Note: Descriptions are shown in the official language in which they were submitted.
CA 02538917 2006-03-08
1
TITLE: MULTISTAGE METHOD AND APPARATUS FOR CONTINUOUSLY
FORMING A COMPOSITE ARTICLE
FIELD OF THE INVENTION
This invention relates to an apparatus and method for making molded
plastic articles. More particularly, this invention pertains to a method and
apparatus
for making composite plastic molded articles, and composite articles so made.
BACKGROUND OF THE INVENTION
Plastic molding is a well-known technique for mass manufacturing
articles simply and inexpensively. As advances in molding technologies are
made
plastic components are being used in ever more numerous applications,
replacing
other materials such as metal and wood. However, to be able to replace such
materials requires the use of advanced techniques to enhance the strength and
stability of the plastic molded articles. One such technique is to use a
composite
structure for the molded article.
For example U.S. Pat. No. 6,863,972, discloses a composite panel having a
synthetic wood layer that is secured to a foamed polymer layer. However, this
patent
teaches using a cellulosic filler material in an amount of about 20% to 70% by
weight
in the synthetic wood layer, to give it the look and feel of wood. However,
such filler
material is somewhat weak and reduces the strength of the synthetic wood
layer,
meaning the size of the composite component needs to be quite large to support
loads.
Stronger and higher load bearing and thinner layers can be made with fiber-
glass or carbon reinforced plastic layers. A preferred method of making such
articles
is through the pultrusion process.
In a typical pultrusion process a fibrous mat or braid is fed into an
injection die,
where it is passed over a mandrel and is impregnated under pressure with a
resin.
From there, the resin impregnated braid is passed to a pultrusion die with a
mandrel
for forming heating and then. pulling the cured reinforced layer from the die
for
CA 02538917 2006-03-08
2
finishing. An example of a pultrusion process for forming a hollow tube is
shown in
US patent 6,395,210. One problem with pultrusion of hollow structures is that
the
cured reinforced layer must still be thick enough to provide the structural
integrity
necessary to withstand the forces of the pulling mechanism.
Attempts have been made to combine the pultrusion process with a foam core
to manufacture composite panels. However, it can be very difficult to bond the
foam
to the pultruded layer. For example, U.S. Pat. No. 5,286,320 discloses
pultruding
composite panels using pre-formed foam core board. Reinforcements, such as
glass
fiber mats and continuous fibers are added to the outside surfaces of the foam
core
board as it passes through a pre-forming die. Next the foam core board and
fiber
reinforcements are pulled through a pultrusion die where the liquid resin is
applied
and cured to form a fiber-reinforced layer.
To help to make a better bond the patent teaches that the foam core board
must have foam cells containing water or other vaporizable material. In the
heated
die the water vaporises, causing the foam to expand thereby pressing the foam
against the reinforced layer. This in turn forces the reinforced layer against
the inner
surface of the die, leading to a smoother outer finished surface. However,
rigid
structural closed cell foams are not capable of being expanded by such a
process
and so the teachings of this patent are not suitable for such foams, and yet
such
foams are highly desirable in structural components.
What is desired is a simple, cost efficient molding apparatus and method that
can be used to pultrude a. fibre reinforced layer having a three-dimensional
profile
onto which a structural foam has been securely and structurally bonded. Such
an
article will be a light weight and inexpensive substitute for other types
materials in
many applications.
SUMMARY OF THE INVENTION
One aspect of the present invention is to provide a multistage molding
apparatus for continuously forming a composite article, said apparatus
comprising: a
first stage for forming a skin, a second stage for applying a structural foam
to said
CA 02538917 2006-03-08
3
skin as said skin is being cured to form said composite -article and a third
stage for
curing said composite article.
In another aspect, the first stage comprises an injection die and a spaced
apart
mandrel to define an injection die cavity therebetween sized and shaped to
continuously receive a skin forming material at one end of said injection die
cavity,
said first stage further including a resin pump to inject a resin into said
skin forming
material in said injection die cavity as said skin forming material passes
through said
injection die.
In yet another aspect, the first stage further includes a means to remove
excess resin from said injection -die cavity and skin forming material as said
skin
forming material passes through said injection die. In a further aspect, said
means to
remove excess resin permits said excess resin to be reused in said injection
die. In
yet a further aspect, the first stage further includes a means to remove air
or any form
of gas from said excess resin.
In another aspect, the second stage includes a pultrusion die, downstream of
said first stage, to cure said skin forming material and said resin to form
said skin.
In another aspect, the third stage includes a curing die to complete the
curing
of said foam and skin composite article.
In another aspect, the apparatus further comprises a fourth stage for applying
a coating to an outside surface of said composite article. In a further
aspect, the
fourth stage includes a coating applicator for smoothly coating said composite
article
with said coating. In yet a further aspect, said coating applicator applies a
photo-
curing coating and said fourth stage further includes a light source for
curing said
coating.
In another aspect of the present invention, there is provided a multistage
method for continuously forming a composite article, said method comprising
the
steps of:
impregnating a skin forming material with a resin at a first stage;
CA 02538917 2006-03-08
4
curing said impregnated skin forming material to form a skin, while
applying a foam to said impregnated skin forming material before said
impregnated skin forming material is fully cured in a second stage; and
curing said foamed skin to form said composite article at a third stage.
In another aspect the method provides that the resin is made from a first
composition and said foam is made from a second composition, wherein said
first and
second compositions have a sufficient amount of a common ingredierit to permit
said
first and second compositions to bond to one another. In a further aspect, the
common ingredient is a type of thermoplastic resin, one example being ABS
plastic.
In another aspect, the method further includes a step of coating said
composite
article with a finish coat.
In another aspect, there is provided a composite article comprising:
a skin layer bonded to a foam layer,
wherein said skin layer is made from a first composition and said foam
layer is made from a second composition, and wherein said first and second
compositions have a sufficient amount of a common ingredient to permit said
first and second compositions to bond to one another.
In a further aspect, said common ingredient is a type of thermoplastic. In yet
a
further aspect, said thermoplastic is ABS plastic.
In another aspect, said composite article further comprising a finish coat
layer
bonded to said_ skin layer. In a further aspect, said finish coat layer is a
type of
photocured finish coat material.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference will now be made to the preferred embodiments of the present
invention with reference, by way of example only, to the following drawings in
which:
Fig. 1 is a schematic diagram of a cross-section of the present invention in
operation and showing. a first stage for forming a skin, a second stage for
applying a
structural foam to said skin as said skin is being cured to form a composite
article and
a third stage for curing said, composite article;
CA 02538917 2006-03-08
Fig. 2 is a schematic diagram of a cross-section of -the invention of Fig. 1,
showing the injection die of the first stage;
Fig. 3 is a schematic diagram of a cross-section of the invention of Fig. 1,
showing the pultrusion die of the second stage;
5 Fig. 4 is an alternate embodiment of the second stage of Fig. 3 showing
vacuum channels for helping to hold the skin against the interior surfaces of
the
pultrusion die;
Fig. 5 is a schematic diagram of a cross-sectional view of the invention of
Fig.
1 showing a coating applicator of a fourth stage for applying a coating to a
bottom
outside surface of the composite article;
Fig. 6 is a schematic diagram of a cross-sectional view of the invention of
Fig.
5 showing an altemate embodiment of the coating applicator capable of applying
the
coating to a top and bottom outside surfaces of the composite article;
Fig. 7A is a side view of a composite article according to an embodiment of
the
present invention in which the foam layer is sandwiched between two skin
layers;
Fig. 7B is a side view of the composite article of Fig. 7A with a coating
applied
to the outside surfaces of both skins;
Fig. 7C is a side view of a composite article according to an embodiment of
the
present invention in which the foam layer is bonded to a skin layer; and
Fig. 7D is a side view of the composite article of Fig. 7C with a coating
applied
to the outside surface of the skin.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is described in more detail with reference to exemplary
embodiments thereof as shown in the appended drawings. While the present
invention is described below including preferred embodiments, it should be
understood that the present invention is not limited thereto. Those of
ordinary skill in
the art having access to the teachings herein will recognize additional
implementations, modifications, and embodiments which are within the scope of
the
present invention as disclosed and claimed herein. In the figures, like
elements are
CA 02538917 2006-03-08
6
given like reference numbers. For the purposes of clarity, not every component
is
labelled in every figure, nor is every component of each embodiment of the
invention
shown where illustration is not necessary to allow those of ordinary skill in
the art to
understand the invention.
A multistage molding apparatus 10 for continuously forming a composite article
12 according to the present invention is disclosed in Fig. 1. The first stage
14
involves forming a skin 16, the second stage 18 involves applying a structural
foam
20 to the skin 16 as the skin 16 is being cured (indicated at 17), and the
third stage 22
involves curing the skin 16 and foam 20 of the composite article 12. A pulling
mechanism 23 located at the downstream end of the apparatus 10 is used to pull
a
skin forming material 34 through the apparatus 10 at a predetermined rate.
Figs. 5
and 6 show a fourth stage 24 which involves applying a gel coat or finish coat
26 to
the composite article 12. A key aspect of the present invention is that the
multistage
molding apparatus 10 allows for a continuous flow-through manufacture of a
finished
composite article 12 without the need for handling or other manipulation
between
stages. The endless composite product produced in this way is cut to size by a
cutter
13 and then finished after exiting the apparatus 10. The finished composite
article 12
is then ready for packaging and shipping.
Referring to Fig. 2, there is shown a schematic diagram of the first stage 14.
The first stage comprises an injection die 28 and a spaced apart mandrel 30 to
define
an injection die cavity 32 therebetween. The injection die 28 may be made by
any
means known in the art, out of any suitable heat conducting material having
the
requisite structural integrity. Aluminium is a preferred material, but steel
may also be
used. The injection die cavity 32 is sized and shaped to continuously receive
a skin
forming material 34 at one end of the injection die cavity 32, and discharge
it at the
downstream end, after it has been impregnated with a resin 36. The skin
forming
material 34 is shaped by the injection die cavity 32 while being impregnated
with the
resin 36 as it passes through the injection die cavity 32. The injection die
28 may be
configured to form the skin forming material 34 into profiles ranging from a
simple
two-dimensional sheet to a complex three-dimensional a hollow member.
CA 02538917 2006-03-08
7
In a preferred embodiment the resin 36 is pumped into the injection die cavity
32 by a resin pump 38 under pressure. The resin pump 38 forces the resin 36
from a
reservoir 40 into channels 42 located in the upstream end of the mandrel 30
which
terminate in a series of injection ports 44 for injecting the resin 36 into
the injection die
cavity 32. However, other means for injecting resin 36 into the injection die
cavity 32
are also contemplated, such as for example, by injecting the resin 36 directly
into the
injection die cavity 32 through channels (not shown) in the upstream end of
the
injection die 28 itself. What is important is that the skin forming material
34 is
impregnated with sufficient resin 36 as it passes through the injection die 28
to create
a reinforced layer having the desired structural properties for the specific
application.
If the resin 36 is of the type that is formed from two or more components
which
must be mixed before use, the components may be provided in separate
reservoirs
40 which are mixed in an appropriate ratio by the resin pump 38, or by a mixer
(not
shown) provided before the resin pump 38.
While the injection die 28 is disclosed herein as the first stage 14 of the
multistage molding apparatus 10, it is contemplated that the injection die 28
may be
used separately in other applications.
Suitable materials for use as the skin forming material 34 are well known in
the
art, and can be selected from a wide variety of materials, such as glass-
reinforcing
fibres, or such other fibres as may be suitable for the desired purpose.
Continuous
length fibers in the form of roving or mats are preferred. What is desired is
to use
fibres that will retain their strength and integrity during the temperature
ranges which
occur during the various stages of the instant invention. In particular, the
fibers must
be able to withstand the pulling forces and temperatures that are during the
various
stages of the instant invention.
Suitable resins useful for impregnating the skin forming material 34 are also
well-known. For example, the resin 36 may be a thermoset resin such as
unsaturated
polyesters, epoxies, phenolics, methacrylates and the like, as well as
thermoplastic
resins such as PP, PU, PPS, ABS, and Nylon 6.
CA 02538917 2006-03-08
8
In one embodiment of the present invention the injection die 28 includes a
means for removing excess resin 46 from the injection die cavity 32 and skin
forming
material 34 as the skin forming material 34 passes therethrough. This is
accomplished via resin removal channels 48 located near the downstream end of
the
injection die 28. The resin removal channels 48 provide a pathway for the
excess
resin 46 to flow from the injection die cavity 32 to the outside of the
injection die 28
and connect to the resin pump 38. It will be noted that the excess resin 46 is
removed from the injection die 28 without being exposed to the atmosphere and
so is
not likely to become contaminated with dust, dirt or the like. In addition,
the resin
removal channels 48 are located sufficiently remote from the injection ports
44 so as
to avoid short circuiting of the resin 36. In other words, the resin removal
channels 48
are sized and positioned so as to create a pressure drop between said
injection ports
44 and said removal channels 48 which is larger than the desired injection
pressure
for said resin 36 in said die 28, so said resin 36 fully impregnates said skin
forming
material 34.
The removed, excess resin 46 may be reused by being re-injected into the
injection die cavity 32. Prior to being reused, however, any entrained air or
other
gases are removed from the excess resin 46 before it is redirected back into
the
injection die cavity 32. Any such entrained air or gases could lead to bubbles
or
blisters in the finished product and are thus undesirable. The air is most
preferably
removed by providing a separate settling tank (not shown), or providing a
settling
chamber (not shown) in the resin pump 38, which allows entrained air or other
gaseous bubbles to rise to the surface and break before the excess resin 46 is
redirected back into the injection die cavity 32 and reused. In addition to
helping to
minimize the amount of resin 36 that is wasted in the first stage 14, the
resin removal
channels 48 also help to eliminate air trapped in the resin impregnated skin
forming
material 34, which helps to minimize the production of voids and maximize
resin
impregnation of the skin forming material 34. The resin recirculation system
disclosed is a closed system, which, in addition to the benefits mentioned
above
CA 02538917 2006-03-08
9
permits complete temperature control of the resin path wherein the resin is
not
allowed to undergo temperatures which would affect its ability to be reused.
As will be appreciated by those skilled in the art, the temperature of the
injection die 28 must be carefully controlled and maintained below a
temperature that
would lead to the curing of the resin 36. It is also well-known that the
length of the
injection die 28 is determined with a goal of providing maximum penetration of
resin
36 into the skin forming material 34, ensuring a very good wet out without
trapping air
or off gas. This is contrasted with the competing goal of keeping the
injection die 28
as short as possible to reduce the pull force required and increase the
production
speed. Good results have been achieved with an injection die 28 having a
length of
about 24 inches.
As shown in Fig. 1, the second stage 18 comprises a pultrusion die 52 which is
connected to the downstream end of the injection die 28. The second stage 18
involves applying a structural foam 20 to the skin 16 as the skin 16 is being
cured.
The temperatures required to cure the skin 16 are typically much higher than
those
desired to wet the skin forming material 34 in the first stage 14.
Accordingly, a means
for controlling the temperature of the injection die 28 is preferably included
at the
downstream end of the injection die 28.
As shown in Fig. 2, the means for controlling the temperature, in the present
embodiment, is a cooler 54 contacting the outside surfaces of the injection
die 28.
However, various coolers and other means for controlling the temperature of
the
injection die 28 will be known to those skilled in the art and are not
described in any
great detail herein. Some preferred examples of coolers comprehended by the
present invention include, water cooling, refrigerating coils, thermal breaks
including
heat conducting fins, or ceramics, etc. A thermal break 56 having heat
conducting
fins, or ceramics or the like is preferred on the upstream end of the
pultrusion die 52.
As a higher heat is required in the pultrusion die 52, to cure the skin 16,
than is
required in the injection die 28 of the first stage 14, the thermal break 56
limits the rise
in the temperature of the injection die 28. Most preferably such a rise is
limited to an
amount below the curing initiation.temperature of the resin 36. As can be
appreciated
CA 02538917 2006-03-08
a temperature rise in the injection die 28 above the curing initiation
temperature of the
resin 36 would result in the premature curing of the resin 36, before the skin
forming
material 34 has had adequate opportunity to become impregnated with the resin
36.
As shown, Fig. 3, the pultrusion die 52 is involved in the second stage 18 to
5 apply the structural foam 20 to the skin 16 and to cure the skin 16 and foam
20 to
form the composite article 12 as it passes therethrough. As will be
appreciated by
those skilled in the art, the length of the pultrusion die 52 depends on many
factors
such as wall thickness, expected speed of production, expected quality of
surface
finish, etc. The length of the pultrusion die 52 also depends on the time
required to
10 bring the resin impregnated skin forming material 34 to the curing
temperature, which
is typically about 400 F. However, a competing factor is that a longer
pultrusion die
52 increases the pull force that is required by the pulling mechanism 23.
Moreover,
proper temperature distribution allows for an increased speed of pultrusion.
Good
results have been obtained with pultrusion dies 52 having lengths of between
about
12 to about 18 inches. As will be appreciated, by persons skilled in the art,
this is
significantly shorter than known pultrusion dies. Due to their shorter length,
the
pultrusion dies utilized by the present invention are fast, easy and cost-
efficient to
fabricate. For example, the pultrusion dies of the present invention may be
fabricated using an axial cutting method, such as wire cutting, to prepare a
tube
shaped die, as opposed to having to cut the die in half and using milling or
grinding to
define separately each half of the profile in each die part. The reason that
the
multistage apparatus 10 of the present invention permits the use of shorter
than
traditional pultrusion dies is that curing of the skin 16 continues in the
adjacent and
downstream second stage 18 and third stage 22.
Referring still to Fig. 3, the mandrel 30 is shown as extending from the
injection
die 28 and most preferably part way into the pultrusion die cavity 58. The
amount by
which the mandrel 30 extends into the pultrusion die cavity 58 is governed by
three
considerations. First, it is important that the mandrel 30 extends to a point
into the
pultrusion die cavity 58 where the skin 16 has not fully cured. At this point
the skin 16
will need to have cured sufficiently to have structural integrity to withstand
the forces
CA 02538917 2006-03-08
11
exerted by the foam 20 which are sufficient to keep the skin 16 pressed
against the
surfaces of the pultrusion die cavity 58. The force of the foam 20 is
sufficient that the
skins no longer need to be supported by the mandrel 30. Second, it is
important that
the foam 20 is applied to the skin 16, before the skin 16 has fully cured.
This ensures
a strong molecular bond will be formed between the skin 16 and the foam 20, in
the
finished composite article 12. Third, it is desirable to have the mandrel 30
as short as
possible, to reduce the pull force that is required by the pulling mechanism
23.
Accordingly, it is preferred that the mandrel 30 extend into the pultrusion
die cavity 58
by the shortest possible amount which will allow the foam 20 to be applied to
a still
curing skin 16. Good results have been obtained with the mandrel 30 extending
into
the pultrusion die cavity 58 by about 4 and 6 inches.
Fig. 4 shows an altemate embodiment of the pultrusion die 52 of the present
invention. As shown, there is a plurality of vacuum channels 80 included in
the
pultrusion die 52, leading from the pultrusion die cavity 58 to the vacuum
pump 82.
The purpose of these vacuum channels 80 is to draw the skin 16 against the
surfaces
of the pultrusion die cavity 58. This configuration is useful when forming
composite
articles 12 in which the foam layer is very thin, by helping to keep the skin
16 layers
conforming to the die shape during the curing stages. This alternate
embodiment is
also useful when using a thermoplastic resin 36 to impregnate the skin forming
material 34.
With reference to Figs. 1, 3 and 4, it will be apparent that the structural
foam
20 is delivered into the pultrusion die cavity 58 through a foam injector 60
located on
the mandrel 30. If the skin 16 is formed in the injection die 28 as a hollow
member,
the foam injector 60 places the foam 20 inside of the hollow member. In other
cases,
the foam injector 60 injects the foam 20 into the pultrusion die cavity 58 so
as to apply
the foam 20 to the surfaces of the skin 16.
The foam 20 is delivered to the foam injector 60 via one or more foam delivery
conduits 62 located in the mandrel 30. As best seen in Fig. 1, the upstream
end of
the foam delivery conduit 62 is connected to a means for preparing the
structural
foam 20, which is.referred to herein as a foamer 64.
CA 02538917 2006-03-08
12
The structural foam 20 prepared by the foamer 64 is preferably a rapidly
curing, closed cell, microcellular thermoplastic foam material capable of
bonding to
the skin 16, as the skin 16 and the foam 20 are curing. Thermoplastic foam
material,
such as polystyrene, is preferred to thermoset foam material because.the
latter will
expand further.during the third stage 22 and contact the skin 16 under
pressure, to
help eliminate voids between the foam 20 and the skin 16. Microcellular
plastics are
characterized by cell sizes in the range of 0.1 to 10 micrometers, cell
densities in the
range of 109 to 1015 cells per cubic centimeter, and specific density
reductions in the
range of 5% to 95%. What is important is to create a large number of bubbles,
smaller than the pre-existing flaws in the foam layer 20. Microcellular
thermoplastic
foam is preferred to unfoamed plastic because it exhibits up to a five-fold
increase in
Chirpy impact strength, toughness, stiffness-to-weight ratio, and fatigue
life.
Furthermore, microcellular thermoplastic foam exhibits high thermal stability,
low
dielectric constant and low thermal conductivity. As will be appreciated by
those
skilled in the art, the thermoplastic materials, as well as other parameters
used to
make the microcellular foam will vary depending on the foam characteristics
that are
required in a particular application. However, one important characteristic of
the foam
is that it should have cell sizes as small as possible.
The foamer 64 used to produce the foam 20 has a first mixing chamber 66,
connected to a second mixing chamber 68, a temperature and pressure controlled
reservoir 70 and a foam pump 72. In order to prepare the closed cell,
microcellular
foam, thermoplastic material is melted and mixed in the first mixing chamber
66 with
an agitator 74. Air is injected into the first mixing chamber 66 by an air
injection
means 76 to entrain air in the thermoplastic material under pressure. Once the
molten, air entrained, thermoplastic material has been thoroughly mixed, it is
moved
into the second mixing chamber 68 which has a mixer 78 and temperature control
to
permit the thermoplastic material to be further mixed and cooled under
pressure. The
second mixing chamber 68 is connected to an outlet 69 for expelling the
thermoplastic material from the second mixing chamber 68 at a lower pressure
than is
CA 02538917 2006-03-08
13
maintained in the chamber 68 into the temperature and pressure controlled
reservoir
70.
The finished foam 20 is then injected from the reservoir 70 into the foam
delivery conduit 62 by the foam pump 72. The foam pump 72 may be a piston or
screw type pump. What is important is that the rate and pressure with which
the foam
20 is delivered to the foam delivery conduit 62, and into the pultrusion die
cavity 58
may be controlled. The present invention comprehends maintaining the foam at a
higher pressure within the foam injection conduit than within the space
adjacent to the
skin. The pressure drop needs to be sufficient to cause the foam to expand as
it
enters into contact with the skin. This expansion then provides the necessary
pressure to permit good bonding to occur according to the present invention.
The
actual pressure drop will vary depending upon the product. The pressure drop
required to maintain the good foam to skin bonding will vary depending upon
the
thickness of the foam layer, the speed of production, the type of foam used
and the
like.
Continuing to refer to Fig. 1, the third stage 22 of the multistage molding
apparatus 10 is shown to follow downstream of the second stage 18. The third
stage
22 includes a curing die 84 to complete the curing of the skin 16 and foam 20
of the
composite article 12. Since the curing die 84 is typically maintained at a
cooler
temperature than the pultrusion die 52, the curing die 84 needs to be
thermally
isolated from the second stage 18, in order to permit the controlled curing of
the
composite article 12. According to one embodiment, thermal isolation is
achieved
with a thermal break 56 at the upstream end of the curing die 84. A cooler 54
may
also be provided at the upstream end of the curing die 84, to help maintain
the
required temperature. Such thermal breaks 52 and coolers 54 of various types,
as
well as other means for controlling the temperature of the curing die 84 are
well
known to those skilled in the art. Without limitation, some examples of
coolers 54
include, water cooling, refrigerating coils, etc. Some examples of thermal
breaks
include heat conducting fins, ceramics or the like. What is important is that
the very
CA 02538917 2006-03-08
14
hot temperatures required, to cure the skin 16 in the pultrusion die 52, do
not affect
the temperature of the curing die 84.
Fig. 5 shows an optional fourth stage 24 which may be provided to the
multistage molding apparatus 10 downstream of the third stage 22. The fourth
stage
24 is for applying a coating 26 to the outside surfaces of the composite
article 12.
The fourth stage 24 includes a coating applicator 86 which smoothly coats the
composite article 12 with the coating 26. The coating applicator 86 shown in
Fig. 5
has one coating dispenser 88 for applying a coating to the bottom of the
composite
article 12. As shown in Fig. 6, the coating applicator 86 has two coating
dispenser 88
for applying the coating 26 to the top and bottom outside surfaces of the
composite
article 12 and a light source 90 positioned downstream of the coating
dispenser 88. It
is contemplated that more than one coating dispensers 88 may be provided in
the
coating applicator 86 for applying the same or a different coating 26 to
different parts
of the composite article 12. The coating 26 is delivered to the coating
dispenser 88
from a coating reservoir 92 under pressure by a coating pump 94. According to
a
preferred embodiment of the present invention, a photo-curing coating 26 is
applied to
the outside surface of the composite article 12 through the coating dispenser
88
which is cured as it passes by the light source 90. The light source 90 may be
any
light source 90 that is required to cure the photo-curing coating 26 being
used, such
as for example a UV light source. Resin supplied by, for example, BASF has
been
found to provide adequate results.
Furthermore, the coating applicator 86 may also be maintained at a higher or
lower temperature than the curing die 84. In order to maintain a different
temperature, the coating applicator 86 is thermally isolated from the third
stage 22
with a thermal break 56 at the upstream end, as shown in Fig. 6. A cooler 54
may
also be provided at the upstream end of the coating applicator 86, to. help
maintain
the required temperature. What is important is that the temperature in the
curing die
84, in the third stage 22, does not affect the temperature of the coating
applicator 86.
CA 02538917 2006-03-08
While the coating applicator 86 is disclosed herein attached to. the curing
die
84 as a part of the multistage molding apparatus 10, it is contemplated that
the
coating applicator 86 may be used separately in other applications.
It can now be understood that the multistage molding apparatus 10 allows for
5 continuously forming a composite article 12 by continuously carrying out
three
processing steps. The first step involves impregnating a skin forming material
34 with
a resin 36 at a first stage 14. The next step involves curing the impregnated
skin
forming material 34 to form a skin 16, while applying a foam 20 to the
impregnated
skin forming material 34 before the impregnated skin forming material 34 is
fully cured
10 in a second stage 18. The next step involves curing the foamed skin to form
the
composite article 12 at a third stage 22. In an optional fourth stage 24 a
finish coat 26
is applied to the composite article 12. The coating step is preferably done
using a
photocuring finish coating material, which is cured by the application of UV
energy.
By the time the continuously formed composite article 12 reaches the pulling
15 mechanism 23 it will be sufficiently cured, so as not to collapse under the
pressures
exerted by the pulling mechanism 23 within the grip region, even with the
skins 16 as
thin as 0.50 mm.
Providing a sufficient amount of the same material in each of the resin 36 and
the foam 20 permits the foam 20 to bond to the impregnated skin forming
material 34,
as the impregnated skin forming material 34 is curing in the second stage 22.
Good
results have been obtained using thermoplastic resin as the common material,
such
as for example ABS. Preferably, the common ingredient is provided in both of
the
foam 20 and the skin 16 in a concentration of about seven percent by weight or
more.
Most preferably, the common ingredient is provided in both the foam 20 and the
skin
16 in a concentration of between about three percent and about seven percent
by
weight.
The molecular bond between the foam 20 and skin 16 is preferred to a
chemical bond, such as one achieved with adhesive for at least two reasons.
The
first is that an adhesive bond requires an additional processing step of
applying the
adhesive, which entails optimization and control over several further
parameters
CA 02538917 2006-03-08
16
including the amount of adhesive to use, which adhesive to use, how long to
allow the
adhesive to cure etc. On the other hand, the molecular bond is controlled with
temperature. The second reason is that, the characteristics of a molecularly
bonded
composite article 12 are more predictable than the characteristics of a
chemically
bonded composite article. Lastly, the molecular bond provides an adequate
strength
bond between the structural foam and the skin to support considerable loads.
As shown in Figs. 7A and 7C, the composite article 12 may be formed with a
foam layer 20 bonded between two skin layers 16 as a sandwich structure, or
with a
skin layer 16 bonded only to one foam layer 20. The finish coating 26 may be
applied
to the skins as shown in Figs. 7B and 7D. Composite articles 12 formed as a
sandwich of a foam layer 20 bonded between two skins 16 as shown in Fig. 7A
and
7B are about 40 times stronger than the foam layer 20 on its own.
Many different uses can be made of the composite articles 12 formed by the
present invention. In particular, the composite articles are suitable for
panels, window
lineals, floors, decks, roofs, sound proof walls, highway barriers, sign
boards,
telephone and light poles, as well as other applications where cost, strength
and
weight are factors. Composite articles 12 having complex shaped profiles are
possible.
While reference has been made to various preferred embodiments of the
invention other variations are comprehended by the broad scope of the appended
claims. Some of these have been discussed in detail in this specification and
others
will be apparent to those skilled in the art. All such variations and
alterations are
comprehended by this specification are intended to be covered, without
limitation.
CA 02538917 2006-03-08
CANADA
PATENT APPLICATION
PIASETZKI & NENNIGER
File No.: MAS004/JTN
Title:
MULTISTAGE METHOD AND APPARATUS FOR
CONTINUOUSLY FORMING A COMPOSITE ARTICLE
Inventor(s):
ANDREW REKRET
