HK1115351B - Multilayer objects and production method thereof - Google Patents

Abstract

The invention relates to a method of producing a multilayer object that forms a rotating body, said object comprising at least a base having a diameter D, which is connected to a side wall having an average thickness E and a height H. The inventive method consists in supplying a coextruded multilayer dose to the cavity of a mould and subsequently compressing the dose in order to form the object, said dose forming a body that rotates around an axis of symmetry. The dose consists of a radial stack of several layers including at least one thin functional layer, the outside diameter of said dose being essentially equal to D. In addition, the compression direction is parallel to the axis of symmetry of the dose and the compression is performed on a face of the dose. The method is characterised in that the dose is compressed only on part of said face.

Description

Multilayer product and method for producing same

Technical Field

The invention relates to a method for producing a multilayer product by compression moulding a co-extruded charge of synthetic resin.

Background

Japanese patent JP 2098415 proposes the manufacture of a multilayer product by compression moulding of a cylindrical multilayer charge comprising a radial stack of several synthetic resin layers. Compression moulding of the charge and radial flow of the charge, along an axis of symmetry parallel to the charge, form a product with a multilayer structure. According to the method disclosed in patent JP 2098415, this charge is extruded and a multilayer product is formed, as shown in figure 3.

It is proposed in patent JP 2098415 to use a three-layer charge as shown in fig. 1, this charge consisting of a first resin 4 forming the central part of the charge, a second resin 3 covering only the first resin side faces and a third resin 2 covering only the second resin side faces. This charge is located in a compression mould 5 comprising a die 6 and a punch 7. The compression of the composite charge in the mould 5 along its axis of symmetry is shown in figure 2. The extrusion forms a radial flow of the charge.

In fig. 3 is shown a multilayer product obtained according to the method disclosed in patent JP 2098415. The multilayer structure obtained is characterized by a bifunctional layer 3 embedded in the thickness direction of the product; the layer 3 is corrugated and has two free ends. The multilayer package formed according to the invention disclosed in patent JP 2098415 has a number of advantages, in particular when the functional layer is an oxygen barrier layer, which improves the preservation of the food contained in the package. However, by adopting the method disclosed in patent JP 2098415, the dual function layer 3 is formed intensively at about the product thickness. In this case, the functional layer is facilitated to approach the inner wall. This structure has the advantage that the amount of molecular migration from the packaged product to the package wall or vice versa is reduced. In the method disclosed in patent JP 2098415, the position of the functional layer in the thickness direction of the component cannot be changed.

There is therefore a need to be able to solve the above problems.

Disclosure of Invention

It will be seen subsequently that the object of the invention is to modify the position of the functional layer of the thickness of the component, placing it at a distance closer to the inner wall than to the outer wall of the product.

The invention includes a method of manufacturing a multilayer product forming an axisymmetric body, said product comprising a substrate of at least diameter D bonded to sidewalls of average thickness E and height H. The process consists in loading a coextruded multilayer charge into a cavity of a die and then compressing said charge to form the product; the direction of compression is parallel to the axis of symmetry of the charge, while compression is applied to one surface of the charge. The charge forms an axisymmetric body around an axis of symmetry and comprises several layers stacked radially, at least one of which is a thin functional layer. The outer diameter of the charge is substantially equal to D. The method is characterized in that the charge is compressed only on one part of said surface.

The invention also consists in producing a multilayer product by compression moulding of a charge of diameter D, comprising several layers stacked radially, at least one of which is a thin functional layer, while in place, according to the invention, the functional layer is adjacent to the inner wall of the package. The multilayer charge is loaded into a mold and compressed in the direction of the axis of symmetry of the charge. The concentration of the charge in the mould is important to obtain the correct distribution of the layers over the entire periphery of the product. Advantageously, the charge is compressed not over its entire surface but only over a central portion, the diameter of which is less than D.

According to a preferred mode of the invention, a multilayer charge having a diameter equal to D is loaded into the moulding cavity; the diameter of the charge approximates the diameter of the die cavity; the diameter of the charge is preferably slightly smaller than the die cavity diameter. The multilayer charge is compressed on a surface substantially equal to (D-2E), E being equal to the thickness of the part being molded. According to this preferred mode of the invention, the charge flows in mostly in the compression direction rather than radially. According to this preferred embodiment, the functional layer is located radially in the charge at a distance between (D-2E)/6 and (D-2E)/2. It has been noted that the multilayer package manufactured according to the method described above has a functional layer very close to the inner wall of the package. This package is particularly advantageous when the functional layer is a barrier layer. The above-mentioned smaller distance (D-2E)/6 constitutes a limit allowing the functional layer to be correctly retained in the wall of the package.

The invention is particularly advantageous for making products having a height H greater than D. For products of this height H which is sufficiently large compared to the diameter D, particularly advantageous properties are obtained, which are related to the fact that the functional layer is close to the inner wall of the product and that only a small part of the product does not have a multilayer structure.

The invention will be better understood hereinafter with the aid of the detailed description of an example illustrated by the following figures.

Drawings

Figures 1 to 3 show a method for manufacturing a multilayer product according to the closest prior art;

fig. 1 shows the first step of a method for manufacturing a multilayer product according to patent JP 2098415, the step of loading a multilayer charge into a mold cavity;

fig. 2 shows the second step of the method for manufacturing a multilayer product according to patent JP 2098415, i.e. the step of compressing the charge in the mould to create a radial flow of the charge;

fig. 3 shows a multilayer product obtained according to the method disclosed in patent JP 2098415. This product comprises a thin functional resin layer 3 embedded between two resin layers 2, 4 forming the product;

figures 4 to 6 show a method of manufacturing a multilayer product according to the invention;

FIG. 4 shows loading of multiple charges into the cavity, the charge diameter D being substantially equal to the cavity diameter;

fig. 5 shows the compression of the charge according to the method of the invention, the compression of the charge taking place only above the central part and creating a flow in the compression direction;

figure 6 shows a multilayer product obtained according to the method of the invention. This product comprises a thin functional resin layer 3 embedded between two resin layers 2, 4 forming the product, the functional resin layer 3 being located in the vicinity of the inner wall of the product;

fig. 7 shows a multilayer preform for forming a hollow body by biaxial stretch blow molding, said preform being made according to the invention, having a functional resin layer 3 near its inner wall;

fig. 8 shows a multilayer preform for forming a hollow body by biaxial stretch blow molding, which preform differs from the preform shown in fig. 7 in that the functional layer 3 is also present in the neck portion.

Detailed Description

The invention relates to a method for producing a multilayer product by compression moulding of a multilayer charge.

The multilayer charge is formed by radially superposing several resins and has a cylindrical geometry with a diameter D. The invention is intended to produce, in a non-exclusive manner, multilayer packages having improved gas and flavour barrier properties. For this purpose, it is preferred that the multilayer charge comprises thin functional layers selected for their barrier properties. This functional layer flows during the manufacture of the product and spreads out inside the product wall. The thin functional resin layer is thus embedded in the charge between the resin layers forming the walls of the product. The functional layer is often combined with two thin layers of adhesive resin on either side of the functional layer to improve the adhesion between the layers. This adhesive layer will not be mentioned in the rest of the patent document so as not to add to the description of the invention. In the same sense, the charge in the invention document comprises only two resins, whereas charges comprising more resins and layers can be easily manufactured, which constitutes a distinct advantage over existing products.

In fig. 4 a multilayer charge is shown for the purpose of illustrating the invention. This cylindrical geometry of charge 1 comprises a first resin forming layers 2 and 4 and constituting at least 80% of the charge volume, a thin functional layer 3 located at a distance R from the axis of symmetry of the charge. It has been found experimentally that the functional layer spreads well in the product when R is between (D-2E)/6 and (D-2E)/2. E is the average thickness of the manufactured product. In the present invention, this aspect of the invention will be described again in more detail.

Multilayer charge 1 is formed by coextrusion of the rods. Preferably, the rod is extruded and cut uniformly at a constant rate to form a continuous multilayer charge. Since methods and apparatuses enabling charges to be produced have been described in the prior art, only the principle of producing charges is described here. Multilayer charge 1 can also be obtained by batch coextrusion to form each charge individually.

A multi-layer charge is injected into the cavity of a mould 5, said mould 5 comprising at least two parts: a first part 6, called the die, for receiving the charge; and a second part 7, called the punch, which compresses the charge when it moves. The charge is placed in the mold so that the axis of symmetry of the charge is aligned with the axis of symmetry of the mold cavity. According to a first aspect of the invention, this comprises forming a charge of diameter D close to the diameter of the mould cavity, as shown in figure 4. The molding apparatus shown in fig. 4 and the following figures is only a schematic for explaining the invention. The moulding equipment required to make a product according to the invention is known and therefore does not fall within the scope of the invention. The cavity formed by the die 6 is not limited to the cylindrical shape shown in fig. 4, but the walls of the cavity may form an angle with the axis of symmetry, which may be a clearance angle of around 3 ° for demolding the product, or, if the product is conical, a larger angle. Within the scope of the invention, the taper of the manufactured product is generally less than 10 °, the taper angle being defined with respect to the axis of symmetry.

The charge 1 is then compressed in the mould in a direction parallel to the axis of symmetry. Contrary to what is described in the prior art, in particular in patent JP 2098415, the charge is compressed only in its central portion; the diameter of the central portion is substantially equal to (D-2E). Fig. 5 shows the punch 7 being lowered for compressing the central part of the upper layer of charge 1. The movement of the punch 7 produces a deformation of the charge and a flow of the uncompressed part of the charge. The functional layer is creased and flows along the wall of the punch 7 while remaining completely embedded between the layers 4 and 2. The flow of the functional layer 3 along the punch wall observed during the test is completely undesirable. This flow occurs under the specific conditions described within the scope of the present invention.

The invention also relates to a multilayer product obtained by the method of the invention.

Figure 6 shows the resulting multilayer product. This product comprises a functional layer 3 forming a double layer embedded between layers 4 and 2, wherein the layers 4 and 2 form the product wall. The functional layer forms a fold flush with the upper end of the product and has two free ends flush with the base of the product. The resulting multilayer product has two functional layers adjacent to the inner wall of the product. Fig. 6 shows the functional layer 3 forming the double layers 3a and 3 b; layer 3a is isolated from the inner wall of the package by layer 2 a; layer 4 separates layers 3a and 3 b; and layer 2b separates layer 3 from the outer wall of the package. The first functional layer 3a is at a distance of less than E/6 from the inner wall of the product, while the second functional layer 3b is at a distance of less than 2E/3 from the inner wall of the product and generally less than E/3. The invention enables the number of molecules migrating from the wall of the package to the packaged article or vice versa to be reduced by at least 30% with respect to the prior art product obtained according to patent JP 2098415.

The products manufactured according to the invention have particularly advantageous properties when their height H is greater than or equal to D. In fact, for products having a height H greater than D, the functional layer forms a barrier layer which is dispersed over at least 80% of the product, which gives a significant improvement in the impermeability of said product.

The radial position of the functional layer in the charge has a greater influence on the distribution of said functional layer within the product. It has therefore been observed that the functional layer is only partially dispersed in the product side wall if it is located in the charge with a radius R smaller than (D-2E)/6. More specifically, it has been found that the functional layer disappears from the end of the product side walls. In most cases it is desirable that the functional layer is spread over the end of the product, but there are some product barrier properties that need only be on a single portion of the product sidewall, so the barrier layer can be located at a distance less than (D-2E)/6. It was also observed that the radial position of the functional layer in the charge could not be greater than (D-2E)/2, so that the functional layer remained embedded in the wall of the product. When the radial position of the functional layer is greater than (D-2E)/2, the functional layer is present all over the surface of the sidewall of the product. In most cases, it is desirable to keep the functional layer embedded, especially when the functional layer is sensitive to moisture.

This method has the great advantage that the multilayer preform for manufacturing the hollow body is formed by a biaxial blow molding method. Figure 7 shows a multilayer preform obtained according to the inventive method. This preform has a thin functional layer 3 on the side wall surfaces forming two protective layers 3a and 3 b. The functional layer 3 is embedded in the majority of the resin 2 forming the wall of the preform, whereas said functional layer 3 has two free ends on the base surface and a fold underneath the neck. The functional layer 3 forms two layers 3a and 3b on the side wall faces; said layers 3a and 3b are located near the inner wall of the preform. The layers 3a and 3b are located at a distance from the inner wall of the preform that is less than E/6 and E/3, respectively, E being the thickness of the preform wall at the location in question. The functional layer 3 is spread over the whole preform except at the base and neck regions. The percentage of functional layer in this product is less than 2%. For example, the present invention allows PET or PP preforms to be formed with a PAMXD6 or EVOH functional layer. An adhesive resin layer may be added to both sides of the functional layer.

The hollow body forming the package is obtained by blow-moulding in a preform mould as shown in figure 7. This hollow body, which comprises a base body, a neck portion and a side wall joining the base body to the neck portion, is particularly advantageous because it has improved barrier properties. More than 90% of the walls of the hollow body have improved impermeability by means of the functional layer. The functional layer forming the double protective layer is close to the inner wall of the hollow body, which significantly limits the migration of molecules from the hollow body to the content or from the content to the hollow body wall. The functional layer is embedded in the majority of the resin forming the wall of the hollow body and has two free ends on the base face and a pleat below the neck. The functional layer forms two layers on the surface of the side wall; the layer is adjacent to the inner wall of the hollow body. The functional layers are located at a distance from the inner wall of the hollow body of less than F/6 and F/3, respectively, F being the thickness of the wall of the hollow body at the location in question. The functional layer is spread throughout the hollow body except at the base and neck surfaces. The functional layer accounts for less than 2% of the hollow body. The migration of molecules from the hollow body to the packaged item or from the packaged item to the hollow body wall is reduced by at least 50% relative to the prior art.

The invention enables the manufacture of a multi-layer hollow body with improved properties. The invention also enables the production of multilayer products having particularly thin layers and having a plurality of layers. This result can be achieved by a continuous co-extrusion process to form the charge. Unlike batch processes like the multi-layer injection molding process currently used, this continuous co-extrusion process enables particularly thin layers and many layers to be obtained.

Fig. 8 shows the possibility of the functional layer 3 spreading into the preform neck without impairing the mechanical properties of said neck. In practice, the invention enables the addition of an adhesive layer on each side of the barrier layer and the extrusion of these layers with a thickness sufficiently thin to form a three layer set of functional layers of less than 2% of the volume of the product. The improvement in adhesion between the layers, combined with the lower thickness of these layers, allows these layers to diffuse to the preform neck without impairing the mechanical properties of said neck.

The hollow body obtained by blow molding in the preform mold shown in fig. 8 comprises a base, a neck and a side wall joining the base and the neck. This hollow body is particularly advantageous because it has improved barrier properties. More than 90% of the walls of the hollow body have improved impermeability by the functional layer. The functional layer forming the double protection layer is close to the inner wall of the hollow body, which significantly limits the migration of molecules from the hollow body wall to the content or vice versa. The functional layer forms two layers on the side wall surface and the neck portion, the layers being located adjacent the inner wall of the hollow body. The functional layers are located at a distance from the inner wall of the hollow body of less than F/6 and F/3, respectively, F being the thickness of the wall of the hollow body at the location in question. The functional layer is dispersed throughout the hollow body except at the base surface. The functional layer exhibits less than 2% of the resin required to form the hollow body. The migration of molecules from the wall of the package to the packaged item or vice versa is reduced by at least 50%.

Molecules migrating from the package wall to the packaged item are low mass molecules either due to this method of manufacturing the resin or due to resin decomposition during the processing method. In the case of PET, for example, these molecules may be monomers, plasticizers, adjuvants or acetaldehyde molecules. By way of further example, the molecules migrating from the packaged item to the package wall may be a fragrance, a colorant, an adjuvant, a stabilizer, a preservative, or a flavoring agent.

The resins used within the scope of the invention correspond to the thermoplastic resins generally used, and more particularly those used in the packaging industry. Among the impermeable resins that can be used to form the functional layer 3, there may be ethylene/vinyl alcohol copolymers (EVOH), polyamides such as nylon-MXD 6, acrylonitrile/methyl acrylate copolymers (BAREX) and fluoropolymers such as polyvinylidene fluoride (PVDF). Some of the resins that can be used to form the product structure 2 are: polyethylene (PE), polypropylene (PP), Polystyrene (PS), Polyamide (PA) and Polyester (PET). These lists are not exhaustive. When selecting a resin, it is important to select a product with similar tack. Generally, it is preferred to use a resin having a tack ratio of less than 10 at the operating temperature. It is preferred to select a viscosity ratio of less than 3.

The compression molding method comprises: charging a synthetic resin multilayer charge in a molten state into a cavity of a mold; forming a product by compression molding said charge within said mold cavity; the product is cooled and then demolded.

In the examples described here, the charge and the product have a simple geometry, but it goes without saying that the invention relates to various charge and product geometries. For example, a charge having an orifice may be used to form a product having an opening on a face of a substrate.

The product obtained according to the invention contains a functional layer 3, wherein the functional layer 3 forms at least one fold flush with the periphery of the product. It is also possible to obtain a product with a second corrugation close to the symmetry axis of the product. An arrangement of zigzag-shaped functional layers is obtained in this product.

It is also possible to use a charge comprising several functional layers 3, all centred on the axis of symmetry of the charge. The obtained multilayer product is characterized in that the functional layers are at least partially superimposed, while each layer forms at least one corrugation.

Claims (7)

1. A method of manufacturing a multilayer product having an axisymmetric body, said product comprising a base body of at least diameter D, bonded to a side wall of average thickness E, and height H, said method comprising the steps of feeding a coextruded multilayer charge into a cavity and then compressing said charge to form the product, the charge forming an axisymmetric body around an axis of symmetry, the charge comprising a radial stack of several layers, at least one of which is a thin functional layer, said charge having an outer diameter substantially equal to D, the direction of compression being parallel to the axis of symmetry of said charge, compression being performed on one surface of the charge, characterized in that the charge is compressed only on a central portion of said surface, the portion of the surface subject to compression being centered on the axis of symmetry of the charge, said central portion of the charge having a diameter substantially equal to (D-2E), and the functional layer in the charge being located radially at a distance from the axis of symmetry less than (D-2E)/2E And greater than (D-2E)/6.

2. Multilayer product obtained according to the process of claim 1, characterized in that the functional layer is located closer to the inner wall than to the outer wall of the product.

3. A multilayer product according to claim 2, characterized in that:

a. the thin functional layer forms a wrinkle;

b. the thin functional layer is provided with two free ends positioned on the surface of the substrate;

c. the thin functional layer forms a bilayer in the sidewall thickness direction.

4. A multilayer product according to claim 3, comprising a multilayer hollow body manufactured by biaxial stretch blow molding, comprising a neck, a base and a side wall of thickness E, E being variable; the sidewall is located between the base and the neck.

5. Multilayer product according to claim 4, characterized in that the height H of the product is greater than or equal to D.

6. A multilayer product according to claim 5, characterized in that for producing the multilayer hollow body by biaxial stretch blow molding a preform is used comprising a neck, a base and a side wall connecting the base and the neck.

7. The multilayer product according to claim 6, wherein the preform has a functional layer, wherein functional layer is less than 2% in the preform.