CA1156135A

CA1156135A - Flame resistant composite panel and process for its manufacture

Info

Publication number: CA1156135A
Application number: CA000359691A
Authority: CA
Inventors: Harald Severus
Original assignee: Schweizerische Aluminium AG
Current assignee: Alcan Holdings Switzerland AG
Priority date: 1979-09-07
Filing date: 1980-09-05
Publication date: 1983-11-01
Also published as: DE3061633D1; YU40883B; DE2940198A1; EP0025412B1; ATE2235T1; JPS5644650A; JPS6332616B2; BR8005685A; YU226280A; DE2940198C2; EP0025412A1

Abstract

ABSTRACT OF THE DISCLOSURE

The invention relates to a flame resistant composite panel which can be shaped at room temperature with non-chip-for-ming processes and is made of a core of foamed thermoplastic material with metallic cover layers on both sides joined to the core by means of adhesive layers.

Composite panels of the above kind which have a plastic core containing e.g. polyolefines suffer from the disadvantage of having unfavourable flammability characteristics which are expressed in DIN 4102 as belonging to the classification of being of normal combustibility. For this reason such compo-site panels find only limited application, and in addition they can not be plastically deformed.

The disadvantages associated with such composite panels are avoided by a number of measures such as providing the foamed rigid PVC core with a special surface finish which permits the use of a relatively thin layer of adhesive bet-ween the core and both cover sheets.

Description

_ ,_.

Flame resistant composite panel ancl process for its manufacture _ .. _ . ._ ¦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.
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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~

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.
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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.

¦ 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 115613~
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.
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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 .¦

~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 ¦

~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- ¦

1156135 ~ 11 ~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.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A flame resistant composite panel which can be shaped at room temperature by non-chip-forming processes and is made of a foamed thermoplastic core and metallic cover layers which are joined together by means of layers of adhesive, wherein:
a) the foamed thermoplastic core layer is made of rigid PVC, which b) contains inorganic additives, and whereby c) uniformly distributed gas bubbles in the rigid PVC of the core are not present at the surface of the core layer, and d) the layer of adhesive between each of the cover layers and the core being substantially non-inflammable.

2. A flame resistant composite panel according to claim 1, in which the inorganic additives are in the form of a powdery inorganic filler in a weight ratio of 1:3 to 1:5, and in an amount of 7 - 10wt%, of said rigid PVC.

3. A flame resistant composite panel according to claim 2, in which said inorganic filler is at least one of a metal oxide and a metal hydroxide.

4. A flame resistant composite panel according to claim 3, wherein said filler comprises Sb2O3 and Al(OH3).

5. A flame resistant composite panel according to claim 2, wherein said ratio is 3:10.

6. A flame resistant composite panel according to claim 2, wherein said filler is in an amount of 13 wt% of said rigid PVC.

7. A flame resistant composite panel according to claim 4, in which the particles of Sb2O3 and Al(OH)3 have a particle size of 0.2 µm to 10 µm.

8. A flame resistant composite panel according to claim 4 or 7, in which the particles of Al(OH)3 are covered with 2% stearic acid (with respect to the weight of Al(OH)3).

9. A flame resistant composite panel according to claim 1, in which said uniformly distributed gas bubbles in said core layer are made up of a gas mixture containing 20 - 70% N2; 5 - 30% C02; 5 - 30% CO and 5 - 30% NH3.

10. A flame resistant composite panel according to claim 9, wherein said gas mixture contains 55% N2; 15% CO2;
15% CO and 15% NH3.

11. A flame resistant composite panel according to claim 1, in which the thickness of the layer of adhesive is in a range of 5 - 100 µm.

12, A flame resistant composite panel according to claim 11, in which the thickness of said layer of adhesive is 10 - 20 µm.

13. A flame resistant composite panel according to claim 1, 2 or 7, in which said core layer has a density in the range of 0.2 - 1.2 g/cm3.

14. A process for the manufacture of a flame resistant composite panel which can be shaped at room temperature by non-chip-forming processes and is made of a foamed thermoplastic core and metallic cover layers which are joined together by means of layers of adhesive, said process comprising the steps of:
a) the production of a foamed core layer in which uniformly distributed gas bubbles are not present at the surface of the core layer, b) the deposition of a layer of adhesive on one side of both metallic cover layers, c) the drying of the layers of adhesive, d) the deposition of a layer of adhesive on both sides of the core layer, and e) the joining together of said core layer and said metallic cover layers at each said adhesive layer by the application of pressure and heat.

15. A process according to claim 14, wherein said drying in c) is carried out in a continuous oven furnace.

16. A process for the manufacture of a flame resistant composite panel according to claim 14, in which, in order to provide a pore free surface on the core layer, the core material is:

a) intensively cooled and b) subsequently smoothed at the exit end of an extrusion die on an extruder.