Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR PRODUCING EXTENSIBLE FAPER
FIELD OF THE INVENTION
This invention relates to a method for producing
extensible paper and a plans for implementing the method.
DESCRIPTION OF THE PRIOR ART
U.S. Pat. No. 3,454,463 discloses a method of
subjecting newsprint paper to controlled compressive .
shrinking including the features of passing the wire side
of a web in contact with the moving smooth surface of a
mechanical compactor and shrinking the newsprint web to a
value substantially above the desired value and then
stretching the web to the desired value.
EP-A-0631014 discloses a process for making soft
tissue products.
An object of the invention is to provide a method
enabling paper to be produced with a high degree of
strength while at the same time with an extensibility both
in the longitudinal direction and in the transverse
direction of practically the same order of magnitude.
A further object of the invention is to provide a
method enabling paper to be produced with a continuous
plant.
A further object of the invention is to provide a
method enabling producing paper with smooth surface in
order to improve its printability characteristics.
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BRIEF SUN~ARY OF THE INVENTION
These and further objects which will be apparent
from the ensuing description are attained according to the
invention.
According to the present invention, there is
provided a method for producing extensible paper,
comprising the steps of:
feeding a mix oi= vegetable fibers to a kneader
member,
mixing said mix with water in said kneader,
beating said mix containing water by rubbing the
vegetable fibers in a multistep unit to obtain a pulp
having a degree of beating of at least 30° SR,
transferring said beaten pulp into a flow chest,
feeding said beaten pulp from said flow chest
onto a paper web formation cloth with reduction of the
water percentage by gravity and vacuum and forming a paper
web,
pressing said paper web with further reduction of
the water content of said paper web,
initial drying of said paper web to a constant
moisture content of between 15o and 65%,
compacting said paper web between at least a pair
of rollers, one of said rollers being a hard material and
having circumferential surface ribs and driven at first
speed, and the other is of soft material with a smooth
surface and driven at second speed,
said second speed being less than said first
speed,
final drying of said paper web to a moisture
content of between 4$ and 150, and
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glazing said paper web.
According to the yresent invention, there is also
provided a plant for producing extensible paper comprising:
a kneader member where vegetable fibers are fed
and mixed with water,
a beating station for beating by rubbing the
vegetable fibers in a multistep unit of discs of lavic
material,
a flow chest wherein the beaten fibers are
transferred,
a paper web formation station with a cloth which
receives said beaten pulp and reduces the water percentage
of said beaten pulp to form a paper web,
a pressing station receiving said paper web for
the subsequent further reduction of the water content,
a first drying station receiving said paper web
from the pressing station for drying said paper web,
a compacting station comprising at least a pair
of rollers for compacting said dried paper web, one of said
rollers is a rubber material, the other roller which is of
hard material, at least one of the hard rollers being
provided with a plurality of circumferential surface ribs,
a second drying station for further drying said
dried paper web, and
a glazing station for glazing said dried paper
web.
BRIEF DESCRIPTION OF THE DRAWINGS
A preferred embodiment of the present invention
is described hereinafter with reference to the accompanying
drawings, in which:
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FIG. 1 is a schematic view of a plant for
implementing the method of the invention;
FIGS. 2, 3, 4 and 5 are schematic views showing
different rollers used in the preforming stage;
FIG. 6 is a schematic view showing the rollers
used in the compaction stage.
DESCRIPTION OF PREFERRED E1~ODIMENTS
As can be seen from the figures, the plant for
producing extensible paper comprises essentially a high
density kneader 1 consisting substantially of a cylindrical
tank 2 with an inverted frusto-conical base and internally
housing a conical impeller 3 comprising on its surface a
helical projection.
The kneader 1 is connected to a storage vat 4
provided with a stirrer 5 and connected to a beating
station 6 formed from beating units 7 of lava disc type
alternating with storage chests 8. The exit from the last
beating unit 7 is connected to a further high density
beating unit 7' of perforated ring type connected to a
storage vat 9 communicating with a flow chest 10 feeding a
station 11 in which the paper web is formed. This station
comprises a cloth 12 taut between two return rollers 13 and
arranged to subject the pulp of water and fibrous raw
materials to progressive water extraction by means of
gravity and vacuum.
The downstream end of the paper web formation
station 11 leads to a pressing station 14, downstream of
which there are provided an impregnation station 23 and a
successive preforming station 15.
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Downstream of the preforming station 15 there is
provided a drying station 16 of hot roller type which
ensures a constant moisture content of the paper web of
between 15o and 650, preferably 500, and a subsequent
compaction station 17 comprising pairs of counter-rotating
rollers of different type and surface consistency, driven
at different speeds and able to compact the web both
longitudinally and transversely. In particular the upper
roller 37 of each pair is of metal, comprises a plurality
of surface circumferential ribs 38 and rotates at greater
speed than the corresponding lower roller 36 which is in
rubber and has its surface smooth.
The exit of the compaction station 17 is
connected to a further drying station 18, which is
connected to a glazing station 39 connected to a successive
paper winding station 19.
The drying station 18 ensures a water content of
the paper web of between 4o and 150, preferably 100.
The purpose of the glazing station 39 is to
improve the printability and bondability characteristics of
the extensible paper obtained and operates with a linear
load of between 10 and 100 kg/cm, preferably between 50 and
52 kg/cm.
Between the drying station 18 and winding station
19 there can be inserted a further impregnation station and
a further drying station for subjecting the paper web to
treatment to improve its printability characteristics, if
required.
The plant according to the invention also
comprises a series of controls and automation devices which
ensure that the operating cycle is correctly implemented
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and which will be mentioned as required during the course
of the following description.
The operation of the plant according to the
invention will now be described with reference to the
passage of the paper web under formation through the
successive stations.
The bales of f fibrous raw material are fed to the
high density kneader 1 together with a predetermined
quantity of water for their mixing. Here the pulp is
kneaded, mixed with water and particular substances added,
the purpose of which is to increase the ultimate strength
of the fibres, to homogenize the water and fibre pulp and
give special characteristics to the paper obtained.
In particular the fibrous raw material consists
of vegetable fibres which can be long-fibre cellulose,
short-fibre cellulose or other fibres obtained from
vegetables other than wood (cotton linters, hemp, flax,
esparto, kenaf). The different raw materials can be worked
on the same line or preferably on different lines.
Rotating the impeller 3 results in progressive
kneading of the fibrous raw material, which preserves the
length of the original fibres and results in their intimate
mixing with the water and the additives fed to the kneader.
In particular, the additives used can include starches,
which are able to bind the fibres together and increase
their ultimate strength, or carboxymethyl-cellulose (CMC),
the purpose of which is to disperse the fibres and hence
prevent their coagulation, or synthetic and/or lactic
resins the purpose of which is to bind the fibres together
to form a sort of elastic t~ond.
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A pulp of fibre, water and additives leaves the
kneader 1 with a dry content of about 150, this pulp being
fed to the successive beating station 6 to be subjected to
the action of the lava disc beating units 7, which work the
fibres substantially without cutting them, but by hydrating
them and by rubbing and conferring particular
characteristics on the pulp. As a result of this treatment,
the fibres are modified such as to facilitate their
consolidation and to form a continuous and homogeneous
structure, essential for the characteristics which the
final product has to present.
The degree of beating of the pulp can be
determined on the basis of objective parameters measured in
SR (Shopper Reagler) units, and according to the present
invention the pulp leaving the beating treatment must be
between 30° SR and 60° SR according to the weight in grames
of the paper to be obtained.
At the exit from the last beating stage the pulp,
which as stated is between 30° SR and 60° SR, is fed into
the perforated ring beating unit 7', which operates at a
density of about 20o and the purpose of which is to hydrate
the fibres, to swell and curl them. The pulp is then fed
into the storage vat 9 and from here into the flow chest
10, from which with a dry content of about 0,5-1o it is
poured onto the underlying cloth 12 of the paper web
formation station 11.
On the initial ~~ortion of this cloth the pulp
tends to progressively eliminate water, firstly by gravity
and then by suction, until at the exit end of the cloth it
has a dry content of about 18%.
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The paper web 20 leaving the station 11 passes to
the pressing station 14 between pressing rollers 21 and
felts 22, losing water to attain a dry content of about
35 0 .
The paper web then passes to the impregnation
station 23 where it is treated with a solution of various
additives the purpose of which is to improve the
extensibility characteristics of the paper and/or to
improve the production technology. This impregnation is
preferably effected by a spray device but can also be
effected by other systems, for example by passing the
forming paper web through tanks containing the impregnation
solution. In either case the quantity of impregnating
substance is controllable, with considerable advantages
both in terms of cost of the substance used and in terms of
exact determination of said substance.
The web impregnated in this manner is subjected
to preforming treatment in the station 15, in which one or
more preforming units are provided. These can be all
identical or different. In particular, each preforming unit
can comprise:
an upper roller 24 with a shaped profile and a
smooth roller 25 with traditional smooth felt 26 (FIG. 2);
a smooth upper roller 27 and a smooth lower
roller 28, between which a felt 29 is interposed having an
external marking structure to suitably deform the forming
paper web interposed between said felt and the upper roller
27 (FIG. 3)~
an upper roller 30 with a shaped profile and a
smooth lower roller 31 (FIGa. 4);
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a smooth upper roller 32, a smooth lower roller
33, a traditional felt 34 and a felt 35 of marking
structure interposed between the felt 34 and the upper
roller 32 (FIG. 5).
The use of several preforming units, which can be
identical or different, enables profiles practically of any
design to be obtained on the paper web, and in particular
designs not obtainable with a single preforming unit.
The paper web preformed in this manner is dried
in the station 16 to a dry content of about 50-60o by
passage through hot roller or a hot air tunnel, before
being subjected to compaction.
In passing from the pressing station 14 to the
compaction station 17 the roller speed is regulated so that
the paper is subjected to a tension such as to undergo
maximum longitudinal elongation compatible with its
ultimate strength, in order to obtain transverse
contraction of the paper, with a corresponding reserve of
transverse extensibility.
Between the preforming station 15 and the drying
station 16 there can be interposed a drying and/or fusion
station, preferably of infrared type.
In the station 17 the compaction, which occur s
both in the longitudinal and in the transverse direction,
is effected by passing the paper web between a pair of
rollers (FIG. 6), of which the lower roller 36 is of rubber
and is driven at a certain speed, whereas the upper roller
37 is of metal and comprising a plurality of surface ribs
38, for example circumferential, and rotates at greater
speed. Because of the pressure effect and the configuration
of the metal roller 37, cooperating with the rubberized
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surface of the other roller 36, the paper web is subjected
to undulation in the transverse direction and at the same
time, because of the different roller speeds, to a braking
action by the rubberized roller and to a consequent
compaction in the longitudinal direction.
On termination of this compaction stage the paper
is subjected to further drying in the station 18 to achieve
a dry content of about 85%, preferably 900.
It should be noted that in passing from the
10 compaction station to the exit of the drying station the
roller speed is regulated (substantially constant) such
that no traction stress is applied, so that the
longitudinally compacted paper loses none of its
longitudinal extensibility.
At the exit of t;~e drying station 18 the paper
web is subjected to glazing in the station 39.
The paper web obtained in this manner, in
particular because of the bE:ating, impregnation, preforming
and compaction treatment, presents a high degree of
mechanical strength and of extensibility both in the
longitudinal direction and in the transverse direction, of
the order of at least 16o transversely and at least 200
longitudinally, for paper having weight for grams included
between 100 and 150 g/m2.
