Embossing Pressure Effect on Mechanical and Softness Properties of Industrial Base Tissue Papers with Finite Element Method Validation

Abstract

Embossing is a converting process in which the surface of a tissue paper sheet is changed under high pressure, allowing different functions. In this work, the authors intend to study how the embossing pressure affects the main properties of tissue paper, using a laboratory embossing system. An optimum pressure was achieved at 2.8 bar to this embossing laboratory set-up. The effect of pressure when densifying the paper sheet gives it a gain in mechanical strength but no differences in terms of liquid absorbency. The two embossing patterns present different behaviors but both evidence losses in mechanical and softness properties. On the other hand, the finite element method (FEM) does not show clear evidence of how the pressure affects the paper strength. For the deco die, it is possible to observe that the amount of yielding is slightly higher for lower pressure (2.4 bar), but this plasticity state parameter is very similar for 2.8 bar and 3.2 bar. For the micro die, FEM simulations of the manufacturing pressure do not show a considerable impact on the amount of plasticity state of the material; only for 3.2 bar, it shows a change in the pattern of the plasticity state of the paper during the embossing processes. In the end, to achieve a final product with excellent quality, it is important to make a compromise between the various properties.

Keywords: FEM simulation; embossing prototype; eucalyptus-based fibrous materials; mechanical properties; pressure; softness; tissue paper.

Figure 1

Scheme of the embossing process with pressure action effects.

Figure 2

Photographs of steel embossing plates: (a) deco embossing, and (b) micro embossing.

Figure 3

Model dimensions and boundary conditions.

Figure 4

Morphological characterization of the two base tissue paper samples.

Figure 5

Results obtained for: (a) apparent density and (b) tensile index with the pressure increase in the base tissue paper densification of the samples A and B.

Figure 6

SEM images of samples A and B at two magnifications (×100 and ×300), at pressures of 2.4, 2.8, and 3.2 bar. The measurements presented in yellow corresponds to the height of the crepe wave.

Figure 7

Water spreading area as a function of time for the non-compressed (blue line) and compressed (green line) base tissue paper sample A. The insets show the spreading area in different instants of time.

Figure 8

Water spreading area as a function of time for the non-compressed (blue line) and compressed (green line) base tissue paper sample B. The insets show the spreading area in different instants of time.

Figure 9

Results obtained for tensile index with the pressure increase in the samples A and B with deco and micro embossing.

Figure 10

Results obtained for handfeel (HF) with the pressure increase in the samples A and B with deco and micro embossing.

Figure 11

The yield function for deco die for different pressures: (a) 2.4 bar, (b) 2.8 bar, and (c) 3.2 bar.

Figure 12

The yield function for micro die for different pressures: (a) 2.4 bar, (b) 2.8 bar, and (c) 3.2 bar.