Experimental Study of the Meltblowing Process

Abstract

High-speed digital imaging techniques and web measurements were used to investigate the meltblowing (MB) process. We evaluated fiber diameter, fiber orientation, fiber entanglement, fiber velocity and fiber acceleration between the die and collector. Three processing variables were studied: primary air pressure, die-to-collector distance and collector surface speed. Although results of this investigation are somewhat preliminary, they provide fundamental information about the MB process and increase our understanding of it. Introduction Meltblowing (MB) is a fast, chaotic and complicated process. These features make it difficult to study the MB process theoretically as well as experimentally and most researchers have simply studied the effects of resin and process variables on web structure or web properties. Some researchers, however, have reported on-line measurements during MB [1–9]. Bansal and Shambaugh measured fiber temperature during single-hole MB using an infrared camera [1]. Wu and Shambaugh measured fiber velocity using laser Doppler velocimetry during single-hole MB [2]. Shambaugh and others reported experimental measurements of fiber motion and fiber diameter using a single-hole die [1–7]. Multiple-exposed photographs using conventional film were produced with a strobe light in a dark room to study fiber motion and single-exposed photographs were used to estimate fiber diameter. The exposure duration of the strobe light (50 μs), however, was not short enough to eliminate image blur and obtain sharp images so the primary air velocity used during MB was low (17–55 m/s). Milligan and Utsman used a similar film-based photographic technique to investigate MB using a 30-hole die [8]. Bresee and Yan used a video imaging technique to investigate the dynamics of web formation at the collector of a 600-hole MB line [9]. Measurements of the dynamics between the die and collector of a high-speed commercial-like MB process would be expected to be especially desirable for understanding MB. To directly observe dynamic motions during this fast process, it is necessary to use a short exposure time to freeze motion in each image and a high framing rate to resolve fast fiber motions. We used a high-speed digital camera from Vision Research Inc. to acquire images as rapidly as 1,000 frames/s. The camera produced image frames with a spatial resolution as great as 512×512 pixels and 8-bit gray level resolution (256 gray levels). Electronic shuttering of the camera provided exposure times as short as 50 μs/frame. To obtain exposure times shorter than 50 μs or to obtain multiple-exposed images, a high-speed pulsed laser from Oxford Lasers, Inc. was used for illumination. The laser produced 100 watt peak power at 805 nm and pulse durations as short as 1 μs were synchronized with the camera.