Note: Descriptions are shown in the official language in which they were submitted.
CA 02290958 1999-11-23
WO 98/54388 PCT/DK98/00216
Plant and process for producing a coated mineral fibre
element.
The present invention relates to a plant for producing a
mineral fibre element comprising a mineral fibre base
layer having a surface coating in the form of a fibrous
non-woven fabric formed of a thermoplastic polymer
material, the surface coating covering at least part of
the surface of the base layer, wherein the plant
comprises one or more coating devices, means for melting
a thermoplastic polymer material, means for supplying the
polymer melt obtained to the coating devices, wherein
each coating device comprises a number of dispensing
units comprising a number of orifices, means for
extruding the polymer melt obtained through the orifices
and distributing the extruded polymer material on the
surface of a mineral fibre base layer, and means for
directing one or more high pressure gas streams closely
past the orifices in order to elongate the extruded
polymer material so as to form thin filaments and/or
fibres.
Mineral fibre material is used i.a. for thermal and
acoustic insulation in a number of connections.
In order to increase the tactility of the mineral fibre
material used during the handling and mounting thereof it
may be coated with a surface layer, e.g. consisting of a
non-woven sheet fabric of polymer fibres.
Furthermore, such a surface coating serves to reduce or
eliminate the release of fibre wads or single fibres from
the mineral fibre material to the surroundings before,
during and/or after mounting.
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2
WO 93/16874 discloses a process and an apparatus for
applying a coating in the form of a fibrous netting of a
thermoplastic polymer material onto the surface of a
mineral fibre material. The apparatus used may be a so-
y called "melt blowing apparatus" or a "hot melt spray
apparatus". The distance between the polymer discharge
orifices of the apparatus and the surface of the mineral
fibre material is from 0,3 to 0,5 m.
US-A-5501872 discloses a method of preparing a six-sided
fibrous batting which is coated with a non-woven
polymeric material by passing the batt sequentially
through three coating stations using melt blowing
technology. Four sides of the batt are coated in the
first two stations, and after the batt has been turned
90°, the final two sides are coated. The distance between
the orifices of the dispensing chamber and the upper side
of the fibrous batting is typically from 6 to 9 inches
15.2 - 22.9 cm). The temperature of the polymer in the
dispensing chamber was 250 °C and the temperature of the
air was 260 °C
The prior art methods suffer from the drawback that the
adhesion of the polymer coating to the mineral fibre
material is insufficient, i.e. the coating is liable to
loosen partly or completely from the mineral fibre
material during further processing, handling, storage and
use.
Thus the object of the present invention is to provide an
apparatus of the type defined in the preamble to claim l,
which is capable of producing mineral fibre elements,
wherein the adhesion of the polymer coating to the
mineral fibre material is improved compared to a product
produced by the prior art apparatuses.
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3
This object is obtained by the apparatus of the invention
which apparatus is characterized in that the distance
between the orifices and the surface of the base layer is
from 50 mm to 150 mm.
The inventors have examined the influence of a number of
process parameters, such as type of polymer used, the
temperature of the polymer melt and the high pressure gas
streams, the distance between the orifices and the base
layer and the weight of the extruded polymer material, on
the strength of the adhesion of the polymer coating to
the base layer. The studies have surprisingly shown that
one parameter is decisive in determining the adhesion
strength, viz. the distance between the orifices and the
base layer. Thus, it has been found that a greatly
improved adhesion may be obtained by using a specific
distance range. It is believed that the improved adhesion
obtained is due to the fact that the polymer
fibres/filaments at the point of impingement with the
mineral fibre material has a higher kinetic energy than
when larger distances are used and that this high kinetic
energy causes the fibres/filaments to penetrate deeper
into the surface layer of the mineral fibre material and
hence become more entangled therewith.
The kinetic energy (Ekin - '-~ m~V'', wherein m is the mass
and V is the velocity) depends primarily on the velocity,
and it is believed that the velocity of the extruded
polymer material is closely related to the distance from
the orifices, which is i.a. due to the fact that the high
pressure gas streams carrying the polymer material is
dispersed in a fan-shaped zone from the orifice.
In order to increase the kinetic energy of the extruded
polymer material it has been attempted to increase the
velocity of the high pressure gas streams. However, such
an increase of gas velocity has not been successful,
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4
since it causes the polymer fibres/filaments to become
too thin to form a suitable coherent non-woven fabric,
i.e. the coating formed is fluffy and tend to adhere to
surfaces, with which it is brought into contact.
However, it has further surprisingly been found that the
said distance cannot be reduced to below a certain limit
of 50 mm, since below the said limit, the non-woven
coating obtained becomes too brittle to resist handling.
When the heated, liquid polymer melt is extruded from the
dispensing unit it is gradually cooled in the surrounding
air as a function of the distance from the orifices of
the dispensing unit, whereby the polymer melt gradually
solidifies. It is believed that the brittleness of the
coating, which occurs at small distances, is due to the
fact that at small distances the extruded polymer melt is
not sufficiently cooled and hence solidified at the point
of impingement with the mineral fibre material.
Thus, the distance range of 50-150 mm according to the
invention is the result of two factors, which point in
opposite directions. On the one hand the smaller the
distance is, the stronger the adhesion between the
polymer material and mineral fibre material is, and on
the other hand the higher the distance is, the less
brittle the coating formed is. The distance range of 50-
150 mm is the range, wherein an acceptable adhesion may
be obtained while at the same time avoiding brittleness
of the coating, the optimum distance being about 90 mm.
In connection with the present invention the term
"extruding the polymer melt through the orifices" means
pressing out the polymer melt through the orifices by
means of an extruder, a pump or another mechanical device
or allowing the gravitation to make the polymer melt run
through the orifices.
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As used in the present invention the term "mineral
fibres" includes rock fibres, glass fibres, slag fibres
and mixtures thereof.
5
As used in the present invention the term "thermoplastic
polymer material" means any natural or synthetic
thermoplastic polymer, copolymer or polymer blend. A
thermoplastic material is characterized by that it is
solid or partially solid at room temperature or at
temperature of use, that it melts when heated and that it
solidifies or resumes a solid or partially solid form
when cooled.
The term "thermoplastic polymer material" also includes
such materials which are ordinarily referred to as
"thermoplastic hot melt adhesives" or "hot melt
adhesives" or simply "hot melts".
By way of examples thermoplastic polymer materials are
polymers of ethylenically unsaturated monomers, such as
polyethylene, polypropylene, polybutylenes, polystyrenes,
poly(a-methyl styrene), polyvinyl chloride, polyvinyl
acetate, polymethyl methacrylate, polyethyl acrylate,
polyacrylonitrile, etc; copolymers of ethylenically
unsaturated monomers, such as copolymers of ethylene and
propylene, ethylene and styrene, polyvinyl acetate,
styrene and malefic anhydride, styrene and methyl
methacrylate, styrene and ethyl acrylate, styrene and
acrylonitrile, methyl methacrylate and ethyl acrylate
etc; polymers and copolymers of conjugated dienes, such
as polybutadiene, polyisoprene and polychloroprene and
polymers of bi- polyfunctional monomers, such as
polyesters, polycarbonates, polyamides and polyepoxides.
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6
Examples of natural thermoplastic polymer materials are
wax and bitumen.
Particularly preferred thermoplastic polymer materials
are polyesters, polyamides, polypropylene and polyvinyl
acetate.
The thermoplastic polymer material as used in the
invention may contain up to 30 ° by weight of additives.
The thermoplastic polymer material to be used in the
plant of the invention should have such a low viscosity
in its molten heated state so that it is capable of
flowing freely through the dispensing unit and so that
the extruded polymer material is capable of being drawn
out readily by the high pressure gas streams.
The base layer used in the invention is made from Man-
Made Vitreous Fibres (MMVF). The coated element produced
by the plant of the invention may be used as thermal or
fire insulation or protection, for noise reduction or
regulation, or as a horticultural growing medium.
The base layer used in the invention may be in any form
and typically it has the form of an endless web, a web, a
mat, a sheet, a slab or a tube, e.g. a pipe insulation,
such as a circular pipe section, i.e. a pipe insulation
having an annular cross section and a longitudinal slit.
Preferably, the distance between the orifices and the
base layer is from 70 mm to 120 mm.
The surface weight of the non-woven fabric is preferably
2-50 g/m2, more preferably 2-15 g/m', and most preferably
4-10 g/mz .
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7
The temperature of the high pressure gas streams measured
in °C is preferably 0-15 % higher than the temperature of
the dispensing unit measured in ° C, more preferably from
o to 10 0. Such temperature levels help to reduce the
5 cooling of the polymer melt leaving the nozzles, the
temperature of the polymer melt approximately
corresponding to that of the dispensing unit, and hence
to facilitate the drawing out of the polymer strands
extruded from the orifices.
Preferably, the plant of the invention comprises means
for supporting and conveying the base layer.
The supporting and conveying means may e.g. have the form
of any suitable transport means, such as rotatable rolls,
e.g. a roller belt or a roller path, a conveyor belt or a
conveyor path or a combination thereof, preferably
rotatable rolls.
A preferred embodiment of the invention is characterised
in that it comprises one or more suction devices,
preferably suction boxes, disposed vis-a-vis the coating
devices. Such suction devices serve mainly to remove
excess polymer material, i.e. polymer fibres/filaments
which are not deposited on the mineral fibre base layer
and to remove polymer vapours contained in the emitted
high pressure gas streams.
The base layer in the plant of the invention may be
placed in horisontal position, in an inclined position or
in vertical position, preferably in horizontal position.
Correspondingly, the coating devices may be placed in
horizontal position, in an inclined position or in
vertical position.
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8
A preferred embodiment of the invention is characterised
in that it comprises six coating sections disposed in
sequence and designed so as to be able to coat all sides
of a six-sided base layer, wherein each coating section
comprises one coating device, a number of rotatable rolls
for supporting and conveying the base layer and a suction
device disposed vis-a-vis the coating device, wherein two
coating devices are disposed at one side of the base
layer and two coating devices are disposed at the
opposite side of the base layer, the said four coating
devices all being disposed in such a manner that the
polymer material is extruded in a substantially
horizontal direction, wherein one coating device is
disposed above the base layer in such a manner that the
polymer material is extruded in a downward substantially
vertical direction, and wherein one coating device is
disposed below the base layer in such a manner that the
polymer material is extruded in an upward substantially
vertical direction.
Preferably, one or more of the coating sections of the
above-described six coating sections embodiment comprises
holder means for keeping the base layer in place, the
holder means being disposed on the upper side of the base
layer. The holder means preferably have the form of
rolls, which abut on the upper surface of the base layer.
The high pressure gas streams used in the plant of the
invention need to have such a kinetic energy that they
may cause a lifting of the base layer from the support
rolls in the coating section having the coating device
placed below the base layer. Such a lifting is
undesirable, since it increases the distance between the
orifices and the base layer resulting in a reduced
adhesion strength of the coating to the base layer. Also,
the gas streams may cause a transverse displacing of the
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9
base layer on the support in the coating sections having
the coating devices placed at the side of the base layer.
Such a displacement is undesirable, since as a result a
part of the base layer side to be coated will not be
coated, and since part of the polymer material will be
deposited on the rolls, which should be avoided, because
the deposited polymer material tend to adhere to the
coating of the following mineral fibre elements and hence
to tear up the said coating.
It has been found that the above-mentioned holder means
placed above the base layer prevent both the lifting and
the transverse displacement of the base layer.
A preferred embodiment of the invention is characterised
in that the coating devices are melt blowing die
apparatuses comprising an oblong polymer dispensing
chamber which via a pump is in liquid communication with
the melting means and which at its distal end comprises a
number of closely spaced orifices, two gas chambers
located along the two side walls of the dispensing
chamber and at the distal end of which a longitudinal
slot is formed, and means for directing a high pressure
gas stream through the said gas chambers and out through
the slots.
Another preferred embodiment of the invention is
characterised in that the coating devices are hot melt
spray nozzle apparatuses each comprising a number of
individual spray nozzles which via a pump are in liquid
communication with the melting means, and which comprise
means for directing one or more high pressure gas streams
past the orifices of the nozzles.
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Yet another preferred embodiment of the invention is
characterised in that the coating devices are spun bond
apparatuses.
5 With respect to the structure and operation of "melt
blowing die apparatuses" and "hot melt spray nozzle
apparatuses", reference is made to international
application No. WO 93/16874, which is incorporated herein
by this reference. Spun-bond fibres of thermoplastic
10 polymers and apparatus for making them are disclosed in
US-A-3,692,618, US-A-5,213,881 and EP-B1-0,480,550, which
are incorporated herein by this reference.
The temperature of the polymer melt to be extruded and
the temperature of the high pressure gas streams depend
primarily on the type of polymer used. In general, it is
desirable to keep the temperature of a polymer melt as
low as possible while maintaining it flowable, since most
polymers tend to decompose at high temperatures. On the
other hand, the melt to be extruded should have a
sufficiently low viscosity so as to be able to be drawn
out by the high pressure gas streams.
The temperature of the polymer melt in the plant is
conveniently controlled by setting the temperature of the
dispensing unit, i.e. e.g. a melt blowing die or a hot
melt spray nozzle, to a desired level selected with due
consideration to the specific polymer used, preferably
180-240 °C, and then adjusting the temperature of the
polymer melt in the polymer melt supply means at the
point of entry into the dispensing unit to a level of
from +5 o to -25 0, more preferably from 0 o to -10 0,
relative to that of the dispensing unit. Also, the
temperature of the high pressure gas streams is
controlled on the basis of the temperature of the
dispensing unit, and preferably the former is adjusted to
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11
be from 0 o to 15 0 of the latter, more preferably from 5
o to 10 0 .
The gas in the high pressure gas streams is preferably
air.
The present invention further relates to a process for
producing a mineral fibre element comprising a mineral
fibre base layer having a surface coating in the form of
a fibrous non-woven fabric formed of a thermoplastic
polymer material, the surface coating covering at least a
part of the surface of the base layer, the process
comprising the steps of melting a thermoplastic polymer
material and supplying the polymer melt obtained to one
or more coating devices comprising a number of
dispensing units having a number of orifices, extruding
the polymer melt through the orifices while directing one
or more high pressure gas streams closely past the
orifices in order to elongate the extruded polymer
material so as to form thin filaments and/or fibres and
so as to distribute the extruded polymer material on the
surface of a mineral fibre base layer.
The process of the invention is characterised in using a
distance between the orifices and the surface of the base
layer of from 50 mm to 150 mm.
The invention will now be described in further details
with reference to the drawings, wherein
Fig. 1 is a perspective view of a preferred embodiment of
the plant according to the invention.
Fig. 2 shows a cross sectional view of the lower part of
a melt blowing die apparatus situated above a mineral
fibre base layer.
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12
Fig. 1 shows a plant according to the invention
comprising six coating sections 1-6 placed in a line,
wherein each coating section 1-6 comprises a melt blowing
die apparatus 7, a suction box 8 and a bed of rotatable
rolls 9 for supporting and conveying a six-sided
rectangular mineral fibre mat 10. The six apparatuses 7
each comprises a die housing 11-16 and a polymer melt
supply conduit 17 and a high pressure air supply conduit
18. The conduits 17 are via pumps (not shown) connected
to a single extruder (not shown), which supplies polymer
melt to all six apparatuses 7. Correspondingly, the
conduits 18 are connected to a single air compressor (not
shown), which supplies high pressure air to all six
apparatuses 7.
Alternatively, each melt blowing die apparatus 7 may be
supplied with polymer melt and/or high pressure gas from
individual extruders with or without the use of pumps and
from individual gas compressors, respectively.
The die housings 11-14 of the first four coating sections
1-4 are disposed alternately at different sides of the
mat 10 in a vertical position and the suction boxes 8 of
the coating sections 1-4 are disposed at the sides
opposite to the die housings 11-14 in a vertical
position. Between coating sections 2 and 3 an
intermediate bed 19 of rotating rolls is placed, in which
bed 19 the mat 10 is rotated 90 around the axis of a
vertically disposed rod 20 extending from the upper
surface of the rotating rolls.
The die housings 15 and 16 are disposed horizontally on
the upper and lower side, respectively, of the mat 10 and
in a transverse direction in relation to the direction of
movement of the mat 10. The suction boxes 8 of the
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13
coating sections 5 and 6 are disposed on the lower and
upper side, respectively, of the mat 10 vis-a-vis the die
housings 15 and 16, respectively.
In coating sections 1-4 two holder rolls 21 is placed on
the upper side of the mat 10 at the site of the die
housings 11-14. The holder rolls 21 only extend across a
smaller part of width of the bed 9. In coating section 6
two holder rolls 22 is placed on the upper side of the
mat 10 vis-a-vis the die housing 16, the holder rolls 22
extending across the entire width of the bed 9.
The mode of operation of the above described plant is as
follows: The mat 10 is conveyed continuously through the
plant on a roller path consisting of the six beds of
rolls 9 and the intermediate bed of rolls 19. In coating
sections 1 and 2, the mat 10 is coated with a non-woven
fabric on opposite short side surfaces 23. On the
intermediate bed of rolls 19, the mat 10 is then rotated
90 ° by means of the rod 20 so as to bring the mat 10
into a position, where the coated short side surfaces 23
are placed perpendicularly to the direction of movement
of the mat 10. In coating sections 3 and 4, the mat 10 is
coated on opposite long side surfaces 24, and in coating
sections 5 and 6 the mat 10 is coated on its upper main
surface 25 and lower main surface, respectively. The melt
blowing die apparatuses 7 are operated in a
discontinuously manner, i.e. polymer material is extruded
from the apparatuses 7 only during the period of time,
wherein the mat 10 passes past the apparatus 7. The
initiation and ending of extrusion of polymer material
are controlled by means of photoelectric cell technology
(not shown) .
The suction boxes 8 serve to remove excess polymer
material, which is not deposited on the surface of the
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14
mat 10 so as to minimise the amount of polymer
fibres/filaments, which are spread to the surrounding
room. Also, the suction boxes 8 serve to remove the air
from the high pressure air streams so as to remove the
polymer vapour contained therein and so as to prevent
that the air streams make turbulence, which is
undesirable, since it may affect the coating process
adversely.
The holder means 21 are disposed so as to exert a small
pressure on the upper surface of the mat 10. Although the
holder means 21 are placed on the upper side of the mat
10 and only extend across a smaller part of the width of
the mat 10, the holder means 21 are capable of preventing
that the kinetic energy of the high pressure air streams
displaces the mat 10 in the transverse direction of the
roller path. The holder means 22 is also placed so as to
exert a small pressure on the upper surface of the mat
10.
Fig. 2 shows the lower part of a melt blowing apparatus
disposed above a mineral fibre mat 31. The apparatus
30 comprises a thermoplastic polymer channel 32, which
ends in an orifice 33, from which a polymer melt P is
25 extruded. At both sides of the channel 32, high pressure
gas chambers 34 are disposed, from which a gas G is
ejected. Finally, Fig. 2 shows the distance D between the
lower end of the orifice 33 and the upper surface 35 of
the mat 31.
Example 1
A stone fibre mat having the dimensions 90 cm x 60 cm x
10 cm (length x width x height) was coated with a non-
woven fabric using a melt blowing die apparatus disposed
CA 02290958 1999-11-23
WO 98/54388 PCT/DK98/00216
at the distances of 90 mm, 110 mm and 130 mm between the
orifices of the die apparatus and the surface of the mat.
The non-woven fabric consisted of polypropylene and the
5 intended surface weight of the fabric coating was 10
g/m2. The mat was conveyed on a roller path at a speed of
m/min. The temperature of the melt blowing die was set
to 200 °C, and the temperature of the polymer melt
entering the die was 190 °C. The pressure and temperature
10 of the high pressure gas stream being supplied to die
apparatus was 80 psi and 210 °C, respectively.
The strength of the adhesion between the coating and the
stone fibre mat was subsequently measured using the
15 following test method: A rectangular iron frame having an
internal size of 100 x 200 mm was heated to a temperature
of about 200 °C, and the heated frame was used to burn
away the coating around a rectanangular piece of coating
having the dimensions of 100 x 200 mm. Then, the said
20 piece of coating was peeled off from the mineral fibre
mat using a dynamometer while maintaining a vertical
direction of pulling throughout the process of peeling
off. The resulting measurement was calculated as the mean
value of the process.
The results obtained appear from Table 1.
As will appear from Table l, the adhesion strength
decreases strongly with increasing distance between the
orifices and the mat surface.
CA 02290958 1999-11-23
WO 98/54388 PCT/DK98/00216
16
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CA 02290958 1999-11-23
WO 98/54388 PCT/DK98/00216
17
Example 2
A stone fibre mat having the dimensions 90 cm x 60 cm x
cm (length x width x height) was coated with a non-
5 woven fabric using a melt blowing die apparatus disposed
at the distances of 90 mm, 10 mm and 130 mm between the
orifices of the die apparatus and the surface of the mat.
The non-woven fabric consisted of polypropylene and the
10 intended surface weight of the fabric coating was 8 g/m~.
The mat was conveyed on a roller path at speeds of 20
m/min, 30 m/min and 40 m/min. The temperature of the melt
blowing die was set to 180°C, and the temperature of the
polymer melt entering the die was 170 °C. The pressure
and temperature of the high pressure gas stream being
supplied to die apparatus was 80 psi and 200 °C,
respectively.
The strength of adhesion between the coating and the
stone fibre mat was then measured using the same test
method as described under Example 1. The results obtained
appear from Table 2.
As will appear from Table 2, the adhesion strength
increases with increasing mat conveying speed and it
decreases with increasing distance between the orifices
and the mat surface.
CA 02290958 1999-11-23
WO 98/54388 PCT/DK98/00216
18
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