エレクトロアクティブ高分子型人工筋肉は，今までのアクチュエータや発電装置，センサー等には無い特性を有した新しいタイプの変換器である．エレクトロアクティブ高分子の中で特に実用化の可能性が高いのは，誘電エラストマーである．駆動原理は，エラストマーの上下に柔軟性を有した電極で挟み通電することにより生じるマクスウェル応力にて，エラストマーを厚さ方向に押し付け，その結果面積を広げ，伸ばすことが可能となる．色々な高分子がこれまで試されたが，NuSil Silicon Technology 社のシリコンゴムをベースにしたものと3 M 社のアクリルをベースにしたエラストマーが最高の性能を得ている．これらの人工筋肉は，スピンコーティング，ディップコーティング，キャスト，スプレーなどの良く知られた技術を用いて製作される¹⁾．
誘電エラストマーを用いた人工筋肉は，硬さが生物の組織に近く，駆動力や伸びが生物の筋肉に匹敵し，形を思い通りに成形することが可能で，コストがとても安く，かつ効率がとても高いため，義手・義足，実際に人間の体を診断するデバイスや医療研究用デバイス等のアプリケーションに向いている．現在，研究・開発している例を挙げると，義足・義手，ハプテッィクやセンシングが可能な柔らかい皮膚，血液等を診断するマイクロ流体システム用のポンプ・バルブや使い捨ての埋め込み型ポンプ・バルブ，人工器官（例，人工横隔膜や心臓の鼓動を補助する装置等）などである．実用化されるには，パッケージングの研究や各種の試験等が必要であるが，近い将来エレクトロアクティブ高分子型人工筋肉を利用した新しい特性を有した医療機器が実現すると思われる．

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In this paper, the correlation between the foaming temperature and the decompression rate (decompression time) of the cell density, the number of cells per unit volume remaining in foamed plastics, will be discussed. The foaming was carried out by the following method. The blowing agent was soaked into the solid resin at high pressures under temperatures higher than the glass transition temperature of the resin. After the foaming agent reached its saturation state, cell nucleation and cell growth were accelerated by decompression. Finally, cell growth was halted by cooling. A device that can accurately control temperature and the decompression rate was designed, produced and verified for accuracy prior to this investigation. Polystyrene (PS) specimens were foamed under various foaming temperatures and decompression rates using the above-mentioned method. The following results were obtained. (1) Cell density of foamed PS shows time and temperature dependence as follows. The cell density increases when the decompression rate is quick, i. e. the decompression time is shortened at low foaming temperatures, and cell density decreases when the decompression rate is slow, i. e. decompression time is lengthened at high foaming temperatures. (2) Correlation is maintained between the temperature dependence and time dependence of the cell density of foamed PS, and it can be expressed with one master curve. (3) Based on this correlation, it is possible to predict the required foaming conditions of plastics having arbitrary cell densities.

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The load displacement and deformation behavior along with the accompanying changes in surface temperature during neck formation and propagation under tensile loading were investigated for poly (butylenes terephthalate (PBT). A numerical model for PBT molding was developed and the neck deformation behavior under tensile loadings was analyzed by the finite element method (FEM). Numerical results were compared with experimental ones.
The experimental results showed that neck formation did not occur immediately after the yield, but instead a homogeneous plastic deformation throughout the test piece proceeded the neck formation and propagation. It was observed that an increase in temperature did not occur before the start of the neck formation. The load-displacement behavior obtained by numerical models could well describe the experimental results when an elastic-plastic model under stable temperature conditions was adopted to describe the necking behavior of the PBT sample. Furthermore, the dependency of strain rate on the neck formation was shown to be affected by the instability of plasticity from the numerical results.

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Resin-coated paper (RC paper), which is manufactured by extrusion coating with polyethylene resin, is mainly used as a support for imaging materials such as ink-jet receiving paper and photographic paper. It is important to clarify the relationship between the curl of the RC paper and the constitution of the RC paper or characteristics of the resin. We analyzed the curl of RC paper based on the assumption that thermal stress actually generated in the resin-coated paper is the driving force for curl. We constructed equations for curl evaluation by the use of a two-dimensional composite beam model, assuming that paper and solid polyethylene resin are both elastic.
We found that the calculated values corresponded well with the experimental values, which gives support for the validity of our curl model. We also found that the actual thermal strain corresponded to about 13.3% of the thermal shrinkage due to ideal solidification. Applying the model to RC papers of varying constitution, we were able to determine the elastic modulus required for the resin to produce a suitable curl in the imaging products.

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