In injection molding, the basic method of upgrading the surface quality in molded articles has remained undeveloped. This paper proposed a technique for obtaining sinkmark-free moldings with fine surface under low injection pressure, instead of conventional shrinkage-compensation molding under high pressure. The technique is based on controlling the amount of heat-discharge originated from the difference in contact thermal resistance between a molten polymer/the cavity surface and the melt/the core surface. The temperature difference arising between both of the resin surfaces by controlling the heat discharge, acts as a driving force to move the resin to the lower cavity side from the higher core side. This results in compensating cooling shrinkage only on the cavity side.
A pair mold having different surface roughness was firstly used. Its cavity surface was mirror-polished and core surface was blasted. Secondly the following combination of the mold surfaces was tried as expected to be more effective; the wettable and insulating cavity surface, treated with SiO₂/the repellent and insulating core surface, treated with teflon-dispersed Ni-plating. The both of the experiments gave us useful information for understanding the idea of new molding technique named "surface transfer/rear shrinkage."
In this report we discussed the generation mechanism of the phenomenon and the possibility of developing an effective mold system for practical use.

抄録全体を表示

セルロース短繊維とシリカ微粒子の添加量を総量で20phrに制御し，得られた天然ゴム系ハイブリッド複合材の引張り特性，膨潤特性，加工特性をそれぞれの強化剤を単独に添加した場合および天然ゴムだけの場合と比較した．その結果，ハイブリッド複合材の引張り弾性率と引張り強さはそれぞれの強化剤を単独で強化した場合の中間的な特性を示すものの，ムーニー粘度などゴムの加工特性を示す指標には複合化した強化剤の効果が大きく現れており，良好な加工特性の向上が認められた．さらに，この複合強化剤の表面をシラン処理すると，引張り特性および加工特性により大きな改善効果がみられた．そこで，EDX，3DマイクロフォーカスX-線CTおよびN-ARC法でこれらの複合強化剤の天然ゴムにおける分散状態に及ぼすシラン処理の効果を検討した．その結果，複合強化剤にシラン処理を施すとそれぞれの強化剤の分散が良くなっていることが確認できた．そして，天然ゴムの強化に対して，セルロース短繊維とシリカとを複合的に用いるだけでなく，複合強化剤にシラン処理を施すと得られる天然ゴム系ハイブリッド複合材の引張り特性や加工性を大きく向上できることが分かった．

抄録全体を表示

Advent of foamed plastics, that allow materials to be reduced and also the mechanical properties to be maintained or even improved, would substantially extend the fields of applications as a resource saving material. In this paper, on an assumption that the mechanical properties of foams are determined by the molecular orientations of cell walls associated with foaming, the study was made on how to enhance the strength of foams, which has revealed the following results. With very fine cell sizes, PS foams attain strengths that are higher than those estimated from the stress concentration and the foam magnification. This was assumed to be due to increase in the surface area of cell walls caused by foaming, as well as enhancement of molecular orientation of cell walls associated with foaming.

抄録全体を表示

The effect of linear low density polyethylene (LLDPE) component blends on heat seal properties for high density polyethylene (HDPE) film was investigated in this study. HDPE films blended with 3-20 wt％LLDPE component were heat sealed at around 110 to 140 degrees C to compare to original HDPE film. The mechanical properties of sealed film were measured by T-shape peeling test and circular notched tensile test. The crystalline structure development in heat seal process was observed by wide angle x-ray diffraction (WAXD) and differential scanning calorimetry (DSC). HDPE film blended with 3 wt％LLDPE component showed low temperature heat sealability in peeling test and then the crystalline orientation was restricted judging from WAXD studies. Melting temperature and crystallinity for HDPE film blended with LLDPE component dropped with increasing LLDPE ratio in DSC studies. However by circular notched tensile test, HDPE film blended with 3 wt％LLDPE component could keep tensile strength which is equivalent to original HDPE film. In conclusion, HDPE film blended with 3 wt％LLDPE component shows low temperature heat sealability and keeps high mechanical property of original HDPE.

抄録全体を表示