Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BP File No. 6052-007
Title: COMPOSITE NOLDED OBJECTS AND PROCE~SS
FIEI.D OF 1~ INVE:NTION
This invention relates to molded objects made of
two layers, namely a first layer of thermoplastic ma~erial
and a second layer of different material embedded therein,
and to a molding process for making such molded objects.
BACl~:ROUND OF THE INVENTION
In blow molding a plastic object, a mold of a
desired shape is provided. A parison of suitable
thermoplastic is placed in the mold; the mold is closed,
and air under high pressure is blown into the parison to
produce an object having said desired shape. An example
of a blow mold is illustra~-ed in ~anadian Patent No.
1278660. Blow molded objects are of a wide variety, from
toys to bottles to automotive parts, because the process
is relatively simple and inexpensive. An added advantage
of blow molded plastic automotive parts is their light
weight as compared to the same parts made of metal.
Furthermore, unlike metal parts, plastic parts will not
rust.
Vnfortunately, the full potential of blow molded
plastic objects has not been exploited since they are too
flexible for many use6. Hence/ the plastic objec~ must be
made significantly thicker or larger than its metal
counterpart to provide comparable stiffness. An
alternative would be to use a stiffer plastic material,
but this tends to make the object ~ore brittle in cold
¦ temperatures, and therefore susceptible to shattering if
j impacted.
J 30 Where blow molded plastic objects are used for
automotive parts, such as for interior automotive door
panel~, the objects are frequently upholstered with a
carpet to provide a d~sired interior finish for the
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automobile. The carpet must be fastened to the plastic
object using an adhesive, staples, rivets or the like,
thus increasing the manufacturing costs of the obiect.
Another disadvantage is that the carpet may separate from
the object with use or if an inappropriate fastener is
used.
It is therefore desired to provide a molded
plastic object, and a process for producing same, wherein
the ob~ect is reinforced in a simple manner to enhance its
stiffness without the need for increasing the object~s
size or providing a stiffer but more brittle plastic.
Where the object is to have a carpeted surface, such as an
interior automotive door panel, it is desired that the
carpet~s backing be mechanically bonded or interlocked
with a surface of the molded plastic object to provide a
carpeted object of one-piece construction.
SU~MARY OF T~æ INVENTI~N
In one aspect the invention provides a process
for molding reinforced thermoplastic objects comprising:
(1) positioning at least one layer of
reinforcing strands of high tensile
strength on at least one inside surface
of a mold;
(2) introducing a thermoplastic polymer
materi 1 in a heated plastic state into
the mold,
(3~ forming said polymer material in said
mold into a molded object and
concurrently therewith causing said
material to envelop said strands thus to
mechanically interlock said strands and
said polymer material; and
(4) opening the mold and discharging the
object so molded.
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In another aspect of the invention, the :~
invention provides a process for molding a composite
structure, comprising:
(1) selecting a piece of substantially
impermeable surfacing material having a
rear surface having surface
irre~ularities, and a front surface;
(2) positioning said surfacing material on at
lease one inside surface of a mold with
said rear surface facing the interior of
said mold;
(3) introducing a thermoplastic polymer
material in a heated plas~ic state into
said mold;
(4) forming said thermoplastic material in
said mold into a molded ob~ect and
concurrently forcing said thermoplastic
material against and into said rear
surface of said surfacing material to
mechanically interlock said surfacing
material to said molded object; and
(5) opening said mold and discharging said
molded object, with said front surface of
said surfacing material forming at least
a portion of the exterior of said
composite structure.
In a preferred embodiment of said process, said
! surfacing material i5 a carpet, and said molded objec~ is
a portion of an interior automotive panel.
In yet another aspect the invention provides a
reinforced sheet of thermoplastic material comprising: :
(1) a con~inuous layer of said thermoplastic
material, and
(2) at least one layer of reinforcing strands
of high tensile strength embedded in and
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adjac0nt at least one surface of said
layer of thermoplastic material, said
strands being covered by said
thermoplastic ma~erial.
In a further aspect the invention provides a
composite thermoplastic structure comprising:
(1) a continuous layer of thermoplastic
material;
(2) a piece of surfacing material having a
rear surface having surface irregularity,
and a front surface; and
(3) said thermoplastic material being molded
into and mechanically interlocked with
said rear surface, said front surface
forming at least a portion of the
exterior of said structure.
In a preferred embodiment of said composite
thermoplastic structure, the composite s~ructure comprises
at least a portion of an automotive inside door panel and
said ~urfacing material is carpet.
D~SCRIPTI~N OF THE ~NI~GS
Preferred embodiments of the present invention
are described below with reference to the accompanying
drawings in whichs
Figure 1 is a cross sectional view through a
mold showing four stages of a blow molding process
according to the present invention,
Figure 2 is a perspective view of a mesh for use
in the process of Figure 1;
Figure 3 is a perspective view of a piece of a
reinforced thermoplastic material from the process of
Figure 1~
Figure 4 shows a graph wherein the vertical axis
represents the force (in pounds) applied to ~hree s~rips
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of reinforced thermoplastic material according to the
present invention and to a strip of said material without
any reinforcement, and the horizontal axis represents the
corresponding deflections (in inches) of said strips;
Figure 5 is a view from the front of an
automotive bumper produced accordin~ to the present
invention;
Figure 6 is a perspective view of a section of
the automotive bumper of Figure 5 and a close-up of a
strip of reinforcement in said bumper;
Figure 7 is a perspective view, as seen from the
bottom, of an automotive gasoline tank according to the
present invention;
Figure 8 is a cut-away perspective view of a
seat back according to the present invention;
Figure 3 is a sectional view of a molcl showing
another molding process according ~o the invention;
Figure 10 shows a composite molded structure
resulting from the Figure 10 process;
Figure 11 is a sectional view of another mold
showing a molding process according to the inven~ion; and
Figure 12 shows à composite molded structure
resulting from the Figure 11 process.
DESCRIPTION OF PREFE~W3D ~MRODIM~ 3Ts
Reference is first made to Figure 1 which shows
a cross section of a mold 1 in various stages of a blow
molding pxocess, starting at Figure 1 ta) and progressing
to Figure 1 (d). The mold 1 is of usual cons~ruction,
having a left portion 3 and a right portion 5. The left
and right portions 3, 5 have left and right inside
surfaces 7, 9, respectively, which provide the external
shape of a reinforced thermoplastic object 11 to be
produced by the mold 1.
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The process for molding the object 11 according
to a preferred embodiment of the present invention
comprises positioning a layer of reinforcing strands or
mesh 13 of high tensile strength on the right inside
surface 9 as shown in Figure 1 (a). The strands 13 may be
arranged in a grid, and in the preferred embodiment the
strands 13 comprise a flexible woven wire mesh as shown in
Fig. 2. Ordinary wire window screen is a suitable mesh.
Good results may also be achieved using strands or a woven
mesh of polyester and nylon with high tensile strength.
Again, mesh in the form of a conventional window screen is
suitable. In very high strength applications, strands of
material known as Kevlar (trade mark), woven into a mesh,
can be used. The mesh material must not, of course, melt
at the temperature used in the molding process.
The mesh 13 may be preformed or may be pressed
against one of the mold inside surfaces, e.g. against the
right inside surface 9, to adopt a similar or identical
profile as that of the surface 9. One or more layers of
mesh 13 may be used. Likewise, one or more layers of the
mesh 13 may be positioned on the lef~ inside surface 7.
Once the mesh 13 is in place, a parison 15 of
suitable molding material, such as a thermoplastic
material, is introduced into the mold 1 be~ween the left
and right inside surfaces 7, 9 as shown in Figure 1 ~b).
The parison 15 may be in the form of an elongate hollow
tube, the desired thicknes~ of the tube wall being
controlled by an outlet opening of a device which feeds
the parison into the mold (not shown). The mold 1 is
then closed, and top and bottom ends 2a, 2b of the mold 1
pinch the parison 15 (Figura 1 (c)). The parison is
"blown" in a known manner by introducing air or other
desired gas into the hollow centre of the parison 15. The
air is injected into the mold 1 and into the parison 15
through one or more openings or needles 17 in the mold,
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which is usually cooled using water or by other suitable
maans. The needle 17 may be provided at any convenient
spot in the mold 1. The air pressure forces the polymer
material outwardly toward the inside surfaces 7, 9,
thereby pressing the mesh 13 against the right inside
surface 9. The pressure forces the polymer material
through the mesh 13 and around each strand of the mesh 13,
thereby surrounding each strand of mesh 13 with the
polymer material.
Once the polymer material sets, usually in 15 to
30 seconds depending on the polymer material used and the
size of the molded object, the mold 1 is opened and the
molded object 11 is removed (Figure 1 (d)). The molded
object 11 will have a hollow core if the parison 15 is
blown. The exterior surface 19 of the molded object 11
will normally be smooth to the touch since the mesh is
embedded just beneath the surface 19. As shown in Fig. 3,
there will be a thin continuous coating 20 of polymer
material between the mesh 13 and the exterior surface 19.
It will be appreciated that if the parison is
insufficiently heated prior to introduction into the mold
or if insufficient pressure is applied in the hlow molding
process, then the mesh 13 may not be completely co~ered
resulting in discontinuities in the exterior surface l9
which can expose the mesh ~o corrosive agents from the
surroundings.
To demonstrate the improved qualities of the
r~inforced molded object 11 produced by the molding
process of the present invention, three thermoplastic
molded objects 11 were produced in khe form of reinforced
sheets or longitudinal strips of equal width. The first
sheet comprised a continuous layer of thermoplastic
material and one layer of reinforcing wire mesh 13
embedded in and adjacent a first exterior surface of the
sheet. The second and third sheets were identical to the
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first sheet except for additional second and third layers
of reinforcing wire mesh placed adjacent the first layer,
respectively (so that the wire mesh was two and three
layers thick). A fourth "control" shee~ with identical
dimensions was produced but omitting the reinforcing wire
mesh. Each of the four sheets was tested in a horizontal
position and supported at each end. The first exterior
surface (ie. the surface to which the mesh was closest)
was oriented downwardly. A force of three pounds was
applied to the opposite (ie. top) surface of each sheet at
its centre line between the supports ancl the deflection of
each sheet at said centre line was measured.
The results are presented in the graph of Figure
4. The deflection of the control sheet was about .055
inches (0.13g cm) as shown at 21-0 whereas the deflection
of the first sheet with the single reinforcing layer was
reduced to about .04 inches (0.102 cm) as shown at 21-1,
a decrease of about 27%. The deflections of the second
and third shee~s were reduced further, to about .035
inches (0.089 cm) and .029 inches ~0.074 cm) respectivPly,
as shown at 21-2 and 21-3. Hence, the deflection of these
sh~ets was reduced signi~icantly ~or, conversely, the
stiffness was increased) as compared to the control sheet.
This was accomplished with a negligible increase in the
weight of the sheets. In addition, the cost of the mesh
13 is very low, and the properties of the thermoplastic
material are not adversely affected.
I~ is noted that the mesh 13 itself is normally
very flexible. However when it is embedded in the
thermoplastic material, its strands are locked in place,
and since any bending movement then tends to stretch the
strands, such bending movement is strongly resisted. When
the mesh 13 is woven, with its strands running in two
directions at right angles to each other as ~hown, then
resistance to bending is enhanced. Thexe is no need to
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introduce special fibres into the thermoplastic material;
the mesh 13 is very easy to lay in place. There is no
need for special compatibility between the mesh 13 and the
thermoplastic material since the mesh is essentially
mechanically held in place.
While the method described employ~,blow molding,
it is also possible to perform the process using similar
techniques, such as vacuum molding.
The embodiments of the present invention so far
described finds numerous uses, some of which are shown in
Figures 5 to 8. Primed numerals are used to identify like
elements fxom the first embodiment in Figures 1 to 3.
The process of the present invention may be used
to produce a hollow reinforced bumper 21 for automobiles
as shown in Figures 5 and 6. Prior art ~plastic~ bumpers
comprise a plastic ~facial~ surrounding a metal bumper
frame. Until now entirely plastic bumpers have been too
flexible and have not demonstrated the required deflection
control to protect against even relatively minor impacts.
Hence, the costly (and relatively h~avy) metal frames must
be inserted to pro~ide th~ bumper with the necessary
stiffness to absorb impacts.
A bumper body 23 made according to the presen
invention is blow molded of a thermoplastic polymer having
a B-shape in cross section tFigure 5) and two strips of
reinforcing mesh 13 embedded in the outwardly curved
portions of th~ B to stiffen the bumper 21 (i-t is
understood that the strips 13 appear exposed in the
figures for illustrative puxposes only). An advantage of
the bumper 21 is that it is stiff enough to adequately
control deflections, yet the bumper 21 is flexible enough
to absorb impacts withouk permanently deforming the bumper
body 23. The bumper 21 weighs less than prior art bumpers
and the cost of the polymer material is much less than
that o~ prior bumpers which have metal frames. It will be
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appreciated that a greater proportion of the bumper body
23 may employ the mesh 13 or several layers may be used to
increase stiffness if need be. The mesh 13 may be of any
desired gauge and strength of metal strands, or of plastic
strands of suitable tensile strengt~, a~ discussed. Bolts
25 used to attach the bumper 21 to the automobile's
chassis may be embedded in the bumper body 23 by inserting
the bolts 25 into the mold 1 during the molding process.
Figure 7 shows the use of the present in~ention
in an automotive gasoline tank 27. The tank ~7 has a
base 29 and front and back walls 31, 33 respectively.
Such tanks are commonly made of polyethylene for its
strength and solvent resistance properties. Since tank
bases have a relatively large surface area and are
subjected to heavy loads (especially when the tank is full
of gasoline), the bases must be supported to prevent
excessive deflec~ions or sag. Prior art tank bases are
particularly susceptible to excessive sag when the
polyethylene base is heated up by hot road surfaces or the
like. Hence the practice in the automobile industry has
been to support ~he base with two or more spacQd metal
ribs (which are part of the vehicle). These ribs tend to
be heavy and are susceptible to corrosionD
The gasoline tank 27 of the present invention is
blow moldedl and where the metal ribs would suppox~ the
base 29, there are two spacad strips of wire or plastic
mesh 13 The strips 13 ex~end transversely across the
base 29 and at least partway up the front and back walls
31, 33. In this embodiment the mesh 13 is again embedded
adjacent the outside surface of the base 29 during the
molding process. One or more strips and layers of mesh 13
may be provided depending on the stiffness required and
the amount of load to be transferred to the front and back
walls 31, 33. As with the bumper 21 discussed above,
advantages of replacing the prior art ribs with the mesh
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strips in the tank 27 are the savings in cost and weight
of materials used. In addi~ion, the cost of installing
the metal ribs in the automotive body is elimînated.
In an alternate embodiment of the gasoline tank,
the entire body 28 of the gasoline tank 27 is lined with
the mesh 13 . Such a configuration may be applied to other
blow molded containers for different liquids. This is
accomplished by lining the entire interior surface of the
mold with mesh before inserting and blowing the parison.
An advantage of this configuration over prior art
containers molded of the polymer material alone is that
the permeation by liquids through the polymer material is
reduced by up to 30%. This reduction in permeation is
attributed partly to reduced expansion of the polymer
mater1al itself due to the resistance to expansion
provided by said mesh, and partly to the reduced
penetrable surface area of polymer material between the
inside and the outside of the container (since the mesh
may typically occupy about 20% of the surface area).
Figure 8 shows a blo~ molded seat back support
35 of the present invention. A common drawback of prior
art seat back supports i~ excessive flex, leading to back
pain and discomfort of the user~ An inexpensive method of
stiffening such seat back supports 35 to reduce flex is
the addition of one or more wire mesh s~rips 13 adjacent
the outside surface 37 of the seat back support ~ie.
adjacent the surface which is in contact with the user).
The quantity of wire mPsh 13 provlded depends on th~
desired stiffness of the seat back.
In yet another embodiment of the invention, as
shown in Fig. 9l a piece 50 of carpe~, fabric, or the like
can be used to line a section of a mold 52. The carpet or
fabric 50 has a backing 50-1 and a pile 50-2. A l~yer of
hot thermoplastic 54 is then blown or forced into the mold
35 52, over the carpet or fabric 50. The hot plastic 54,
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which is semi-molten, fuses into the backing 50-1. This
produces a one-piece structure S6 as shown in Fig. 10,
with a carpet or fabric facing 58.
An alternative arrangement is shown in Fig.
ll(a), in which carpet or fabric 50 lines one side of a
blow mold 60. If a carpet 50 is used, then it is placed
with the pile adjacent the inside surf~ce of the mold 60
(as shown in Yig. 9). Nhen the mold is closed to pinch
the parison 62 and the parison 62 is blown (Fig. ll(b)),
the mold 60 is opened and a structure 64 results.
Structure 64 can be, for example, an automotive door panel
as shown in Figure 12 with the surface 66 which faces the
interior of the vehicle suitably upholstered. This
eliminates the current need for an extra step to attach an
upholstery layer to a panel mechanically or by adhesive.
The carpet or fabric can be held in place in the mold by
any suitable means. ~or example suction may be applied
through passages 68 if there is little or no pile 50-2 and
the carpet backing 504 is very tightly woven to create the
required suction force/ or by plastic ties which can be
cut after the molded structure has been formed.
The thermoplastic material 54 or 62 is forced
with considerable pressure against the back of the layer
of carpet or fabric 50, typically sn p.s.io The pressure
should be kept below 150 p.s.i. in order not to crush or
collapse most carpets. Higher pressure might be used for
relatively non-crushable carpets. Despite the pressures
exerted, the thermoplastic material cannot penetrate the
backing 50-1 of the carpet or fabric 50 because the
backing 50-1 is formed of an impermeable material.
However the rear surface of the backing 50-1 has
considerable surface irregularity, so that the
thermoplastic material can penetrate into the interstices
of the rear surface and mechanically interlock therewith.
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Suitable ranges of extruding temperatures for
different thermoplastic materials to form the required
interlock with a carpet backing are: approximately 380
- 450 F for polyethylene; approximately 400 - 450 for
polypropylene; and approximately 450 - 500 F for
polyolefins.
The carpet 50 may line all or sections of the
mold 60. The thermoplastic material tends not to creep
around the edges of the carpet 50 onto the pile 50-2
because the thermoplastic stretches radially outwardly
from the center of the backing 50-1 and so it moves away
from the edges of the carpet. If necessary, appropriate
means, e.~. clamps, might be used to ensuxe that the
thermoplastic material does not force its way between the
edges of the carpet or fabric 50 or the mold surface.
An advantage of the present invention is that
the resultant structure can be wholly recyclable. To
illustrate, if both the carpet 50 and the thermoplastic 54
of the resultant structure 64 are both composed of
polypropylene/ then the carpet and structure may be
recycled together without separating them.
Another advantage of ~he present invention is
that the carpet 50 can reinforce any points of weakness of
the structllre 54. For instance, if the one part of door
panel 64 in Figure 12 was integrally hinged to rotate
relative to another part of the panel 64, then carpet
upholstery can be bonded to the hinge to increase its
durability and rotational stiffness.
If desired, a layer of foam may be added between
the carpet backing 50-l and the layer of thermoplastic
material. This application is suitable, for example,
where extra cushioning is required, such as for the back
support of a seat. The foam must be glued or suitably
attachPd to the carpet backing since the thermoplastic
does not penetrate the foam to form any bond be~ween the
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foam and the carpet backing 50-1. In turn, the
thermoplastic and the foam might not sufficiently
mechanically interlock together, and so the foam should be
compatible with the thermoplas~ic for both to chemically
bond together. If extra bonding between the thermoplastic
and foam is desired, then a pressure sensitive or heat
sensitive adhesive (for example, polyurethane or
polyester) may be provided between both.
The above description is intended in an
illustrative rather than a restrictive sense and
variations to the specific configuration and materials
described may be apparent to skilled persons in adapting
the present invention to specific applications. Such
variations are intended to form part of the present
invention insofar as they are within the spirit and scope
of the claims below.
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