| Summary: | 博士 === 逢甲大學 === 紡織工程所 === 95 === The aims of this dissertation are to investigate the influence of the applied electrostatic conditions on the fiber web uniformity for carded-web nonwoven process. In this study, besides the investigation of methods for electrostatic elimination during carding process, the feasibility investigation of the electrostatic method, which was applied on the carding process to improve the uniformity of carded-web, was continued to apply for different types of fiber, so as to understand the mechanism of electrostatic carding with the aid of modified measurement for roller fiber loading and fiber web uniformity.
The results showed 0.8 d and 2 d PET fibers would generate a few negative charges after the tribo-electrification of carding, and the surface potential on worker increases in negative potential when the negative voltage applied to working roller. 0.8 d PET fiber (about 100 to 250 volts) generates more charges than 2 d one (tens of volts) after carding under the equal weight of fibers due to its bigger surface area. Nylon 6 and PP fiber generates a large number of positive charges after the tribo-electrification of carding, and the maximum value for Nylon 6 and PP fiber could reach to14 kV and 4 kV, respectively. The original measured surface potential on working roller would be neutralized by the applied negative voltage. Thus, the static electricity caused by the friction during carding process can be eliminated effectively by the combination of application of static electricity to carding machine, environmental humidity control, and installation of electrostatic eliminator in suitable place for carded nonwoven process, and it would help to smooth the process.
Additionally, it was found that the change of fiber loading on working roller depended on the polarities in tribo-electrification process and ones that the static electricity was applied on. After the application of negative static electricity, the most decreasing percentage of the fiber load on 4th worker is about 5 % for 2 d PET fiber, and Nylon 6 and PP fibers can reach to 21~31 % and 9 % of increasing percentage, respectively. It signified that the electrostatic method affected the uniformity of fiber web. When the polarities between the fibers and the applied static electricity to working roller are opposite, the fiber transformation from cylinder to working roller and doffer would increase. Thus, the electrostatic application increased the carding efficiency and basis weight of fiber web. The basis weight and image gray value of Nylon 6 fiber web raised 12.3 % and 4.6 % respectively at application of –2 kV, and the CV of image gray value reduced to 9.5 % from 10.8 %. The basis weight and image gray value of PP fiber web raised 17 % and 16.2 % respectively at application of –2 kV, and the CV of image gray value reduced to 13.4 % from 19.3 %. Besides the increasing of the throughput of carding machine and the fiber web uniformity, the electrostatic method lifted the ratio of MD/CD tensile strength of nonwoven fabric as well. The surface potential of working roller increased slightly with increasing cylinder speed for 2 d PET fibers, and then the fiber web uniformity would be improved. However, the fiber loading decreased with increasing cylinder speed after application of negative static electricity of worker roller. With the narrow of the setting between cylinder and working roller, the fiber loading of worker, fiber web uniformity, and ratio of MD/CD tensile strength of nonwoven fabric would increase, but the initial discharge voltage and average surface potential of worker decrease.
On the experiment of application of positive static electricity on the 4th working roller for 2 d PET fiber, the use of opposite polarity of static electricity could improve the carding performance. Furthermore, the application of opposite polarity of triboelectrical one of fiber would improve significantly the fiber web uniformity. The basis weight of fiber weight increased 3.6 and 1.2 g/m2 for 0.8 d and 2 d PET fibers, respectively, and increased 3.8 and 3.6 g/m2 for Nylon 6 and PP fibers as well, respectively. On the experiment of application of positive static electricity on the 4th working roller for 2 d PET fiber, the use of opposite polarity of static electricity could improve the carding performance. Furthermore, the application of opposite polarity of triboelectrical one of fiber would improve significantly the fiber web uniformity. The basis weight of fiber weight increased 3.6 and 1.2 g/m2 for 0.8 d and 2 d PET fibers, respectively, and increased 3.8 and 3.6 g/m2 for Nylon 6 and PP fibers as well, respectively. The CV of gray values of divided images could decrease to 8.5 % from 11 % for both of 0.8 d and 2 d PET fibers, 9.3 % from 11 % for Nylon 6 fibers, and 12 % from 19.2 % for both of PP fibers. For strength of nonwoven fabric, the ratio of MD/CD strength increased to 2.69 from 2.57 for 0.8 d PET fiber, 4.43 from 3.71 for 2 d PET fiber, 3.26 from 2.91 for Nylon 6 fiber, and 3.74 from 3.35 for PP fiber.
In this study, it was found that area divide of image of fiber web can reflect the fiber web uniformity objectively, and reduce the error of brightness of image due to the variation of illumination during image capture. The whole results showed that the appropriate electrostatic conditions really could improve the carding performace and fiber web uniformity, and increase the throughput of carding process.
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