Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
123~7Z~;l
Method of making a moulded
body of ~oam plastics material
_______________________________
The present invention relates to a method of
making a moulded body of foam plastics material,
particularly but not exclusively where the visible side
thereof is heavily textured or profiled, smooth and
non-porous with a unit weight of less than 200 kg/m3.
Moulded bodies of this type typically comprise
cornices or like decorative profiled sections of a
length of 2m, which produce a stucco effect after they
have been fixed at the join between a wall and a ceiling.
Such moulded bodies have in the past been produced by
introducing a plastics mixture to be foamed into a two-
part mould provided with a separation medium therein.
The mould parts are conventionally made from silicone
rubber or ~rom polyurethane elastomers. It has been
observed that the moulds swell because they ~bsorb
fluid components from the foaming reaction mixture,
and have to be regenerated after lO mould openings.
Also the dimensions of the moulded articles deviate
to a considerable ex~ent from the admissible
measurement tolerances as a result of the swelling
effect.` Consequentally, wastage of up to 15% is
produced. Moreover, the maximum number of components
~Z37;~6~
-- 2 --
which may be produced using these moulds is only
approximately 250 to 300 per mould which has a
de-trimental effect on the pr:ice of the moulded body.
In addition, the moulds made from silicone rubber or
polyurethane elastomers are ~ifficult to tem~er, which
consequently makes reproduceable production difficult.
Further moulds of this type cannot be de-aerated easily
as a result of their softness, which leads to bubbles
on the surface. It should also be noted that
additional problems are caused by the use of separation
means which are generally very difficult to remove from
the mould body.
It might be thought possible to counter the
latter two drawbacks by foaming onto film which has
previously been deep drawn. This is only possible,
however, with relatively thick film, and the mould
bodies obtained are heavily distorted since they are
only laminated on one side. Thus, a method of this
( type is not suitable for the production of moulded
bodies having a unit weight of less than 200 kg/m3.
Also a method of this type is expensive in terms of
apparatus cost and power consumption.
In order to counter these drawbacks we have
considered the possibility of using a very thin, elastic,
heat-deformable film, which would remain elastic in
the end product so as not to lead to any distortion of
the mould body. The elastic, heat-deformable film
~ ~37261
-- 3 --
would be clamped between two mould por-tions and the
plastics mixture to ~e foamed introduced through the
upper mould portion such that the film is pressed by
the mixture -to be foamed against the lower mould portion.
This method is only successful, as tests carried out by
the applicants have shown, with foam plastics mi~tures
producing moulded bodies with a unit weight of more than
, 500 kg/m3, as it is only mixtures to be foamed of this
type which produce the foam pressure required to press
the film accurately into fine textured contours of the
mould.
With a view to overcoming the aforesaid
difficulties and drawbacks the present invention
provides a method of making a moulded body of foam
plastics material, comprising
providing a thin heat de~ormable film between
two portions of a mould.
providing foaming plastics material in a space
between a first of the mould portions and the film.
producing a partial vacuum between the film
and the second of the mould portions,
and causing the film to become heated such that
the film is urged by the partial vacuum and by pressure
of the foaming material into intimate contact with the
second mould portion.
37~36~
-- 4 --
The invention therefore provides a method which
enables the production of longi-tudinal or round, non-
distorted, moulded bodies having a unit weight of less
than 200 kg/m3, whose visible sides have an accurately
produced surface which is heavily textured or profiled,
smooth, bubble-free and has no separation elements.
In addition, the method is designed to enabl~ the
production, using a mould which has an upper and a lower
mould portion, of up to one million moulded articles,
with a wastage of less than 2%.
In a preferred form, the invention provides a
combination of features which comprise the use of a
thin, elastic, heat-deformable film, which retains or
recovers its elasticity after moulding, in the use of
a foaming plastics mixture which emits heat for the
additional heating of the film as well as the use of
a tempered mould device and the evacuation of the hollow
chamber formed between the film and the lower mould
portion, for the purposes of supporting the deformatlon
of thin, elastic, heat-deformable film by the foaming
pressure.
The invention therefore relates to a method for
the manufacture of mould bodies from foam plastics, the
visible side of these bodies being heavily textured
profiled, smooth, non-porous and free from separation
elements and having a unit weight of less than 200 kg/m~
which is characterised in that
~23726~
a) a thin, elas-tic~ heat-deformable film is
inserted between two heated mould portions i~ such a
way that the film edges are clamped between the super-
imposed mould edges of the two mould portiorls,
b) a reactive, heat emitting, foaming plastic
mixture is introduced through the upper mould portion
in such a way that it may be distributed on the film,
! and
c) the hollow chamber formed between the film and
the lower mould portion is evacuated during foaming,
so that the film which is heated both by the heated
mould portions and by the heat of reaction given off
by the reaction mixture is pressed by the foam pressure
together with the vacuum provided so that its contours
accurately fit the heavily textured or profiled mould
surface of the lower mould portion.
For the purposes of the $nvention any thin
elastic or ductile, heat-deformable plastics film,
~ which has an elastic or ductile nature after moulding,
is suitable. Film having a thickness of 180 to ~a~m
is preferred, and in particular film of this type made
from soft polyvinyl chloride.
Whilst carrying out the method, the mould
device, or the two mould portions, is kept at a
temperature of 55 to 65C. For this purpose, the
mould portions are provided with passages through
which a corresponding heated medium flows.
-- 6 --
Mixtures known to persons skilled in the art are
suitable for use as foaming plas-tics mixtures for the
purposes of the invention. Two component mixtures
which produce a polyurethane hard foam are particularly
preferred as foaming plastics mixtures. Similarly, use
may also be made of epoxy resin foams or phenol resin
foams. With respect to the production of hard
polyurethane foams, reference should be made to the
"Kunststoffhandbuch" (Plastics handbook), Vol.Vll,
Polyurethane, by Vieweg/Hoechtlen (Karl Hanser-Verlag,
Munich 1966) and to the references given therein.
In order that the invention may be more fully
understood an embodiment thereof will now be described
by way of illustrative example with reference to the
accompanying drawings wherein:
Figure 1 is a cross-sectional view of a moulded
body in the form of a cornice, made by a method according
to the invention;
Figure 2 is a schematic perspective view of a
pattern of recesses and projections which runs along
the length of the cornice, and
Figure 3 is a schematic cross-sectional view of
a two part mould for mou~ding the cornice shown in Fig.l
~2~ 61
. , .
-- 7 --
In the Figures, the reference numerals have
the following significance:
l. Upper mould portion
2. Lower mould portion
3. Film
4. Foam
5. Heating ducts
6. Vacuum chamber
7. Vacuum nozzles
8. Recesses
9. Projections
Figure l shows a cross section through an orn-
amental profiled section moulded body in the form e.g.
of a cornice, made from plastics foam 4, typically a
hard polyurethane foam as aforesaid, and a heat de-
formable plastics film 3, typically of P.V.C. as afore-
said. Recesses 8 and projections 9 are disposed
'~ along the length of the body as shown schematically
in Fig.2. The recess 8 and the projection 9 show~ in
Fig.l do not lie in the same cross-sectional plane,
but behind one another. The recesses 8 and the pro-
jections 9 may be formed as shown in outline in Fig.2
and may be ornaments,
Figure 2 is a diagrammatic perspective view of
the recesses 8 and the projections 9, wherein it can be
seen that these recesses and projections may have the
form of ornaments.
~23~:6~
Figure 3 is a cross-section through the mould
device, which comprises an upper mould portion l and
a lower mould portion 2 which are each provided with
the heating ducts 5. The mould portion 2 is provided
with a surface pattern which de~ines the recesses 8
and projections 9,together with the rest of the
ornamental pattern for the cornice. The lower mould
portion 2 also in use defines a vacuum chamber 6 and
has vacuum nozzles 7, which are connected to a vacuum
source(not shown).
To make the moulded body, the two mould portions
1,2 which are preferably of cast aluminium or a different
metal or alloy are initially seperated from one another
They are brought to the required temperature, typically
55 65C by passing a heated fluid through the ducts 5.
A thin, highly elastic plastics deformable film (i.e.
the film 3)is inserted between the mould portions 1,2
such as to overlie the lower mould portion. The
mould portions 1 and 2 are then brought together such
that the film 3 is sandwiched between edge regions o
the portions. Then,plastics foam mixture is injected
into the mould into a space between the upper mould
portion 1 and the film 3, such as to be distributed
over the film. ~fter the predetermined starting
time the mixture begins to foam and is thereby distributed
throughout the mould. The heat of reaction of the
~237;~
g
foaming material and also the heat from the mould
portions l, 2 causes softening of the film 3. After
distribution, i.e. when the mould is full of foam, an
overpressure is crea-ted. This overpressure presses
the film 3 onto the mould surface of the lower mould
member 2. Components produced soley in this way do
not have sharply defined edges, in particular in the
case of deep recesses, In order to prevent or solve
this, a vacuum is provided between the lower mould
portion 2 and the film 3 whilst the foam pressure is
rising in the mould. This partial vacuum helps to
bring the film into contact with the mould in all areas
and corners. The vacuum therefore aids the foam
pressure during simultaneous uniform foaming in causing
intimate contact of the film 3 with the lower mould
portion surface. As the film lies flat, in the first
instance, in the mould and assumes the mould contour:;
'~ as a result of the foam pressure, the formation of air
bubbles on the surface is completely avoided. In
addition, the film also acts as a separation layer
(between the foam and the lower mould portion). Further,
the film 3 can provide a final surface ornamentation,
for example in the form of different colours, or as a
printed wood grain imitation, for different types of
decor.
~23726~
~- 10 -
A two component system as aforesaid for the
production of polyurethane hard foam is used as the
foaming mixture and the resulting moulded body has a
unit weigh-t of less than 200 kg/m3.
Long decorative profiled sections such as
cornices, and also rosettes and dadoes may be produced
in the manner described above.
