Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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RIGID COLOURED ARTICLE
The invention relates to a method of making coloured rigid articles and to the
articles
themselves. While the invention can be applied to a wide range of articles it
is seen to
particular advantage in making panels for motorised machines/vehicles and so
it will be
described in relation to such items, with the reminder that the invention is
of wider
applicability.
Some vehicles, especially heavy use industrial vehicles such as earth diggers
are prone
to damage. While the vehicles can have metal panels as an exterior covering it
would
be more economic if the panels were made of a less expensive more robust
material.
Plastics are obvious candidate materials but these do not have an attractive
colour. EP-
A-0266107 discloses an article said to be useful as an automobile body panel
and
comprising a cast weatherable polymer film made up of a pigmented acrylic
layer
joined by adhesive to a pvc film and supported on a polymer layer. The article
is made
by injecting curable polymer behind the film placed in a mould with the pvc
film facing
innermost. There is a need for a method of making a rigid impact resistant
panel which
has an attractive bright colour.
In one aspect the invention provides a method of making a coloured rigid
article, the
method comprising:
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i) applying a layer of impact resistant pigmented material to a sheet of
impact resistant thermoplastic polymer to form the precursor of the skin
of the article;
ii) vacuum forming the layered sheet to a predetermined shape appropriate
to the skin of the article.
iii) contacting the shaped layered sheet with a shaped shell in a pressure
and temperature resistant mould with the pigmented layer contacting a
wall of the shell;
iv) supplying a curable resin composition to contact the exposed face of the
sheet, closing the mould and allowing or causing the composition to
cure, whereby the cured composition has the same shape as the sheet,
and
v) removing the formed coloured rigid article.
The skin should be capable of being thermoformed (i. e. under vacuum) and have
a
suitable colour and gloss. The skin should be weather and impact resistant and
have
stability to ultraviolet light. If required, the skin should be capable of
bonding to the
resin substrate. The thermoplastic layer may be acrylonitrilebutadienestyrene
CABS);
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an ester of acryionitrilestyreneacrylic(ASA); polycarbonate and derivatives
thereof;
impact modified unplasticised polyvinylchloride (PVC-u); and uv-resistant high
impact
polystyrene (HIPS). Most preferably the impact resistant thermoplastic polymer
is
AB S and the pigmented layer is a glossy pigmented layer in a plastics Garner,
e. g. a
polyacrylate. Most preferably the sheet and layer are a coextrusion which is
available
under the trade mark "IRIDON".
The formed article will need to be secured to a frame or companion articles
and it is an
advantageous feature of the invention that for this purpose a fixing element
may be
anchored in the curable composition. The shell may be shaped to engage the
free end
of the fixing elements.
The sheet is preferably formed of ABS, i.e. acrylonitrilebutadienestyrene, and
the
polyacrylate Garner for the pigment is preferably polymethylinethacrylate. The
ABS is
preferably a high impact form having the following combination of properties:
an Izod
impact of 380-420 J/m at 23°C; a tensile strength of 30-40 MPa; a
density of about 1.1
gms/cc.
The coextrusion sheet is first vacuum formed, i. e. thermoformed, in a male
mould to
nave the desired profile. This is then placed in a shell which most preferably
is
distortion resistant, i.e. resistant to the pressure and temperatures arising
when the
resin composition is cured in the mould. Most preferably the shell comprises
shell
halves of cured epoxy GRP (which can be made to particularly tight
tolerances).
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Advantageously the shell halves are located in a mould which is then held m a
pressure
resistant press.
The shaped sheet is laid in the shell half with the acrylate layer face down,
so that the
shaped ABS sheet then acts as a former for the curable resin composition.
Because the
shaped sheet contacts the inner layer of the mould a mould release agent is
not needed.
It is a much preferred feature of the invention that fibres are present to
reinforce the
curable composition. Preferably the fibres have tensile and ductile
properties. Such
fibres may be loose but preferably take the form of a mat. While the fibres
may be
selected from a wide range of materials, e.g. metals, non-metals, composites
such as
titanium, carbon, aluminosilicate, plastics such as polypropylene, it is
preferred to use
glass fibres. They may be bonded together in the mat in an emulsion binder,
selected
to be compatible with the curable composition. The fibre material is
preferably
VETROTEX MS available from Vetrotex (UK) Ltd.
The resin composition should be selected to have mechanical properties
according to
the intended end use of the article. A high strength to weight ratio is
preferred,
together with compatibility with the other components. Optionally the resin
composition may be selected for sound attenuation, flowability (to allow the
moulding
of complex shapes); and be capable of being pigmented and colour matched.
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The resin composition may be selected from a range of curable materials such
as PVC,
acrylic polymer, polyethylene, polyester, polyurethane and the like. The
composition is
preferably adapted to form a rigid form, the strengths of which are selected
appropriate
to the intended end use. Most preferably the composition is selected to form a
formed
polyurethane in which case it comprises a polyol component, an isocyanate
component
and a catalyst. Other ingredients may be present such as fillers, blowing
agents,
extenders, colouring agents; and the like. The polyol may be based on a
polyester,
polyepoxy, polyethers, polybutadiene; the isocyanate may be
methyldiisocyanate,
napthalene diisocyanate, tolylene diisocyanate or the like. It is a much
preferred
feature of the invention that the curable resin composition is a polyurethane
because
that will provide a rigid article in a short time period, e.g. less than five
minutes and
typically from I .5 to about three minutes. As a result the articles may be
made guickly
and on a mass production basis.
It is a much preferred feature of the invention that a fixing element is
anchored in the
resin composition before curing. Such element may be a threaded bolt the head
of
which is anchored in the composition. Several such elements may be included.
Curing is then initiated chemically or by temperature or other radiation.
Foaming may
be caused in known manner.
In another aspect the invention provides a method of making a coloured rigid
article
comprising the steps of placing a shaped skin having a pigmented surface in a
shaped
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shell in a pressure and temperature resistant mould with the pigmented surface
contacting a wall of the shell followed by a curing resin behind the skin
characterised
in that the skin is a vacuum formed co-extrusion of a layer of an impact
resistant
pigmented layer and a sheet of impact resistant thermoplastic polymer
In other aspects the invention provides a rigid shaped article comprising an
outer layer
of pigmented impact resistant material, a sheet of impact resistant
thermoplastic
polymer and an inner layer of foamed plastics; preferably the article includes
fibre
reinforcement in the foamed plastics layer and preferably the article
including a fixing
element anchored in the foamed plastics layer.
In order that the invention may be well understood it will now be described by
way of
example only, with reference to the accompanying diagrammatic drawings, in
which:
Figure 1 is a side elevation of a coextrusion; and
Figure 2 is a vertical section through a mould containing shell halves and
before
curing of the resin composition.
A coextrusion 1 comprising an acrylonitrile butadiene styrene 1 A and a layer
of
pigmented impact modified polymethacrylate 1B is thermo or vacuum formed in a
suitable vacuum mould (not shown) at about 160° to 170°C to a
required profile P of
the skin of the intended article. The coextrusion is selected according to the
properties
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required for the end use; in a preferred case the coextrusion has a density of
about 1.1
gms/cc and a thickness of about 2 mm; a tensile strength of about 30 to about
40 MPa
and a flexural strength of about 50 to about 55 MPa, and a flexural modulus of
about
2.2 Gpa. Typically the coextrusion will have a Vicat softening temperature of
about
97 to about 101°C.
A rigid foam backing B is applied to the profile P in a mould shown in Figure
1. The
mould comprises a base 2 and a lid 3; and has side walls 4. The sidewalls are
in
bottom and top halves 4A, 4B respective shaped to hold the free edges of the
profile P.
A paste of a self setting filler composition 5, e.g. a filled plastics is
placed in the lower
half of the mould box to form the intended shape M. A lower shell half H1 is
placed
on the setting paste. The lower shelf half H 1 has a shaped upper wall against
which
the profile P is placed (with the layer 1 B facing downwards), and pipes 6 at
the rear
through which a heating medium flows. The shell half is made of glass
reinforced
epoxy plastics or the like to tight tolerances, so that the profile is an
accurate fit, and
will not move during the moulding step. A mat of VETROTEX material (not shown)
is placed and then uncured polyurethane composition 7 is poured on to the
upper, i. e.
backing face 1 A of the profile P. An insert 8 is placed at one end. A top
shell half H2
is placed on top followed by more of the paste 5, and then the lid 3 is placed
in
position. The whole is put in a hydraulic press, not shown. Hot water is
passed
through the pipes 6, to provide heat to cause the polyurethane composition to
foam
and cure. This takes about two minutes. The water supply is shut off, and the
mould
M removed from the press and dismantled. The profile P with its high density
rigid
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foam backing is removed and trimmed to size and shape. In this way a highly
rigid
panel has been made with a glossy paint finish and at low cost. The shell
halves are
reusable.
The invention is not limited to the embodiment shown. The coextrusion may have
a
shaped face to key to the foam layer.
