| Polytetrafluoroethylene(PTFE) is called as "plastic king", possessing excellent overall performance, it is widely used in many fields such as chemical, energy, electronics, aerospace industry, medical equipment and so on. Some drawbacks of this polymer are its poor creep resistance, poor wear and radiation resistances, limiting its application in some areas such as seal and space environment. In particular, its low surface energy and poor hydrophilicity restrict its application in filter, dyeing, finishing fields. Improving its surface property was essential for many applications. The hydrophilic monomer acrylic acid(AAc) was grafted onto the surface of PTFE microporous film treated by low temperature plasma for improving hydrophilicity, the product was denoted as PTFE-g-PAAc. Firstly, the low temperature plasma treatment-induced radicals on the PTFE microporous film were investigated by an electron spin resonance(ESR) spectroscopy. The effects of treatment atmosphere, treatment time and radio frequency(RF) power on the formation of radicals were compared. Additionally, the concentration of radicals and storage condition were optimized to successfully graft AAc onto the surface of PTFE microporous film. The results showed that peroxyl radicals were the free radicals existed in PTFE microporous film induced by low temperature plasma treatment at room temperature, which were relatively stable, even after decay at room temperature for 180 d, 85.0% of the radicals were still retained. In general, low temperature plasma treatment in Ar treatment atmosphere, RF power at 100 W, a time of 2~4 min was suitable for grafting AAc onto the surface of PTFE microporous film. Simultaneously, the effects of reaction time, reaction temperature, and monomer concentration on the degree of grafting(DG) were investigated and compared. Chemical structure, crystal structure, surface morphology, hydrophilicity and water flux of PTFE microporous film before and after modification were characterized. The results showed that the hydrophilicity of PTFE-g-PAAc microporous film was obviously improved by grafting reaction. After grafting 10.0% AAc, the water contact angle decreased from 138.8° to 81.6°. However, the water flux greatly decreased with the increase of DG. In general, a suitable DG should be confirmed to obtain good hydrophilicity and water flux for PTFE microporous film.In addition, for its excellent dielectric properties, the PTFE film coated with Cu has a potential application in flexible printed circuit board which can be widely used in navigation equipment, aircraft instrumentation, digital cameras, LCD TVs, laptops and other electronic products. In this work, the PTFE film was grafted with AAc and the PTFE-g-PAAc film was coated with a layer of copper without activation of Pd, the product was denoted as PTFE-g-PAAc-Cu. The effects of time and temperature for electroless copper deposition on the performance of the copper layer were investigated. The surface topography, crystal structure, resistivity and surface resistivity were investigated. Additionally, the adhesion between the grafted PTFE film and copper layer was also evaluated. The results showed that the temperature of 40 °C and time of 30 min was a suitable condition for electroless copper deposition, the gloss of copper layer was preferable and copper layer had no pores. The copper was uniformly deposited on the surface of PTFE-g-PAAc film assured by XRD, SEM, and AFM analysis. 3M taping method assessment according to ASTM D3359 indicated that the copper layer was tightly bonded on the grafted PTFE film so that 3M tape could not tear down the copper layer from the surface of grafted PTFE film. Electrical performance showed that the surface resistance and resistivity of PTFE-g-PAAc-Cu decreased to 1.27×10-2 Ω/sq and 5.01×10-5 Ω?cm, respectively. The conductivity was improved from a level of insulator to a conductor(10-6~10-3 Ω?cm), which could be potentially used as the flexible copper clad. |
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