U.S. patent application number 10/591116 was filed with the patent office on 2007-08-09 for synthetic multilayer object.
Invention is credited to Jacques Thomasset.
Application Number | 20070184236 10/591116 |
Document ID | / |
Family ID | 34923298 |
Filed Date | 2007-08-09 |
United States Patent
Application |
20070184236 |
Kind Code |
A1 |
Thomasset; Jacques |
August 9, 2007 |
Synthetic multilayer object
Abstract
An axisymmetrical multilayer object forming a wall of thickness
E, said object being composed of a first resin forming the
structure of the object and representing at least 80% of the volume
of the object, and of a second resin forming at least two fine
functional layers, said functional layers being imprisoned
separately in the first resin, the multilayer structure being
characterized in that a. the functional layers are distributed in
separate parts of the object b. the functional layers form bodies
of revolution centered on the axis of symmetry of the object c. the
two functional layers are placed partially one on top of the other
in a direction perpendicular to said wall.
Inventors: |
Thomasset; Jacques; (Vouvry,
CH) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Family ID: |
34923298 |
Appl. No.: |
10/591116 |
Filed: |
February 26, 2005 |
PCT Filed: |
February 26, 2005 |
PCT NO: |
PCT/IB05/50706 |
371 Date: |
August 30, 2006 |
Current U.S.
Class: |
428/68 |
Current CPC
Class: |
B29L 2009/00 20130101;
Y10T 428/1352 20150115; Y10T 428/1393 20150115; B29B 11/12
20130101; B29K 2025/00 20130101; B29K 2105/255 20130101; Y10T
428/24273 20150115; Y10T 428/1383 20150115; B29B 11/14 20130101;
Y10T 428/23 20150115; Y10T 428/13 20150115; Y10T 428/1379 20150115;
Y10T 428/249921 20150401; B29C 48/21 20190201; B32B 1/08 20130101;
Y10T 428/139 20150115; B29B 11/10 20130101; Y10T 428/24322
20150115; B29C 43/203 20130101; B29C 2043/3433 20130101; B29K
2023/12 20130101; B29C 48/08 20190201; B29C 2793/009 20130101; B29C
48/304 20190201; B29K 2077/00 20130101; B29K 2023/06 20130101; B29K
2027/16 20130101; Y10T 428/24612 20150115; B29K 2023/086 20130101;
Y10T 428/239 20150115; B29L 2031/565 20130101; B29K 2067/00
20130101; Y10T 428/31504 20150401 |
Class at
Publication: |
428/068 |
International
Class: |
B32B 3/02 20060101
B32B003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 1, 2004 |
CH |
CH 00336/04 |
Oct 4, 2004 |
CH |
CH 01619/04 |
Dec 8, 2004 |
CH |
CH 02034/04 |
Dec 8, 2004 |
CH |
CH 02033/04 |
Claims
1. An axisymmetrical multilayer object forming a wall of thickness
E, said object being composed of a first resin forming the
structure of the object and representing at least 80% of the volume
of the object, and of a second resin forming at least two fine
functional layers, said functional layers being imprisoned
separately in the first resin, the multilayer structure being
characterized in that a. the functional layers are distributed in
separate parts of the object b. the functional layers form bodies
of revolution centered on the axis of symmetry of the object c. the
two functional layers are placed partially one on top of the other
in a direction perpendicular to said wall.
2. The object as claimed in claim 1, characterized in that the
superposition distance is at least equal to the thickness E of the
object.
3. The multilayer object as claimed in claim 1, characterized in
that the functional layers themselves form a multilayer structure
comprising a layer of barrier resin imprisoned between two layers
of adhesive resin.
4. The object as claimed in claim 1, characterized in that the
first resin represents at least 85% of the volume of the
object.
5. A multilayer object obtained by compression molding of a
multilayer dose, said multilayer dose in a radial stacking of a
plurality of layers, containing at least 2 fine functional layers
imprisoned between layers composed of a first resin, the layers
constituted by the first resin representing at least 80% of the
volume of the dose, the distance of the first layer to the axis of
symmetry being less than or equal to half the distance of the
second layer to the axis of symmetry.
6. A multilayer dose with an axis of symmetry for the realization
of multilayer objects by compression molding, the multilayer
structure of which consists in a radial stacking of a plurality of
layers, said multilayer structure containing at least 2 fine
functional layers imprisoned between layers composed of a first
resin, the multilayer structure being characterized in that a. the
layers constituted by the first resin represent at least 80% of the
volume of the dose b. the distance of the first layer to the axis
of symmetry is less than or equal to half the distance of the
second layer to the axis of symmetry.
7. The multilayer dose as claimed in claim 6, characterized in that
the functional layers themselves form a multilayer structure
comprising a layer of barrier resin imprisoned between two layers
of adhesive resin.
8. The multilayer dose as claimed in claim 6 comprising at least
three functional layers, characterized in that the ratio of the
radial distances between two neighboring layers is less than or
equal to 0.5.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for realizing
multilayer objects by compression molding of a multilayer dose.
PRIOR ART
[0002] U.S. Pat. No. 4,876,052 describes a multilayer object (FIG.
1), characterized in that a first synthetic resin 3 is fully
imprisoned inside a second synthetic resin 2. This multilayer
object is obtained by compression molding of a composite dose in
which the first resin is totally imprisoned in the second resin.
The multilayer structure described in U.S. Pat. No. 4,876,052 is
particularly interesting for objects such as receptacles or lids.
However, the objects obtained according to the method described in
U.S. Pat. No. 4,876,052 require a large proportion of functional
resin in the object, thereby engendering two major drawbacks: the
first being a prohibitive cost and the second a lowered resistance
to mechanical stresses. The lack of adhesion between the functional
resin and the outer resin reduces the solidity of the object and
creates a risk of decohesion of the outer layer. Another drawback
of U.S. Pat. No. 4,876,052 lies in the fact that the respective
quantity of the resins 2 and 3 is only poorly adjustable. As will
be shown further below in the account of the invention, these
quantities are fixed by the geometry of the object and by the flows
during the compression of the dose. This method likewise calls for
the intermittent extrusion of the first resin inside a second
resin. U.S. Pat. No. 4,876,052 describes a coextrusion device
having a shut-off valve mechanism for the first synthetic
resin.
[0003] To eliminate the drawbacks of U.S. Pat. No. 4,876,052,
Japanese patent JP 2098415 proposes the realization of a multilayer
object by compression molding starting from a composite dose,
characterized in that the second synthetic resin covers only the
side faces of the first synthetic resin. The compression molding of
this dose along its axis of symmetry produces an object having a
multilayer structure (FIG. 2), characterized in that a first resin
2 partially imprisons a second resin 3. However, the multilayer
objects realized from two resins according to patent JP 2098415
have two major drawbacks: the first being that of having the
barrier resin 3 exposed on a central surface area of the object
over at least 10% of the total surface area of the object, and the
second being that of requiring a quantity of barrier resin 7 in the
object amounting to at least 30% of the total quantity of resin.
This produces, on the one hand, objects having a prohibitive cost
and, on the other hand, objects having heavily modified mechanical
properties, mainly in the center of the object. Another drawback of
patent JP 2098415 lies in the fact that the respective quantity of
the resins 2 and 3 is only slightly adjustable, these quantities
being fixed by the geometry of the object and by the flows during
the compression of the dose.
[0004] In patent JP 2098415, it is proposed to use a triple-layer
dose in order partially to eliminate the aforesaid drawbacks. This
dose is constituted by a first resin 4 forming the central part of
the dose, by a second resin 3 covering only the side faces of the
first resin, and by a third resin 2 covering only the side faces of
the second resin. The crushing of this composite dose along its
axis of symmetry produces a multilayer object (FIG. 3). The use of
a triple-layer dose has the advantage of reducing the quantity of
functional resin 3 used and produces objects having slightly
modified mechanical properties in relation to the same object
containing a single resin 2. However, the second resin 3 does not
cover the central part of the multilayer object, which produces
multilayer objects without barrier property close to the axis of
symmetry. This central region of the object not covered by the
barrier resin layer 3 weakens the barrier performance of the object
and renders this solution less effective.
[0005] Patent application CH01619/04 describes multilayer objects
(FIG. 4) realized from a compression-molded multilayer dose. The
objects described in this patent application have a multilayer
structure characterized by the position of the functional layer
forming a zigzag-shaped double fold. The functional layer is
distributed correctly throughout the object, even in the central
part. The method for realizing multilayer objects which is
described in patent application CH01619/04 also allows control of
the thickness of the functional layer. An adhesive layer can be
added between the resin forming the surface of the object and the
functional resin. However, the compression of the dose calls for a
method and a specific molding device. This method calls especially
for additional die tool movements relative to the basic compression
process, setting the two parts of the mold in relative motion. In
the case of high-speed molding, it can be detrimental to use a
compression device as described in patent application
CH01619/04.
[0006] Patent EP926078 describes the obtention of a plug liner
(FIG. 5) by compression molding of a dose containing a laminar
multilayer structure. The functional resin 3 forms strips dispersed
in the resin 2. The method consists in extruding a laminar dose
(millefeuille sort) with a strip-generating device, then in
compressing the dose so as to form the liner. In the thickness of
the liner (FIG. 5), a multilayer structure of the millefeuille type
is found. This method consists in compression-molding a laminar
alloy, the number of strips in the dose being very large in number.
This method has the drawback of requiring a high barrier resin
percentage (in the order of 20%) in order significantly to reduce
the permeability of the object, since the strips do not form a
continuous layer. Another drawback of patent EP926078 lies in the
fact that the position of the strips in the object cannot be
controlled. The result is that the resin forming the surface layer
of the multilayer object is a mixture of different dose-forming
layers. This can limit the use of the objects described in patent
EP926078, for hygiene reasons, when the packaged product is in
contact with the laminar multilayer object. Another drawback of
patent EP926078 is linked to the limited choice of resins, which
must exhibit viscosities and melting temperatures which allow the
strips to be maintained during the compression of the dose.
SUBJECT OF THE INVENTION
[0007] The invention relates to the realization of multilayer
objects realized by compression molding of a multilayer dose, while
allowing the elimination of the aforesaid drawbacks.
SUMMARY OF THE INVENTION
[0008] The invention consists in an axisymmetrical multilayer
object forming a wall of thickness E, said object being composed of
a first resin forming the structure of the object and representing
at least 80% of the volume of the object, and of a second resin
forming at least two fine functional layers, said functional layers
being imprisoned separately in the first resin, the multilayer
structure being characterized in that [0009] a. the functional
layers are distributed in separate parts of the object [0010] b.
the functional layers form bodies of revolution centered on the
axis of symmetry of the object [0011] c. the two functional layers
are placed partially one on top of the other in a direction
perpendicular to said wall.
DETAILED DESCRIPTION OF THE INVENTION
[0012] A better understanding of the invention will be gained below
from a detailed description of the examples illustrated by the
following figures.
BRIEF DESCRIPTION OF THE FIGURES
[0013] FIGS. 1 to 5 illustrate multilayer objects of the prior
art.
[0014] FIG. 1 shows a multilayer object described in U.S. Pat. No.
4,876,052. This object 1, realized by compression molding,
comprises a functional resin layer 3 fully encapsulated in a resin
2 forming the visible surface of the object.
[0015] FIG. 2 illustrates a multilayer object described in patent
JP2098415. This object 1 comprises a functional resin layer 3
partially encapsulated in a resin layer 2 forming the visible
surface of the object.
[0016] FIG. 3 shows another multilayer object described in patent
JP2098415. This object comprises a fine layer of functional resin 3
imprisoned between two layers of resins 2 and 4 forming the
object.
[0017] FIG. 4 shows a multilayer object described in application
CH01619/04. This object is characterized by the zigzag-shaped
double fold of the functional layer 3.
[0018] FIG. 5 shows an object comprising a laminar multilayer
structure described in patent EP926078.
[0019] FIGS. 6 to 11 show multilayer objects corresponding to the
invention.
[0020] FIG. 6 illustrates a first multilayer object conforming to
the inventive concept. The multilayer structure is observed in a
sectional plane passing through the axis of symmetry of the object.
The functional layers 3, 5 and 7 form an overlap.
[0021] FIG. 7 shows a second example of a multilayer object having
a central surface area S not covered by the functional layers.
[0022] FIGS. 8 and 9 illustrate objects realized according to the
invention and having an orifice 15.
[0023] FIG. 10 shows a multilayer plug realized according to the
invention.
[0024] FIG. 11 shows a multilayer preform realized according to the
invention.
[0025] FIG. 12 illustrates the flow profile during the compression
of the dose.
[0026] FIG. 13 shows the method for obtaining multilayer objects
and, in particular, the relationship between the dose and the
object.
[0027] FIG. 14 shows how the ratio S/Sp, of the surface area not
covered by the functional layer over the surface area of the
object, varies as a function of the compression rate H/E.
[0028] FIG. 15 illustrates the realization of an object according
to patent JP 20418415.
[0029] FIG. 16 shows how the ratio S/Sp varies as a function of H/E
for an object realized according to patent JP 20418415.
[0030] FIG. 17 shows another example of the realization of an
object according to the invention.
DETAILED DESCRIPTION OF THE FIGURES
[0031] The invention relates to a multilayer object possessing at
least two independent layers of functional resin distributed in
fine layer in a second resin forming the structure of the object,
said layers being distributed in separate parts of the object and
forming a partial overlap. The term "functional resin" designates a
resin chosen for its barrier properties with respect to gases or to
aromas.
[0032] FIG. 6 illustrates a multilayer object corresponding to the
invention. The thickness of the object is observed along a section
realized perpendicular to the surface of the object and passing
through the axis of symmetry. This figure shows the distribution of
the functional layers in the thickness of the part. The functional
resin forms the fine layers 3, 5 and 7 distributed in the base
resin forming the structural layers 2, 4 and 6 of the object. The
quantity of functional resin represents generally less than 10% of
the total resin volume. In order to obtain advantageous barrier
properties, it was observed that the functional layers had to be
placed partially one on top of the other so as to form the overlap
L. In a preferred embodiment (not illustrated), a value of the
overlap L ranging between 1 and 3 times the thickness E allows a
permeability to be obtained which is close to that obtained with a
single continuous layer of identical thickness. In FIG. 6, the
central part of the object is formed by the layer 7 of functional
resin. The quantity of functional resin forming the central layer 7
of the object represents less than 5% of the total resin volume and
generally less than 3%. The central layer 7 of functional resin is
present over a surface area S representing less than 3% of the
total surface area of the object, and preferably less than 1%. The
ends 9, 10 and 11 of the functional resin layers 3, 5 and 7 are
situated proximate to the top and bottom surfaces of the object,
the ends of which aforementioned layers can lie flush with the
surface of the object or be totally encapsulated. The functional
layers 3, 5 and 7 form, respectively, the folds 12, 13 and 14. The
fold 12 of the layer 3 is generally situated proximate to the side
wall of the object so as to have impermeability properties over the
whole of the surface of the object. In certain cases, it is not
necessary to make the whole of the surface of the object
impermeable, in which case the invention allows said layer 3 to be
spread solely in the part in which the object must be impermeable.
The folds 13 and 14 of the functional resin layers 5 and 7 are
placed one on top of the other at the ends 9 and 10 of the
functional layers 3 and 5 and form an overlap. The overlap of the
functional layers allows a good level of impermeability to be
assured, despite the discontinuity created by the different
layers.
[0033] FIG. 7 shows a second example of a multilayer object
realized according to the invention, this object being
distinguished from the object presented in FIG. 6 by its central
part. The object presented in FIG. 7 shows the arrangement of the
independent functional layers 3, 5 and 7 in the resin layers 2, 4,
6 and 8 forming the structure of the object. The functional resin
layers 3, 5 and 7 form the respective folds 12, 13 and 14. The
folds 13 and 14 are placed one on top of the other at the ends 9
and 10 of the functional resin layers 3 and 5 and form an overlap
by which a good level of impermeability can be assured. The ends 11
of the functional resin layer 7 do not cover the central part of
the object, leaving a permeable surface area S. The leak created by
the surface area S was found to be very small, considering the
ratio S/Sp of the surface area not covered by the functional layers
over the total exposed surface area. The invention allows a ratio
S/Sp of less than 2% to be obtained, which produces negligible
leaks.
[0034] FIG. 8 illustrates a third multilayer object realized
according to the inventive method. This object 1 contains a central
orifice 15, as well as two fine layers 3 and 5 of functional resin
distributed between the layers 2, 4 and 6 of the resin forming the
structure of the object. The functional layers 3 and 5 form folds
12 and 13, the fold 13 being superposed with the ends 9 of the
functional layer 3.
[0035] FIG. 9 shows another example of a multilayer object, having
an orifice. This object differs from the object presented in FIG. 8
by the orientation of the folds 12 and 13 of the functional resin
layers 3 and 5.
[0036] The method for realizing multilayer objects which is set out
below is particularly advantageous for realizing objects such as
plugs, lids, preforms, or, indeed, tube shoulders. This method can
likewise advantageously be used to realize preforms in the form of
a slab, which slabs are then used in thermoforming or blow
thermoforming to form multilayer objects. FIG. 10 illustrates a
multilayer structure which might be obtained in a geometry of a
plug-type object and FIG. 11 shows a multilayer preform realized
according to the invention. These objects have a partial
superposition of the functional resin layers, by which the
impermeability of the object can be assured.
[0037] FIG. 10 shows that the functional layer 3 is generally the
combination of three fine parallel layers 3a, 3b, 3c, the layers 3b
and 3c being adhesive layers situated on either side of the barrier
layer 3a. This combination allows resins of different nature to be
combined, while assuring good adhesion between the different
layers, which prevents possible problems of delamination or
decohesion in the multilayer objects. The adhesive and barrier
layers lie parallel and are small in quantity. The aggregate of the
adhesive layers 3b and 3c and of the barrier layer 3a forming the
functional layer 3 generally represents a quantity of resin less
than 15% of the total resin volume forming the dose, and preferably
a quantity interior to 10%.
[0038] The method for realizing multilayer objects according to the
invention is particularly advantageous, for it requires very little
modification of the existing devices. As will be show further
below, this method allows multilayer objects to be realized at high
production speed.
[0039] The method consists in coextruding a cylindrical or tubular
multilayer dose, in feeding this multilayer dose in the molten
state into a compression device, then in compressing said dose in a
mold so as to form the object, this method being characterized by
the geometry of the multilayer dose (height, diameter) and the
position of the functional layers in said dose.
[0040] In order to gain a better understanding of the spirit of the
invention, it is necessary to grasp the link connecting the
multilayer dose to the multilayer object. FIG. 12 shows the flow of
the resins during the compression of the dose. This flow is mainly
dependent on the rheological properties of the resins during the
compression, as well as on the geometry of the object. FIG. 12
shows that this flow is faster midway between the walls than close
to the walls of the die tool. Proximate to the walls of the die
tool, the displacement velocity of the particles tends toward zero,
but the shear deformation is high. Conversely, midway between the
walls, the velocity of the particles is at a maximum and the shear
deformation is at a minimum. During the flow, the functional resin
layer is entrained and deformed in a non-uniform manner according
to its position in the flow profile. The final position of the
functional resin layer in the object is thus determined by the
original position of the functional layer in the dose and by the
sum of the deformations suffered during the flow.
[0041] FIG. 13 shows the multilayer dose 16 used to realize a
multilayer object 1. A cylindrical dose 16 corresponding to a
portion of coextruded multilayer rod comprises two fine layers 3
and 5 of functional resin imprisoned between the layers 2, 4 and 6
of the base resin. The dose 16 corresponds to a radial stacking of
tubular layers, the central layer 6 being cylindrical. The
proportion of functional resin does not generally exceed 20% of the
volume of the dose, and this quantity is generally less than 10%.
The compression of this dose generates a flow of resin toward the
periphery, which entrains and deforms the functional layers 3 and 5
in this direction. The obtained multilayer object 1 is illustrated
in FIG. 13. In this object can be found the functional resin layers
3 and 5 forming a fold in the direction of the flow, the fold 13 of
the functional layer 5 forming an overlap L with the end 9 of the
functional layer 3. The value of the overlap L and the spread of
the fold 12 out to the end of the object are linked to the original
geometry of the dose and to the position of the functional layers
in the dose. To obtain a multilayer object as illustrated in FIG.
13, it is necessary to position the resin layers 3 and 5 correctly
in the dose. The geometry of the dose and the position of the
functional layers in the dose can be defined by calculation or
experimentally. It is observed experimentally that the ratio of the
radial positions Ri and Rj of two adjacent functional layers i and
j is constant and less than or equal to 0.5, the layer i being
situated closer to the axis of symmetry than the layer j.
[0042] The object 1 illustrated in FIG. 13 has a central surface
area S not covered by the functional layer. The ratio S/Sp,
corresponding to the ratio to the non-covered surface area over the
surface area of the object, is presented in FIG. 14. This ratio has
been found to depend on the compression rate of the dose, that is
to say on the ratio H1/E, H1 corresponding to the height of the
dose and E to the thickness of the object. FIG. 14 shows how the
ratio S/Sp varies as a function of H1/E. It is observed
experimentally that for compression rates of 5, the ratio S/Sp of
the object 1 was less than 10%, and for a compression rate of 10,
this ratio was less than 2%. This result indicates that for a
compression rate of 10, the leak-engendering surface area S
represents less than 2% of the surface area of the object.
[0043] In order to show the advantage of objects realized according
to our invention, these have been compared to objects obtained
according to the method described in patent JP 2098415.
[0044] FIG. 15 illustrates the compression of a dose such as
proposed in patent JP 2098415 so as to demonstrate the limits of
the multilayer objects obtained according to this method and better
understand the object of the present invention. FIG. 15 shows a
triple-layer dose 16 realized according to patent JP 2098415. This
dose contains a first resin 4 forming the central part of the dose,
a functional resin 3 covering only the side faces of the first
resin, and a third resin 2 covering only the side faces of the
functional resin. FIG. 15 illustrates the object 1 obtained
following compression of the dose 16. The functional layer 3 has
spread out to the end of the object, while remaining encapsulated
at the level of the periphery of the object. As FIG. 15 shows, the
functional layer has not spread into the central part of the object
1.
[0045] The experimental findings corresponding to the realization
of multilayer objects according to patent JP 2098415 have been
plotted in FIG. 16. This figure shows how the fraction of surface
area not covered by the functional layer S/Sp varies as a function
of the compression rate H/H1. It is observed experimentally that
for compression rates of 5 the ratio S/Sp of the object 1 is
greater than 25%, and for a compression rate of 10 this ratio close
to 20%. This finding indicates that for a compression rate of 10,
the leak-engendering surface area S represents approximately 20% of
the surface area of the object.
[0046] The barrier properties of objects realized according to
patent JP 2098415 (FIG. 15) and according to the invention (FIG.
13) have been compared. Disks of 1 mm thickness and of 40 mm
diameter have been realized starting from cylindrical multilayer
doses of height H1 close to 10 mm and of diameter substantially
equal to 12.7 mm. The base resin used is an HDPE (high-density
polyethylene), the functional resin used is an EVOH (ethylene vinyl
alcohol). The measure of oxygen permeability shows that objects
realized according to the invention are approximately 5 to 10 times
more barrier-forming than objects realized according to patent JP
2098415. In both cases, 8% of functional resin was used. The
overlap L of the functional layers measures approximately 1 mm.
[0047] FIG. 17 illustrates a second example of the realization of
multilayer objects. A dose 16 comprising functional resin layers 3,
5 and 7 encapsulated laterally in the resin layers 2, 4 and 6. The
functional resin layer 7 forms the central part of the dose. This
dose is realized from a rod which has been coextruded and
periodically cut as it leaves the coextrusion head. This dose is
next transferred into a compression mold, then compressed. The
vertical compression of the dose 16 along its axis of symmetry
produces the object 1 represented in FIG. 17. The functional resin
layer 7 renders the central part of the object impermeable.
[0048] The method for realizing multilayer objects according to the
invention calls for the realization of multilayer doses. A first
method consists in coextruding a multilayer rod or tube at constant
flow rate and in periodically cutting the rod or tube, as it leaves
the die tool, in order to form the doses. This first method can be
advantageous for making multilayer objects at high speed. A second
method consists in forming the doses by virtue of a discontinuous
periodic flow, the quantity of material coextruded over a period
forming a dose. This second method can be advantageous for
obtaining multilayer doses having great regularity in terms of
weight.
[0049] The cutting of the dose can be realized according to known
methods. In this connection can be cited, for example, rotary
cutters for cutting the rod as at leaves the extruder. This type of
cutter can simultaneously be used to transfer the dose into the
mold. A dose-cutting method by shutting off the extrusion duct is
used in discontinuous extrusion devices.
[0050] The transfer of the dose can be effected by known methods,
such as by gravity or by means of a transfer device. The
positioning of the dose in the compression mold must be precise
and, in particular, the axis of symmetry of the dose must be
precisely aligned with the axis of symmetry of the cavity of the
mold. The doses are compressed along the axis of symmetry of the
dose.
[0051] The multilayer doses are extruded in the molten state at
temperatures suited to the resins used. The multilayer doses remain
in the molten state during the step of being transferred into the
compression mold. The doses are compression molded and the object
obtained is at least partially cooled in the mold prior to
ejection.
[0052] The resins used within the scope of the invention correspond
to the thermoplastic resins currently being used, and more
particularly to those used in the packaging industry. Amongst the
barrier resins which may be used to form the functional layers 3, 5
and 7 can be cited ethylene vinyl alcohol copolymers (EVOH),
polyamides such as Nylon-MXD6, acrylonitrile-methyl acrylate
copolymers (BAREX), fluorinated polymers such as PVDF. In this
connection can also be cited a few resins which may be used for the
layers 2 and 4, 6 and 8 forming the structure of the object:
polyethylene (PE), polypropylene (PP), polystyrene (PS), polyamide
(PA), polyester (PET). This list is not exhaustive. In the choice
of resins, it is important to select products which have
neighboring viscosities. In general, it is preferable to use resins
which, at working temperature, have a viscosity ratio less than 10,
and preferably a viscosity ratio less than 3 will be chosen.
[0053] The devices used in the realization of objects according to
the invention are known. The device minimally comprises means for
coextruding multilayer doses, means for transferring the multilayer
dose into a compression mold, and means for compressing the dose so
as to form the object.
[0054] The invention has the advantage of allowing the production
of multilayer objects at high production speed without substantial
modifications relative to a device used in the realization of
single-layer objects.
[0055] The invention calls for the replacement, in particular, of
the single-layer extrusion device by a multilayer extrusion
device.
[0056] In the examples which are presented here, the doses and the
objects are of simple geometry, but the invention obviously relates
to any geometry of dose and of object.
[0057] The objects obtained according to the invention contain at
least two functional layers, each forming a fold and placed
partially one on top of the other. The invention also allows
objects to be obtained which contain a plurality of functional
layers placed one on top of the other, each of which is able to
form more than one fold. Zigzag-shaped functional layers are
obtainable.
[0058] Numerous arrangements of the functional layers in the dose
are possible. It may be advantageous to couple to the invention a
particular arrangement of the functional layers, said arrangement
being characterized in that the functional layers have a variable
distance to the axis of symmetry. According to this variant, at
least one functional layer forms the shell of a body of revolution
centered on the axis of symmetry, and the distance of said layer to
the axis of symmetry is variable.
[0059] Other dose geometries may be used. It has been observed that
doses which have a part of their surface concave are particularly
advantageous. Such dose geometries facilitate good distribution of
the functional layers in the multilayer object.
[0060] The realization of packagings or packaging components for
food applications calls for good hygiene properties. It is thus
often desirable for the functional layers not to be in direct
contact with the packaged product. It may be advantageous to
imprison the functional layers totally in the dose, such that said
functional layers are totally imprisoned in the object.
[0061] Alternatively, it is possible for just one end of the
barrier layer not to be imprisoned.
* * * * *