A Celli, in cooperation with inventor Guglielmo Biagiotti,
has developed
what it calls 'Memopaper®', so named
because the paper
'memorizes' an embossed pattern before final drying on the paper
machine
By Guglielmo Biagiotti
To make Memopaper®, the web is formed and dried
in the conventional way to a dry content of 40-50% or more. Then
the paper is removed
from its support and is passed through the nip formed by a two
steel embossing rollers engraved with a very particular pattern.
After embossing the wet embossed paper is passed through a drying
unit which can be any known system and the water content is lowered
to a level at which the paper is considered dry.
Drying the paper in this way after it has been embossed
enables it to retain
formation in a very stable way (like ironing a shirt after applying
starch on it). It creates in the web a kind of 'memory' (hence
the trademark Memopaper®, which
had been filed to
protect the name of the product obtained by the patented process).
In other words, with this new process the web structure contains
millions of paper springs which make it return to its initial
shape when it is put under tension and then released. The paper
can then either be directly wound on rollers (from patents) or
can be wound after calendering (10) which improves its surface
quality.
The advantages expected from this invention are
listed below: a significant increase in paper bulk; lower fibre
consumption for the same bulk; reduced power to dry the paper
for the same bulk; increased water absorbency; structured aspect
of the web; consistent quality over the life of the sheet; higher
production for the same bulk of paper compared to a conventional
sheet; zero risk of fire due to blade change or blade-yankee contact;
and reduced paper dust generation during paper production and
converting.
The aspects that can be improved in this invention
are: hand feel is not as smooth as with a conventional web; there
is limited stretch in the web; and very high speed running has
not been tried.
EXPERIENCES
The experiences on which the above considerations are based
have been carried out in the laboratory of the Paper Department
of Karlstad University in Sweden, which is very well equipped
to study paper problems. It has the necessary laboratory equipment
and also a machine which can produce sheets of paper at up to
600 m/min and a calender which can be used either to reduce water
content in the web or to calender it at the end of the process.
It also has a big heated roller to dry the previously prepared
sheet, simulating the effect of the yankee dryer on the paper.
The only equipment missing was a small embossing
unit but this need was fulfilled by preparing a dedicated unit
in a reduced scale with the characteristics needed in the real
embossing unit. This was equipped with two different embossing
patterns in two different series of tests to evaluate its influence
in the finished web.
Multiple tests were done with different parameters
in the paper and in the process and the results found analyzing
the webs produced confirm that the patented process allows: 25-30%
less drying power consumption; 15-25% less fibre consumption;
increase of 25-50% in web caliper at the end of the process.
The next step was to find a real paper machine to
modify in order to
produce Memopaper® on a real industrial
scale to compare real
data with lab results.
MILL AGREEMENT
After a long search an important mill was found in Europe which
showed interest in the project and made available one of its paper
machines to support the modifications needed. The machine was
of the wet crepe type because it was equipped with a first drying
yankee cylinder and a second drying system to completely dry the
web and was modified with the addition of an embossing unit
A special steel-to-steel embossing unit was installed
in the paper machine
between the first and second drying systems. This unit is different
from those used in converting because of the pattern, which is
characterized by a number of points (51.28/m2) and a depth of
engraving of 1.02 mm in both rollers. In addition, the rolls open
much more than usual: 80mm minimum compared to the standard 5-6mm.
Other needs for these particular rollers were a
very careful finishing of the engraving surface after machining
and an effective cleaning system.
The quality of the finished sheet can be strongly
influenced by the embossing pattern,fibre mix and chemical additives.
After the installation of the embossing unit, which
took 2.5 days, the
paper machine produced Memopaper® to
convert as rolls
and folded products for 4.5 days. During production, conventional
paper was produced at first to be used as a reference. This was
followed by production of the new web with and without the use
of a creping blade on the first drying section (yankee) and different
parameters were monitored.
Unfortunately the machine made available for experiences
was very old and the web produced using recycled fibres had various
limits in basis weight and quality.
RESULTS
The results obtained are summarized in the charts below. These
confirms: an increase in web caliper of about 59%, or a proportional
reduction in fibre consumption to obtain the same caliper; an
increase of about 40% in water absorbency; the appearance of the
web, in which the embossing pattern is repeated. The run in the
new configuration was too short to confirm the other expected
advantages.
The experience reported in this article has been
made possible by
putting together some ideas of Dr Memo Biagiotti and the resources
made available by A Celli Paper, an important Company operating
in the field of paper machines. Biagiotti, after a long experience
as technical director of Fabio Perini SpA, filed a number of paper
machine patents involving the inclusion of embossing technology,
very common in converting. A Celli invested all the needed financial,
human and technological resources. TW
