Paper Technology Journal 17 - Voith

6
9
62
Fig. 6: Base paper
PPS roughness results – VPM4.
Fig. 7: SC Paper
PPS roughness results – VPM4.
Fig. 8: Missing dots (%) – VPM4.
Fig. 9-12: PrintFlex demonstrates superior
printability compared to standard press fabric.
PPS (microns)
Sheet Quality
Depending on the application, the surface
characteristics of the press fabric can
have a variable degree of influence on
paper properties. In shoe press systems,
a long-nip residence time will positively
affect dewatering dynamics, but can also
generate some negative sheet quality
issues. The effect of the press fabric surface
properties on paper quality has
gained a lot of attention in recent years,
especially with single- and tandem-shoe
press configurations.
It is also important to investigate the
influence of the fabric properties beyond
17/04
6
5
4
3
2
1
0
Very fine
batt
Medium
batt
PrintFlex P
7
PPS (microns)
1.50
1.25
1.00
0.75
0.50
0.25
0
Very fine
batt
Medium
batt
PrintFlex P
to the end user. Finished paper quality
issues, such as missing dots, can often
be linked to the surface characteristics of
the press fabrics used. Base and finished
sheet properties were evaluated during
the pilot machine trials. PrintFlex P gave
improved PPS results for both the base
and finished paper (Figs. 6 and 7). The
results also confirmed the clear correlation
between the press fabric surface
characteristics and paper smoothness.
Understanding the influence of the press
fabric on finished paper properties has
become an essential segment of Voith
Fabrics’ continued research and development
work.
10 11
8
Missing dot area, top side (%)
7
6
5
4
3
2
1
0
Very fine
batt
Medium
batt
PrintFlex P
The paper was then submitted for missing
dots evaluation (Fig. 8). As expected,
the ‘medium batt’ fabric had the highest
area of missing dots. PrintFlex P gave an
improvement of over 30 % against this,
with measurable benefits also seen
against the ‘very fine’ fabric.
From a comparison of standard press
fabrics and PrintFlex P (Fig. 9), results
taken from paper made in commercial trials
has confirmed that a reduced fiber
impression within the press nip (Fig. 10),
contributes directly to a smoother sheet
surface profile (Fig. 11) and a significant
improvement in measured printability
(Fig. 12).