BLOW MOLDING TOOL, STRETCHING BLOW MACHINE AND METHOD FOR MOLDING A CONTAINER

Description

[0001] The present invention relates to a blow molding tool, a stretch blow molding machine and a method for forming a container according to the preamble of the independent claims.

[0002] Different methods and devices for forming a container are known from the prior art.

[0003] The production of hollow plastic containers is typically done using blow molding processes. The most common blow molding processes are extrusion blow molding and stretch blow molding. Both blow molding processes have in common that the final shape of a hollow plastic body is created in a blow molding tool.

[0004] These two blow molding processes differ in important respects.

[0005] The extrusion blow molding process is characterized by the fact that a hollow body is produced from an elongated thermoplastic tube. In the stretch blow molding process, however, hollow bodies are produced from a prefabricated hollow body, namely a preform, by stretching it circumferentially and longitudinally. The plastic of the container is then biaxially stretched.

[0006] In general, it can be said that a person skilled in the art would expect that a molded article produced using the extrusion blow molding process can still be easily deformed immediately after inflation. This is not necessarily the case with a stretch-blown article, because a person skilled in the art knows that stretched plastic resists subsequent deformation.

[0007] For containers manufactured using these blow molding processes, the process used can also be determined on the finished container.

[0008] Extrusion blow-molded containers have a pinch seam in or on the base. In stretch-blown containers, only a gate point is visible on the base, which is created during the production of the preform. Containers produced using the extrusion blow-mold process can also be identified by the fact that the inner contour essentially follows the outer contour. A thread formed on a bottle neck using the extrusion blow-mold process is therefore recognizable as a negative contour inside the container. In stretch-blown containers, however, there is an inner contour that deviates from the outer contour, particularly in the area of ​​the pouring opening, which is typically produced using injection molding. The outer contour can, for example, have a thread and the inner contour can be smooth-walled. This is necessary for demolding the preforms in the preceding injection molding process.

[0009] A blow mold is typically formed from two mold halves, although the structure can also consist of more than two parts. The blow mold has a mold body with a cavity, thus providing a so-called mold cavity for forming a container. Depending on the container shape, this cavity is symmetrical or asymmetrical. In asymmetrical molds, the two or more mold halves can be divided in such a way that their parting lines are formed at preferred locations on the final container and therefore do not necessarily have to be divided into equal fractions.

[0010] A blow mold for a container is typically divided into three areas: a base area, a middle area, and a head area. A finished container typically has a container base, a container body, and a container shoulder. The container shoulder is the area adjacent to a pouring opening. The pouring opening typically has means for attaching a closure, such as a screw cap. The container shoulder is formed in the head area of ​​the blow mold. During blow molding of the container, the container shoulder is typically only inflated below the means for attaching a closure. Following the container shoulder, in other words between the container shoulder and the container base, the container body is inflated. This essentially corresponds to the middle area of ​​a blow mold. The container base, in turn, is created in the base area.

[0011] Mold construction is subject to various restrictions. On the one hand, this concerns requirements regarding the blow mold itself. For example, these must have cooling channels, which in turn requires a minimum size for the blow mold. On the other hand, this concerns requirements dictated by the final shape of a container and / or its material. For example, it is only possible to create sharp edges in a stretch blow molding process by using special materials such as PP or copolymer PET. Sharp edges are edges with a radius of less than 1.2 mm.Due to shrinkage and shrinkage, the inflated containers are not dimensionally accurate around corners and edges, and dimensions can vary from batch to batch or even from container to container. Temperatures cannot be precisely maintained in these areas, for example, and even small differences in material flow or in the type and quantity of the original material can have a significant impact on the amount of material that ultimately ends up in the corners and edges. The smaller the desired radius, the greater this effect.

[0012] In the stretch blow molding process, a preform is inflated in the cavity of the blow mold and then stretched using a mandrel. The wall thickness of the preform becomes thinner during the inflation process. When the preform is placed against the mold wall, the wall of the preform cools down and further inflation of the preform can no longer take place evenly. Typically, the first contact of the preform to be inflated is point-like or linear. From this point on, the material of the preform to be inflated flows unevenly because the cooling makes the material at the contact point more viscous. In other words, towards theoretically sharp edges the material flows increasingly slowly and accordingly becomes thinner until it forms a weak point. The material flow is also hindered by friction between the wall of the partially inflated preform and the cavity.

[0013] State-of-the-art blow molding processes are known from documents JPS5656830A, KR101116169B1, US5389332A, EP0393370A2, US5035604A, US2018 / 257264A1 and GB882790A.

[0014] However, there is a need to design containers, especially stretch blow-molded containers, with sharp edges, for example for better stackability or for optical reasons.

[0015] The object of the invention is therefore to remedy at least one or more disadvantages of the prior art. In particular, a blow molding tool with a molded body, as well as a stretch blow molding machine comprising a blow molding tool and a method, are to be provided that enable the molding of a container that maintains its dimensions over multiple production cycles, is particularly reliably reproducible, preferably has an attractive appearance, and is particularly precisely manufacturable.

[0016] This object is achieved by the features of claim 1. Further embodiments emerge from the dependent patent claims.

[0017] A blow molding tool according to the invention, in particular a blow molding tool for a stretch blow molding process, comprises a molded body having a cavity as a mold cavity. The cavity has a bottom region, a central region, and a head region. When the blow molding tool is closed, the central region is displaceable relative to the head region and / or the bottom region.

[0018] This makes it possible to change the dimensions of the cavity before and / or during and / or after the blow molding process. In particular, it is possible to reduce the cavity size during and / or after the blow molding process. An inflated container located in the cavity can thus be compressed during and / or after the blow molding process. This counteracts material thinning and allows for the formation of sharp edges at the intersection points of the relative movement.

[0019] Preferably, the molded body is formed in several parts and has a head part on which the head region is formed, a middle part on which the middle region is formed and a bottom part on which the bottom region is formed.

[0020] Accordingly, a container shoulder of the inflated container can be moved relative to a container body, and a compression can be made between the container shoulder and the container body, thereby forming a sharp edge. If the bottom area is relatively displaceable, a container bottom is moved relative to the container body, and a compression can be made between the container body and the container bottom, creating a sharp edge.

[0021] It can be provided that a sharp edge is formed both between the container body and the container bottom and between the container body and the container shoulder.

[0022] A multi-part design of the blow molding tool allows the individual parts to be moved separately and independently of one another, while also allowing the individual elements to be replaced easily and with minimal effort. If, for example, a container base needs to be reshaped, it is sufficient to replace the corresponding base part.

[0023] It goes without saying that, for example, the middle part, the bottom part and / or the head part can each be formed in two parts in order to enable a corresponding division of the mold along a longitudinal axis in order to form a finished container from the blow molding tool.

[0024] As explained above, a multi-part division is also possible and / or a division that is asymmetrical to the longitudinal axis.

[0025] In a preferred embodiment, the central region can be displaceable together with the base region relative to the head region.

[0026] This type of design forces compression only in a specific area, thus creating a sharp edge. In this case, a sharp edge forms between the container body and the container shoulder of the finished container.

[0027] It can be provided that the middle part and the base part are formed in one piece.

[0028] This allows for easy manufacturing and easy movement of the base part together with the middle part.

[0029] Alternatively, it can be provided that the central area can be moved together with the head area relative to the base area.

[0030] This type of design forces compression only in a specific area, thus creating a sharp edge. In this case, a sharp edge forms between the container body and the container base of the finished container.

[0031] It can be provided that the middle part and the head part are formed as one piece.

[0032] This allows for easy manufacturing and easy movement of the head section together with the middle section.

[0033] The one-piece design naturally reserves the right to have a two- or multi-part design of the blow molding tool as such, which allows the blow molding tool to be separated to demold the finished container.

[0034] Preferably, the head region is arranged at least partially within the central region.

[0035] This allows the head section to be shifted relative to the center section within the center section. This simplifies the compression process.

[0036] Preferably, the blow molding tool is formed from two tool halves.

[0037] The production of the blow molding tool is simplified. Symmetrical and, in particular, identical elements can be used for each half of the tool.

[0038] A further aspect of the present invention relates to a stretch blow molding machine comprising a blow molding tool as described herein.

[0039] The stretch blow molding machine can be fully preconfigured together with the blow molding tool, whereby all parameters can be coordinated with one another.

[0040] A further aspect of the present invention relates to a method, in particular a stretch blow molding method, for forming a container, in particular for forming a preferably sharp edge on a container as described herein. The method comprises the following steps: Introducing a preform into a cavity of a blow molding tool, in particular a blow molding tool as described here, wherein the cavity has a head region, a middle region and a bottom region, inflating the preform to form a container, displacing the middle region relative to the head region and / or to the bottom region in such a way that the container is compressed at least in one region to form the edge.

[0041] This process enables the formation of a particularly sharp edge and prevents a container from becoming very thin-walled and / or weakened in the area of ​​an edge.

[0042] Compressing prevents or counteracts material thinning.

[0043] During the inflation of the preform into a container, it is stretched, in particular with a stretching rod, so that the finished container is biaxially stretched, on the one hand in the circumferential direction by the inflation and on the other hand in the axial direction by the stretching of the preform.

[0044] Preferably, the edge is formed with a radius of less than 0.5 mm, which is a PET preform inflated with a stretch of 1 to 10 to 1 to 16 and a degree of crystallization of 10% to 40%.

[0045] In a preferred form of the method, the central region is displaced together with the base region towards the head region.

[0046] This allows a sharp edge to be formed between a container body and a container shoulder.

[0047] Alternatively, it can be provided that the central area is moved together with the head area towards the floor area.

[0048] This allows a sharp edge to be formed between the container base and the container body. Such an edge, for example, can facilitate container stacking due to its precision.

[0049] The method can be continued in such a way that after the central region and the base region have been moved together, the base region is moved towards the central region to form another edge.

[0050] Accordingly, a container can be formed with two sharp edges.

[0051] Preferably, during the displacement inside the container, a pressure greater than 20 bar, in particular greater than 30 bar, preferably a pressure of around 40 bar, is maintained.

[0052] This guarantees that one wall of the container is permanently in contact with the cavity and that the inflated container, which is still warm and accordingly soft at this point, does not collapse or become undesirably deformed.

[0053] An embodiment of a blow molding tool according to the invention is described in more detail with reference to the following schematic figures. They show: Figure 1: A schematic structure of a blow molding tool; Figure 2: A schematic representation of the formation of an edge in the prior art; Figure 3: A schematic representation of a blow molding tool; Figures 4A - 4C: A schematic sequence of the blowing process; Figures 5A - 5B: A detailed view of an edge formation; Figure 6: The blow molding tool and a formed container after edge formation.

[0054] Figure 1shows a schematic structure of a blow molding tool 100. The blow molding tool 100 is designed as a two-part blow molding tool and has a molded body 101, which is also designed in two parts. The blow molding tool 100 has two cavities 102 in the molded body 101, although only one of the two cavities 102 is labeled. The molded body 101 is also designed in two parts. The cavities 102 are designed here to inflate a bottle. The cavities 102 can be divided into three regions: a head region 1, a middle region 2, and a bottom region 3.

[0055] The Figure 2shows a schematic representation of the shaping of an edge as it is formed in the prior art. During the blow molding process, a wall of the preform 4 lies against a corresponding wall of a cavity 102 of a molded body 101. In an area that is remote from a corner or edge to be formed, the inflated preform 4 has a wall thickness S0. The wall thickness S0 is shown in an area in which a radius R0 is infinite. In other words, the wall of the preform 4 lies completely against an inner wall of the cavity 102. By further inflating the preform 4, the material of the preform 4 is pressed towards the corner. Due to the previous cooling in the area of ​​the infinite radius and due to friction between the wall of the preform 4 and the inner wall of the cavity 102, the material flows only to a limited extent towards the corner.

[0056] By reducing the edge radius, in the Figure 2 As indicated by the radius R1, the wall thickness of the inflated preform 4 also decreases, which is indicated by the wall thickness S1, which is smaller than the wall thickness S0. Further inflation further increases this effect. As can be seen, with a very small radius R2, the wall thickness S2 is already so thin that a weak point later forms in the container.

[0057] The Figure 3shows a blow molding tool 100. The blow molding tool 100 has a mold body 101 in which a cavity 102 is arranged. The cavity 102 is divided into three regions: a head region 1, a central region 2, and a base region 3. The central region 2, together with the base region 3, is relatively displaceable relative to the head region 1. For this purpose, the central region 2 is designed as a central part 20, and the base region 3 is designed as a base part 30, each independently. The central part 20, together with the base part 30, is designed to be displaceable relative to a likewise separately formed head part 10. The head part 10 is at least partially arranged within the central part 20 and thus slides in certain regions within the central part 20.

[0058] The Figure 3 shows a schematic flow of the blowing process. In a first step, which is Figure 4AAs shown, a preform 4 is introduced into the cavity 102 of a blow molding tool or into the cavity 102 of a molded body 101. The preform 4 is designed in such a way or interacts with a head part 10 of the blow molding tool in such a way that they are mutually engaged. The preform 4 was appropriately tempered before being introduced into the cavity 102. As soon as the preform 4 has been introduced into the cavity, it is stretched along its longitudinal axis with a stretching mandrel and simultaneously subjected to pressure such that the shape of the preform 4 changes and it is inflated.

[0059] In the Figure 4BThe state is shown in which the preform 4 has already reached its essentially full length and is already in contact with an inner wall of the cavity 102 in a central region. In this region, the preform 4 cools down somewhat and the material adjacent to this region flows correspondingly more slowly during the inflation process. By further inflation, the preform 4 also comes into contact with an inner wall of the head part 10. This has the same effect as the contact of the preform 4 with the inner wall of the cavity 102, or with the inner wall of the central part 20. The material of the preform 4 cools down and is prevented from flowing towards the corner to be formed. In the prior art, the blowing process would typically be interrupted at this point, so that a relatively large radius remains at the corner (compare the radius R2 in the Figure 2). In order to nevertheless form a sharp edge, it is therefore intended, in contrast to the prior art, to move the middle part 20 towards the head part 10 and thus compress the preform in the area of ​​the corner or the edge to be formed. This process is described in the following Figures 5A and 5B explained in detail.

[0060] The Figures 5A and 5B show a detailed view of an edge formation. The Figure 5A corresponds to the condition of the Figure 4C As already explained in the Figure 5A As can be seen, the head part 10 is decoupled from the middle part 20 and can be displaced relative thereto, or in the present case, the middle part 20 is displaced relative to the head part 10. As soon as a wall of the preform 4 has reached a correspondingly thin wall thickness, the middle part 20 is displaced towards the head part 10 in the direction of the arrow (see Figure 5B). The wall of the preform 4 is compressed and an edge K is formed. The edge K is formed as a sharp edge K with a radius of less than 0.5 mm. Figure 5B It is also evident that in the area of ​​the edge K the wall thickness of the preform 4 is correspondingly thicker and thus has increased stability in the area of ​​this edge.

[0061] The Figure 6 shows the blow molding tool 100 and a molded container after edge formation. The blow molding tool 100 is shown in the Figure 6shown in its final position. The preform 4 is fully inflated and formed into a container 5. The middle part 20 was moved toward the head part 10, and a sharp edge was formed between a container shoulder 51 and a container body 52. ​​In addition, a bottom part 30 was also moved toward the head part 10, thus also forming a sharp edge between the container body 52 and a container bottom 53. In the present case, the container bottom 53 has virtually no axial extension.

[0062] It is understood that the present description of the figures shows a view of an open blow molding tool 100. In other words, one half of the blow molding tool 100 is shown in each case. All statements apply analogously to the second half of this two-part blow molding tool 100.

Claims

1. Stretch blow method for forming a sharp edge on a container - wherein the method has the following steps: - introducing a preform into a cavity (102) of a blow mold (100), wherein the cavity (102) has a top region (1), a center region (2), and a bottom region (3) and wherein, when the blow mold (100) is closed, the center region (2) can be moved relative to the top region (1) and / or relative to the bottom region (3), - inflating the preform to form a container, - relative movement of the center region (2) to the top region (1) and / or to the bottom region (3), such that the container is compressed at least in a region for forming the edge.

2. Method according to claim 1, characterized in that the edge is formed with a radius of less than 0.5 mm.

3.

3. Method according to claim 1 or 2, characterized in that the center region (2) together with the bottom region (3) is moved in the direction of the top region (1).

4. Method according to claim 1 or 2, characterized in that the center region (2) together with the top region (1) is moved in the direction of the bottom region (3).

5. Method according to claim 4, characterized in that, after the joint movement of the center region (2) and the bottom region (3), the bottom region (3) is moved in the direction of the center region (2) in order to form a further edge.

6. Method according to one of claims 10 through 14, characterized in that a pressure greater than 20 bar - in particular, greater than 30 bar, and preferably approximately 40 bar - is maintained inside the container during movement.