Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 95/12496 ,~ PCT/GB94/02419
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FORMING MOULDING WITH SIMULATED WOOD GRAIN SURFACE
This invention relates to the production of synthetic
resin mouldings having a simulated wood grain surface.
It is known that products such as panels, doors, door
frames, window frames, artificial wooden beams, etc., can
be produced with a moulded synthetic resin surface to which
a simulated wood grain finish has been applied by effecting
contact, usually with pressure, between a surface of a
fluid body of curable synthetic resin, e.g. polyester
resin, and a mould surface designed to impress the
simulated wood grain effect on said resin surface. The
curable resin is then normally maintained in contact with
the mould surface until it has been cured to the state
where the fine detail of the impressed finish is not lost
or significantly undesirably impaired when the moulding is
parted from the mould.
The desired surface of the mould may be obtained, for
example, by forming the mould against a suitable wooden
surface. The effect may be enhanced by causing the wooden
surface to swell, e.g. by soaking it, prior to its use as
the former.
The wood grain-like finish on the synthetic resin
moulding may be further improved by suitable pigmentation
of the resin and/or by surface treatment.
While the method is widely used and very good results
may be obtained, there is still room for improvement in the
quality of finish. Furthermore, the finishes currently
WO 95/12496 PGT/GB94102419
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obtained normally require at least two further treatments,
namely, staining and varnishing, in order to obtain a
quality product, and these add significantly to the cost,
especially since often more than one staining step is
required. Moreover, the product recovered
from the mould cannot b~e sanded because every scratch is
highlighted in any subsequent staining treatment.
It has been proposed e.g. in FR-A-2469263 and
W092/18341 to achieve a further improvement in the
simulated wood grain effect achieved by this procedure by
coating the surface of the mould with a colourant such as
a pigment or dye, so that when the curable resin is applied
against the surface of the mould, the colourant transfers
to the surface of the resin and is retained thereon when
the cured resin moulding is subsequently parted from the
mould.
To achieve a wood grain effect that simulates as
nearly as possible its natural equivalent, it is desirable
for the colourant to accumulate in the valleys of the
moulding. This means that the colourant must be
concentrated on the peaks of the mould from which the
moulding is obtained. However, in the method employed in
FR-A-2469263, the colourant tends to be concentrated in the
valleys of the mould and while W092/18341 suggests
restricting the coating to the higher areas of the mould,
the procedures described therein for the purpose, namely
application of the colourant with a stiff pad or use of a
carbon paper or coloured transfer paper, have serious
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drawbacks in practice because they do not lend themselves
to automation, are -labour-intensive, require a skilled
labour force and/or require the use of expensive materials.
This problem is solved by the process of the present
invention which involves first applying the colourant over
the mould surface and thereafter wiping the surface.
Contrary to what would be expected from such a procedure,
it has been found that this has the effect of concentrating
the residual colourant on the peaks of the mould surface.
This is particularly surprising in view of the disclosure
in W092/18341 which teaches that wiping a mould surface on
which a colourant has been deposited removes the colourant
from the high points of the surface.
Not only is the colourant concentrated on the peaks of
the mould surface, and thus in the valleys of the resultant
moulding, but it has been found that a greater depth of
colourant-is found on the higher peaks, thus automatically
providing a very desirable gradation of colour tone in the
valleys of moulding obtained from the moulds, with the
deeper valleys having a deeper tone of colour, as in a
natural wood product.
The first step of the process involves applying the
colourant over the mould surface. The preferred method
involve applying it to the whole, or substantially the
whole, surface. A light coating is adequate.
The colourant, e.g. pigment or dye, may be applied as
a dxy powder or as a suspension or solution in a suitable
liquid medium which may be aqueous or non-aqueous: e.g. an
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WO 95/12496 PCT/GB94102419
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ink. Where a pigment is employed in suspension in a liquid
medium the latter may suitably include a binder.
Application may be by any suitable method such as spraying, .
doctor knife coating, brushing, using a cloth, etc. and as
the whole or substantially the whole area of the mould
surface may be coated with the colourant, this coating step
is readily automatable. It is not essential for the whole
surface to be coated or for the coating to be uniform but
if it is desired not to coat chosen areas of the mould
surface, they can be protected by masking.
The second step of the process involves wiping
the coated surface of the mould. Where the colourant has
been applied dry, e.g. as a powder, no intermediate
treatment is required but where it has been applied in
combination with a liquid, e.g. as a solution or
dispersion, the coated mould surface is preferably first dried.
The surface should be wiped in a manner as if to
remove.colourant deposited in the first step; however, the
manner of wiping does not appear to be critical and any
suitable method and material may be employed provided that
the surface of the mould is not defaced or damaged. For
example, the wiping may be by means of soft bristle,
sponge, cloth or other suitable material. The wiping step,
like the coating step, is readily adaptable to automation,
e.g. by advancing the coated mould surface under a brush,
sponge or cloth rotating about an axis parallel to the
plane of the mould surface, Any part of the mould surface
not to be subjected to the wiping may be protected by
WO 95/12496 ~ ~ ~ ~ ~ ~ ~ PCT/GB94102419
masking.
Contrary to expectations, the wiping step has the
effect of concentrating colourant on the high points or
peaks of the mould surface, relative to other areas. While
the perceived concentration may be apparent, in that it is
the result, at least in part, of selective removal of
colourant from other areas by the wiping, redistribution of
the colourant over the surface of the mould during the
wiping step may also be a contributory factor. In any
event, the result is that colourant becomes selectively
concentrated on the high points and peaks and moreover, the
local concentration of colourant increases with the height
of the peak or high point. While the colourant is
concentrated on the peaks and high areas, this is not to
say that the remaining areas are free of colourant; indeed
for some finishes, it may be desirable to leave at least
traces of colourant on other areas of the surface. The
method of wiping and pressure applied during wiping may be
adjusted by trial and error to achieve the desired effect.
If desired more than one colourant may be applied
before the wiping step and the colourants may be deposited
on different areas of the mould surface or the second
colourant may at least partly overlay the first. In the
latter case, the wiping step will selectively concentrate
the second colourant, Where it overlays the first, on the
high points and peaks.
Likewise, the step of applying the colourant and then
wiping the mould surface may be repeated, if desired, using
WO 95/12496 PC17GB94/02419
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different colourants. Sy this means two or more colourants
may be applied and a wide variety of wood surfaces may be
simulated. Further variation may be achieved, if desired,
by selective removal of colourant from the resultant
moulding, e.g. by sanding the high points.
The desired moulding is obtained by bringing a fluid
body of curable synthetic resin into contact with the mould
surface, preferably with applied pressure, causing or
allowing the resin to cure and harden while in contact with
the mould surface and then parting the resultant moulding
from the mould. If desired the fluid body of curable resin
may comprise a layer supported by a backing, e.g. a rigid
board or a surface of cured resin. By this means the
colourant on the mould surface is transferred to the
moulding and since the colourant is concentrated on the
high points and peaks of the mould, it will be concentrated
in the valleys of the moulding. Moreover, as the deeper
valleys will have the higher concentrations of colourant,
a gradation of colour which is remarkably similar to that
found in the surface of natural wood, is achieved.
Furthermore, because the curable resin is in the fluid
state when it is contacted with the mould surface,
significant quantities of the colourant may be incorporated
into the body of the resin as well as on the surface,
thereby providing a finish which is more resistant to
damage.
The effect achieved by the process of the invention
varies with the kind of wood grain surface simulated by the
W095JI2496 ' '~ ~ ~ ~ ~' ~ 9 PCT/GB94/02419
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mould, the colour of the dye or pigment and the colour of
the resin and the best results for any particular
combination require trial and experiment. In general,
however, it is desirable for the colour of the resin and
' the colour of the dye or pigment to provide a good
contrast, in particular a contrast similar to that which
exists in real wood, e.g. as in a dark coloured, e.g.
black, pigment or dye in the deeper grained areas of the
moulding and a paler base colour for the resin which is
similar to that of the desired wood effect.
In general, a mould release agent will be applied to
the surface of the mould prior to application of the
colourant.
The invention is now described in greater detail with
reference to one embodiment thereof and with the aid of the
accompanying drawings, wherein
Figure 1 shows, in diagrammatic and much enlarged
form, a section of a part of a mould intended to produce a
moulding with a simulated wood grain effect;
Figure 2 shows in cross-section the surface of the
mould of Figure 1 after- application of colourant in
accordance with the first step of the invention.
Figure 3 shows in cross-section the surface of the
mould of Figure 1 after completion of the second step of
the invention.
Figure 4 shows in cross-section the surface of a
moulding obtained from the mould of Figure 3.
Referring to Figure 1, 1 is a mould having a surface
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with valleys 2 and peaks 3 and formed to impart a simulated
wood grain finish to a synthetic resin moulding. The mould
may be obtained by casting a suitable mould-forming
material, e.g. polyester, polyurethane elastomer or
silicone rubber, against the surface of a sheet of wood in
which preferably the surface grain has been exaggerated by
previously soaking the surface of the wood in water to
cause it to swell.
As illustrated in Figure 2, in a first step, a
colourant is applied to the surface of the mould 1 to form
a coating 4.
In a second step, the coated surface is wiped by any
of the methods described above such that a residue 5 of the
coating is concentrated on the high points or peaks of the
mould surface as illustrated in Figure 3.
After completion of the second step, a layer of
curable synthetic resin, e.g. polyester, having a colour
which is a contrast to the pigment in the residue 5, is
applied to the mould surface preferably with the
application of pressure to ensure good contact, and is
allowed to remain in contact with the mould surface until
cure of the resin is substantially complete. By means of
the contact of the resin with the mould surface, the
pigment is transferred to the resin surface 6, producing
the moulding 7 illustrated in Figure 4. The moulding 7
comprises a resin layer principally the valley areas 8 of
which are coated or impregnated with pigment. The high
areas or peaks 9 of the moulding 7 are the colour of the
resin.
WO 95/12496 ~ ~' ~" ~ pCT/GH94/02419
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As will be well understood by those skilled in the
art, the resin layer may be the external layer of a complex
moulding which may, for example, include further backing
layers of resin at least one of which may include filler
and/or fibrous reinforcement. The moulding having the
resin layer as an outer face may also include one or more
preforms such as of blocks of wood or rigid plastics foam
which are located behind and bonded to the resin layer or
layers.
The process of the invention provides a simple and
readily automatable way of obtaining a simulated wood
moulding wherein the colourant is associated with the
grain, as in natural wood.
The wood grain effect on the surface of the moulding
of the invention is closer to the real thing than that
produced by the processes of the prior art Where the
pigment tends to be concentrated in the valleys of the
mould and hence on the peaks of the moulding. Moreover,
the product of the invention does not require staining
prior to varnishing, and may not require varnishing.
Further, by means of the invention, many colours
and/or shades of colour can be achieved in the panel and
where the pigment ar dye is incorporated into the resin
layer the result is more resistant to damage from everyday
use than a conventional stain finish.
Yet a further advantage of the invention is that the
need for staining is avoided although the product may be
stained if desired.
W0 95112496 PCTIGB94102419
Another advantage is that the product more readily
accepts stains and varnishes. This is believed to be due
to the presence on or in the resin surface of pigment
particles which enhance the ability of the surface to
absorb the stain or varnish.
Further improvement may be achieved by sanding or
otherwise abrading the surface prior to staining or
varnishing. Moreover, contrary to what is found With resin
mouldings with simulated wood-grain surfaces and without
the pigmentation provided by the process of the present
invention, sanding does not mar the finish. In fact, it
can enhance the finish in some cases, e.g. where it is
employed to remove any pigment or dye from the high points
of mouldings.
While the invention has been described with reference
to forming the simulated wood grain surface in resin it
will be understood that it is also applicable to any other
mouldable settable material such as gypsum plaster or a
thermoplastics material employed in the heat-softened
state.
