Moulds and mould tools

Abstract

An inner mold tool (10) is provided that forms part of a mold (30) used during injection molding of plastic articles, such as plastic tops for liquid food packaging. The inner mold tool (10) includes an outer surface (16) that defines the interior surface of the plastic article to be produced, and is provided at a longitudinal end of the inner mold tool (10) with a bushing (40) that has a flat surface (42) that defines the longitudinal end of the inner mold tool (10) and is configured to contact the mating outer mold tool (20) during injection molding. The bushing (40) is provided with a sidewall (44) extending from the flat surface (42), and the sidewall (44) forms part of the outer surface (16) of the inner mold tool (10).

Description

[Technical field]

[0001] The present invention relates to a mold, in particular to a mold used for injection molding. The present invention also relates to a tool forming part of the mold. [Background technology]

[0002] Injection molding is a well-known process used to manufacture articles by injecting molten material into a mold and allowing the material to harden before being removed from the mold. In recent years, injection molding techniques have spread to the packaging industry, where they can be used to manufacture packaging containers having a plastic portion injection molded onto a cardboard-based sleeve.

[0003] Such packaging combines the environmental benefits of cardboard-based packaging with the structural benefits of plastic tops and has been particularly successful in packaging for storing liquid foods, one example being the Tetra Top® package and its various configurations.

[0004] When producing such a package, an open sleeve made of a cardboard-based material is placed on a mandrel. One end of the mandrel, extending axially from the end of the sleeve, forms the inner mold tool during the injection molding of the plastic top. Two outer mold tools move towards the inner mold tool to form a cavity in the shape of the plastic top to be produced. When the outer mold tools reach their working position relative to the inner mold tool, injection molding is carried out, whereby the plastic top is produced directly on the cardboard-based sleeve. When the outer mold tools are separated and moved away from the inner mold tool, the cardboard-based sleeve can be removed from the mandrel. At this point, the open sleeve is provided with a plastic top, which is then sealed, for example using a threaded top. Filling of the package can then be carried out through the open bottom end, before the bottom end is sealed and formed into a suitable, often flat, shape.

[0005] As the mandrel carrying the inner mold tool rotates towards its injection molding position, the outer mold tool moves towards the inner mold tool in a plane. In this position, the mandrel is arranged vertically, which means that the outer mold tool moves upwards and horizontally towards the inner mold tool to reach their working position. In order to produce a plastic top with the required dimensions, the outer mold tool must be aligned with the inner mold tool in the vertical direction and in the horizontal plane. For the purpose of alignment in the vertical plane, the upper part of the inner mold tool is provided with a bushing that contacts the outer mold tool, thus providing a vertical guide for the outer mold tool. The horizontal alignment between the inner and outer mold tools is provided by the entire lid forming unit as shown in FIG. 1.

[0006] The above mentioned packages are typically manufactured in high speed filling machines, i.e. the entire injection molding process for one plastic top is carried out in approximately 1.5 seconds. Due to the high speed application which requires very fast cooling of the mold, the outer mold tool is usually made of aluminum. Any misalignment between the outer mold tool and the bushing of the inner mold tool will lead to wear of the outer mold tool and eventually cause leakage of the injection molding material outside the intended dimensions of the plastic top. Injection molding defects appear as burrs at the top end of the plastic top, i.e. at the edge of the pouring spout of the package. Since the edge of the pouring spout is in direct contact with the lips of the consumer, it is highly desirable to avoid burrs, especially for smaller packages.

[0007] One solution is to replace the outer mold tooling more frequently before wear induces burrs. However, it would be more desirable to provide an improved mold that would extend the life of the mold tooling by reducing the risk of burrs, and thus increase safety for consumers who consume food directly from packages with cardboard laminates and injection molded parts. Summary of the Invention [Problem to be solved by the invention]

[0008] It is an object of the present invention to at least partially overcome one or more of the limitations of the prior art identified above. [Means for solving the problem]

[0009] To solve these objects, an inner mould tool is provided, which forms part of a mould used during injection moulding of plastic articles, such as plastic tops for liquid food packaging, the inner mould tool includes an outer surface defining an inner surface of the plastic article to be produced, and a longitudinal end of the inner mould tool is provided with a bushing, the bushing having a planar surface defining the longitudinal end of the inner mould tool and configured for contact with a mating outer mould tool during injection moulding, the bushing being provided with a sidewall extending from the planar surface, the sidewall forming part of the outer surface of the inner mould tool.

[0010] The bushing may have a cylindrical shape, which is advantageous in that the entire circumference of the bushing may be used to define the article to be injection molded.

[0011] The bushing may be supported by at least one spring biasing the bushing in a longitudinally extended position, in this way the contact area between the bushing and the outer tool is increased and occurs only in a horizontal plane, reducing the risk of wear on the outer forming tool.

[0012] The inner mold tool can include a neck portion and a spout portion, with the side walls of the bushing forming the longitudinal ends of the spout portion, the bushing thereby terminating the mold cavity, thereby reducing the risk of flash at the spout of the package.

[0013] The bushing may protrude longitudinally from the body of the inner mold tool and the radius of the bushing may be less than the radius of the body, whereby the bushing can move inside the body, meaning that the bushing is guided by the body during its movement.

[0014] The bushing may be attached to the body of the inner mould tool by means of one or more screws, whereby a robust fixation of the bushing is achieved.

[0015] According to a second aspect, there is provided a mould for use during injection moulding of plastic articles, such as plastic tops for liquid food packaging. The mould comprises an inner mould tool and at least two outer mould tools, said mould tools together defining a cavity for receiving molten plastic material during injection moulding. A bushing is provided at a longitudinal end of the inner mould tool, the bushing having a planar surface defining the longitudinal end of the inner mould tool and configured for contact with the mating outer mould tool during injection moulding. The bushing is provided with a sidewall extending from the planar surface, said sidewall being located at a distance from the outer mould tools during injection moulding.

[0016] The distance between the side wall of the bushing and the outer mold tool can form part of the injection molding cavity, which is advantageous in that no part of the side wall of the bushing acts as a guide surface for the outer mold tool.

[0017] The inner mold tool may be placed on a mandrel configured to receive a sleeve of packaging material into which the plastic article is to be injection molded, and the outer mold tool is configured to contact an outer surface of the sleeve during injection molding. Efficient and reliable guiding of the outer mold tool is thereby achieved.

[0018] The outer mould tool may be guided in a first direction by the flat surface of the bushing and in a second direction by the outer surface of the sleeve, providing sufficient guidance of the outer mould tool in all required directions.

[0019] According to a third aspect, there is provided a method for injection moulding a plastic article into a sleeve of packaging material, the method comprising: placing the sleeve of packaging material onto a mandrel, moving two outer mould tools towards an inner mould tool placed on said mandrel, pressing said outer mould tools against the inner mould tool, whereby the outer mould tools are guided in a first direction by a plane of a bushing provided on the inner mould tool and in a second direction only by the outer surface of the sleeve, and injecting molten plastic material into a cavity formed between the inner mould tool and the outer mould tool.

[0020] The first guiding direction may be arranged perpendicular to the second guiding direction, which provides efficient and reliable guiding of the outer mould tool in all required dimensions.

[0021] The pressing of the outer mould tool against the inner mould tool may be performed such that the bushing is pressed towards the sleeve of packaging material in the longitudinal direction of the sleeve.

[0022] Still other objects, features, aspects and advantages of the present invention will become apparent from the following detailed description and drawings.

[0023] Embodiments of the present invention will now be described, by way of example, with reference to the accompanying schematic drawings. [Brief description of the drawings]

[0024] [Figure 1] FIG. 2 is an isometric view of the injection molding station of the filling machine. [Diagram 2] FIG. 2 is an isometric view of two parallel molds of the injection molding station shown in FIG. 1. [Diagram 3] FIG. 2 illustrates an isometric view of a portion of a mold according to one embodiment. [Figure 4] FIG. 2 is a cross-sectional view of a mold according to one embodiment. [Figure 5a-d]1 is a cross-sectional view of a mold during a closing sequence showing an outer mold tool moving towards an inner mold tool to define an injection mold cavity. [Figure 6] 1 is a schematic diagram of a method according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] In Fig. 1 a non-limiting example of an injection molding station 1 that can be incorporated in a filling machine (not shown) is shown. The term filling machine is used to characterize a machine configured to receive cardboard-based packaging material laminates in rolls or in the form of independent workpieces in order to perform the operations necessary to form sleeves or packaging containers for containing food products under certain hygienic requirements and to finally seal the packaging containers for further distribution.

[0026] In this case, the filling machine is typically configured to produce an independent consumer package enclosing a liquid food product, while the injection moulding station 1 is configured to apply a plastic top onto a sleeve made from a cardboard-based packaging material.

[0027] Two parallel mandrel wheels 2 are provided at the top right of the machine 1. Each mandrel wheel 2 carries four mandrels 4, spaced 90° apart in the same plane. Each mandrel has a longitudinal extension in the radial direction of the associated mandrel wheel 2 and is terminated by an inner mould tool 10. In operation, the mandrel wheels 2 rotate. In one position, for example where the mandrel 4 points to the right in the figure (indicated by the reference PA), a sleeve of packaging material is provided on the mandrel 4. As the mandrel wheel 2 rotates clockwise, the next position of the mandrel 4 is the injection moulding position, which is further shown in FIG. 2.

[0028] At the next successive position, cooling of the injection molded article may occur, thereby allowing the sleeves (and their associated plastic tops) to be pulled from the mandrel 4 .

[0029] 2, molds 30 are formed at the injection molding location. Each mold 30 includes an inner mold tool 10, i.e., the longitudinal ends of a mandrel 4, and two movable outer mold tools 20.

[0030] In the injection molding position shown in FIG. 2, the outer mold tool 20 is placed in close proximity to the inner mold tool 10 so that a cavity is formed therebetween to receive molten plastic material according to available injection molding techniques.

[0031] In Figure 3, the mould 30 is shown in cross section, with one outer mould tool 20 omitted for ease of understanding. The inner mould tool 10 is placed at the longitudinal end of the mandrel 4, as explained above. The mandrel 4 has a rectangular cross section, but with rounded corners, to define the shape of the cardboard-based package. The inner mould tool 10 has a neck portion 12 which extends into a spout portion 14, the terminal end of which is formed by a bushing 40. The bushing 40 is provided with a side wall 44, which forms the longitudinal end of the spout portion 14.

[0032] The inner mold tool 10 includes an outer surface 16 that defines the inside surface of the plastic article being produced, i.e., the plastic top in the illustrated embodiment. The bushing 40 has a planar surface 42 that defines a longitudinal end of the inner mold tool 10 and extends between sidewalls 44. The planar surface 42 is in contact with the mating outer mold tool 20 during injection molding.

[0033] Turning now to Figure 4, the mould 30 is shown in cross section. A cavity 50 is formed within the mould 30, which cavity defines the shape of the article to be produced. In this embodiment, the cavity has an annular cross section to define a plastic upper neck and spout. The cavity 50 has a bottom 52 which forms an interface with a sleeve 60 of cardboard-based packaging material, which is only shown diagrammatically in Figure 4. The cavity 50 extends across the neck portion 12 of the inner mould tool 10 as well as across the spout portion 14 of the inner mould tool 10. The cavity 50, which has a circular or annular upper end 54, terminates at the planar surface 42 of the bushing 40 such that the side wall 44 of the bushing also forms the boundary of the cavity 50. The side wall 44 of the bushing 40 thereby forms part of the outer surface 16 of the inner mould tool 10.

[0034] The bushing 40 has a cylindrical shape and extends downwards (opposite to the axial direction BD in FIG. 4) in a T-shape. One advantage of the T-shape is an improved longitudinal guidance of the bushing 40. However, the inventors would like to point out here that the bushing 40 can also function without the T-shape. As can be seen in FIG. 4, a number of springs 70 are arranged under the bushing 40 to support the bushing 40 against the body 18 of the inner mold tool 10. In this exemplary embodiment, six compression springs 70 are distributed at equal angular distances (60°) from each other. However, as can be easily understood, a different number of compression springs 70 and other types of springs (such as leaf springs) may be used.

[0035] The spring 70 biases the bushing 40 in the longitudinal direction BD to a longitudinally extended position, away from the mandrel 4. This longitudinally extended position, and the bushing 40 moving, are shown in Figures 5a-d.

[0036] Figures 5a-d show the sequence of the outer mould tool 20 moving from a remote position to the injection moulding position. To fully understand the complex movements of the inner mould tool 10 and the outer mould tool 20, reference is made again to figures 1 and 2. The outer mould tools 20 are moving towards their working position and during this movement the inner mould tool 10 is also moving into the injection moulding position by a rotational movement. This means that the outer mould tools 20 cannot move in a straight line, but they must be separated in the horizontal plane and in the longitudinal direction from the inner mould tool 10 to allow the inner mould tool 10 to rotate into its desired position. To achieve this, the movement of the outer mould tool 20 may be controlled by a belt drive 80, for example as described in WO 2004050327 by the same applicant. The belt drive 80 is configured to thereby open and close the mold 30 by moving the outer mold tool 20 in a first direction that is radial to the hub of the mandrel wheel 2, and in a second direction that is perpendicular to the first direction and oriented in the plane of the circular movement of the inner mold tool 10. Preferably, the outer mold tool 20 is moved such that their central axes are coincident throughout the entire movement. The movements in the first and second directions are preferably performed simultaneously.

[0037] In FIG. 5a, the position of the outer mold tool 20 is away from the inner mold tool 10, and the position shown corresponds to when the inner mold tool 10 has reached its injection molding position, but the outer mold tool 20 still has some distance to travel.

[0038] In Figure 5b, the outer mold tool 20 reaches the inner mold tool 10 such that the flat surfaces 42 of the bushings 40 are in contact with the mating flat surfaces 22 of each outer mold tool 20. Because these flat surfaces 42, 22 are in contact with each other, no cavity is formed between them.

[0039] In Fig. 5c, the outer mould tools 20 are further moved towards each other in a second direction, i.e. horizontally, such that the vertical end faces of the outer mould tools 20 are pressed towards each other (interfaces indicated by the reference MT in Fig. 5c). During the movement towards its horizontal end position, each outer mould tool 20 is guided by a sleeve 60 (see Fig. 4). This also means that there are no vertical faces (i.e. side walls 44) of the bushing 40 in contact with the vertical faces of the outer mould tools 20, which is particularly advantageous for the purpose of reducing wear of the outer mould tools 20. During the step in Fig. 5c, the polymer material intended to form the upper part of the packaging container is injected into the cavity 50 between the inner mould tool 10 and the outer mould tool 20.

[0040] In Fig. 5d the final position of the outer mould tool 20 is shown. Here, the outer mould tool 20 has been moved vertically, thereby pushing the bushing 40 upwards and compressing the spring 70. In this final step of the moulding process, the polymer melt injected into the cavity 50 between the inner 10 and outer mould tool 20 is pressed between the tools by the movement of the outer mould tool 20 relative to the fixed inner mould tool 10. The maximum longitudinal distance travelled by the bushing 40 is in the range of 0.2-0.7 mm, e.g. 0.5 mm. As can be seen in Fig. 5d, the radius of the bushing 40 is less than the radius of the body 18 of the inner mould 10. Thereby, the bushing 40 is slidably guided by the body 18 during its repetitive movements.

[0041] The bushing 40 is attached to the body 18 of the inner mold tool 10 by one or more screws 46. This attachment allows for a robust connection, while still allowing movement of the bushing 40. The screws 46 are therefore not connected to the bushing by threads, but only determine the final axial position (end stops) of the bushing 40.

[0042] A cap 48 may be provided to cover the screw 46 .

[0043] Turning now to FIG. 6, a method 100 for injection molding a plastic article onto a sleeve of packaging material is shown in a schematic manner. The method 100 comprises a first step 102 of placing the sleeve of packaging material onto a mandrel and a second step 104 of moving two outer mold tools towards an inner mold tool placed on said mandrel. In step 106, when the two outer mold tools come into contact with each other, the molten polymer material is injected into the cavity formed between the inner and outer mold tools. Finally, in step 108, the outer mold tool is pressed against the inner mold tool, so that the outer mold tool is guided in a first direction by the plane of a bushing provided on the inner mold tool and in a second direction only by the outer surface of the sleeve. In this step 108, the molten polymer material is pressed inside the cavity formed between the inner and outer mold tools by the movement of the outer tool relative to the inner tool.

[0044] From the above description, although various embodiments of the present invention have been described and illustrated, the present invention is not limited thereto and may be embodied in other ways within the scope of the subject matter defined in the following claims.

Claims

1. 1. An inner mould tool (10) forming part of a mould (30) used in making packages for storing liquid food by injection moulding a plastic top onto a sleeve of cardboard based packaging material, comprising:

1. An inner mold tool (10) including an outer surface (16) defining an inner surface of the plastic upper part to be produced, the inner mold tool (10) being provided at a longitudinal end with a bushing (40) having a planar surface (42) defining the longitudinal end of the inner mold tool (10) and configured for contact with a mating outer mold tool (20) during injection molding, the bushing (40) being provided with a sidewall (44) extending from the planar surface (42), the sidewall (44) forming a part of the outer surface (16) of the inner mold tool (10); the inner mold tool (10) includes a neck portion (12) and a spout portion (14), the side walls (44) of the bushing (40) form the longitudinal ends of the spout portion (14), and the inner mold tool (10) is positioned on a mandrel configured to receive a sleeve of the cardboard-based packaging material. Inner mold tool (10).

2. The inner mold tool (10) of claim 1, wherein the bushing (40) is supported by at least one spring (70) that biases the bushing (40) toward the longitudinally extended position.

3. The inner mold tool (10) of claim 2, wherein the bushing (40) projects longitudinally from a body (18) of the inner mold tool (10), and a radius of the bushing (40) is less than a radius of the body (18).

4. The inner mold tool (10) of claim 3, wherein the bushing (40) is attached to the body (18) of the inner mold tool (10) by one or more fastening devices (46).

5. The inner mold tool (10) of claim 1 , wherein the bushing (40) has a cylindrical shape.

6. A mold (30) for use in injection molding a plastic top onto a sleeve of cardboard-based packaging material to produce a package for storing liquid food, comprising an inner mold tool (10) and at least two outer mold tools (20), said inner mold tool (10) and said at least two outer mold tools (20) together defining a cavity (50) for receiving molten plastic material during injection molding, and bushings (40) at the longitudinal ends of said inner mold tool (10) and at the longitudinal ends of said inner mold tool (10), said bushings (40) being connected to said inner mold tool (10) and said at least two outer mold tools (20) together defining a cavity (50) for receiving molten plastic material during injection molding, said bushings (40) being connected to said inner mold tool (10) and said at least two outer mold tools (20) a mold (30) provided with a bushing (40) defining the longitudinal ends of the inner mold tool (10) and having a flat surface (42) configured for contact with a mating outer mold tool (20) during injection molding, the bushing (40) provided with a side wall (44) extending from the flat surface (42), the side wall (44) being positioned at a distance from the outer mold tool (20) during injection molding, the inner mold tool (10) being positioned on a mandrel configured to receive a sleeve of the cardboard-based packaging material. Mold (30).

7. The mold (30) of claim 6, wherein a distance between the sidewall (44) of the bushing (40) and the outer mold tool (20) forms a portion of the cavity (50).

8. The mold (30) of claim 6 or 7, wherein the outer mold tool (20) is configured to contact an exterior surface of the sleeve of packaging material during injection molding.

9. 9. The mold (30) of claim 8, wherein the outer mold tool (20) is guided vertically by the planar surface (42) of the bushing (40) and horizontally by the outer surface of the sleeve (60).

10. 1. A method for producing a package for storing liquid food products by injection molding a plastic top onto a sleeve of cardboard-based packaging material, comprising: placing the sleeve of cardboard based packaging material onto a mandrel; moving two outer mold tools toward an inner mold tool disposed on the mandrel until the two outer mold tools contact each other; injecting molten plastic material into a cavity formed between the inner mold tool and the outer mold tool; pressing the outer mold tool against the inner mold tool, thereby pressing the injected molten plastic material inside the cavity formed between the inner mold tool and the outer mold tool, whereby the outer mold tool is guided vertically by a plane of a bushing provided on the inner mold tool and horizontally only by an outer surface of the sleeve, the bushing being provided with a side wall extending from the plane, the side wall forming part of the outer surface of the inner mold tool; The method includes:

11. The method of claim 10, wherein the pressing of the outer mold tool against the inner mold tool is performed such that the bushing is pressed toward the packaging material sleeve in the longitudinal direction of the sleeve.

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