Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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"Method for manufacturing panels and panels obtained
thereby"
This invention refers to a method for manufacturing panels
in sheet form and the product obtained thereby.
There are known panels composed of incoherent material.s of
various kinds, impregnated with suitable binders and then
moulded in a press.
A typical example of application of this technique
consists of panels composed of fragments of wood of
suitable particle size, lmpregnated with thermosetting
resin. This material is cold-preformed into the shape of a
slab which is subsequently compressed into its final
configuration in a heated mould, where the binder is
polymerized. ~ :
Panels of this kind have extensive empty spaces inside
them, due to the fact that the quantity of binding resin
must be maintained within permissible limits from the
economic and technolo~ical point of view. In certain
applications their consequent poor mechanlcal strength and
high hygroscopicity is not appreciated.
Likewise, there are known panels obtained by milling and
suhsequently hot-pressing scraps and rejects of
multilayered materials; the methods used for obtaining
such panels are descrihed in patents DE-A 2.258.169 and
DE-B 1.~51.374.
Due to the lntrinsic properties of the raw material used,
these panels have an uneven surface which prevents them
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from being given an aesthetically perfect finish either by
painting, or by applying a paper coating.
The scope of this invention is to obtain panels composed
internally of scraps of multilayered materials and
externally of fine particle-sized wood shavings. Said
panels are consequently characterized by a low degree of
hygroscopicity, limited swelling in water, good thermal
and acoustic insulation, d.eriving from the first component
material, and an excellent finish and even surface
deriving from the second component material.
The method for manufacturing panels according to the ~- --
invention is characterized by the fact that fine,
particle-sized wood shavings, suitably mixed with resins,
are distributed on the outside of a mass of fragments of
sheet material composed of thermoplastic resin coated ~-~
cardboard, the composition thus obtained being compressed -
in a mould at a temperature higher than the softening ;~
point of the thermoplastic material and higher than the
polymerizing temperature of the resin used, and
subsequently cooled.
The invention also refers to the panel obtained by such
method.
During the course of this description, the term
multilayered material, or bonded sheet material, refers to
a composite material comprising a layer of cardboard and
at least one layer of thermoplastic material on one of its
outer surfaces.
Further layexs may also be present, such as for example a
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sheet of aluminium foil.
The use of these multilayered materialfi as the basic
ingredient for preparation of the panels, offers the
advantage of perfectly even distribution of.th~ plastic ~-
material on each of the fragments and, consequently,
within the mass of the panel itself, resulting in optimal ~.
adherence between the Gomponent fragments and a singularly . -
compact structure of the panel thus obtained.
A further essential advantage of the invention lies in the
fact that scraps of multilayered mater.ial are widely
available and exceptionally low in cost, in that they can
be obtained from material discarded from the manu~acture
of boxes which use this material as a constituent.
The cost of disposing of these scraps weighs heavily on
~ .
the industries which make up these boxes, and so the cost ~: -
of acquiring the scraps from which the fragments are made
may even be zero, or compensated with the cost of
conventional disposal.
The plastic layer of the bonded sheet material referred to
herein consists of a sheet of polyethylene, even though
the presence of other thermoplastic materials is not
excluded.
To carry out the procedure according to the invention, the ~ ::
sheet material is broken up into fragments, preferably
having minimum dimensions of not less than 2 mm and .
maximum dimensions of around 40 mm, of the most diverse
shapes, from substantially circular to elongated in the :~
form of fibres. --
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According to the experiments conducted by the applicant, a
percentage of thermoplastic binding material suitable for
forming the panel ranges from 5 to 15~ in weight of the
fragments, and more specifically around 10~, which is the
same order of magnitude as the percentage in weight of the
thermoplastic fraction contained in ~ardboaxd-polyethylene
or cardhoard-aluminium-polyethylene mu]tilayer ~heets, so
that the use of fragments made from scraps of this
material ensures an adequate quantity of bonding resin.
It may prove advantageous, however, to add additives to
the simple fragments of multilayer materials on the
market, such as those used directly for packagin~
foodstuffs in particular.
These additives may consist of an additional quantity of
the same plastic material contained in the multilayer
material, as well as other thermoplastic substances. The
thermoplastic resin added to the fragments will have a
sufficiently fine par~icle size so as to be suitably
distributed throughout the mass, typically with a basic
particle size not exceeding the average size of the
fragments.
It was found to be advantgeous, in certain applications,
to add other plastic materials of the thermosetting class,
in order to favourably affect the properties of the panel,
and to facilitate the technique of forming the mass to be
introduced into the mould, as well as to enable the panel
to be removed easily from the mould. Synthetic resins
which can be polymerized by adding a cataly~t may also be
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used.
To form the two outer layers, use is made of wood shavings
with a particle size ranging from 0.25 to 1.2 mm, with the
- - addition of ureic resin or, preferably, melar,linic resin,
which gives better characteristics in terms of
hygroscopicity and limited swelling.
Special care should be taken in preparing the initial
slab, since it is essential to ensure a certain amount of
compenetration between the wood shavings and the fragments
of cardhoard in order to prevent detachment of the surface
layers composed of wood shavings from the support composed
of fragments of multilayered material.
The thickness of the layers of wood shavings may vary from
0.3 to 1.5 mm. -
It was found that the panels are formed satisfactorily
when the initial slab is subjected to pressure.s in the
region of 15-25 kg/cm2 and heated to a temperature ranging
,from 120 to 1~0C. The length of time that the fragments
must remain under compression between the hot plates of
the press varies according to the final thickness of the
panel, in order to ensure a sufficientiy even distri~ution
of the temperature throughout the mass. It has proved to
be advantageous, for example, to keep the panel under the
heated press plates for a period ranging from 15" to 30"
per millimetre of thickness of the panel obtained.
Whençver a thermosetting resin or a resin polymerized by
catalysis is used as an additive, it was found that, in
the time required for polvmerization and cross-linking of ~ ;
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the resin, the polyethylene melts to improve the
aggregating action between the resin and the fragments of
multilayered material, resulting in a singularly compact
and sturdy product.
Resins of the most diver.se kinds have proved useful in
manufacturing panels according to the invention, such as
for example
phenolic resins (phenol-formaldehyde, cresol-formaldehyde,
phenol-furfural), amino-plasts (urea-formaldehyde,
melamine-formaldehyde), polyesters (phthalic, maleic),
epoxy, vinyl, acrylic, polystyrene, polyolefin and
isocynate.
The mechanical properties and compactness of the end
product can be improved by the addition of fillers of
various different materials of suitable particle size, in
widely varying percentages, typically from 5 to 10~, such
as cellulose, cotton staple, sawdust, fibre glass, kaolin,
calcium carbonate.
The addition of paraffin to the wood shavings and the use
of melamine glues reduces the hygroscopicity and moisture
expansion of the material.
The addition of monoammonium phosphate dispersed in the
mass in percentages of 8-15~ makes it possible to obtain a
substantially fire-proof product.
This exemplificative indication obviously does not in any
way limit the choice of inert fillers which can in any
case be added during the formation of the panel according
to the inventlo~ to give it any desired specific
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characteristics.
The procedures for carrying out the method according to
the invention will be more clearly evident from the
following practical example.
E X A M P L E
100 kg of dry ureic resin were treated with 52 kg of water
- to obtain a milky suspension to which ammonium chloride
was added up to a percentage ranging from 2 to 3%
(approximately 2.8 kg). -~
720 kg of fragments obtained by triturating scrap~ of
multilayered materials (cardhoard, aluminium and
polyethylene) were added to approximately 53 litres of
thls mixture.
After having been vigorously stirred in appropriate
apparatuses referred to as "resinators", this mixture was
,evenly distributed over a layer of previously resinated
fine wood shavings. ~ -
The upper surface, composed of fragments of resinated
multilayered material, was also covered with a further
layer of resinated fine wood shavings.
The operation of distributing the three alternate layers ~ -
was carried out by means of special distributing machines
referred to as "moulding machines" placed in succession
above a conveyor belt.
The slab thus formed was cut into suitably si~ed modules
with a specific weight of approximately lOO0 kg/m3, which
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were then introduced between the hot plates of a gang
press.
After having reached the softening point of the
polyethylene in the core of the panels, the press plates
were cooled to reduce the temperature of the panels to
below the softening point, while keeping the panels
constantly subjected to a specific pressure higher than
the pressure exerted by the water vapour at the same
temperature, during the heating and cooling phases.
The panels were subsequently removed from the press, cut
transversally and longitudinally and then smoothed.
In view of the relatively low thermal conductivit~ of the
material compacted to form the panel, it may be
advantageous to preheat the mass before introducing it
into the mould, thereby reducing the length of time it
must remain inside the hot press for the core of the panel
to reach the temperature required for the thermoplastic
resin to soften and for polymerization of any
thermosetting binder that may be used.
The preheating temperature must obviously be below the
point which causes the thermoplastic resin to soften to
such a degree as to cause it to run or to adhere
excessively on contact, which could negatively affect the
distribution of the resin within the mass.
It was also found that a high degree of moisture in the
scraps of multilayered material, as is generally the case,
may negatively affect the properties of the panel, and
especially its compactness.
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A further feature of the manufacturing method according to
this invention is consequently that of subjecting the
fragments after milling to pre-drying in order to reduce
the moisture content to values below 4~., preferably around
2%. The drying can easily be carried out under a stream of
hot air.
In addition or as an alternative, also in order to speed
up production and achieve hetter dimensional stabilization
of the product, after the heating phase and after having
exceeded the softening point of the raw material, the
panel can be cooled under pressure, with release of any
vapour that may have formed in the mass of mater~al.
To compress fragments of multilayered materials use can be
made, in particular, of the currently known single or
multiple-die presses. In particular, the cycle can be
carried out with:
a) three single-die presses in line, the first of which
, presses hot, the second re-presses hot and the third cools
and stabilizes the product;
b) two single-die presses, the first of which heats and
the second cools and stabilizes the product under
pressure;
c) multiple-die press with hot/cold cycle;
d) continuous press with hot area upstream and cold area
downstream.
On account of their compactness, the panels lend ;~
themselves satisfactorily to machining and surface
finishing.
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The panels obtained according to the invention lend
themselves to a wide range of applications in the most
diverse fields. In addition to the conventional uses for
. ~. products of this kind, they can also be su.itable for uses
which call for resistance to passive stress, in view of
their good mechanical strength. Moreover, due to their low
degree of impregnability and expansion in water, the
panels according to the .i.nvent.ion can be used in the
building industry.
Lastly, it should be pointed out that the utilization of
scraps of multilayered materials is an aspect of
considerable importance, since at present they d~ not
prove to be of any practical use and are extremely
difficult and expensive to dispose of, while they can be
made into panels having the same character1stics in terms
of finish as the known panels manufactured with particle ~:
board and can consequently be subjected to the same
finishing techniques as the latter.
