Note: Descriptions are shown in the official language in which they were submitted.
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Method for the manufacture of a mat-like product
The present invention relates to a method as set forth in
the preamble of the appended claim 1 for the manufacture of
a mat-like product.
International publication No. WO 82/03359 published October
14, 1982 discloses a method for making a moldable mat from
wood fibers such that the wood fibers are intertwined with
thermally bondable binder fibers which bond the fibers
together upon melting and setting. The mat is formed by
using a so-called dry process on a moving belt by means of
an air flow, which transports the fiber: onto the belt and
travels through the mat. This is followed by a mat bonding
process by carrying t:he thus formed mat through an oven,
having a sufficientl.~T high temperature for softening the
binder fibers, which are of thermoplastic plastics
material, and bringing them in an adhesive state for
bonding the wood fibers to each other.
The use of wood fibers and other cellulosi_c fibers of
vegetable origin for manufacturing products made of fibers
is attractive in the sense that the question is about
reclaimable natural raw materials, which are abundantly
available, pleasant t=o handle as a mat=erial, and do not
create health hazard:. A fibrous mat manufactured from
these fibers is also an effective heat insulation. However,
this is the very feature that causes a problem in
manufacturing the product, if the above process is to be
employed. When treating the product in an oven, it is
namely necessary to g=_ve the oven a considerable length for
heat to penetrate also in the interior of a mat-shaped
product for bonding the fibers. If the purpose is to
manufacture products of considerable thickness, it would be
necessary to make the ovens unreasonably long for bonding
the mat properly also in its middle sections upon leaving
the oven. Another alternative would be a drastic increase
of temperature which would, however, lead to damages in
the surface structure of a product, since the thermoplastic
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fibers included therein would then melt or fuse completely
away as globular drops not capable of bonding the fibers
together and the mat would break up. It is obvious that
the above processes are not feasible _in terms of energy
consumption, either.
For eliminating this drawback, there i~~ known a method as
well as an apparatus, by means of which it is possible to
manufacture even very thick fibrous m<~ts of wood fibers
having an excellent heat insulation capability. Here
thermoplastic binder fibers acting as heat-activatable
binder material and intertwined wit=h vegetable-based
cellulosic fibers arE~ activated, i.e. ~~oftened already in
an air flow carrying the fibers to a forming platform by
setting the temperature of the air flow sufficiently high.
The heat insulation properties of the i_ibers will thereby
not be detrimental. Thermoplastic binder fibers bond wood
fibers to each other already at the manufacturing stage of
a mat. In practice, this facilitates the manufacture of
even a very thick mat, since fresh fibers bonding into a
mat can be stacked basically in quantities as large as may
be desired on top of a mat previously formed at the
manufacturing site of a mat.
The above-mentioned method is restricted to the use of
cellulosic fibers. Now it has been discovered that the
method is also suitable for manufacturing such products
where instead of the cellulosic fibers which are not
activatable by heat, the base material forming the mat can
be constituted of particles activatable at a higher
temperature than the binder material, such as of mineral
fibers ("rock fibers" and glass fibers) or other
thermoplastic fibers.
The invention will now be described in more detail with
reference made t;o they accompanying drawings, in which
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PCT/FI94/0039G
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fig. 1 is a cut-away side view of a mat forming
assembly included in an apparatus used in the
method of the invention,
fig. 2 is a cut-away plan view of the assembly shown
in fig. 1,
fig. 3 is a larger-scale view of a detail included in
the assembly shown in fig. 1.
fig. 4 illustrates schematically the operating prin-
ciple for an entire apparatus.
Fig. 1 illustrates a mat forming assembly, including a
feeding mechanism 1l for separate particles. The feeding
mechanism may comprise either a per se known vertical
device lla for bringing the particles by means of an air
flow, or a horizontal conveyor lib, whose inlet end can
be provided with per se known pretreating means. The bottom
end of feeding mechanism 11 is provided with a feeding
rall 2 having pins on its surface in a dense pattern. Facing
tawards the surface of feeding roll 2 is a horizontal
narrow slit orifice at the end of a first air conduit 3.
Below the slit orifice is located an inlet for a second
air conduit 4, with a constriction point formed between its
bottom wall and the surface of feeding roll 2. Downstream
of this constriction point there is an obliquely declining,
expanding air chamber 6, having its lower end closed with
an air permeable forming platform 1. On the opposite side
of forming platform 1 lies a collecting chamber 10.
The forming platform 1 is formed of an endless belt,
extended around cylinders and adapted to travel across
chamber 6. Downstream of chamber 6 said forming platform
travels across a second air chamber 8, providing a bottom
surface therefor.
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The inlet end of first air conduit :~ iF provided with
mutually parallel tans 12 for producing a uniform air flow
across the entire width of duct 6. These fans 12 are shown
by dash lines in f ig . 2 . A duct serving as the inlet end
of second air conduit 4 ig alAO provided with a tan 13,
which is adapted to blow air heated by a heater 7 into
said second air conduit 4. llpater 7 can be for example a
conventional gas burner.
l0 The mat-forming process in the apparatus 1R such that
separate particles forming bane structure of the mat,
which have been manufactured earliAr, ara delivered by
weans of the fRedi.ng mectsaniRm towards feeding roll 2.
Fig. 3 shows the subsequent mat-forming process in more
detail. The rotating feeding roll 2 includes pins 2a,
indicated in the figure ae the outermost layer of the
feeding roll, for picking up and carrying the particles
further. In tha rotating diractiar~ of the feeding roll,
the fibers arrive next in the range of action of a horizon-
tal slit orifice 3a, located at the end of first air conduit
3 and extending across the width of said roll. A high-
epaed air flow A1 discharging from the alit orifice dis-
engages the particles from feeding roll 2 while rushing
along the roll surface and carri4s them across the inlet 4a
of second sir conduit 4 into a constriction point 2b between
the bottom wall of said inlet 4a and the surface of leading
roll 2. J~fter the conetxiction point, the particles are
completely disengaged from leading roll 2 and proceed into
an air chamber 6, having a cross-section which expands in
their advancing direction and having a width which is
constant and corresponds to the width of a mat to be
m~tnulacturod. The expansion yr flare of the chamber is
achieved ~n a manner such that the front and rear walls,
extending in the axial direction of feAding roll 2, 1.s.
in the lateral direction of a mat being manufactured,
diverge from each ether.
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PCT/FI94/00396
Said second air conduit 4 is used for delivering air as an
air flow A2 into said inlet 4a. The temperature of this
second air flow A2 is higher than that of said first air
flow A1 supplied through said first air conduit 3. As a
5 result of the ejector effect produced by constriction
paint 2b, this air flow A2 merges into air flow A1 and
blends therewith for an air flow A carrying particles to the
outlet end of air chamber 6. The supply rate of this higher-
temperature air flow A2 is arranged to be such that the
temperature of air flow A carrying the particles in air
chamber 6 is sufficient to cause the activation of a
thermally activatable binder material blended with the
particles to a degree that makes it capable of bonding
the particles into a mat. However, this temperature is
lower than the activation temperature of the separate
particles forming the base of the mat, such that essential
changes do not occur in this material. This thermally
activatable binder material is well exposed to the action
of air, since they travel in the air flow in bare condition
either as separate binder particles, such as binder fibers,
or incorporated in the particles on the surface of the
material forming the base of the mat. The outlet or trailing
end of air chamber 6 is closed by a forming platform 1,
which travels across the chamber and can be a woven wire
fabric or a like air-permeable flat piece of material. The
particles hitting the bottom at the inlet of a conveyor,
i.e. downstream of the air chamber front wall, immediately
build up a bonded mat and an identically bonded mat of a
continuously increasing thickness begins to gather on top
of that. Since the resulting mat is porous in nature, said
air flow A is able to progress through the mat and said
forming platform 1 therebelow into a collecting chamber 10
on the opposite side.
Fig. 1 illustrates the subsequent processing of a mat.
Downstream of chamber 6 in the traveling direction of
forming platform 1 is mounted a packing cylinder 14, whose
distance from forming platform 1 is adjustable. The packing
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cylinder prevents the passage of air in the traveling
direction of forming platform 1 out of the air chamber
from above the mat. Downstream of the packing cylinder,
said forming platform 1 carries the mat into a second air
chamber 8 located above forming platform 1. The top end of
air chamber 8 is provided with an air conduit 9. The second
air chamber 8 has a flaring or expanding configuration.
towards forming platform 1 in the flowing direction of an
air current supplied from air conduit 9, i.e. the chamber
walls located on the inlet and outlet side of the forming
platform are diverging from each other. For example, the
pressure of an air flow B supplied into the chamber can be
applied for further compressing the mat to a desired degree
for providing a desired value for its density. Thus, the
air flow is delivered through the porous mat and the forming
platform 1 supporting it from below and into a second
collecting chamber 15 located on the opposite side. Thus,
said air flow B supplied into second air chamber 8 has
such a temperature that the binder fibers still remain in
a softened state where the fibers allow the deformation o:~
the mat for shaping or molding the mat to a desired density
such that the deformation is permanent. Downstream of
second chamber 8, the mat is transferred from forming
platform 1 onto a conveyor 16 for carrying the bonded mat
shaped product forward for further processing.
If a product of a particularly low density is desired,
the further processing effected by means of second air
chamber 8 can be omitted. The product density can also be
controlled already during a mat-forming operation by means
of the f low rate of air current A advancing in air cham-
ber 6, said flow rate dictating the force by which tl~ae
fibers strike into a mat configuration.
Fig. 4 illustrates schematically one possible arrangement
for air flows in the invention. The air currents are
circulated such that the mat-forming air flow or current A
arriving in collecting chamber 10 is delivered by way of
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PCT/FI94/00396
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fan 12 into first air conduit 3. During this period the
air flow has time to cool to such a degree that the first
air flow A1 discharging from air conduit 3 through slit
orifice 3a is below the temperature capable of bringing
the binder material to an activated state. Thus, this air
flow A1 only serves for detaching the particles from feeding
roll 2. However, it can be used for providing a preheating,
whereby the air flow A2 discharging from air conduit 4
need not be given a particularly high temperature. Said
air flow A2 is delivered into second air conduit 4 from
heater 7 by means of fan 13. The air conduit 4 branches
for .an air conduit 9 connected to second air chamber 8,
whereby some of the heated air flow A1 blown by the fan is
extracted as an air flow B performing the further processing
of a mat. This also secures that in the further processing
said air flow B has a sufficiently high temperature and,
since it originates from air conduit 4, which only contains
the flow of heated air, its temperature is in fact higher
than that of air chamber 6. However, this air does not
harm the material, as it is less exposed to it, surrounded
by the mat base material contained in the articles and, on
the other hand, the flow rate of air per unit area remains
quite low due to the extent of chamber 8.
The air flow B received in second collecting chamber 15 on
the other side of forming platform l is circulated back to
heater 7 by way of an air conduit 18. The chamber 8 also
receives air carried along with a mat from chamber 6. This
air advances through collecting chamber 15 merging with
the return air flowing to heater 7. In order to maintain
the air balance, some of the air progressing in first air
canduit 3 is delivered out along a duct 17. This is compen-
sated for by delivering to heater 7 not only circulated
air but also compensation air from outside. Air can also
be circulated from duct 17 to heater 7, but this degree of
circulation is determined by impurities accumulated in the
air during the mat manufacturing process.
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2~'~~.~3fl
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Fig. 4 further illustrates normal measuring and regulation
equipment for setting the temperatures of air flows as
desired. '
All possible product forms are conceivable for the product: ,
manufactured in accordance with the invention, starting
from a flexible mat to a stiff plate, in a wide range of
grammages.
All particles activatable at a certain temperature to a
state where they become bonded to each other can be applied
in the method as the particles forming the base structure
of the mat. Such particles can be fibers which have been
originally manufactured of a molten material, such as
mineral melt (°°rock fibers" i.e. rock wool fibers, and
glass fibers), or thermoplastic plastics material. The
density of the mat can be influenced by selection of the
fiber grade and ratios. It is, nevertheless, possible to
use also particles of other kind which can be made to form
a mat by means of an air flow.
One example of the thermally activatable binder material
that can be used is thermoplastic material, such as ther-
moplastic polymer, of which can be mentioned polypropylene
and polyester. The thermoplastic material is activated to
a bonding state when it softens under the influence of
heat. It is also possible to employ bicomponent material
containing polymer softening at a lower temperature on the
surface of the particles. Such particles, for instance
bicomponent fibers, can be used either as the binder
material for binding other particles, which form the base,
or as the particles themselves forming the base, whereby
their material activatable at the higher temperature serves
as the mat base forming material.
The temperature of air current A flowing in air chamber 6
can be set according to the activating point of a binder
material and this point, at which the binder material
WO 95/07169 2 ~'~ 14 3 0 PCT/FI94/0039G
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softens to an adhesive or tacky state, is within the range
of 100...200°C on the most commonly used thermoplastic
polymer materials. The activating temperature of the
material forming the base is higher than this. It is thus
possible to employ a higher-melting thermoplastic material
as the base material and a lower-melting thermoplastic
material as the binder material. The mat structure can
also be controlled by selecting the proportions between
the thermoplastic binder material and base material. The
basic raw material for the structure of the product consists
of the base material, which preferably makes up most of the
total mass of a mat.
The resulting mats can have weights per unit area within
the range of 40 g/mz - 3000 g/m2, and their densities can
range from 18 kg/m3 to 400 g/m3.
The products obtained can be used, depending on the kinds
of particles and the mat thickness and stiffness, for
various applications, such as heat insulation, filters,
lining of various interiors such as buildings and vehicles,
etc. The product can also be used for various applications
in the form of a half-fabricate that can be pressure-molded
again by heat. The obtained products can also be after
treated for improving some properties.
