【正文】 o the maximum at apoint quite close to the solidified on the same reason,the subskin layer,mainly prised of elongated dispersed phase,turns thinner along the melt flowdirection,while the core layer containing mainly spherical domains gets thicker and thicker from gate to nongate end. The higher the melt flowrate is,the shorter the time is needed for mold filling,and the stronger the shear and elongational fields ,high injection speed promotes the deformation and the breakup of mentioned above,the final morphology is the product of the balance between deformation and Figs 3– 8(圖略 ),it was found that the deformation played apredominant role in the formation of the subskin layer since with the increase of the injection speed,the diameter of the elongated particles decreased increase of injection speed shifted the position of the subsk in layer toward the bar surface(.,the solidified layer became thinner),increased the aspect ratio of the dispersed particles,and reduced the diameter of the dispersed particles in the subskin ,for high speed injection molding,after mold filling,the melt exhibited relatively higher temperature than the case of low speed injection because the melt was exposed less time to acold mold and more heat was generated by the viscous friction during mold ,the solidified layer was thinner at the moment of subskin layer formation,and the subskin layer started to develop at aposition closer to the effect also contributed to the subskin layer the core zone,as observed in the SEM micrographs,the dispersed domains assumed the form of spheres and ellipsoids regardless of the injection the other hand,high injection speed brought about strong elongational and shear rate fields to promote the deformation and breakup of the dispersed phase int osmaller ,the longer cooling time enabled the smaller particles to the shape of the dispersed particles obtained at high injection speed was close to spherical and their size were smaller than those at lowinjection ,Ghiam and White[14]observed that the lower the injection rate,the finer is the phase morphology of the injection molded nylon 6/PE blend argued that the influences of the associated pressure and shear viscosity rise caused by the decrease of injection rate overe the effect of weaker elongational and shear rate fields. 翻譯：熔體流動(dòng)速率越高，充模所需時(shí)間就越短，剪切和拉伸場(chǎng)也就越強(qiáng)。因此，高的注射速度會(huì)引起微粒的變形和破裂。正如前述，最終形態(tài)是變形與破裂平衡的產(chǎn)物。從圖 38(圖略 )可以看出，變形對(duì)皮下層的形成起了重要作用，而注射速度的提高，拉伸微粒的直徑急劇減小。注射速度的提高使皮下層的位置移到了棒表面(也就是固化層變薄了 )，使分散相粒子的拉伸比增大并且使皮下層的分散粒子的直徑減小。此外，對(duì)于高的注射速度，在充模后，熔體的溫度高于低注射速度的熔體溫度，這是由于高注射速度的熔體與冷模具的接觸時(shí)間更短，而且充模 時(shí)粘性磨擦又升高了溫度。因此，當(dāng)皮下層變形時(shí)，固化層變得更薄，并且皮下層開始在靠近皮層的地方生長(zhǎng)，最后使皮下層變厚。如 SEM 圖所示，在芯層區(qū)域，分散相呈現(xiàn)球狀和橢球狀，并且不受注射速度影響。另一方面，高的注射速度會(huì)引發(fā)強(qiáng)的拉伸和剪切場(chǎng)，引起分散相的變形和破裂，最后形成更小的微粒。除此之外，長(zhǎng)的冷卻時(shí)間會(huì)使小微粒復(fù)原。因此，高注射速度下獲得的分散相粒子形狀更接近于球狀，并且它們的尺寸會(huì)小于低注射速度的分散相粒子。然而， Ghiam 和 White[14]觀察到注射速率越低，注射的 PA6/PE 混合物部件的相形態(tài)越好。 他們認(rèn)為由剪切速率減小引起的壓力和剪切粘度的上升的影響超過了弱的拉伸和剪切場(chǎng)的影響。 五 .綜合應(yīng)用題 某公司生產(chǎn)擬投產(chǎn)生臺(tái)式計(jì)算機(jī)鍵盤。 (1)試從使用性能、成型加工性、材料加工、加工成本等方面考慮，為該公司選擇什么高分子材料。 生產(chǎn)鍵盤的材料主要有二種： ABS 和 HIPS(俗稱 475)。一般較低檔的采用 475，高檔的用 ABS。另外，按鍵有時(shí)用專用的鐳雕 ABS 生產(chǎn)，它的特點(diǎn)是經(jīng)過鐳雕處理后，黑色的產(chǎn)品上顯示白色的字符。 (2)通過查閱有關(guān)資料列出大致配方、注塑成型工藝條件，并作必要解釋。 (3)如果要降低成本 ，可以從哪些方面考慮對(duì)材料進(jìn)行改性。材料改性后，注塑成型工藝應(yīng)做哪些調(diào)整。 ABS 塑料制作的鍵盤，其耐磨，耐高溫特性還需提高；可換用 TPU(熱可塑性聚氨酯 )制作鍵盤，它是一種環(huán)保塑膠制品 ,TPU 具有強(qiáng)度高、韌性好、耐磨、耐寒、耐油、耐水解、耐老化、耐氣候等優(yōu)良特性。用 TPU 制鍵盤，其特征是在通過將 TPU片進(jìn)行熱成型制得的鍵盤中，該熱塑性聚氨酯樹脂片是使以六亞甲基二異氰酸酯(A1)為主要成分的有機(jī)二異氰酸酯 (A)、以聚碳酸酯二醇 (B1)為主要成分的多元醇(B)及以 C2~C10 的脂肪族二醇 (C1)為主要成分的鏈 增長(zhǎng)劑 (C)反應(yīng)制得的樹脂粒料進(jìn)行熔融成型的片材。使用的 TPU，其二次成型性、耐油酸性、耐變色性、透明性、印刷適性良好。 特別聲明： 1：資料來(lái)源于互聯(lián)網(wǎng)，版權(quán)歸屬原作者 2：資料內(nèi)容屬于網(wǎng)絡(luò)意見，與本賬號(hào)立場(chǎng)無(wú)關(guān) 3：如有侵權(quán)，請(qǐng)告知，立即刪除。