Note: Descriptions are shown in the official language in which they were submitted.
1181
DUCTILE COMPOSITE MATERIAL AND
PROCESS FOR ITS MANU~ACTURE
Back~round of the Invention
1. Field of the Invention
The invention relates to a laminate, with a
sandwich-like structure, of a thermoplastic material as
inner layer and aluminum foil as cover layers, said
composite material having metal-like stability properties.
2. Description of the Prior Art
Composite foils of a polyolefin support layer and
metal cover layers are known. A process for their manu-
facture by combining the layers by means of an adhesion
promoting layer is described in German Application
1,779,55~. The composite materials produced in this manner,
however, have the drawback that their mechanical properties
are primarily determined by the material properties of the
center layer of thermoplastic material. That means that a
high share of the stability properties of the metallic cover
layers of the composite remain unused.
Similar to metals, thermoplastic materials,
particularly partially crystalline materials, have the
characteristic of cold work hardening, that is, their
stability increases when they are wor~ed when cold. Cold
working is a method frequently used in metal processing
where the material to be worked is subjected to compressive
or tensile treatment at temperatures below the crystallite
melting point, that is, while "cold". Thus, for instance,
in the case of a 6,6-polyamide semi-finished material, the
tensile strength increases by a multiple of its original
stability if the material i5 subjected to a cross-section
reduction by cold rolling. At the same time, the breaking
elongation is considerably reduced so that the thermoplastic
material obtains ductile properties which correspond with
those of selected metallic materials.
Such cold work-hardenecl thermoplastic materials
display relaxation effects after transformation, that is,
molded parts produced therefrom, such as foils, tend to go
back to their original shape in the course of time and
particularly when exposed to thermal influences.
A purpose of the invention was to develop a
ductile composite material, the mechanical properties of
which correspond with aluminum, whereas the other physical
properties are determined by the inner plastic layer.
Summary of the Invention
This invention relates to a composite material of
a thermoplastic material as inner layer and aluminum foils
as cover layers wheerein the inner layer is a cold-worked
thermoplastic material.
Description of the Preferred Embodiments
Useful as thermoplastic materials for the inner
layer are partially to highly crystalline plastic materials
such as polyolefins, for instance, high and low density
polyethylene or polypropylene, polyamides, for instance,
polyamide-6, polyamide-6,6 or polyamide-12, and polyether
sulfones, polycarbonates, and saturated polyesters.
7~
Preferred are polyamide-6 or polyamide-6,6 which are filled
with 5 percent by weight to 40 percent by weight of aluminum
needles or aluminum grids. The thickness of the inner layer
may vary within wide ranges between 0.5 millimeter and 15
millimeters, preferably between 1 millimeter and 10 milli-
meters.
The cover layers consist of aluminum foils which
preferably are 0.1 millimeter to 5 millimeters thick.
In one embodiment of the invention, the inner and
cover layers are adhered by the use of melt adhesives or
adhesion promoting foils. Suited for this purpose are
normal plastics such as ethylene/acrylic acid-, ethylene/-
vinyl acetate- or hydrogenated butadiene/styrene copolymers.
In accordance with this invention, cold worked
thermoplastic materials are used. The cold working of the
plastic layer may be carried out in the nor~al manner, for
instance, by rolling at temperatures below the crystallite
melting point, preferably at room temperature, achieving a
reduction in the thickness by 10 to 80 percent, preferably
between 30 and 70 percent.
In a preferred process for the manufacture of the
laminates of this invention, the inner layer is combined
with the cover layers, and, if used, the adhesion promoting
foils and the laminate is pressed at a temperature above the
softening temperature of the plastic material and adhesion
promoting foil at a pressure of 20 bars to 200 bars~
preferably 50 bars to 100 bars for a period of 5 seconds to
60 seconds, preferably 15 seconds to 40 seconds.
17s~9
The plastic foil may be rolled off a coil and the
laminate, due to its ductile properties, may also be wound
on a coil. The material can be pressed using commonly used
machinery, for instance, heatable multi-platen-presses.
The laminates of this invention may be used for
the production of deep-drawing parts and intrusion molded
parts such as pitchers, cams, beakers, cups and sleeves such
as condenser sleeves or cartridge sleeves for ammunition for
hunting or target practice.
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Example
A 4 millimeter thick foil of polyamide-6,6 was
cold rolled resulting in a 50 percent recluction of the
cross-section. On a multi-platen-press, the cold rolled
polyamide-6,6 was pressed together with 0.3 millimeter thick
aluminum foil pre-heated to 235C under a pressure of 50 to
100 bars for a period of 30 seconds. A well adhering
laminate was obtained.
For comparison purposes, a composite material was
produced using a polyamide which had not been cold rolled.
The tensile strength and the breaking elongation
according to DIN 53 455 was measured using the composite
materials and the raw materials.
The results are presented in the table below.
Tensile Breaking
Strength Elongation
[N.mm~2] %
Polyamide foil (not cold rolled) 50 200
Polyamide foil (cold rolled) 75 22
Aluminum foil 185 2
20 Laminate (unrolled PA) 58 18
Laminate (cold rolled PA)130 5
