Method and injection mould for producing a two-layer or multi-layer preform

Abstract

The invention relates to a method and an injection mould for producing a two-layer or multi-layer preform (20) for producing a container. The preform has a preform base, a preform body and a preform neck. The method comprises the steps of: - providing a semi-finished product (50) in an injection mould, wherein the semi-finished product (50) consists of at least 90%, preferably at least 95%, in particular at least 98%, PEF or PEF copolymers, - overmoulding said semi-finished product (50) in a second step with a material different from PEF, wherein said material comprises at least 60%, preferably 80%, in particular at least 95% PET. The material is injected at a temperature which is 40°C to 80°C above a melting temperature of the semi-finished product (50).

Description

[0001] Method and injection mold for the production of a two- or multi-layer preform

[0002] The present invention relates to a method and an injection mold for producing a two- or multi-layered preform. This preform is then used to produce a container.

[0003] These containers are typically designed to hold liquids, especially carbonated and pressurized liquids. They are usually made of PET because this material is lightweight, readily recyclable, and has a relatively small carbon footprint, particularly compared to glass or metal alternatives.

[0004] A disadvantage of containers manufactured in this way is that the material PET does not have particularly good barrier properties with regard to oxygen, carbon dioxide, sulfur dioxide, water, light and other contaminants.

[0005] Therefore, prior art already provides for the interior of preforms and / or containers to be at least partially coated with materials such as polyamide, EVOH, PVC or PVDC.

[0006] While these coatings improve barrier properties, they lead to problems in recycling and are sometimes incompatible with the contents. Many contents should not come into direct contact with the polyamide or EVOH. On the one hand, these materials bond poorly with the PET of the container, necessitating the use of adhesive layers, for example. On the other hand, separating the individual materials during the recycling process is difficult. Because the bond between the materials is poor, there is a risk of delamination, which could damage the container and / or at least give the customer the impression of damage. As an alternative, it has already been proposed to apply barrier layers to the inside of the containers using plasma coating, such as Diamond Like Coatings (DLC) or Glass Like Coatings (SiOx).Since such coatings are not flexible, they must, or rather can only, be applied once the corresponding container has been completely blown and has its final shape. In other words, this must happen either at the bottler, who provides the finished containers, or at the preform manufacturer's plant, who also blows the containers into their final shape. The latter necessitates transporting the finished containers to the bottler. It is evident that transporting finished containers, rather than preforms, requires significantly larger transport volumes, which makes transport both more expensive and more complex.

[0007] The object of the invention is to overcome at least one or more disadvantages of the prior art. In particular, a method and / or an injection mold is to be provided which makes it possible to improve, preferably, the barrier properties of a container and / or to improve its strength or resistance to delamination.

[0008] This problem is solved by the methods and devices defined in the independent patent claims. Further embodiments are described in the dependent patent claims.

[0009] A method according to the invention is a method for producing a two- or multi-layered preform, in particular a precisely two-layered preform, for producing a container. The preform has a preform base, a preform body, and a preform neck. The method comprises the following steps:

[0010] - Providing a semi-finished product in an injection mold, wherein the semi-finished product consists of at least 90%, preferably at least 95%, in particular at least 98% of PEF or a PEF copolymer containing (diethylene glycol (DEG), isosorbide, terephthalic acid, isophthalic acid) which contains more than 50% by weight of a furandicarboxylic acid

[0011] - Overmolding this semi-finished product in a second step with a material different from PEF, wherein this material comprises at least 60%, preferably 80%, and in particular at least 95% PET. The material is injected at a temperature that is 40°C to 80°C above the melting temperature of the semi-finished product or the material of the semi-finished product.

[0012] The semi-finished product has cooled down before the overmolding process and has at least a surface temperature that is below its melting point.

[0013] The percentage values ​​for PET and PEF refer to the respective weight of the material, i.e., for example, the weight of the material of the semi-finished product or the material used in the overmolding process.

[0014] This results in the second material bonding very well with the semi-finished product, and the different layers can be welded together in particular. Specifically, the overmolding with PET, which is overheated relative to the semi-finished product, causes the semi-finished product to melt, at least superficially, and the PET to interlock with the PEF.

[0015] Preferably, the injection process, or the overmolding process, heats the surface of the semi-finished product above its melting point. In other words, the surface of the semi-finished product liquefies, allowing it to mix with the liquid components of the overmolded PET.

[0016] Because the second material contracts significantly during the cooling process (shrinkage), a very high compression of the two materials occurs. The liquid boundary layers are pressed against each other under very high pressure.

[0017] In other words, the two interfaces are in liquid form. This allows entire molecules or parts of molecules to penetrate the respective other layer and react completely or partially with the other molecules, triggering copolymerization. This creates a high-strength bond between the two layers. In other words, the penetration of PET molecules, or at least chain components of PET molecules, into the PEF, and vice versa, of PEF molecules or chain components of PEF molecules into the PET, results in an excellent bond that can be compared to welding.

[0018] The PEF exhibits good barrier properties. The strong bond between the PEF and the PET reduces the risk of delamination.

[0019] Preferably, the surface of the semi-finished product is liquefied to a depth of at least 0.05 mm. This ensures that a minimum degree of interlocking, i.e., penetration of the molecules into the mutual interfaces of the individual materials, is achieved.

[0020] It may be provided that the surface of the semi-finished product is liquefied to a maximum depth of 0.1 mm.

[0021] This maximum depth ensures that the liquefied surface remains in place and prevents the components from shifting, for example due to gravity.

[0022] This maximum depth naturally applies under the premise that in every case a residual wall thickness of the semi-finished product remains that is not liquefied or melted. This residual wall thickness is preferably at least 0.05 mm. Preferably, the semi-finished product has a temperature at an interface before overmolding that is 5 °C, and in particular 10 °C, below the melting temperature of the semi-finished product or below the melting temperature of the material of the semi-finished product.

[0023] This makes it possible to keep the additional energy input required to liquefy the surface of the semi-finished product as low as possible and / or to prevent excessively rapid resolidification.

[0024] The semi-finished product can have a wall thickness between 0.1 mm and 1.1 mm.

[0025] Since the material PEF is significantly more expensive compared to the usual materials, efforts are made to keep its components as low as possible.

[0026] In particular, the layer thickness should be chosen so that the required barrier properties are met. Additional material that is not necessary for this requirement can be saved accordingly.

[0027] In particular, elements or components that are not relevant for food compatibility or barrier properties can be made from a cheaper material, such as PET.

[0028] Preferably, the semi-finished product is manufactured in an injection mold, the injection mold comprising a core and a cavity. Two or more support elements are provided in the cavity so that the core is positioned, or can be positioned, relative to the cavity. The core and the cavity provide a void which is filled with the injected material.

[0029] The support elements are preferably provided in the area of ​​a future preform base. Typically, the preforms to be injection-molded, or the associated semi-finished product, are essentially elongated. There is a risk that at typical injection pressures, usually between 500 bar and 5000 bar, an undesirable effect can occur in which the core is pushed slightly to the side. So-called floating cores or off-center cores, e.g., 0.1 mm from the center, are usually not a problem in conventional injection molding. Uneven material distributions or uneven wall thicknesses can be compensated for by the strain hardening of the PET material. However, in thin-wall injection molding, as in this case, 0.1 mm can pose a problem. With a wall thickness of 0.2 mm, a 0.1 mm core shift means that the wall thickness in one area is only 0.1 mm, while on the opposite side there is a wall thickness of 0.3 mm.The desired barrier effect can no longer be achieved, or there is a risk that the semi-finished product will develop a hole during subsequent overmolding.

[0030] By providing support elements, this displacement of the core can be prevented, ensuring a uniform wall thickness.

[0031] However, the inclusion of support elements leaves small defects, such as small holes, in the semi-finished product in the area of ​​the support elements. These defects can be easily closed again during the subsequent overmolding process and the corresponding melting or liquefaction of the semi-finished product, so that the semi-finished product, or rather the inner layer it provides, is once again complete and free of defects. In other words, the defects created by the support elements are melted and sealed by the overmolding process in the second step. Alternatively, it is also possible to remove the support elements during the production of the semi-finished product. In other words, the support elements can be removed during the injection molding process of the PEF (Polymer Elastomeric Forming).

[0032] In particular, the support elements can be removed once a cavity created by the core and the cavity is filled to at least 70%, preferably at least 80%, and particularly preferably at least 90%. This filling stabilizes the core with respect to the cavity and / or, in particular, keeps it centered, so that support by the support elements is replaced, at least towards the end of the injection process, by the PEF located in the cavity.

[0033] Preferably, for the overmolding process, the core is at least partially demolded, in particular demolded together with the semi-finished product from the cavity. The core and the semi-finished product are then provided accordingly in a second cavity.

[0034] The core of the first injection mold and the cavity of the second injection mold provide the negative of the preform to be injected.

[0035] Demolding together with the core is particularly advantageous because, as already explained, the semi-finished product has a thin wall and therefore retains a corresponding stability by remaining on the core.

[0036] Preferably, the PEF is provided with an intrinsic viscosity that is lower than the intrinsic viscosity of PET.

[0037] By selecting the appropriate material, the strengths of the two materials can be matched. Typically, PEF has a higher mechanical strength than PET. By selecting the appropriate intrinsic viscosity, or by addressing the aforementioned difference, the mechanical stiffnesses can be matched so that the bonded materials behave similarly.

[0038] In particular, it may be provided that the PEF or PEF copolymer is supplied with an intrinsic viscosity of 0.3 dl / g to 0.7 dl / g, preferably 0.4 dl / g to 0.6 dl / g, and in particular 0.45 dl / g to 0.55 dl / g.

[0039] The PET can be provided with an intrinsic viscosity of 0.7 dl / g to 1.2 dl / g, preferably 0.84 dl / g to 1.0 dl / g, in particular 0.84 dl / g to 0.88 dl / g.

[0040] The intrinsic viscosity is determined according to the ASTM D4603 method.

[0041] The combination of PET and PEF, particularly with the properties described here, makes it possible to provide a preform and a container that are less susceptible to delamination compared to containers with a DLC or SiOx coating. A soft inner layer is much less prone to delamination than a hard inner layer. Recyclability is improved compared to containers with coatings made of materials such as polyamide, EVOH, PVC, or PVDC. Unlike polyamide and EVOH, the barrier layer can come into direct contact with the contents, such as alcoholic beverages.

[0042] It is also possible to improve the barrier properties with respect to light. For example, the semi-finished product can be colored dark with a brown or black dye, and the PET with a white dye, so that the dark barrier layer remains invisible, as is the case with milk cartons. In this arrangement, less white dye is required than in a multilayer arrangement with a barrier layer in a middle layer. The pigment titanium oxide, with pigments between 100 and 500 nm, can usually be reduced by more than 50% compared to known arrangements.

[0043] This achieves a particularly high light barrier; in particular, more than 99% of incident light in the wavelength range between 300 nm and 550 nm can be blocked. Vitamins, especially vitamin B2, can be more effectively protected.

[0044] A further advantage of the aforementioned preform structure is that the quality requirements for the outer layer, i.e., the overmolded layer, can be lower. Since this layer does not come into contact with the food being stored due to the presence of a barrier layer, recycled material can be used. In recycled material, the limits for contaminants, particularly benzene, BPA, acetaldehyde, and formaldehyde, especially non-intentionally induced contaminants (NIAS), are higher compared to virgin material (e.g., virgin PET), as their penetration into the food is reliably prevented by the PEF (preform overmold).

[0045] Another advantage can be the reduction of gas exchange between the contents and the environment. In particular, this reduces the loss of CO2 (carbonization), N2 (nitrogen), and SO2 (sulfur dioxide used to stabilize beverages).

[0046] An adhesion promoter or adhesive to bond the layers together, as is sometimes necessary for polyamide or EVOH, can be avoided.

[0047] Since PEF is more expensive than PET, the barrier layer should be as thin as possible. Furthermore, the weight of the preform should not be increased, or only minimally, to avoid increased material and transportation costs. Preferably, the barrier layer comprises less than 40% of the preform.

[0048] in particular less than 20%, and preferably less than 10% of the preform weight.

[0049] Another aspect concerns an injection mold for carrying out the process described herein, in particular the process for producing the semi-finished product. The injection mold comprises a core and a cavity. The injection mold also includes two or more support elements for supporting the core within the cavity, so that, in the closed state of the injection mold, the core is positioned relative to the cavity.

[0050] Such an injection mold makes it possible to produce very thin-walled elements, as displacement of the core in relation to the cavity can be prevented.

[0051] The two or more support elements are preferably designed to be movable, in particular to be displaceable essentially perpendicular to a corresponding surface of the core.

[0052] The support elements are therefore preferably arranged in the cavity and movably mounted within it. They are shaped in such a way that the cavity remains sealed to the environment in every position of the support elements, so that any introduced melt cannot escape through gaps between the support elements and the cavity.

[0053] This makes it possible to remove the support elements during the injection process, as already described.

[0054] In the closed state of the injection mold, the core is preferably spaced between 0.1 mm and 1.1 mm from the cavity.

[0055] The injection-molded part can therefore be made correspondingly thin-walled.

[0056] Another aspect concerns an injection molding machine for producing a two- or multi-layered preform. The injection molding machine includes an injection mold as described herein.

[0057] Another aspect concerns a preform for manufacturing a container. The preform has a base, a body, and a neck. The preform is multilayered, in particular two-layered. It has an inner layer that completely covers the interior of the preform. The preform also has an outer layer that completely encloses the inner layer. The preform is manufactured, in particular, using a process as described herein and / or, in particular, using a device such as an injection mold and / or an injection molding machine, as described herein.

[0058] Such a preform exhibits improved barrier properties compared to, for example, single-layer preforms.

[0059] Preferably, the inner layer of the preform consists of at least 90%, preferably at least 95%, and particularly at least 98% of PEF or PEF copolymers. The outer layer consists of a different material, in particular a material comprising at least 60%, preferably 80%, and particularly at least 95% PET.

[0060] This combination, welded under pressure and heat, results in very good barrier properties and makes it possible to use this preform, or a container subsequently manufactured from it, for a wide variety of applications.

[0061] The inner layer can have a wall thickness of 0.1 mm to 1.1 mm. This ensures, on the one hand, that the desired barrier properties are maintained, and on the other hand, that the preform does not become excessively heavy. Preferably, the inner and outer layers have a common mixing zone, into which molecules or molecular chains and their components penetrate each other, and which is 0.05 mm to 0.1 mm thick. This is still provided that a sufficiently thick wall of at least 0.05 mm remains in the inner layer.

[0062] The outer layer can be made thicker than in comparable multilayer processes. More viscous and stiffer materials can be used for this outer layer. This has the advantage that more viscous materials expand less under the corresponding internal pressure in the subsequently produced container, for example, a bottle, and less gas escapes from the liquid into the container head area.

[0063] This can reduce or slow down the CO2 loss of a liquid.

[0064] This diffusion zone ensures that the two materials interlock sufficiently, thus reducing the risk of delamination.

[0065] The invention is explained below using schematic figures. These show:

[0066] Figure 1: An injection mold for the production of a semi-finished product;

[0067] Figure 2: a semi-finished product;

[0068] Figure 3: an injection mold for producing the preform;

[0069] Figure 4: a preform.

[0070] Figure 1 shows an injection mold 40 with a core 41 and a cavity 42. The cavity 42 and the core 41 form a hollow space 44 into which the material is injected. Support elements 43 are formed in the base of the preform, which support the core 41 with respect to the cavity 42, so that the core 41 cannot move within the cavity 42.

[0071] The cavity 44 provides a wall thickness of 0.3 mm in this case. To manufacture a semi-finished product 50 (see Figure 2), PEF is injected into the cavity 44.

[0072] Figure 2 shows a semi-finished product 50, which was manufactured in the cavity 44 of the injection mold 40 according to Figure 1. For clarity, the semi-finished product 50 is shown in Figure 2 without the core 41. As can be seen, the semi-finished product 50, or rather its wall, is uniform, and there are two defects 51 in the base area, caused by the support elements 43. Only two of these defects 51 are visible in Figure 2. Typically, there are three such defects, since the core 41 is preferably held at three points by the support elements 43.

[0073] To produce a two-layer preform, the core 41, together with the semi-finished product 50 still mounted on it, is placed into a second cavity 60. Analogous to the injection mold 40, the core 41 and the second cavity 60 also provide a cavity that corresponds to the negative of the finished preform 20 (see Figure 4). This initial state is shown in Figure 3.

[0074] The semi-finished product 50 is thus arranged within the cavity 60 on the core 41. PET is injected into the remaining cavity so that the semi-finished product 50 can be overmolded. The PET has a temperature that is 40 °C above the melting point of the PEF of the semi-finished product 50. This injection temperature ensures that the surface of the semi-finished product 50 melts and liquefies. On the one hand, this closes the defects 51, and on the other hand, the molecules of the injected PET can diffuse into the material of the semi-finished product 50 and vice versa. This allows a reliable and permanent bond to be created between the PEF, which provides an inner layer, and the PET, which provides an outer layer.

[0075] Figure 4 shows a two-layer preform 20. The preform 20 has a preform base 21, a preform body 22, and a preform neck 23. The preform 20 has an inner layer 24, which in this case has a thickness of 0.3 mm, analogous to the dimensions of the cavity 44 as described for Figure 1. The inner layer 24 completely covers the interior of the preform 20. Likewise, the outer layer 25 completely covers and encloses the inner layer 24. Thus, the inner layer 24 completely separates the outer layer 25 from any subsequent contents of the preform, or from the contents of a bottle blown from the preform 20. Diffusion of substances into or out of the interior of the preform 20, or of the container, can be reliably prevented.

Claims

Patent claims 1. Method for producing a two- or multi-layer preform (20) for producing a container, wherein the preform (20) has a preform base (21), a preform body (22) and a preform neck (23), comprising the steps: - Providing a semi-finished product (50) in an injection mold, wherein the semi-finished product (50) consists of at least 90%, preferably at least 95%, in particular at least 98% of PEF or PEF copolymers, - Overmolding this semi-finished product (50) in a second step with a material different from PEF, wherein this material comprises at least 60%, preferably 80%, in particular at least 95% PET, characterized in that the material is injected at a temperature that is 40°C to 80°C above a melting temperature of the semi-finished product (50).

2. Method according to claim 1, characterized in that the injection process heats a surface of the semi-finished product (50) above its melting point.

3. Method according to claim 2, characterized in that the surface of the semi-finished product (50) is liquefied to a depth of at least 0.05 mm.

4. Method according to claim 2 or 3, characterized in that the surface of the semi-finished product (50) is liquefied to a maximum depth of 0.1 mm.

5. A method according to any one of claims 1 to 4, characterized in that the semi-finished product (50) has a temperature prior to overmolding that is at least 5°C, in particular at least 10°C, below the melting temperature of the semi-finished product (50).

6. A method according to any one of claims 1 to 5, characterized in that the semi-finished product (50) has a wall thickness between 0.1 mm and 1.1 mm.

7. Method according to one of claims 1 to 6, characterized in that the semi-finished product (50) is manufactured in an injection mold (40) comprising a core (41) and a cavity (42), - wherein two or more support elements (43) are provided to support the core (41) in the cavity (42) so that the core (41) is positioned relative to the cavity (42).

8. Method according to claim 7, characterized in that defects (51) caused by the support elements (43) are melted and sealed by the overmolding process of the second step.

9. Method according to one of claims 7 or 8, characterized in that the support elements (43) are removed during the manufacture of the semi-finished product (50).

10. Method according to claim 9, characterized in that the support elements (43) are removed as soon as a cavity (44) created by the core (41) and the cavity (42) is filled to at least 70%, preferably to at least 80% and particularly preferably to at least 90%.

11. Method according to one of claims 7 to 10, characterized in that, for the purpose of carrying out the overmolding process, the core (41) is at least partially demolded, in particular demolded together with the semi-finished product (50) from the cavity (43), and is provided in a second cavity (60).

12. A method according to any one of claims 1 to 11, characterized in that the PEF is provided with an intrinsic viscosity that is lower than the intrinsic viscosity of PET.

13. A method according to any one of claims 1 to 12, characterized in that the PEF is provided with an intrinsic viscosity of 0.3 dl / g to 0.7 dl / g, preferably 0.4 dl / g to 0.6 dl / g, in particular 0.45 dl / g to 0.55 dl / g.

14. Method according to any one of claims 1 to 13, characterized in that the PET is provided with an intrinsic viscosity of 0.7 dl / g to 1.2 dl / g, preferably 0.84 dl / g to 1.0 dl / g, in particular 0.84 dl / g to 0.88 dl / g.

15. Injection mold (40) for carrying out the method according to one of claims 7 to 14, comprising a core (41) and a cavity (42), characterized in that the injection mold (40) comprises two or more support elements (43) for supporting the core (41) in the cavity (42), such that in the closed state of the injection mold (40) the core (41) is positioned relative to the cavity (43).

16. Injection mold (40) according to claim 15, characterized in that the two or more support elements (43) are designed to be movable, in particular to be displaceable substantially perpendicular to a surface of the core (41).

17. Injection mold (40) according to one of claims 15 or 16, characterized in that in the closed state of the injection mold (40) the core (41 ) is spaced between 0.1 mm and 1.1 mm from the cavity (43 ).

18. Injection molding machine for producing a two- or multi-layer preform (20) comprising an injection mold (40) according to one of claims 15 to 17.

19. Preform (20) for manufacturing a container (30), wherein the preform (20) comprises a preform base (21), a preform body (22), and a preform neck (23), characterized in that the preform (20) is multilayered and comprises an inner layer (24) which completely covers the interior of the preform, and an outer layer (25) which completely encloses the inner layer (24), in particular manufactured in a process according to one of claims 1 to 14 and / or using an injection mold or an injection molding machine according to one of claims 15 to 18.

20. Preform (20) according to claim 19, characterized in that the inner layer (24) consists of at least 90%, preferably at least 95%, in particular at least 98% of PEF and the outer layer (25) is made of a different material, in particular a material comprising at least 60%, preferably 80%, in particular at least 95% PET.

21. Preform (20) according to claim 19 or 20, characterized in that the inner layer (24) has a wall thickness of 0.1 mm to 0.8 mm .

22. Preform (20) according to one of claims 19 to 21, characterized in that the inner layer (24) and the outer layer (25) have a common mixing zone which is 0.05 mm to 0.1 mm thick.

Images