EP1720691A1

EP1720691A1 - Synthetic multilayer object

Info

Publication number: EP1720691A1
Application number: EP05708854A
Authority: EP
Inventors: Jacques c/o AISAPACK S.A. THOMASSET
Original assignee: Aisapack Holding SA
Current assignee: Aisapack Holding SA
Priority date: 2004-03-01
Filing date: 2005-02-26
Publication date: 2006-11-15
Also published as: KR101154849B1; KR20060132740A; JP2007525347A; BRPI0508331A; EP1727657A1; EP1720690B1; JP4865696B2; US20070178276A1; BRPI0508338B1; JP2007525348A; CA2557584A1; CA2557622A1; JP2007525349A; BRPI0508336A; US20070184237A1; KR101149790B1; US7923085B2; US20070184223A1; CN1926027A; CN1925962B

Abstract

The invention relates to a multilayer axisymmetric object which forms a wall having thickness E and comprises a first resin forming the object structure and constituting at least 80 % of the volume thereof and a second resin forming at least two functional layers which are separately entrapped in the first type of resin. The inventive multilayer structure is characterised in that (a) the functional layers are distributed in the distinct portions of the object, (b) the functional layers form the bodies of rotation centred on the axis of symmetry of the object and (c) the two functional layers are partly superimposed in a direction perpendicular to said wall.

Description

Multilayer synthetic object

Field of the invention

The present invention relates to a method of producing multilayer objects by compression molding a multilayer dose.

State of the art

US Pat. No. 4,876,052 describes a multilayer object (FIG. 1) characterized in that a first synthetic resin 3 is completely trapped 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 trapped in the second resin. The multilayer structure described in US Pat. No. 4,876,052 is particularly useful for objects such as containers or lids. However, the objects obtained according to the method described in US Pat. No. 4,876,052 require a large proportion of functional resin in the object; which generates two major disadvantages; the former being a prohibitive cost and the second a resistance to mechanical stress diminished. The absence of adhesion between the functional resin and the external resin reduces the solidity of the object and creates a risk of cohesion of the outer layer. Another disadvantage of US Pat. No. 4,876,052 resides in the fact that the respective quantity of resins 2 and 3 can only be slightly adjusted. As will be shown later in the description of the invention, these quantities are fixed by the geometry of the object and by the flows during compression of the dose. This method also requires the intermittent extrusion of the first resin within a second resin. U.S. Patent 4,876,052 discloses a coextrusion device with a valve shutter mechanism for the first synthetic resin

In order to overcome the drawbacks of US Pat. No. 4,876,052, Japanese Patent JP 2098415 proposes to produce a multilayer object by compression molding. starting from a composite dose characterized in that the second synthetic resin covers only the lateral faces of the first synthetic resin. The compression molding of this dose along its axis of symmetry leads to an object having a multilayer structure (FIG. 2) characterized in that a first resin 2 partially traps a second resin 3. However, the multilayer objects made from two resins according to patent JP 2098415 have two major disadvantages; the first being to have the barrier resin 3 exposed in the central surface of the object on at least 10% of the total surface of the object; and the second being to require an amount of barrier resin 7 in the subject of at least 30% of the total amount of resin. This leads on the one hand to objects having a prohibitive cost, and on the other hand to objects with highly modified mechanical properties mainly in the center of the object. Another disadvantage of patent JP 2098415 resides in the fact that the respective quantity of resins 2 and 3 can only be slightly adjusted, these quantities being fixed by the geometry of the object and the flows during compression of the dose. .

It is proposed in patent JP 2098415 to use a tri-layer dose to partially remedy the aforementioned drawbacks. This dose consists of a first resin 4 forming the central part of the dose, a second resin 3 covering only the lateral faces of the first resin, and a third resin 2 covering only the lateral faces of the second resin . The crushing of this composite dose along its axis of symmetry leads to a multilayer object (Figure 3). The use of a tri-layer dose has the advantage of reducing the amount of functional resin 3 used and leads to objects having slightly modified mechanical properties compared to the same object comprising a single resin 2. However, the second resin 3 does not cover the central part of the multilayer object which leads to multilayer objects without barrier property close to the axis of symmetry. This central zone of the object not covered by the barrier resin layer 3 reduces the barrier performance of the object and makes this solution less efficient. The patent application CH01619 / 04 describes multilayer objects (FIG. 4) made from a multilayer dose molded by compression. The objects described in this patent application have a multilayer structure characterized by the position of the functional layer forming a double zigzag-shaped fold. The functional layer is correctly distributed throughout the object, even in the central part. The method for producing multilayer objects described in the patent application CH01619 / 04 also makes it possible to control the thickness of the functional layer. An adhesive layer may be added between the resin forming the surface of the object and the functional resin. However, the compression of the dose requires a method and a specific molding device. This method requires in particular additional tooling movements compared to the basic compression process setting relative movement of the two parts of the mold. In the case of high speed molding, it may be disadvantageous to use a compression device as described in the patent application CH01619 / 04.

Patent EP926078 describes obtaining a cork liner (FIG. 5) by compression molding a dose comprising a lamellar multilayer structure. The functional resin 3 forms lamellae dispersed in the resin 2. The method consists of extruding a lamellar dose (sort of millefeuille) with a device for generating lamellae, then compressing the dose in order to form the liner. We find in the thickness of the liner (Figure 5) a multilayer structure of the millefeuille type. This method consists in compression molding a lamellar alloy; the number of lamellae in the dose being very large. This method has the disadvantage of requiring a percentage of high barrier resin (of the order of 20%) to significantly reduce the permeability of the object because the lamellae do not form a continuous layer. Another disadvantage of patent EP926078 lies in the fact that the position of the lamellae in the object can not be controlled. As a result, the resin forming the surface layer of the multilayer object is a mixture of the different layers forming the dose. This may limit the use of the objects described in EP926078 for hygiene reasons when the packaged product is in contact with the lamellar multilayer object. Another disadvantage of patent EP926078 is related to limited choice of resins that must have viscosities and melting temperatures to maintain the lamellae during compression of the dose.

Object of the invention

The invention relates to the production of multilayer objects produced by compression molding a multilayer dose while at the same time making it possible to remedy the aforementioned drawbacks.

Summary of the invention

The invention consists of an axisymmetric 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 a second resin forming at least two thin functional layers; said functional layers being trapped separately in the first resin; the multilayer structure being characterized by the fact 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 overlap partially in a direction perpendicular to said wall.

Detailed description of the invention

The invention will be better understood hereinafter by means of a detailed description of the examples illustrated by the following figures. Brief description of the figures

Figures 1 to 5 illustrate multilayer objects of the prior art.

Figure 1 shows a multilayer object described in US4876052. This object 1 made by compression molding comprises a functional resin layer 3 completely encapsulated in a resin 2 forming the visible surface of the object.

Figure 2 illustrates a multilayer object described in JP2098415. This object 1 comprises a functional resin layer 3 partially encapsulated in a resin layer 2 forming the visible surface of the object.

Figure 3 shows another multilayer object described in JP2O98415. This object comprises a thin layer of functional resin 3 trapped between two layers of resins 2 and 4 forming the object.

FIG. 4 shows a multilayer object described in the application CH01619 / 04. this object is characterized by the double zigzag fold of the functional layer 3.

FIG. 5 shows an object comprising a lamellar multilayer structure described in patent EP926078.

Figures 6 to 11 show multilayer objects corresponding to the invention.

Figure 6 illustrates a first multilayer object responding 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 a covering.

FIG. 7 shows a second example of a multilayer object having a central surface S not covered by the functional layers FIGS. 8 and 9 illustrate objects made according to the invention and having an orifice 15.

Figure 10 shows a multilayer plug made according to the invention.

Figure 11 shows a multilayer preform made according to the invention.

Figure 12 illustrates the flow profile during dose compression.

Figure 13 shows the method of obtaining the multilayer objects and in particular the relation between the dose and the object.

Figure 14 shows how the S / Sp ratio of the area not covered by the functional layer on the surface of the object varies as a function of the O / W compression ratio.

Figure 15 illustrates the making of an object according to JP 20418415.

Figure 16 shows how the ratio S / Sp versus O / W varies for an object made according to JP 20418415.

FIG. 17 shows another embodiment of an object according to the invention.

Detailed description of the figures

The invention relates to a multilayer object having at least two functional resin independent layers distributed in a thin 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 covering. The term "functional resin" denotes a resin chosen for its barrier properties to gases or aromas. FIG. 6 illustrates a multilayer object corresponding to the invention. The thickness of the object is observed in a section made perpendicular to the surface of the object and passing through the axis of symmetry. This figure shows the distribution of functional layers in the thickness of the room. The functional resin forms the thin layers 3, 5 and 7 distributed in the base resin forming the structural layers 2, 4 and 6 of the object. The amount of functional resin is generally less than 10% of the total resin volume. In order to obtain advantageous barrier properties, it has been observed that the functional layers should be partially superimposed in order to form the cover L. In a preferred mode that is not illustrated, a value of the covering L of between 1 and 3 times the thickness E makes it possible to obtain a permeability close to that obtained with a single continuous layer of identical thickness. In Figure 6, the central portion of the object is formed by the layer 7 of functional resin. The amount of functional resin forming the core layer 7 of the object is less than 5% of the total resin volume and generally less than 3%. The central layer 7 of functional resin is present on a surface S representing less than 3% of the total surface of the object and preferably less than 1%. The ends 9, 10 and 11 of the functional resin layers 3, 5 and 7 are close to the upper and lower surfaces of the object; the ends of the raised layers can be flush to the surface of the object or fully encapsulated. The functional layers 3, 5 and 7 respectively form the folds 12, 13 and 14. The fold 12 of the layer 3 is generally close to the side wall of the object so as to have impermeability properties over the entire surface of the object. In some cases, it is not necessary to make the entire surface of the object impermeable; the invention then makes it possible to propagate said layer 3 only in the part where the object must be impermeable. The folds 13 and 14 of the functional resin layers 5 and 7 are superimposed on the ends 9 and 10 of the functional layers 3 and 5 and form a covering. The overlapping of the functional layers makes it possible to guarantee a good level of impermeability, despite the discontinuity created by the different layers. FIG. 7 shows a second example of a multilayer object produced according to the invention; this object is distinguished from the object shown in Figure 6 by its central part. The object shown 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 layers of functional resins 3, 5, and 7 form the respective plies 12, 13 and 14. The plies 13 and 14 are superimposed on the ends 9 and 10 of the functional resin layers 3 and 5 and form a covering which makes it possible to guarantee a good level of impermeability. The ends 11 of the functional resin layer 7 do not cover the central part of the object leaving a permeable surface S. It was observed that the leak created by the surface S was very small considering the S / Sp ratio of the area not covered by the functional layers on the total surface exposed. The invention makes it possible to obtain an S / Sp ratio of less than 2%, which leads to negligible leakage.

FIG. 8 illustrates a third multilayer object produced according to the inventive method. This object 1 comprises a central orifice 15 and two thin layers 3 and 5 of functional resin distributed between the layers 2, 4 and 6 of the resin forming the structure of the object. Functional layers 3 and 5 form folds 12 and 13; the fold 13 overlapping with the ends 9 of the functional layer 3.

Figure 9 shows another example of a multilayer object having an orifice. This object differs from the object shown in FIG. 8 by the orientation of the folds 12 and 13 of the functional resin layers 3 and 5.

The method for producing multilayer objects described below is particularly advantageous for producing objects such as plugs, lids, preforms or tube shoulders. This method can also be used advantageously to produce preforms in the form of slabs; these wafers are then used in thermoforming or blowing thermoforming to form multilayer objects. Figure 10 illustrates a multilayer structure that could be obtained in a geometry plug-type object, and Figure 11 shows a multilayer preform made according to the invention. These objects have a partial superposition of functional resin layers to ensure the impermeability of the object.

FIG. 10 shows that the functional layer 3 is generally the combination of three thin parallel layers 3a, 3b, 3c; the layers 3b and 3c being adhesive layers located on either side of the barrier layer 3a. This combination makes it possible to combine resins of different nature while guaranteeing good adhesion between the different layers, which avoids the possible problems of delamination or decohesion in the multilayer objects. The adhesive and barrier layers are parallel and in small quantities. The set of adhesive layers 3b and 3c and the barrier layer 3a forming the functional layer 3 generally represents an amount of resin less than 15% of the total volume of resin forming the dose, and preferably an internal amount of 10%.

The method of producing multilayer objects according to the invention is particularly advantageous because it requires very little modification of the existing devices. As will be shown later, this method allows the realization of multilayer objects at high production rates.

The method consists in co-extruding a cylindrical or tubular multilayer dose, supplying this multilayer dose in the molten state in a compression device, then compressing said dose in a mold to form the object; this method being characterized by the geometry of the multilayer dose (height, diameter) and the position of the layers function it in said dose.

In order to better understand the spirit of the invention, it is necessary to grasp the link that unites the multilayer dose with the multi-layer object e. Figure 12 shows the flow of the resins during the compression of the dose. This flow depends mainly on the rheological properties of the resins during the compression as well as the geometry of the object. Figure 12 shows that this flow is faster halfway between the walls than near the walls tooling. In the vicinity of the tooling walls, the speed of movement of the particles tends to zero, but the shear deformation is high. Conversely, halfway between the walls, the particle velocity is maximum and the shear deformation is minimal. During flow, the functional resin layer is driven and deforms non-uniformly depending on its position in the flow profile. Thus, the final position of the functional resin layer in the object is determined by the initial position of the functional layer in the dose and the sum of the deformations experienced during the flow.

FIG. 13 shows the multilayer dose 16 used to produce a multilayer object 1. A cylindrical dose 16 corresponding to a coextruded multilayer rod portion comprises two thin layers 3 and 5 of functional resin trapped between the layers 2, 4 and 6 of the base resin. The dose 16 corresponds to a radial stack 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 generally this amount is less than 10%. The compression of this dose generates a flow of the resin towards the periphery, which causes and deforms the functional layers 3 and 5 in this direction. The multilayer object obtained 1 is illustrated in FIG. 13. This object contains 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 a cover L with the end 9 of the functional layer 3. The value of the cover L and the propagation of the fold 12 to the end of the object are related to the initial geometry dose and functional layer position in the dose. In order to obtain a multilayer object as illustrated in FIG. 13, it is necessary to correctly position the resin layers 3 and 5 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; layer i being located closer to the axis of symmetry than layer j. The object 1 illustrated in FIG. 13 has a central S surface that is not covered by the functional layer. The ratio S / Sp corresponding to the ratio to the uncovered surface on the surface of the object is presented in FIG. 14. It was found that this ratio depended on the rate of compression of the dose, that is to say the ratio H1 / E; H1 corresponding to the height of the dose, and E to the thickness of the object. Figure 14 shows how the ratio S / Sp varies as a function of H1 / E. It is observed experimentally that for compression ratios of 5, the S / Sp ratio of object 1 was less than 0%, and for a compression ratio of this ratio was less than 2%. This result indicates that for a compression ratio of 10, the area S causing leaks represents less than 2% of the surface of the object.

In order to show the advantage of the objects made according to our invention, these have been compared with objects obtained according to the method described in patent JP 2098415.

Figure 15 illustrates the compression of a dose as proposed in JP 2098415 to demonstrate the limitations of the multilayer objects obtained by this method and to better understand the object of the present invention. FIG. 15 shows a tri-layer dose 16 produced according to patent JP 2098415. This dose comprises a first resin 4 forming the central part of the dose, a functional resin 3 covering only the lateral faces of the first resin, and a third resin 2 covering only the lateral faces of the functional resin. FIG. 15 illustrates the object 1 obtained after compression of the dose 16. The functional layer 3 has propagated to the end of the object while remaining encapsulated at the periphery of the object. As shown in FIG. 15, the functional layer has not propagated in the central part of the object 1.

The experimental results corresponding to the production of multilayer objects according to patent JP 2098415 have been reported in FIG. 16. This figure shows how the surface fraction not covered by the functional layer varies.

S / Sp depending on the compression ratio H / H1. It is observed experimentally that for compression ratios of 5, the ratio S / Sp of the object 1 is greater than 25%, and for a compression ratio of 10 this ratio close to 20%. This result indicates that for a compression ratio of 10, the area S causing leakage represents about 20% of the surface of the object.

The barrier properties of objects made according to patent JP 2098415 (FIG. 15) and according to the invention (FIG. 13) were compared. Discs with a thickness of 1 mm and a diameter of 40 mm were produced starting from cylindrical multilayer doses with a height H1 close to 10 mm and a diameter substantially equal to 12.7 mm. The base resin used is HDPE (high density polyethylene); the functional resin used is an EVOH (ethylene vinyl alcohol). The measurement of the oxygen permeability shows that the objects made according to the invention are approximately 5 to 10 times more barrier than the objects made according to the patent JP 2098415. In both cases, 8% of functional resin was used. The overlap L of the functional layers is about 1 mm.

Figure 17 illustrates a second embodiment of multilayer objects. A dose 16 comprising the 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 portion of the dose. This dose is made from a coextruded rod and periodically cut at the output of the coextrusion head. This dose is then transferred to a compression mold and compressed. The vertical compression of the dose 16 along its axis of symmetry leads to the object 1 shown in FIG. 17. The functional resin layer 7 makes the central part of the object impermeable.

The method of producing multilayer objects according to the invention requires the production of multilayer doses. A first method is to co-extrude at a constant rate a ring or multilayer tube and periodically cut the rod or the tool outlet tube to form the doses. This first method can be advantageous for manufacturing multilayer objects at a high rate. A second method consists in forming the doses by means of a discontinuous periodic flow; the amount of co-extruded material during a period forming a dose. This second method may be advantageous for obtaining multilayer doses having a great regularity in weight.

The cut of the dose can be made according to known methods. For example, the rotary knives for cutting the rod at the extruder outlet. This type of knife can be simultaneously used to transfer the dose into the mold. An extrusion channel shutter dose cutting method is used in discontinuous extrusion devices.

The transfer of the dose can be done by the known methods; as by gravity or via 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 mold cavity. The doses are compressed along the axis of symmetry of the dose.

The multilayer doses are extruded in the molten state at temperatures adapted to the resins used. The multilayer doses remain in the molten state during the transfer step in the compression mold. The doses are molded by compression and the object obtained is at least partially cooled in the mold before ejection.

The resins used in the context of the invention correspond to the thermoplastic resins commonly used, and more particularly those used in the packaging sector. Among the barrier resins that can be used to form the functional layers 3, 5 and 7, mention may be made of ethylene vinyl alcohol copolymers (EVOH), polyamides such as nylon-MXD6, and acrylonitrile methyl acrylate copolymers (BAREX). fluorinated polymers such as PVDF. There are also some resins that can be used for 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. When choosing resins, it is important to select products with similar viscosities. In general, it is preferable to use resins which at working temperature exhibit a viscosity ratio of less than 10, and preferably a viscosity ratio of less than 3 is selected.

The devices used to produce objects according to the invention are known. The device comprises at least means for co-extruding multilayer doses, means for transferring the multilayer dose into a compression mold, and means for compressing the dose to form the objective.

The invention has the advantage of allowing the production of mu lticouches objects at high production rates without significant changes compared to a device used to make monolayer objects. The invention necessitates replacing the single-layer injection device with a multilayer extrusion device.

In the examples presented here, the doses and the objects are of simple geometry, but it goes without saying that the invention concerns any dose and object geometry.

The objects obtained according to the invention comprise at least two; functional layers each forming a fold and overlapping partially. The invention also makes it possible to obtain objects comprising several functional layers superimposed and each capable of forming more than one fold. Zigzag-shaped functional layers can be obtained.

There are many provisions of the functional layers in the dose. It may be advantageous to couple to the invention a particular arrangement of the functional layers; said arrangement being characterized by the fact that the functional layers have a variable distance to the axis of symmetry. According to this variant, at least one functional layer forms the envelope of a body of revolution centered on the axis of symmetry, and the distance of said layer to the axis of symmetry is variable. Other dose geometries can be used. It has been observed that doses having a part of their concave surface are particularly advantageous. Such dose geometries facilitate a good distribution of the functional layers in the multilayer object.

The production of packaging or packaging components for food uses requires high hygiene properties. It is thus often desirable that the functional layers are not in direct contact with the packaged product. It may be advantageous to completely enclose the functional layers in the dose, so that said functional layers are totally trapped in the object.

Alternatively, only one end of the barrier layer may not be trapped.

Claims

claims

1. axisymmetric 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 a second resin forming at minus two thin functional layers; said functional layers being trapped separately in the first resin; the multilayer structure being characterized by the fact that d. The functional layers are distributed in separate parts of the object e. The functional layers form bodies of revolution centered on the axis of symmetry of the object f. The two functional layers overlap partially in a direction perpendicular to said wall.

2. Object according to claim 1 characterized in that the superposition distance is at least equal to the thickness E of the object.

3. multilayer object according to claim 1 or 2 characterized in that the functional layers themselves form a multilayer structure comprising a barrier resin layer trapped between two layers of adhesive resin.

4. Object according to any one of the preceding claims characterized in that the first resin represents at least 85% of the volume of the object.

5. Multilayer object obtained by compression molding a multilayer dose; said multilayer dose in a radial stack of several layers; having at least 2 thin functional layers trapped between layers composed of a first resin; the layers made of the first resin representing at least 80% of the volume of the dose; the distance from the first layer to the axis of symmetry being less than or equal to half the distance from the second layer to the axis of symmetry

6. Symmetry-axis multilayered dope for the production of multilayer objects by compression molding, the multilayer structure of which consists of a radial stack of several layers; said multilayer structure having at least 2 thin functional layers trapped between layers composed of a first resin; the multilayer structure being characterized by the fact that a. The layers made of the first resin represent at least 80% of the volume of the dose b. The distance from the first layer to the axis of symmetry is less than or equal to half the distance from the second layer to the axis of symmetry

7. Multilayer dose according to claim 6 characterized in that the functional layers themselves form a multilayer structure comprising a barrier resin layer trapped between two layers of adhesive resin.

8. multilayer dose according to claims 6 or 7 comprising at least three functional layers characterized in that the ratio of radial distances between two adjacent layers is less than or equal to 0.5;