聚烯類低溫正溫度係數複合材料之製備與研究

The preparation and investigation of polyolefin low temperature positive temperature coefficient composites

王于瑞(Yu-Jui Wang)

指導教授 ： 黃繼遠

大同大學/工程學院/材料工程學系所/碩士(2007年)

摘要

本研究將碳黑與乙烯醋酸乙烯酯(EVA)基材以適當加工條件進行混煉進而製備成低溫正溫度係數(PTC)複合材料。並探討EVA種類、碳黑種類、碳黑含量、混煉加工條件、化學交聯方式及交聯劑添加量、EVA基材之電漿前處理條件、添加第二相基材含量等加工因素對EVA/CB複合材料其電性性質表現之影響，包括了常溫電阻值、正溫度係數(Positive Temperature Coefficient, PTC)強度及負溫度係數(Negative Temperature Coefficient, NTC)強度之變化；並對經各種改質之複材進行表面型態和物理性質的測試分析。由交聯EVA/CB複材之變溫電阻值量測及表面型態觀察發現，複材進行化學交聯後確實有交聯結構之形成；且於高交聯劑添加量(2phr)下，交聯複材確實可利用交聯結構性來大幅提升PTC強度且幾乎完全消除NTC行為，然而常溫電阻值卻大幅地提昇並且PTC行為轉換溫度提前、轉換程度之效率衰退，可能由於交聯結構之生成使非晶區域增加、高分子鏈於更低溫區間即開始滑移所致。因而嘗試先將基材進行電漿前處理再製備成交聯複材，期望可改善基材與碳黑間之黏著度、相容性，進而使常溫電阻值下降。但對電漿前處理基材與碳黑所製備之複材而言，其電性表現些許類似於交聯複材，因此將電漿處理搭配化學交聯改質將更使上述電性表現加層明顯化。此外嘗試添加第二相基材(LLDPE)至EVA/CB複材中，利用兩相不相容特性來抑制碳黑隨分子鏈滑移之移動程度。實驗發現不同之加工方式、LLDPE與EVA含量比例、碳黑含量皆會影響、改善EVA/LLDPE/CB複材之電性表現；且發現第二相基材(LLDPE)添加對交聯EVA/CB複材更有顯著之改善效果，包括了：降低常溫電阻值，延遲PTC行為之作動轉移溫度，利用二階PTC特性來提升PTC強度，延遲並消除NTC現象之產生。

關鍵字

正溫度係數 ； 導電性複合材料 ； 熱敏電阻 ； 乙烯醋酸乙烯酯 ； 碳黑

並列摘要

In this study, the low temperature positive temperature coefficient (PTC) composites were produced by blending the carbon black (CB) particles, which concentration is above the critical volume fraction, with Ethylene-vinyl acetate (EVA) as the semi-crystalline polymer matrix in proper processing condition. The effects of the EVA matrix type, the CB type, the relative content between EVA and CB, the blending condition, the processing method of chemical crosslinking, the crosslinking agent content, the condition of plasma treatment, and the secondary matrix content in immiscible-blend composites on the electrical performances of PTC composite were investigated. The change of electrical performances includes the variation of room temperature resistance, PTC and NTC effect. After that various analysis of the morphology, physical properties were carried out on the various EVA/CB composites. In the investigation of chemical crosslinking of EVA/CB composites, the morphology of the crosslinked structure was observed, the PTC intensity increased obviously, and the NTC effect was almost eliminated in the crosslinked composites with high BPO content (0.2phr), whereas the room temperature resistance increased and the switching efficiency /temperature (Tsw) decreased greatly. It was perhaps due to the crosslinking reaction expanded the amorphous region, and made the polymer chains move in earlier temperature region. In addition, EVA pellets were pretreated with different plasma treatment conditions then blended with CB to be expected for enhancing the compatibility and adhesion between polymer chains and CB particles and lowering the room temperature resistance. However, the observed morphology and the electrical performances were slightly similar to the crosslinked EVA/CB composites.
In addition, the PTC composite was prepared by melt-mixing of immiscible powder blends of EVA, LLDPE (Linear low-density polyethylene), and CB particles. Three major factors-the weight ratio of EVA and LLDPE, the carbon black content, and the processing method had remarkable effects on electrical performances of the immiscible blends composite. With high EVA/LLDPE weight ratio, the EVA formed as the continuous phase, where CB particles were selectively located, and the LLDPE formed as the dispersed phase, the PTC effect of the uncrosslinked blends composite, mainly caused by the melting of EVA crystallites, was similar but slight decreased to those of CB-filled neat EVA composite and the NTC effect was delayed to higher temperatures and even eliminated. Even the interlocking, co-continuous structure might be formed at the lower EVA/LLDPE weight ratio or in the crosslinked blend composite; both phenomenon of suppressing the PTC effect and delaying the NTC effect became more remarkable. In addition, the room temperature resistance could also be decreased more obviously.

並列關鍵字

positive temperature coefficient ； conductive composites ； thermistor ； ethylene-vinyl acetate ； carbon black

參考文獻

1.Brogly M., Nardin M., Schultz J., J. Appl. Polym. Sci., 64(10), 1903–1912 (1997)

2.Arsac A., Carrot C., Guillet J., J. Appl. Polym. Sci.,74(11), 2625–2630 (1999)

6.曹耕毓, 大同大學材料科學與工程學系碩士論文, 耐高電壓PTC奈米高分子複合材料之製備與研究, July (2005)

7.胡伯謙, 大同大學材料科學與工程學系碩士論文, 聚烯類低溫正溫度係數熱敏電阻之開發與研究, July (2006)

9.Lux. F., J. Mater. Sci., 28, 285 (1993)