Effect of processing parameters on the uniformity of adhesive meltblown web.

INTRODUCTION

Because of the ability to produce a nonwoven web with the polymer as the starting material, the melt-blowing technology has been studied by many researchers for producing good quality meltblown webs or developing new products (1-5). In our previous work (6), we produced an adhesive meltblown web on the pilot-scale melt-blowing equipment with the added accessory air and accessory air chamber shown in Fig. 1, using a low-melting-point copolyamide polymer resin as the raw material. The produced adhesive web can be used in such fields as clothing fusing interlining, special filtrations material binder. And webs produced with this method exhibit better quality, having pores of more uniform size and more regular shape, and finer and more uniform fibers. Also, in our previous work, effects of the main processing parameters, including the primary air pressure, the accessory air pressure, the melt throughput rate, and the die-to-collector distance (DCD) on the fiber diameter were investigated. In this article, we further investigate the effects of the above parameters on the uniformity of the web.

[FIGURE 1 OMITTED]

EXPERIMENTAL

Melt-Blowing Experiments

The melt-blowing equipments and the processing parameters used to conduct the experiments are the same as that used in our previous work (6). With all the processing conditions, 19 kinds of webs were produced.

Web Unevenness Measurements

The methods used to analyze the web uniformity are the subsample weight measurement and the subsample thickness measurement.

For every web kind, 100 subsamples were obtained randomly from the web sample. The subsamples were respectively weighed with the balance, and then the weight unevenness (coefficient of weight variation) was calculated. As the produced web is very thin, only smaller subsamples can lead to good analysis for the web uniformity. Therefore, a ring-knife with the diameter of 4 mm is used to cut the sample, and the obtained subsample has an area of 12.56 [mm.sup.2]. The balance used to weigh the subsamples is JN-B precise torsion balance, having the weight range of 0-5 mg and the scale of 0.01 mg. At the same time, the thickness of the subsamples is measured using the YG141D digital fabric thickness gauge having the range of 0.1-10 mm and the scale of 0.01 mm, and the thickness unevenness was calculated.

RESULTS AND DISCUSSION

The weight unevenness and the thickness unevenness for the 19 web types are listed in Table 1, together with the corresponding processing parameters.

TABLE 1. Weight unevenness and thickness unevenness of the
webs.

                   Processing parameters

Sample  Throughput rate   Primary   Accessory   DCD
          (g/min/hole)   air (MPa)  air (MPa)  (mm)

 1          0.0337         0.38      0.15       850
 2          0.0577         0.38      0.15       850
 3          0.0817         0.38      0.15       850
 4          0.1057         0.38      0.15       850
 5          0.0577         0.10      0.15       850
 6          0.0577         0.20      0.15       850
 7          0.0577         0.25      0.15       850
 8          0.0577         0.35      0.15       850
 9          0.0577         0.40      0.15       850
10          0.0577         0.22      0.18       850
11          0.0577         0.22      0.2        850
12          0.0577         0.22      0.22       850
13          0.0577         0.22      0.25       850
14          0.0697         0.35      0.20       850
15          0.0697         0.35      0.20       900
16          0.0697         0.35      0.20      1000
17          0.0697         0.35      0.20      1100
18          0.0697         0.35      0.20      1150
19          0.0697         0.35      0.20      1200

Sample    Weight unevenness   Thickness unevenness

 1             0.1404                0.0975
 2             0.2157                0.1077
 3             0.2672                0.1117
 4             0.5625                0.1434
 5             0.3230                0.1120
 6             0.2496                0.1109
 7             0.2278                0.0722
 8             0.2596                0.0872
 9             0.3088                0.1632
10             0.2480                0.1120
11             0.3499                0.1152
12             0.3986                0.1208
13             0.5529                0.1338
14             0.3993                0.1427
15             0.3880                0.096
16             0.3860                0.0944
17             0.3334                0.0827
18             0.3936                0.1364
19             0.4690                0.1683

Effect of Melt Throughput Rate on Web Unevenness

Figure 2 shows the effect of melt throughput rate on the web unevenness. It can be seen from this figure that the weight unevenness and the thickness unevenness increases, i.e., the quality of the web gets worse in terms of the uniformity, with the increased throughput rate. Our previous research work shows that the fiber diameters in the web increase with the increasing throughput rate (6). So, when the web basic weight keeps constant, the fiber number in the web decreases with the increasing fiber diameter, leading to the increasing web unevenness.

[FIGURE 2 OMITTED]

Effect of Primary Air Velocity on Web Unevenness

The primary air is the key element for attenuating the fiber. The air velocity increases with the increasing air pressure, so the air pressure recorded from the pressure gauge is used to delegate the air velocity. Figure 3 shows how the web unevenness changes with the varying primary air pressure.

[FIGURE 3 OMITTED]

Plots in Fig. 3 show that the web unevenness decreases firstly and then increases with the increasing primary air pressure. The fundamental reason is that the initial increasing primary air velocity leads to the decreasing fiber diameter, and then the decreasing web unevenness. However, when the air velocity increases continually though the fiber diameter decreases continually, the high velocity influences the path of fiber landing to the collector (the fiber departs from the spinning line at high level) and leads to more uneven fiber distribution in the web. This coincides with our previous research results (7).

Effect of Accessory Air Velocity of Web Unevenness

Figure 4 shows the effect of accessory air pressure on the web unevenness while other processing parameters are held constant. It can be seen from this figure that the web unevenness increases when the accessory air pressure increases over the observed range of the air pressure. In the melt-blowing experiment studied here, the accessory air is used mainly to help solidify the molten copolyamide filament and reduce the possibility of the fibers to cling together, so as to improve the web quality. Our previous research result shows that the web produced by using the accessory air exhibits more uniform appearance. However, when the accessory air velocity is too high, the fibers will be very disheveled and entangled before they land the collector, leading to an unevenness web. therefore, the accessory air velocity should not be very high.

[FIGURE 4 OMITTED]

Effect of DCD on Web Unevenness

Figure 5 shows how the web unevenness changes with the varying DCD. The plots in this figure indicate that the web unevenness declines firstly and then increases with the increased DCD. At about 1100 mm, the web unevenness presents the smallest value, i.e., the web quality is the best. When DCD is short, the fiber tends to cling to each other before collected on the collector surface due to the short solidifying time. However, when DCD exceeds a certain extent, the long travel time of the fiber before collection causes the fiber to entangle more severely, and the produced web presents to be more uneven. Therefore, the DCD should not be short and not be long for obtaining uniform web.

[FIGURE 5 OMITTED]

The plots in all the above figures show that the process parameters have a similar effect on the web weight unevenness and the web thickness unevenness, only the thickness unevenness level is lower than the weight unevenness level. The probable reason is that the web thickness is pressed with the heavy balance when measured.

CONCLUSIONS

In this study, we investigated the process parameters, including the melt throughput rate, the primary air pressure, the accessory air pressure, and the DCD, on the meltblown adhesive web uniformity in terms of the web weight unevenness and the web thickness unevenness. There are similar variation trends for the effects of the process parameters on the web weight unevenness and the web thickness unevenness, so both the weight unevenness and the thickness unevenness, so both the weight unevenness and the thickness. The web unevenness increases with increases in melt throughput rate. The web unevenness decreases firstly and increases later with the increasing primary air pressure. The web unevenness increases with the increasing accessory air pressure. The web unevenness decreases firstly and then increases later with the increasing DCD.

REFERENCES

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(2.) Y. Lee and L.C. Wadsworth, Polym. Eng. Sci., 30, 1413 (1990).

(3.) R.R. Bresee. Int. Nonwovens J., 13, 49 (2004).

(4.) A.Y.A. Khan, L.C. Wadsworth, and CM. Ryan, Int. Nonwovens., 7. 69 (1995).

(5.) D.H. Muller and A. Krobjilowski, Int. Nonwovens J., 10, 11 (2001).

(6.) X.M. Wang and Q.F. Ke, Polym. Eng. Sci., 46, 1 (2006).

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Xiaomei Wang, Qiming Zhao

Department of Textiles and Apparel, Wuyi University, Jiangmen, Guangdong 529020,

People's Republic of China

Correspondence to: Xiaomei Wang; e-mail: [e-mail]

DOI 10.1002/pen.21155

Published online in Wiley InterScience (www.interscience.wiley.com).

[C] 2008 Society of Plastics Engineers