Note: Descriptions are shown in the official language in which they were submitted.
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1 1156135
Flame resistant composite panel ancl process for its
manufacture
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¦The invention relates to a flame resistant composite panel
¦which can be shaped at room temperature by non-chip-form-
¦ing processes and which is made of a core of foamed
¦thermoplastic plastic with, on both sides, metallic cover
¦sheets which are joined to the core by means of layers of
¦adhesive, and relates too to a process for manufacturing
¦the said composite panel.
~he known composite panels of the above kind can be divided
~asically into two groups:
~n the first group the plastic core usually employed is a
.2 - 10 mm thick layer of compact thermoplastic plastics.
~sually metallic cover sheets in the form of foil or sheet
~aterial, 0.1 to 2.00 mm thick, are provided on both sides
f the core. Such composite panels are relatively light and
igid, and can be subsequently shaped plastically without
sing chip-forming methods, e.g. by means of bending
pparatus or by deep drawing in presses.
I
uch forming methods causes the metal outer layers to be
! eformed beyond the yield point (0.2 % proof stress), with-
ut the outer layers crumpling and without causing delami-
ation at the join between the metal and the thermoplastic
lastic~
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Basically the following properties are particularly impor-
tant for such composite panels:
a) High specific stiffness (E . ~ /g) i.e. the modulus of
elasticity of the metallic outer layer times the moment
of inertic of the outer layer divided by the specific
weight or weight per m2 of the composite.
b) The plastic (non-chip-forming~ shaping property which
requires the relatively light plastic core to have
sufficient shear strength that the metallic outer
layers do not buckle or crumple.
I
Up to now the composite panels of the above mentioned kind
which contain as the plastic core e.g. polyolefines have,
however, suffered the disadvantage of being rather flammable,
which is expressed in a classification according to DIN 4102
!as these composites being of "normal combustibility" ~normal
entflammbar). For this reason such composite panels have
been limited in their application.
¦ The second group of composite panels has an analogous lami-
~ nate structure viz., metal-plastic-metal. The overall thick-
ness lies between lQ and 100 mm and the plastic core is made
of a relatively light foamed material with a very low speci-
ic welght of 0.2 g/cm3.
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¦ Such products are indeed also light and stiff but can not
be plastically deformed as the foamed core possesses too low
la shear strength and therefore does not provide adeq~ate
¦support to the metallic cover layers so that the metallic
¦cover layer on the compression side in particular buckles
or crumples when the composite is bent; furthermore, when
Ishaped by non-chip-forming processes shear fractures occur,
¦as a result of which the join between the cover sheet and
¦the core is damaged.
¦It is an object of the present invention to provide a flame
~esistant composite panel and a process for the production
~f such a composite panel, by means of which the above men-
~ioned disadvantages of the previously describedl known
~inds of composite panel are avoided, and which exhibit
the properties of being light, stiff, plastically formable
(by non-chip-forming methods) and of being "flame resistant"
(schwer entflammhar) in accordance with DIN 4102.
his object is achieved by way of the invention by the combi-
ation of the following features viz.,
) that the foamed thermoplastic core is made of a rigid
PVC, which
) contains inorganic additives, and whereby
uniformly distributed gas bubbles in the rlgid PVC of the
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core layer are not present at the surface of the core
layer and, that
d) the layer of adhesive between each of the cover layers
and the core layer being substantially non-inflammable or,
in other words, exhibiting favourable burning characteristics
(g~nstiges Brandverhalten).
The method for manufacturing the flame resistant
panel is characterized by the adoption of the following process
steps:
. 10 a) the production of a foamed core layer in which uniformly
; distributed gas bubbles are not present at the surface
of the core layer, followed by
b) the deposition of a layer of adhesive on one side of
both metallic cover layers,
c) the drying of the layer of adhesive especially in a
continuous furnace/oven,
d) the deposition of a layer of adhesive on both sides
of the core layer and
e) the joining together of all layers by the application
of pressure and heat.
l 115fil~5
- 6 ~
Further advantageous versions of the composite panel and
modes of procedure for manufacturing the same are revealed
in the following description.
The accompanying drawing shows a photograph of a cross-
section through the core of a composite panel 1 with foamed
core layer 2 and on both sides of this metallic cover sheets
3 and 4, which are joined to tlle core 2 by means of a layer
of adhesive 6. The relatively thin layer of adhesive can
not be seen here.
The core 2 of the composite panel 1 is made of a thermo-
plastic material which, when heated strongly, tenas to form
a dense, solid crust on its surface, and not to drip. One
such suitable thermoplastic material is a rigid PVC (poly-
vinyl-ohloride) without softener, which is usually preferably
foamed for use as a core layer. The rigid PVC is more flame
resistant than the PVC with softener which is normally emp-
loyed for known composite panels. By foaming the PVC the
density of the core layer 2 is lowered and, as will be des-
cribed in greater detail, the formability of the composite
panel is increased to a notable degree. The preferred core
layer thickness is 0.1 to 10 mm. In order to improve the
ability of the composite panel to withstand fire, a powdery,
inorganic flller is added to the thermoplastic material of
the core 2, and namely a metal oxide and/or hydroxide such
as, for example, Sb2O3 (antimony trioxide) and Al(OH~3 (alu-
minium hydroxide) in a weight ration of 1 : 3 to 1 : 5,
_ 7 _
in particular of 3 : 10 and in amounts of 7 - 20 wt~, pre-
ferably 13 wt% to rigid PVC.
I . ,
¦The said Sb2O3 and A1(OH)3 have a particle size of 0.2 to
¦10~um. ~lso, the Al(OH)3 particles are coated with stearic
¦acid, which amounts to 2 % by weight with reference to the
l weight of Al(OH)3.
I
This coating leads to a uniform, good distribution of the
~l(OH3) and also the Sb2O3 in the rigid PVC.
l s already mentioned, a fbamed thermoplastic material is
¦ sed by way of preference for the core 2 of the composite
anel 1, in which uniformly distributed gas bubbles 5 are
ntroduced into the rigid PVC to lower the density.
he finely distributed gas bubbles 5 in the core layer 2 are
ade up mainly of a gas mixture of 20 - 70 ~ N2; 5 ~ 30
2; 5 ~ 30 % CO and 5 - 30 % NH3, preferably of a gas
ixture of 55 % N2; 15 % CO2; 15 % CO and 15 % NH3. By
overing the core of rigid PVC and inorganic additives
ith metal cover sheets 3 and 4 which are impermeable to
asl the gas remains in the pores in the rigid PVC i.e. in
he core, and there is therefore no exchange with the sur-
ounding air via diffusion through the plastic.
he foaming of the core layer 2 causes a reduction of the
riginal density of the rigid PVC from 1.4 g/cm3 to 0.7 g/cm .¦
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~y the addition of the previously mentioned inorganic sub-
~tances viz., Sb2O3 and Al(OII)3 to the extent of 13 wt% of
~the PVC in the core, the density rises to a final value of
~a. 0.8 g/cm3. From the reduction of the density the compo-
site panel achieves a higher specific strength and from
this a higher formability at room temperature. The density
s prefèrably maintained within a range of 0.2 to 1.2 g/cm3.
~s can be seen from the figure, the uniformly distributed gas
~ubbles 5 in the rigid PVC do not appear as depressions on
¦ he surface of the core layer 2, but are always under the
urface of the core layer 2. This intentional effect is
chieved by intensively cooling the extruded rigid PVC core
ayer at the exit of the shaping tool of an extruder, not
l hown here, and subsequently smoothing it. The resultant
¦ niform surface thus obtained on the foamed core layer 2 is
f particular importance as this ensures good adhesion bet-
een the core 2 and the metallic cover layers 3 and 4 by
pplying a relatively thin layer of adhesive e.g. of about
l 5 ~m in thickness. The very favourable flame behaviour of
¦ he thin adhesive layer 6 is of great importance as this
akes an especially positive contribution to the flame resis-
ance of the composite panel 1 compared with that of the
omposite panels known up to now.
he adhesives used to bond the plastic core to the metallic
! uter layers must not, when exposed to fire conditions, be-
ome soft so that no shear forces are able to be transmitted ¦
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~etween the core and the outer cover layers. This prevents
¦the core 2 from being able to slide out from between the
¦cover sleets 3 and 4, or the cover sleets from being able
l o lift away from the core and bend outwards. Furthermore,
~dheslves which do not contribute to the fire must be
closen, for example adhesives which are not easily com-
ustible or are not highly exothermic in burnin~.
esides the usual two component adhesives based on epoxy
l esin and/or polyurethane, thermoplastic fusion adhesives
¦ f good heat resistance are used.
referred, however, are phenolic or resorcin resins modified
ith nitrile rubber, which exhibit thermoplastlc to duro~
lastic properties, and/or adhesives based on acrylic resins.
l he thickness of the layer of adhesive is between 5 and lOO~un ,
¦ referably 10 - 20~um, and ideally 15 ~um.
he metallic cover layers 3 and 4 are preferably made of
luminium, copper or iron or an alloy of these metals, the
¦ trip employed for this being 0.1 to 0.2 mm thick.
l he composite is produced ln a continuous process as follows:
rhe extruded and calibrated core 2 of foamed rigid PVC is
coated on both sides with adhesive 6 and then covered on
oth sldes with alumlnium sheet which, as described pre- ¦
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~viously, is pretreated with adhesive on one side and a thin
¦layer of lacquer, which is decorative and flame resistant,
¦on the other side.
l ~,
¦The composite panel according to the present invention has
S ¦extremely superior flammability characteristics in compari-
¦son with the composite panels known up to now, and at the
¦same time is readily formable at room temperature.
