymers which shows high strength,toughness and durability has been being developed as a sea matrix by blending and hybridization STPE andacrylic resin having silyl group. The development goals of the adhesive are 15-20MPa strength and more than100% of elongation. And also the curing trigger will be UV, not heating. UV cure can provide very fast cureand on-demand cure which is stably uncured until UV irradiation. We believe that our new technology couldprovide non-heating for application and curing of adhesive in production line in the future.

Adhesions based on direct covalent bond formation or host-guest interaction have been investigated.Suzuki-Miyaura cross-coupling, azide alkyne cycloaddition（ CuAAC） and Sonogashira cross-coupling reactionswere employed to realize direct adhesion of materials via very thin adhesive layer. These methods couldbe applied by using other chemical reactions to form covalent bonds between any kind of materials. Hostguestinteractions by using cyclodextrins（ CDs） were also used for adhesion. Cross-linkings by host-guestcomplexations were found to bind materials having host or guest moieties on their surface. The adhesionbased on host-guest chemistry showed selective bonding between various materials. And, the adhesions arecontrollable by using stimuli responsive guest moieties on the surface of materials. Rupture stress of thehost-guest bonding was found to be higher than that of covalently cross-linked adhesion because of theirsupramolecular structure in adhesive layer. Furthermore, the host-guest adhesion was found to have selfhealingproperty due to reversible nature of host-guest cross-linking. These adhesions would contribute to thevarious field of engineering using materials that conventional bonds cannot adhere.