BLOW MOLDING, STRETCH BLOW MOLDER AND METHOD FOR FORMING A CONTAINER

Abstract

The invention relates to a blow mold comprising a mold base having a cavity, the cavity having a lower region, a central region, and an upper region. When the blow mold is closed, the central region can move relative to the upper region and / or relative to the lower region.

Description

BLOW MOLDING, STRETCH BLOW MOLDING MACHINE AND METHOD FOR FORMING A CONTAINER FIELD OF INVENTION The present invention relates to a blow mold, a stretch blow molder, and a method for forming a container according to the preamble of the independent claims. BACKGROUND OF THE INVENTION Various methods and devices for forming a container are known from the prior art. The production of hollow plastic containers is typically done using blow molding methods. The most common blow molding methods are extrusion blow molding and stretch blow molding. Both of these methods share the characteristic that the final shape of a hollow plastic body is created in a blow mold. These two blow molding methods differ in essential points. The extrusion blow molding method is characterized by the production of a hollow body from a thermoplastic hose stretched to its length. In contrast, in the stretch blow molding process, hollow bodies are produced from a prefabricated hollow body. Ref. 333681 specifically, a preform, which is stretched in the circumferential and longitudinal directions. The container plastic is subsequently stretched biaxially. Generally speaking, someone skilled in the technique would expect that an inflated object, produced using an extrusion blow molding method, could still easily deform after inflation. In the case of a stretch blow molded object, this is not necessarily expected, as someone skilled in the technique knows that stretched plastic resists subsequent deformation. In the case of containers produced by these blow molding methods, the method by which they are produced can also be determined from the finished container. Extrusion blow-molded containers have a crimp seam on or over the bottom. In stretch blow-molded containers, only one injection point is visible on the bottom; this injection point is created during preform production. Containers produced using the extrusion blow-molding method can also be recognized because the inner contour substantially follows the outer contour. Therefore, a thread formed in the extrusion blow-molding method on a bottle neck can be discerned as a negative contour on the inside of the container. However, in stretch blow-molded containers, an inner contour that deviates from the outer contour is present, particularly in the pouring opening region, which is typically produced by injection molding.In this way, the outer contour can have a thread, for example, and the inner contour can have a smooth surface. This is necessary for demolding the preform in the injection molding method described above. 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 base with a cavity, thus providing a mold cavity for forming a container. Depending on the container mold, this mold cavity can be symmetrical or asymmetrical. In the case of asymmetrical molds, the two or more mold halves can be divided so that their parting lines are formed at preferred locations on the subsequent container, and consequently, they do not necessarily have to be divided into uniform portions. A blow mold for a container is typically divided into three regions: a bottom region, a middle region, and a top region. A finished container typically has a bottom, a body, and a shoulder. The shoulder is the region to which a pouring opening is connected. The pouring opening typically has a means for holding a closure, such as a twist-lock. The shoulder is formed in the top region of the blow mold. During blow molding, the shoulder is typically inflated first, below the means for holding a closure. After the shoulder, that is, between the shoulder and the bottom, the body is inflated. This essentially corresponds to the middle region of a blow mold.The lower part of the container in turn forms the lower region. The mold construction is subject to various restrictions. On the one hand, these relate to requirements specific to the blow mold itself. For example, these molds must have cooling channels, which in turn necessitates, for instance, a minimum size for the blow mold. On the other hand, these relate to requirements predetermined by the final shape of a container and / or its material. For example, sharp edges can only be formed in a stretch blow molding method by using special materials such as PP or PET copolymer. Sharp edges are defined as edges with a radius less than 1.2 mm.As a result of shrinkage and contraction, inflated containers are not dimensionally accurate in the corner and edge regions and may have different dimensions from batch to batch or even container to container. This is because, for example, temperatures cannot be precisely maintained in such regions, and even small differences in material flow or in the shape and quantity of the original material have a significant influence on the amount of material that ultimately ends up in the corner and edge regions. The smaller the desired radius, the greater this effect. In the stretch blow molding method, a preform is inflated in the blow mold cavity and then further stretched using a stretch mandrel. The preform's wall thickness is thinner during the inflation process. When the preform is pressed against the mold wall, it cools, and the subsequent inflation process is no longer uniform. Typically, the initial contact of the inflated preform is either point-like or linear. From this point onward, the material flows differently, as it becomes more viscous at the contact point due to cooling. In other words, the material flows increasingly slowly in the direction of the theoretically sharp edges, becoming progressively thinner until it forms a weak point.In addition, the flow of material is also impeded by friction between the wall of the partially inflated preform and the cavity. frzaann / zznz / E / YiAi However, there is a need to form containers, in particular stretch and blow-molded containers, also with sharp edges, e.g., for better stacking ability or for visual reasons. SUMMARY OF THE INVENTION Therefore, the objective of the invention is to overcome at least one or more disadvantages of the prior art. In particular, a blow mold with a mold base and a stretch blow molder comprising a blow mold and a method for forming a container that is dimensionally accurate over several production cycles, is, in particular, reliably reproducible, preferably has a pleasing appearance, and, in particular, can be manufactured with precision, shall be provided. This objective is achieved by means of the devices and methods defined in the independent claims. Additional embodiments arise from the dependent claims. A blow mold according to the invention, in particular a blow mold for a stretch blow molding method, has a mold base having a cavity. The cavity has a lower region, a middle region, and an upper region. When the blow mold is closed, the middle region can move relative to the upper region and / or relative to the lower region. This makes it possible to change the cavity dimensions before, during, and / or after the blowing process. In particular, it is possible to reduce the cavity size during and / or after the blowing process. Therefore, an inflated container placed in the cavity can be compressed during and / or after the blowing process. This makes it possible to counteract material thinning and to create sharp edges at the interfaces of relative movement. The mold base is preferably formed in multiple parts and has a top part in which the upper region is formed, a middle part in which the middle region is formed, and a bottom part in which the lower region is formed. Therefore, a shoulder of the inflated vessel can move relative to the vessel body, and compression can consequently occur between the shoulder and the vessel body, thus forming a sharp edge. In the case of relative mobility of the lower region, a lower portion of the vessel moves correspondingly relative to the vessel body, and compression occurs between the vessel body and the lower portion, resulting in a sharp edge. In this way, it can be anticipated that a sharp edge will form between the body of the container and the bottom of the container and between the body of the container and the shoulder of the container. The multi-part design of the blow mold makes it possible, on the one hand, to move the respective parts separately and independently of each other, and, on the other hand, to replace the respective elements easily and with little effort. If, for example, a container bottom is to be produced with a new mold, it is sufficient to replace the corresponding bottom part. It is obvious that, for example, the middle part, the bottom part and / or the top part can each be formed in two parts, to allow a corresponding division of the mold along a longitudinal axis to form a finished container from the blow mold. As explained above, a division into multiple parts is also possible, and / or a division that extends asymmetrically to the longitudinal axis. In a preferred embodiment, the central region can move together with the lower region, relative to the upper region. Through this formation, compression, and therefore the formation of a sharp edge, is forced only in a specific region. In the present case, a sharp edge is formed between the vessel body and the vessel shoulder of the finished vessel. In this way, it can be planned that the central part and the lower part are formed in one piece. This allows for simple manufacturing and simple movement of the bottom part along with the middle part. Alternatively, it may be envisaged that the central region can move together with the upper region, relative to the lower region. Through this process, compression, and therefore the formation of a sharp edge, is forced only in a specific region. In this case, a sharp edge is formed between the body of the vessel and the bottom of the finished vessel. In this way, it can be planned that the central part and the upper part are formed in one piece. This allows for simple manufacturing and simple movement of the top part along with the middle part. In the formation of a piece, of course, the formation of two or multiple parts of the blow mold as such is maintained, allowing the separation of the blow mold to demold the finished container. Preferably, the upper region is at least partially located within the central region. As a result, the upper region can move, relative to the middle region, within the middle region. This simplifies the compression process. Preferably, the blow mold is formed from two mold halves. The manufacturing of the container closure is simplified. Symmetrical and, in particular, identical elements can be used for each mold half. An additional aspect of the present invention relates to a stretch and blow molder comprising a blow mold as described herein. The stretch and blow molder can be fully pre-configured together with the blow mold, where all parameters can be coordinated with each other. An additional aspect of the present invention relates to a method, in particular a stretch blow molding method, for forming a container, specifically 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 mold, in particular, a blow mold as described in the present case, wherein the cavity has an upper region, a central region and a lower region, inflating the preform to form a container, relative movement of the central region to the upper region and / or to the lower region, such that the container is compressed in at least one region to form the rim. This method allows the formation of a particularly sharp edge and prevents a container in the rim region from having very thin walls and / or becoming weakened. Through compression, material thinning is avoided, or material thinning is counteracted. During the inflation of the preform to form a container, it is stretched, in particular, with a stretching rod, so that the finished container is stretched biaxially, on the one hand, in the circumferential direction by means of inflation and, on the other hand, in the axial direction by means of stretching the preform. Preferably, the rim is formed with a radius less than 0.5 mm, where this is a preform made of PET that is inflated with a stretch of 1 to 10 to 1 to 16 and a degree of crystallization of 10% to 40%. In a preferred form of the method, the central region moves together with the lower region in the direction of the upper region. As a result, a sharp edge can form between a vessel body and a vessel shoulder. Alternatively, it may be planned that the central region will move together with the upper region in the direction of the lower region. As a result, a sharp edge can form between the bottom of a container and the body of the container. Such an edge can, for example, facilitate the stacking of containers due to its precision. The method can be carried out in such a way that, after the joint movement of the central region and the lower region, the lower region moves in the direction of the central region to form an additional edge. Therefore, a container with two sharp edges can be formed. Preferably, a pressure greater than 20 bar, in particular greater than 30 bar, and preferably a pressure of approximately 40 bar, is maintained inside the vessel during movement. This ensures that one wall of the container is permanently in contact with the cavity and the inflated container, which, at this point in time, is still hot and therefore soft, and does not collapse or become undesirably deformed. BRIEF DESCRIPTION OF THE FIGURES One embodiment of a blow mold according to the invention is described in further detail with reference to the following schematic figures. The following are shown: frzaann / zznz / E / YiAi Figure 1: a schematic structure of a blow mold; Figure 2: a schematic illustration of a rim formation in the prior technique; Figure 3: a schematic illustration of a blow mold; Figures 4A - 4C: a schematic sequence of the blowing process; Figures 5A - 5B: a detailed view of a rim formation; Figure 6: The blow mold and a container formed after the formation of a rim. DETAILED DESCRIPTION OF THE INVENTION Figure 1 shows a schematic representation of a blow mold 100. The blow mold 100 is a two-part blow mold with a mold base 101 that is also formed in two parts. The mold base 101 has two cavities 102, only one of which is labeled. The mold base 101 is also formed in two parts. In this case, the cavities 102 are designed to inflate a bottle. The cavities 102 can be subdivided into three regions: an upper region 1, a middle region 2, and a lower region 3. Figure 2 shows a schematic illustration of a rim formation as performed in the prior art. During the blowing process, a wall of the preform 4 rests against a corresponding wall of a cavity 102 in a mold base 101. In a region away from a corner or rim to be formed, the inflated preform 4 has a wall thickness SO. The wall thickness SO is shown in a region where a radius R0 is infinite. In other words, the wall of the preform 4 rests completely against an inner wall of the cavity 102. Upon further inflation of the preform 4, the material of the preform 4 is pressed in the corner direction. Due to prior cooling in the region of 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 in the corner direction.With the reduction in the edge radius, indicated in Figure 2 by the radius Rl, the wall thickness of the inflated preform 4 also decreases, as shown by the wall thickness SI, which is less than the wall thickness SO. This effect is further amplified by additional inflation. As can be seen, with a very small radius R2, the wall thickness S2 is already thin, such that a weak point forms further down the vessel. Figure 3 shows a blow mold 100. The blow mold 100 has a mold base 101 in which a cavity 102 is arranged. The cavity 102 is divided into three regions: frzaann / zznz / E / YiAi an upper region 1, a central region 2, and a lower region 3. The central region 2 is relatively mobile, along with the lower region 3, relative to the upper region 1. For this purpose, in each case, the central region 2 is independently formed as a central part 20, and the lower region 3 is independently formed as a lower part 30. The central part 20 is formed to be mobile, along with the lower part 30, relative to an upper part 10, which is formed separately in the same way. The upper part 10 is at least partially disposed within the central part 20 and, therefore, in some regions, slides within the central part 20. Figure 3 shows a schematic sequence of the blow molding process. In the first stage, shown in Figure 4A, a preform 4 is introduced into cavity 102 of a blow mold or cavity 102 of a mold base 101. The preform 4 is formed or interacts with an upper part 10 of the blow mold in such a way that they are mutually coupled. The preform 4 was tempered accordingly before being introduced into cavity 102. As soon as the preform 4 is introduced into the cavity, it is stretched along its longitudinal axis with a stretching mandrel and simultaneously subjected to pressure in such a way that the mold of the preform 4 is changed, and the latter is inflated. Figure 4B shows the state in which preform 4 has reached substantially its full length and is in contact with an inner wall of cavity 102 in a central region. In this region, preform 4 cools slightly, and the material adjacent to this region flows correspondingly more slowly during the blowing process. As a result of further blowing, preform 4 also comes into contact with an inner wall of the top part 10. This has the same effect as the contact of preform 4 with the inner wall of cavity 102 or with the inner wall of the central part 20. The material of preform 4 cools and is prevented from flowing in the direction of 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 radius R2 in Figure 2).However, to form a sharp edge, it is therefore planned, in contrast to the previous technique, that the central part 20 will move in the direction of the upper part 10, and thus the preform will be compressed in the region of the corner or edge to be formed. This process is explained in detail with reference to Figures 5A and 5B below. Figures 5A and 5B show a detailed view of edge formation. Figure 5A corresponds to the state already explained in Figure 4C. As can be seen in Figure 5A, the upper part 10 is decoupled from the central part 20 and can therefore move relative to it, or, in this case, the central part 20 can move relative to the upper part 10. As soon as a wall of the preform 4 has reached a correspondingly thin wall thickness, the central part 20 moves in the direction of the upper part 10 in the direction of the arrow (see Figure 5B). The wall of the preform 4 is thus compressed, and an edge K is formed. In this case, the edge K is formed as a sharp edge K with a radius less than 0.5 mm.It can also be observed in Figure 5B that the wall thickness of preform 4 is shaped to be correspondingly thicker in the K-edge region, and therefore has greater stability in that edge region. Figure 6 shows the blow mold 100 and a container formed after rim formation. The final position of the blow mold 100 is shown in Figure 6. The preform 4 is fully inflated and formed into a container 5. The central part 20 has moved in the direction of the top part 10, and a sharp rim has formed between a container shoulder 51 and a container body 52. ​​In addition, a bottom part 30 has moved in the same way in the direction of the top part 10, and therefore a sharp rim has also formed between the container body 52 and a container bottom 53. In the present case, the container bottom 53 has practically no axial extension. The figures shown here depict an open view of a blow mold 100 in each case. In other words, one half of the blow mold 100 is shown in each case. All the variations apply analogously to the second half of this two-part blow mold 100. It is hereby stated that, as of this date, the best method known to the applicant for carrying out the aforementioned invention is the one that is clear from the present description of the invention.

Claims

1. A blow mold with a mold base having a cavity like the mold cavity, wherein the cavity has a lower region, a central region and an upper region, characterized in that, when the blow mold is closed, the central region can move relative to the upper region and / or relative to the lower region.

2. Blow mold according to claim 1, characterized in that the mold base is formed in multiple parts and has an upper part in which the upper region is formed, a middle part in which the middle region is formed, and a lower part in which the lower region is formed.

3. Blow mold according to one of claims 1 or 2, characterized in that the central region together with the lower region can be moved in relation to the upper region.

4. Blow mold according to claim 3, characterized in that the central part and the lower part are formed in one piece.

5. Blow mold according to one of claims 1 to 2, characterized in that the central region together with the upper region can be moved in relation to the lower region.

6. Blow mold according to claim 5, characterized in that the central part and the upper part are formed in one piece.

7. Blow mold according to any one of claims 1 to 6, characterized in that the upper region is at least partially disposed within the central region.

8. Blow mold according to any one of claims 1 to 7, characterized in that the blow mold is formed from two mold halves.

9. Stretch and blow molder, characterized in that it comprises a blow mold according to one of claims 1 to 8.

10. A method for forming a container, in particular for forming a rim on a container, characterized in that it has the following steps: introducing a preform into a cavity of a blow mold, in particular a blow mold according to any one of claims 1 to 8, wherein the cavity has an upper region, a central region and a lower region, inflating the preform to form a container, relative movement of the central region to the upper region and / or to the lower region, such that the container is compressed at least in one region to form the rim.

11. Method according to claim 10, characterized in that the edge is formed with a radius less than 0.5 mm.

12. Method according to claim 10 or 11, characterized in that the central region together with the lower region moves in the direction of the upper region.

13. Method according to claim 10 or 11, characterized in that the central region together with the upper region moves in the direction of the lower region.

14. Method according to claim 13, characterized in that after the joint movement of the central region and the lower region, the lower region moves in the direction of the central region to form an additional edge.

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

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