| Summary: | 碩士 === 遠東技術學院 === 機械研究所 === 96 === ABS has the excellent plating quality. The mechanical and thermal properties of PC/ABS blend are better than that of ABS. Therefore, the PC/ABS blend is widely used in the 3C products. The morphology of PC/ABS blend is homogenous at its composition. Most of the physical properties of PC/ABS blend followed the addition rules. Some properties of PC/ABS even showed a synergy effects. There is an advanced molding machine which can produce a sandwich structure part, such as ABS/PC/ABS. This means that the molded part has two layers, one is skin layer (ABS) and the other is core layer (PC). Undoubtedly, this sandwich structure should possess good plating quality than PC/ABS blend, due to the skin layer of 100%ABS in sandwich structure. There is a little literature to study the physical properties of sandwich structure part. Therefore, we investigated the plating, mechanical, and thermal properties for both sandwich structure part and blend part.
The composition of PC/ABS blend is homogenous in all the part. But, the composition of sandwich structure molded by co-injection molding is different at different locations. This represented different physical properties at different locations. Here, we chose a composition, 50%ABS/50%PC, to represent the co-injection molded part. There are four blends, ABS、70%ABS /30%PC、30%ABS /70%PC and PC in this study.
Twinshot co-injection molding machine was made by CLF, Taiwan, in 2005. PC and ABS were synthesized by Chi-Mei. The physical properties included the mechanical properties (Tensile, Flexural, Impact, and Hardness), thermal properties (HDT, TGA, and DMA), morphology structures, weight change, and plating quality. The plating quality included the thickness of plating layer and adhesive between plating layer and plastic.
The results indicated that the mechanical properties of sandwich structure part obeyed additive rules, such as tensile strength and modulus, breakage elongation, flexural strength and modulus, Impact strength. Rockwell Hardness has a synergy effect, which value was twice of additive value. Molded parts showed warpage in co-injection molded part, whereas, all blends showed that there were no warpages.
The HDT of ABS is 86.0℃ and that of PC is 138.4℃. The HDT of co-injection molded part is 104.7℃, which indicated an addition effect. There were two decomposition temperatures (ABS 416℃, PC 514℃) for co-injection molded part in TGA, which indicated two different materials. DMA also indicated there were two Tg. For plating pretreatment, the surfaces of ABS and co-injection molded part showed same morphology structures by SEM, which showed almost same number and size of pore distribution. The number of pore decreased in PC/ABS blend when PC amount increased. The higher the mold temperature is, the larger the pore size is.
Under same plating conditions, molded part made by sandwich structure, ABS, and 70%ABS /30%PC were plated very well, whereas, part made by PC and 30%ABS /70%PC were not plated at all. The thickness of plating of ABS at 60℃(17.8 μm) was larger that at 90℃(15.0 μm).
The adhesive between plating layer and plastic, the part made by sandwich structure, ABS, and 70%ABS /30%PC were passed by Cross Cut Tester, the plating layer were stuck in the plastic. The results are same for the part made by sandwich structure, and ABS under tensile and flexure broken testing. The part made by 70%ABS /30%PC showed a split layer between plating layer and plastic under tensile and flexure broken testing. Under HDT testing, when reaching it HDT temperature, the plating layer of part made by ABS, or 70%ABS /30%PC showed thermal expansion, whereas, the plating of sandwich structure showed no affect.
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