岸 肇

Carbon fibre reinforced composite materials have become familiar as structural materials, especially for weight-critical aeroplane parts, using their high strength, high modulus and light weight. Thermosetting resins such as epoxy resins have been used for the matrix resins of composites rather than thermoplastic resins, due to their better processability in prepregs, their tackiness and drapability. However, the low fracture toughness (compressive strength after impact energy (CAI)) of thermoset resin matrix composites compared with metals is one of the factors which limits their application as primary structural materials. Therefore, improvement of fracture toughness has been a hot topic of the composites industry.

© 2015 International Committee on Composite Materials. All rights reserved. Within several candidates of matrix polymers for carbon fiber reinforced thermoplastic composites (CFRTP), acrylic polymers have high potential in terms of low-temperature processing. We focused on the improvement in the interfacial adhesive properties between CFs and the acrylic polymers using several functional monomers for the co-polymerization with methyl methacrylate (MMA). Several functional acrylic monomers were co-polymerized with the MMA, and applied as the matrix polymers of the acrylic CFRTPs. It was observed that the copolymer matrices well-adhered to the surfaces of CFs, compared to the pure PMMA. The copolymer with acrylamide (AAm) indicated higher interfacial adhesive strength than that with hydroxyethyl acrylate (HEA). The hydroxyethyl acrylamide (HEAA) copolymer having both amide groups and hydroxyl groups showed very high adhesive strengths to CFs, which resulted in the high flexural strengths of the CFRTPs. The flexural strength of the pure PMMA CFRTP was 450 MPa. On the other hand, the co-polymerized acrylic matrices gave the increase in the flexural strength for the CFRTPs. Especially, the 3mol% HEAA copolymer achieved the two-fold flexural strength (900 MPa) on the acrylic CFRTP. The strength was equivalent level to the epoxy CFRP. The fatigue resistance of the HEAA copolymerized CFRTPs were also evaluated, in relation to the interfacial adhesive strength.

© 2015 International Committee on Composite Materials. All rights reserved. Epoxy resins are utilized in various industrial areas as adhesives and matrix of composite materials because of the higher stiffness, strength and heat resistance. Toughening with rubber particles is one of the most popular method to enhance the fracture toughness. For the structure uses, the fatigue resistance is very important property as well as the static mechanical properties. In this study the effect of molecular weight between crosslinks (crosslink density) on the fatigue crack propagation properties of rubber-toughened epoxy resin. Several DGEBA epoxy resins with different average molecular weight were used in this study. Core shell rubber (CSR) particles, the diameter of 100nm, were well dispersed in the epoxy. The fracture toughness of Core Shell Rubber-modified epoxy monotonously enhanced with increasing molecular weight between crosslinks, and the effect of core-shell rubber became larger as the molecular weight between crosslink increased. On the other hand, the fatigue threshold had a peak against molecular weight between crosslinks. Whereas there is positive effect of core shell rubber in fatigue resistance for molecular weight between crosslink of 1440g/mol, the fatigue threshold of the core shell rubber modified epoxy is lower than that of unmodified one for molecular weight between crosslinks of 3040g/mol. TEM observation from the side surface of the crack tip revealed that the size of the plastic deformation zone was well related to the fatigue resistance. The core shell rubber particles enhanced the shear plastic deformation region at the crack tip for molecular weight between crosslinks of 1440g/mol, and the particles largely lowered the deformation region. These results was caused by the deformation ability of the epoxy resin under plane-stress state.

オリゴマーの平均分子量が同じで分子量分布の異なるエポキシ樹脂を作製し，微細構造および力学特性に及ぼす影響を調べ，これらの関係について検討した。主剤に平均分子量の異なる4 種類のビスフェノールA 型ジグリシジルエーテルを用いてさまざまな配合比で混合し，平均分子量が同じで分子量分布が異なる4 組成のブレンド樹脂を作製した。作製した樹脂について，微細構造観察および力学特性評価を行った。動的粘弾性試験の結果，分子量分布が広くなるほどガラス転移領域が広くなり，材料内部の架橋密度差が大きくなることが分かった。架橋密度差の拡がりとともに不均質構造のサイズも大きくなった。特に，分子量分布がもっとも広い系では，硬化時に反応誘起型相分離が生じたことが分かった。曲げ弾性率，曲げ強度は，分子量分布およびそれに伴う内部構造変化の影響を受けなかったが，破壊靭性値は分子量分布が広くなるにつれて高くなった。微細構造モデルを提案し，そのモデルを用いて破壊靭性向上のメカニズムについて考察した。

Stability of nanostructures of epoxy/acrylic triblock copolymer blends was studied. PMMA-b-PnBA-b-PMMA triblock copolymers (acrylic BCPs) having several compositions on the ratio of the block chains and the molecular weight were initially prepared and were blended with diglycidyl ether of bisphenol-A epoxy thermosets. The blends were cured using phenol novolac with tri phenyl phosphine (TPP) as the catalyst. Several nanostructures, such as spheres, cylinders, curved lamellae, were observed in the cured blends. The nanostructures were controlled by the molecular weight of the immiscible PnBA-block chain and the ratio of the PnBA in the blends. Moreover, the effect of the gel time to the nanostructures was examined by altering the trace amount of the TPP in the blends. The types of the nanostructures were almost kept irrespective of the gel time of the blends when the composition of the blends was maintained. This suggested the stability of the nanostructures of the epoxy/acrylic BCP blends made via the self-assembly mechanism, therefore a phase diagram of the cured blends was proposed.

Effects of gamma-ray irradiation on a cyanate ester/epoxy resin composed of dicyanate ester of bisphenol A (DCBA) and diglycidyl ether of bisphenol A (DGEBA) were investigated by changes in physicochemical and mechanical properties after the gamma-ray irradiation with dose of 100 MGy as maximum at around 40 degrees C under vacuum. After the irradiation, gases of hydrogen, carbon monoxide and carbon dioxide were evolved, glass transition temperature decreased, and flexural strength also decreased. It was concluded that ether linkages bonded to cyanurate, isocyanurate and oxazolidinone structures are mainly decomposed by the irradiation. After 100 MGy irradiation, the flexural strength of DCBA/DGEBA was maintained more than 170 MPa which is 90% of initial value of 195 MPa. Flexural modulus and density slightly increased to the values of 3.9 GPa and 1.211 g/cm(3) from initial values of 3.4 GPa and 1.199 g/cm(3), respectively. (C) 2014 Elsevier Ltd. All rights reserved.

Fatigue resistance of toughened epoxy resins with preformed polymer particles were studied in terms of the fatigue threshold and the fatigue crack propagation (FCP). The toughening modifiers were polyamide-12 (PA12) and core-shell rubber (CSR). The PA12 toughened epoxy achieved higher stress intensity factor range (AK) than the pure epoxy, irrespective of the molecular weight between cross-links (Mc) of the epoxy matrices. The crack bridging of the PA12 particles was the major mechanism of the fatigue resistance. Meanwhile, the fatigue behavior of the CSR / epoxy resins depended on the Mc. The whole FCP curve of the CSR / epoxy with low Mc was in the high AK. However, the fatigue threshold of the CSR / epoxy with high Mc was in the lower AK than that of the pure epoxy. The plastic deformation of the epoxy matrix with high Mc was localized, which decreased the fatigue resistance.

The influence of tackifier structure on the temperature dependence of tack for a polystyrene block copolymer/tackifier system was investigated. A blend of polystyrene-block-polyisoprene-block- polystyrene triblock and polystyrene-block-polyisoprene diblock copolymers was used as the base polymer. Four different tackifiers were used: special rosin ester resin (RE), rosin phenolic resin (RP), hydrogenated cyclo-aliphatic resin (HC), and aliphatic petroleum resin (C5). Tack at 20 degrees C increased with the tackifier content for both RE and HC tackifier systems. Tack is affected by two factors: the work of adhesion at the adherend interface and the viscoelastic properties of the adhesive. The good balance of these two factors brought high tack. The adhesive with 10 wt.% tackifier exhibited the highest tack at 20 degrees C, whereas those with 30 and 50 wt.% tackifier were lower than those systems with 10 wt.% of the RP or C5 tackifiers. The adhesive with overly high hardness lowered the work of adhesion and the tack was not improved with more than 30 wt.%. A compatibility test in toluene solution and in solid state showed that tackifier RE has good compatibility with both polyisoprene and polystyrene, whereas tackifier RP has lower compatibility. Tackifiers HC and C5 had good compatibility with polyisoprene, but poor compatibility with polystyrene, and that of C5 was poorer. Pulse nuclear magnetic resonance (NMR) analyses indicated that tackifiers RE and HC effectively restrict the molecular mobility of polyisoprene phase.

a- and b-axis-oriented Bi3. 25Nd0. 75Ti3O12 (BNT) nanoplates, 3. 0-μm thick, were fabricated on conductive Nb:TiO2(101) substrates with 0. 79 mass% Nb at 650 °C by high-temperature sputtering. Successively, the fabrication of inorganic-organic composites was carried out by introducing an epoxy resin to the spaces between the BNT nanoplates. The fourier transform infrared spectroscopy (FTIR) and the energy dispersive X-ray (EDX) elemental mapping results confirmed that the fabricated composites were inorganic-organic hybridized materials with cured epoxy resin introduced into the spaces between the BNT nanoplates. Piezoelectric response measurements of the fabricated BNT-epoxy resin composites by using piezoresponse force microscopy (PFM) showed that the composites have potential as piezoelectric microelement materials. © 2013 The Korean Physical Society.

Peel adhesive strengths of multi-layered laminates composed of two polypropylene (PP) sheets and an inserted polyethylene (PE) layer (the middle layer) between the PP layers were evaluated. PE-glycidyl methacrylate (GMA) copolymers and a maleic-anhydride grafted PP (MAPP) were compared to the PE homopolymer and the PP homopolymer. The peel adhesive strength of PE-GMA/MAPP laminates was much higher than that of PE homopolymer/PP homopolymer laminates. Meanwhile, the blends composed of the PE-GMA and three types of PE homopolymer (PE-GMA+LDPE, PE-GMA+MDPE, PE-GMA+HDPE) were formulated as the PE middle layer of the multi-layered laminates. The PE blends had the same amount of glycidyl groups, and the deformation capacity was different in each. Namely, the PE blend of LDPE had higher elongation to break than the PE blend of HDPE. The peel adhesive strength of the multi-layered laminates with the middle layer of the LDPE blend was highest among the three types of laminates with the middle layer of the PE blends. Scanning electron microscopy on the fractured surfaces revealed that the large plastic deformation of the LDPE blended middle layer was responsible for the high energy absorption, and resulted in the high peel strength.

異種高分子多層成形体において，層間の反応をもたらす官能基量が剥離接着強さに与える影響について検証した。まず，エチレン—グリシジルメタクリレート(GMA)共重合体(PE－GMA)とポリプロピレン(PP)との多層積層体の剥離接着強さを評価した。その際，同じPE－GMAシートに対し，PPシート表面に酸素プラズマ処理を施すことで官能基量を変え，多層積層体の剥離接着強さとの関係を評価した。また，剥離面のSEM観察を行い，剥離接着強さの発現機構について考察した。反応サイト数（化学結合数）の増加に伴い,PE/PP界面接着性は向上する｡その結果，力学的拘束を受ける界面近傍のPEに空洞化を伴う膨張的塑性変形が発生することがわかった。界面接着向上により増加したPEのバルク塑性変形は，PE－PP間の剥離接着強さ向上をエネルギー的に説明する因子として重要である。

New wood-based epoxy resins were synthesized from alcohol-liquefied wood. Wood was first liquefied by the reaction with polyethylene glycol and glycerin. The alcohol-liquefied wood with plenty of hydroxyl groups were precursors for synthesizing the wood-based epoxy resins. Namely, the alcoholic OH groups of the liquefied wood reacted with epichlorohydrin under alkali condition with a phase transfer catalyst, so that the epoxy groups were put in the liquefied wood. The wood-based epoxy resins and the alcohol-based epoxy resins as reference materials were cured with polyamide amine. The glass transition temperature (Tg), the tensile strength, and the modulus of elasticity of the wood-based epoxy resin were higher than those of the alcohol-based epoxy resin. Also, the shear adhesive strength of the wood-based epoxy resin to steel plates was higher than those of the alcohol-based epoxy resins, which was equivalent to the level of petroleum-based bisphenol-A type epoxy resins. The higher Tg of the wood-based epoxy resin than that of the alcohol-based epoxy resin is one of the evidences that the wood-derived molecules were chemically incorporated into the network structures. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 745-751, 2011

Phase structures and mechanical properties of epoxy/acryl triblock copolymer alloys using several curing agents were studied. PMMA-b-PnBA-6-PMMA triblock copolymers synthesized by living anionic polymerization were applied as the toughening modifiers for the epoxy resins. An aromatic amine, an acid anhydride and an anionic polymerization catalyst as curing agents resulted in macro-phase separation in the epoxy/triblock copolymer blends during the cure process. However, a phenol novolac as the curing agent created nano-phase structures in the epoxy blends. The size of the spherical phases or cylindrical phases was about 40 nm in diameter, and the main component in the nano-phases was the PnBA of the triblock copolymer. The fracture toughness of the epoxy/triblock copolymer alloys with the nano-cylindrical phases reached 2530 J/m(2). The fracture toughness was more than twenty fold relative to the unmodified epoxy resin, and was equivalent to the toughness of polycarbonates. (C) 2010 Elsevier Ltd. All rights reserved.

パルス法NMRの測定で得られる FID signal は高分子物性に関する情報が非常に多いデータである。この FID signal を直接数値微分することにより緩和スペクトルを求めるプログラムの作成を行ってきた。今回，我々はスチレン系ブロックポリマーについてパルス法 NMR と動的粘弾性 (DMA) の測定を行い，緩和スペクトルと DMA の温度分散との関係を解析した。その結果，次のことが明らかとなった。 (1) -50℃から0℃の低温域では緩和スペクトルのピーク時間が大きくシフトする温度領域と，損失弾性率Eが変化する温度域が同じである。これらはともに高分子の流動性の変化を測定していることになる。 (2) 100℃付近の40µs以下の緩和スペクトルは，PSブロックがハード相として存在していることを示している。同温度域の DMA と比較すると，SI ジブロック含量の多いポリマーは PS ドメインを形成したまま流動していると考えられる。

異種高分子の組み合わせは一般には相溶性や相互の接着性に乏しいため，これらの多層成形体には界面剥離が生じやすく，単一樹脂成形体より脆性・低強度なものになりがちである。回転成形でも同様，ポリエチレン層とポリプロピレン層の2層成形体は，層間剥離が生じる。しかしながら，これら2層の間に，ポリエチレンとポリプロピレンの混合パウダーを中間層として投入することで，剥離強さが著しく向上することを見出した。また，その中間層のポリエチレンの密度を変化させると，剥離強さが変わることが知られた。この中間層の相構造や，剥離表面の観察を行ない，中間層におけるポリエチレンの塑性変形挙動と剥離強さ発現メカニズムについて検証した。

Composites consist of carboxyl-terminated butadiene acrylonitrile rubber (CTBN) / epoxy resin blends and carbon-black (CB) were formulated. The impact-energy absorbability of the composites depended on the kneading temperature of the resin and the CB. Strong interaction at the interface between CTBN and CB particles was the key factor to achieve the high impact-energy absorbability.

Wood-based epoxy resin was synthesized from resorcinol-liquefied wood. First, wood components were depolymerized and liquefied by reaction with resorcinol. The resorcinol-liquefied wood with plenty of hydroxyl groups could be considered as a precursor for synthesizing wood-based epoxy resin. Namely, the phenolic-OH groups of the liquefied wood reacted with epichlorohydrine under alkali condition. By the glycidyl etherification, epoxy functionality was introduced to the liquefied wood. The wood-based epoxy resin was cured with 4, 4'-diamino diphenyl sulphone (DDS) and the thermal and mechanical properties were evaluated. The flexural modulus and strength of the cured wood-based epoxy resin were comparable to those of the petroleum-based bisphenol-A type epoxy resin (diglycidyl ether of bisphenol-A: DGEBA). The mechanical and adhesive properties of the wood-based epoxy resins suited well for matrix resins of fiber reinforced composites. Therefore, biomass composites consist of ramie fibers and the wood-based epoxy resin were fabricated. The flexural modulus and strength of the biomass composites were equivalent to those of the same fiber reinforced bisphenol-A type epoxy composites.

エポキシ樹脂は、ネットワーク構造を有するゆえに耐溶剤性や耐クリープ性に優れる一方で脆性破壊しやすい。そのため、破壊靭性を向上させるべく種々の改質手法が試みられてきた。ここではまず、反応誘起型相分離を用いた強靭化技術と微粒子添加型強靭化技術を工業的視点から対比する。また、微粒子添加型強靭化技術の中でも、ゴム微粒子、ガラス微粒子、熱可塑性樹脂微粒子といった添加材料の違いにより強靭化機構が異なることを解説し、改質剤粒子とマトリックスとしてのエポキシ樹脂の役割について述べる。

Resin coatings and linings are very useful methods for corrosion prevention of steel structure exposed to hot steam or acid liquid. Vapor permeation is one of the most important properties for corrosion resistant coatings. Nano filler dispersion is well known to improve the vapor permeation for the nylon and the other plastic materials, and is expected to reduce the vapor permeation of the coating resin and expand the lifetime of the coating system. The aim of this study is to clear the effect of the nano filler on the vapor permeation property of the vinyl ester resin. One montmorillonite clay and three organophilic clays with different surface treatment were dispersed in the bisphenol vinyl ester resin system. Scanning electron microscopy and optical microscopy revealed that the different surface treatment resulted in the different dispersion characteristic. The vapor permeation of the nanocomposites was measured under 40°C, showing that the nano filler addition reduced the vapor permeation and the nanocomposite with the better dispersion of the clay had the lower permeation rate. The undispersion index, defined as the area ratio of the residual aggregate particles on the surface, showed the fairly good correlation with the permeation rate. The mechanism of the vapor permeation of the nanocomposites was discussed.

Carboxyl-terminated butadiene acrylonitrile (CTBN) rubber/ epoxy (diglycidyl ether of bisphenol-A) / diamino diphenyl methane polymer blends with 60 wt% of CTBN were formulated to evaluate the viscoelasticity and the damping properties. When the blend resins had micro-phase separated morphologies composed of epoxy-rich dispersed phases larger than 500 nm in diameter surrounded by a rubber-rich continuous phase, the loss factors (eta) of the steel laminates adhered with the resin significantly depended on the environmental temperature and the resonant frequencies. The resins with epoxy-rich phases smaller than 200 urn in diameter had broad glass-transition temperature range that resulted in the high loss factor (eta > 0.1) of the steel laminates in the broad temperature range. Inhomogeneous nano-gel structures with 20 similar to 30 nm sizes were observed in more compatible resins by scanning probe microscopy, although appreciable micro-phase separation was detected by none of SEM and TEM. Pulse NMR suggested that the fraction of interfacial phase in the resins increased with increasing the compatibility of the blends. The large interfacial phase in the inhomogeneous nano-gel structures seems to play an important role in the damping mechanisms.

The degradation mechanism in molecular order by electron beam (EB) irradiation for three types of thermosetting polymers (bisphenol type vinylester, Novolak-type vinylester and tetra functional epoxy resin) is confirmed by dynamic mechanical thermal analysis (DMTA) and the swelling test in this study. The level of degradation in molecular order is quite high. The same result was observed in Novolak-type vinylester but not in tetrafunctional epoxy resin. The results of the swelling test showed that the cross-linking networks were destroyed by gamma- or electron beam irradiation remarkably for both the vinylester resins. For the tetrafunctional epoxy resin, gamma- or electron irradiation does not give any effect even in molecular order in high radiation intensity such as 20 MGy. However, the mechanical properties such as bending strength, modulus and fracture toughness of all composites (both vinylester resin and tetrafunctional epoxy resin composites) reinforced by a chopped-strand glass mat or flake-like mica change a little after 20 MGy EB irradiation. (c) 2007 Curtin University of Technology and John Wiley & Sons, Ltd.

Carboxyl-terminated butadiene acrylonitrile (CTBN) liquid rubber/epoxy (diglycidyl ether of bisphenol-A: DGEBA) / diamino diphenyl methane (DDM) resins, in which CTBN was 60 wt % as the major component, were formulated to evaluate the damping and adhesive properties. In cases where acrylonitrile (AN) was 10 similar to 18 mol % as copolymerization ratio in CTBN, the blend resins showed micro-phase separated morphologies with rubber-rich continuous phases and epoxy-rich dispersed phases. The composite loss factors (q) for steel laminates, which consisted of two steel plates with a resin layer in between, depended highly on the environmental temperature and the resonant frequencies. On the other hand, in the case where AN was 26 mol % in CTBN, the cured resin did not show clear micro-phase separation, which means the components achieve good compatibility in nano-scale. This polymer alloy had a broad glass-transition temperature range, which resulted in the high loss factor (eta > 0.1) for the steel laminates and excellent energy absorbability as the bulk resin in a broad temperature range. Also the resin indicated high adhesive strengths to aluminum substrates under both shear and peel stress modes. The high adhesive strengths of the CTBN/epoxy polymer alloy originated in the high strength and the high strain energy to failure of the bulk resin. (c) 2007 Wiley Periodicals, Inc.

Dicyandiamide (DICY)-cured epoxy resins are important materials for structural adhesives and matrix resins for fiber reinforced prepregs. The objective of this study was to examine the mechanical and physical properties as well as the gel structures of the cured resins and discuss the relationships among them. Diglycidyl ether of bisphenol-A (DGEBA) oligomers were chosen as the common chemical structure of the epoxy resins. Four kinds of resin mixtures were formulated using the seven types of DGEBA oligomers having different molecular weight distributions. Three resin formulations having bimodal-type molecular weight distributions were designed to have almost identical rubbery plateau values of the storage modulus in dynamic mechanical analyses after curing, means that they had almost equivalent average crosslink density and basic chemical structure. However, the toughness, ductility, and environmental (heat and solvent) resistance of these three formulations were different. Atomic force microscopy revealed the existence of inhomogeneous nanoscale gel structures in these cured resins. The morphological differences in the gel structures in terms of their size, the connectivity, and the relative magnitude of the heterogeneity would cause the difference in several properties of the DICY-cured epoxy resins. (C) 2007 Wiley Periodicals, Inc.

A novel adhesive, consisting of well-formulated epoxy resins and thermally expansive fillers has been developed. The cured adhesive resin showed characteristic viscoelasticity with both the storage modulus higher than 3 GPa in the glassy state under the glass transition temperature (Tg) around 100 °C and the rubbery modulus less than 2 MPa over the Tg. As the results, the joint bonded with the adhesive was strong at ambient temperature under 80 °C and they could be dismantled easily at high temperature due to the expansion force caused by expandable graphite as the fillers. The technique of the dismantlable adhesive joints should be important in terms of material recycling because carbon fiber reinforced plastics (CFRP) has to be separated in the recycling process from the other materials such as steel or aluminum alloy used as parts of automotives, for example.

A T-g-less epoxy resin was easily obtained by curing with ionomer. In this system, the storage modulus did not drop and maintained a high level as if it were in a glassy state even at an elevated temperature of 300 degrees C. Investigation of the curing process for the epoxy resin mixture with ionomer, using DSC and FT-IR, revealed that the curing reaction was initiated from the nucleophilic addition of - COO- to the epoxy group to form an ester linkage, and that the chain propagation subsequently occurred by anionic ring opening polymerization of the epoxy group to form an ether linkage. On the basis of the results, the mechanism of 'T-g-disappearing phenomenon' is also discussed. (C) 2007 Curtin University of Technology and John Wiley & Sons, Ltd.

カルポキシル基末端ブタジエンニトリルゴム(CTBN)をエポキシ樹脂（ビスフェノールAジグリシジルエーテル:DGEBA)と反応ブレンドした樹脂組成をマトリックス材全体あるいは一部として用いた炭素繊維強化複合材料(CFRP)積層板の衝突エネルギー吸収特性を評価した。ゴムリッチ相とエポキシリッチ相に相分離した樹脂2種および電子顕微鏡で相構造を認識できない相溶性良好な樹脂1種を比較したところ，樹脂のエネルギー吸収性の序列と，これらをマトリックス材としたCF織物積層複合材のエネルギー吸収性の序列は一致した。しかしながら，エネルギー吸収性が高くなるほど樹脂弾性率は低下し，そのCF織物積層複合材にはエネルギー吸収性向上の一方で強度・弾性率が低下するトレードオフ関係が見られた。そこで，上記CTBN/エポキシ反応ブレンド樹脂をCF織物に含浸させたプリプレグを，既存の硬質エポキシマトリックスー方向強化CFプリプレグの層間に挿入したハイブリッド積層複合材を調製したところ，前述の単一マトリックス織物積層複合材よりエネルギー吸収性と弾性率のバランスが向上することが知られた。