Blow molding mold, stretch blow molding machine, and container molding method

Abstract

The invention relates to a blow molding mold (100) having a molding body (101) with a cavity (102) as a mold cavity, wherein the cavity (102) has a bottom region (1), a middle region (2) and a top region (3). The middle region (2) is movable relative to the top region (1) and / or the bottom region (3) in the closed state of the blow molding mold (100).

Description

Technical Field

[0001] This invention relates to a blow molding die for forming containers in a stretch blow molding process, having a molded body having a cavity serving as a mold cavity, wherein the cavity has a top region, a middle region, and a bottom region. The invention also relates to a stretch blow molding machine having such a blow molding die and a stretch blow molding process for forming sharp edges on containers. Background Technology

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

[0003] Typically, hollow plastic containers are manufactured using a process known as blow molding. The most common blow molding methods are extrusion blow molding and stretch blow molding. What these two methods have in common is that the final shape of the hollow plastic body is created in a blow molding die.

[0004] These two blow molding methods are fundamentally different.

[0005] The characteristic of extrusion blow molding is that the hollow body is made from an elongated thermoplastic tube. In stretch blow molding, the hollow body is made from a pre-formed hollow body, also known as a preform (or preform), by stretching the pre-formed hollow body in both the circumferential and longitudinal directions. The plastic of the container is then stretched bidirectionally.

[0006] Generally speaking, those skilled in the art would expect that objects blow-molded in a mold using extrusion blow molding would still be easily deformable directly after blow molding. For stretch blow-molded objects, this is not necessarily expected, as those skilled in the art know that stretch plastics resist subsequent deformation.

[0007] For containers manufactured using these blow molding methods, it is also possible to determine from the finished containers which method they were manufactured using.

[0008] Extrusion blow-molded containers have a cut-off joint in or on the bottom. For stretch blow-molded containers, only one injection point is visible at the bottom, which is created during the manufacturing of the preform. Containers produced using extrusion blow molding can also be seen from the fact that the inner contour essentially follows the outer contour. Therefore, it can be seen that the threads formed by extrusion blow molding on the neck of the container are a negative contour of the container's interior. However, for stretch blow-molded containers, in particular, there is an inner contour that differs from the outer contour in the area of ​​the gate, which is typically manufactured using injection molding. For example, the outer contour may have threads, while the inner contour may have smooth walls. This is necessary for demolding preforms formed using the previous injection molding method.

[0009] Typically, a blow molding die consists of two die halves, but this structure can also consist of more than two parts. The blow molding die has a cavity-like molded body, thus providing a so-called mold cavity for container molding. Depending on the shape of the container, the mold cavity can be symmetrical or asymmetrical. In the case of asymmetrical shapes, the two or more die halves can be divided such that their dividing lines are formed at preferred locations in the later container, thus they do not necessarily have to be divided into equal parts.

[0010] Typically, a blow molding die for a container is divided into three areas: a bottom area, a middle area, and a top area. The finished container typically comprises a bottom, a body, and a shoulder. The shoulder is the area where the gate connects. The gate typically has a tooling for securing a cap (e.g., a screw cap). The shoulder is formed in the top area of ​​the blow molding die. Typically, during the blow molding process, the shoulder is inflated only below the tooling for securing the cap. Following the shoulder, in other words, between the shoulder and the bottom, the body is inflated. This essentially corresponds to the middle area of ​​the blow molding die. The bottom is formed in the bottom area.

[0011] Mold making is subject to various limitations. On the one hand, this involves requirements related to the blow molding mold itself. For example, cooling channels are required, which in turn necessitates a minimum size blow molding mold. On the other hand, this involves requirements due to the final shape of the container and / or due to the pre-defined material. For example, sharp edges can only be formed in stretch blow molding by using special materials such as PP or copolymer PET. The radius of the sharp edge is less than 1.2 mm. Due to shrinkage, the dimensions of blow-molded containers in the corner and edge areas are not accurate, and dimensions can vary between batches and even between containers because temperatures cannot be precisely maintained in these areas, and small differences in the type and quantity of material flow or raw material flow have a non-negligible effect on the amount of material ultimately located in the corner and edge areas. The smaller the required radius, the greater this effect.

[0012] In stretch blow molding, a preform is inflated within the cavity of a blow molding die and further stretched using a stretch mandrel. The wall thickness of the preform thins during the blow molding process. When the preform is pressed tightly against the die wall, the preform wall cools and the preform can no longer undergo a uniform further blow molding process. Typically, the first contact point of the preform to be inflated is point-like or linear. From this contact point, the material of the preform to be inflated flows differently because the material at the contact point flows more slowly due to cooling. In other words, in the direction of the theoretically sharp edge, the material flows slower and thinner accordingly until it forms a weak point. Furthermore, friction between the wall of the partially inflated preform and the cavity also hinders the flow of material.

[0013] However, there is a demand for containers, especially stretch blow-molded containers, to also have sharp edges, for example, to improve stackability or for optical reasons. Summary of the Invention

[0014] Therefore, the object of the present invention is to eliminate at least one or more disadvantages of the prior art. In particular, the following should be provided: a blow molding die having a molded body, a stretch blow molding machine having a blow molding die, and a method for molding a container that is dimensionally accurate, particularly reproducible, and preferably has a satisfactory appearance over multiple production cycles.

[0015] This objective is achieved by the apparatus and method according to the invention. Further embodiments are described below.

[0016] The blow molding die according to the invention, particularly a blow molding die for stretch blow molding, has a molding body having a cavity serving as a mold cavity. The cavity has a bottom region, a middle region, and a top region. When the blow molding die is closed, the middle region is movable relative to the top region and / or the bottom region.

[0017] This allows for changes in the cavity dimensions before, during, and / or after the blow molding process. In particular, it allows for reduction in cavity dimensions during and / or after the blow molding process. Therefore, the container inflated within the cavity can be compressed during and / or after the blow molding process. This allows for resistance to material thinning and the formation of sharp edges at interfaces of relative movement.

[0018] Preferably, the molded body has a multi-part structure and has a top, a middle and a bottom, with a top region formed on the top, a middle region formed on the middle and a bottom region formed on the bottom.

[0019] Therefore, the shoulder of the inflated container can move relative to the body, so compression occurs between the shoulder and the body, creating a sharp edge. Similarly, with the bottom region also movable, the bottom moves relative to the body, resulting in compression between the body and bottom, also producing a sharp edge.

[0020] One option is to create sharp edges between the container body and the container bottom, and between the container body and the container shoulder.

[0021] The multi-part construction of blow molding dies allows each part to move independently and separately, and enables easy and cost-effective replacement of individual components. For example, if the bottom of the container needs a new shape, simply replacing the bottom is sufficient.

[0022] Obviously, for example, the middle, bottom and / or top can each be composed of two parts so that the mold can be separated accordingly along the longitudinal axis, thereby forming the finished container by the blow molding mold.

[0023] As mentioned above, it can be divided into multiple parts and / or divided asymmetrically with respect to the longitudinal axis.

[0024] In a preferred embodiment, the middle region can move relative to the top region together with the bottom region.

[0025] This construction forces compression to occur only in specific areas, thus creating sharp edges. Here, a sharp edge is formed between the container body and the shoulder of the finished container.

[0026] One option is to design the middle and bottom sections as a single unit.

[0027] This makes manufacturing simple and allows for easy movement of the bottom and middle sections together.

[0028] Alternatively, the middle area can be configured to move relative to the bottom area along with the top area.

[0029] This construction forces compression to occur only in specific areas, thus creating sharp edges. Here, a sharp edge is formed between the container body and the bottom of the finished container.

[0030] One option is to design the middle and top sections as a single unit.

[0031] This makes manufacturing simple and allows for easy movement of the top and middle sections together.

[0032] Of course, the one-piece design retains the two- or multi-part design of the blow molding mold itself, so that it can be separated from the blow molding mold to demold the finished container.

[0033] Preferably, the top is at least partially located within the middle region.

[0034] This causes the top region to move relative to the middle region within the middle region. This simplifies the compression process.

[0035] Preferably, the blow molding die consists of two die halves.

[0036] The manufacture of blow molding dies is simplified. Symmetrical, and especially identical, components can be used for each half of the die.

[0037] Another aspect of the invention relates to a stretch blow molding machine that includes a blow molding die as described herein.

[0038] The stretch blow molding machine and the blow molding die can be fully pre-configured together, with all parameters coordinated with each other.

[0039] Another aspect of the invention relates to a method, particularly for container molding, especially for forming preferred sharp edges on containers as described herein, using a stretch blow molding process. The method includes the following steps:

[0040] - A preform is introduced into a blow molding die, particularly a blow molding die as described herein, wherein the cavity has a top region, a middle region, and a bottom region.

[0041] - Blow-molding preforms into containers.

[0042] - Move the middle region relative to the top and / or bottom regions so that the container is compressed at least in the region used to form the edges.

[0043] This method can create particularly sharp edges and prevent the container from becoming very thin-walled and / or weak in the edge areas.

[0044] Compression prevents or resists the thinning of materials.

[0045] In the process of blow molding a preform into a container, the container is stretched using a stretch bar, so that the finished container is stretched biaxially, on the one hand by blow molding in the circumferential direction and on the other hand by stretching the preform in the axial direction.

[0046] Preferably, the edge is formed to have a radius of less than 0.5 mm, wherein the preform is made of PET and blow-molded to have a stretch ratio of 1:10 to 1:16 and a crystallinity of 10% to 40%.

[0047] In a preferred form of this method, the middle region moves together with the bottom region toward the top region.

[0048] This creates a sharp edge between the container body and the container shoulder.

[0049] Alternatively, the middle area can be set to move together with the top area towards the bottom area.

[0050] This creates a sharp edge between the bottom of the container and the container body. For example, this edge, due to its precision, helps with the stacking of containers.

[0051] The method can continue as follows: after the middle and bottom regions move together, the bottom region moves toward the middle region to form another edge.

[0052] Therefore, it is possible to form a container with two sharp edges.

[0053] Preferably, during the movement inside the container, the pressure is maintained at greater than 20 bar, particularly greater than 30 bar, and preferably about 40 bar.

[0054] This ensures that the container walls remain in constant contact with the cavity, and that the inflated container remains warm and soft at this point, without collapsing or developing unwanted deformation. Attached Figure Description

[0055] Embodiments of the blow molding die according to the present invention are described in more detail with reference to the following schematic diagram. The diagram shows:

[0056] Figure 1 : A schematic structure of a blow molding die;

[0057] Figure 2 : A schematic diagram of the shape of the edge in the prior art;

[0058] Figure 3 : Schematic diagram of blow molding die;

[0059] Figures 4A-4C A schematic diagram of the blow molding process;

[0060] Figures 5A-5B Detailed view of the edges;

[0061] Figure 6 Blow molding mold and the molded container after edge formation. Detailed Implementation

[0062] Figure 1A schematic structure of a blow molding die 100 is shown. The blow molding die 100 is designed as a two-part blow molding die and has a molding body 101, which is also designed to be two parts. The blow molding die 100 has two cavities 102 in the molding body 101, only one of which is marked. The molding body 101 is also designed to be two parts. This cavity 102 is designed to blow mold a bottle within it. The cavity 102 can be divided into three regions: a top region 1, a middle region 2, and a bottom region 3.

[0063] Figure 2 A schematic diagram of the shape of an edge as formed in the prior art is shown. During blow molding, one wall of the preform 4 is in close contact with the corresponding wall of the cavity 102 of the molded body 101. In the region away from the corner or edge to be formed, the blown preform 4 has a wall thickness S0. The wall thickness S0 is marked in the region where the radius R0 is infinitely large. In other words, the wall of the preform 4 is completely in close contact with the inner wall of the cavity 102. By further blow molding the preform 4, the material of the preform 4 is compressed towards the corner. Due to the previous cooling in the region of infinite radius and due to the friction between the wall of the preform 4 and the inner wall of the cavity 102, the material flows only restricted towards the corner. With the edge radius (by... Figure 2 As the radius R1 in the diagram decreases, the wall thickness of the blown preform 4 (represented by wall thickness S1, which is less than wall thickness S0) also decreases. This effect is further enhanced through further blow molding. It can be seen that with a very small radius R2, the wall thickness S2 is already very thin, which will create weak points in the container later.

[0064] Figure 3 A blow molding die 100 is shown. The blow molding die 100 has a molding body 101, in which a cavity 102 is provided. The cavity 102 is divided into three regions: a top region 1, a middle region 2, and a bottom region 3. The middle region 2 is movable relative to the top region 1 together with the bottom region 3. Furthermore, the middle region 2, which is the center 20, and the bottom region 3, which is the bottom 30, are designed to be independent. The center 20 is designed to be movable relative to the equally independently designed top 10 together with the bottom 30. The top 10 is at least partially disposed inside the center 20, and thereby partially slides within the center 20.

[0065] Figure 3 A schematic diagram of the blow molding process is shown. Figure 4AIn the first step shown, the preform 4 is introduced into the cavity 102 of the blow molding die or the cavity 102 of the molded body 101. The preform 4 is designed, or interacts with, the top 10 of the blow molding die as follows, such that they engage with each other. The preform 4 is preheated accordingly before being introduced into the cavity 102. Once the preform 4 is introduced into the cavity, it is stretched along its longitudinal axis using a stretching mandrel while pressure is applied, causing the shape of the preform 4 to change, thereby inflating the preform.

[0066] Figure 4B The diagram shows the preform 4 having reached its substantially full length and already in contact with the inner wall of the cavity 102 in the middle region. In this region, the preform 4 cools slightly accordingly, and the material adjacent to this region flows more slowly during the blow molding process. Through further blowing, the preform 4 also comes into close contact with the inner wall of the top 10. This has the same effect as if the preform 4 were in close contact with the inner wall of the cavity 102 or the inner wall of the middle 20. The material of the preform 4 cools and is prevented from flowing toward the corner to be constructed. In the prior art, the blow molding process is usually interrupted at this location, thus retaining a relatively large radius at the corner (for comparison). Figure 2 (Radius R2 in the middle). Therefore, in order to form a sharp edge, unlike the prior art, the middle 20 is moved towards the top 10, thereby compressing the preform in the area of ​​the corner or the area of ​​the edge to be constructed. Refer to the following Figure 5A and 5B The process will be explained in detail.

[0067] Figure 5A and 5B A detailed view of the edge formation is shown. Figure 5A Corresponding to what has already been based on Figure 4C The state of explanation. From Figure 5A As can be seen, the top 10 is detached from the middle 20, and therefore can move relative to the middle, or in this case, the middle 20 can move relative to the top 10. Once the wall of the preform 4 reaches a correspondingly thin wall thickness, the middle 20 moves in the direction of the arrow towards the top 10 (see...). Figure 5B The wall of the preform 4 is compressed during this process, forming edge K. Here, edge K is designed to have a radius less than 0.5 mm. From Figure 5B It can also be seen that the preform 4 has a correspondingly thicker wall in the region of edge K, thereby having enhanced stability in the region of edge.

[0068] Figure 6 The blow molding die 100 and the molded container after edge formation are shown. The blow molding die 100 is in... Figure 6The container 5 is shown in its final state. The preform 4 is fully inflated to form the container 5. The middle portion 20 moves toward the top 10, thus forming a sharp edge between the container shoulder 51 and the container body 52. ​​Furthermore, the bottom portion 30 also moves toward the top 10, thus forming a sharp edge between the container body 52 and the container bottom 53. In this case, the container bottom 53 no longer has any axial expansion.

[0069] Clearly, this accompanying drawing shows views of the open blow molding die 100. In other words, it shows two halves of the blow molding die 100. All embodiments are understood to apply, in a literal sense, to the second half of the two-part blow molding die 100.

Claims

1. A blow molding die (100) for forming a container in a stretch blow molding process, having a molding body (101) having a cavity (102) as a mold cavity, wherein the cavity (102) has a top region (1), a middle region (2) and a bottom region (3). Its features are, With the blow molding die (100) closed, the middle region (2) can move relative to the top region (1) and / or the bottom region (3) to form a sharp edge on the container.

2. The blow molding die (100) according to claim 1, wherein, The molded body (101) has a multi-part structure and has a top (10), a middle (20) and a bottom (30), with the top region (1) formed on the top (10), the middle region (2) formed on the middle (20) and the bottom region (3) formed on the bottom (30).

3. The blow molding die (100) according to claim 1 or 2, characterized in that, The middle region (2) is movable relative to the top region (1) together with the bottom region (3).

4. The blow molding die (100) according to claim 2, characterized in that, The middle region (2) is movable relative to the top region (1) together with the bottom region (3), and the middle (20) and the bottom (30) are designed as a single unit.

5. The blow molding die (100) according to claim 1 or 2, characterized in that, The middle region (2) is movable relative to the bottom region (3) together with the top region (1).

6. The blow molding die (100) according to claim 2, characterized in that, The middle region (2) is movable relative to the bottom region (3) together with the top region (1), and the middle (20) and the top (10) are designed as a single unit.

7. The blow molding die (100) according to claim 1 or 2, characterized in that, The top region (1) is at least partially located within the middle region (2).

8. The blow molding die (100) according to claim 1 or 2, characterized in that, The blow molding die (100) consists of two die halves.

9. A stretch blow molding machine having a blow molding die (100) according to any one of claims 1 to 8.

10. A stretch blow molding method for forming sharp edges on containers, wherein, The method includes the following steps: - A preform is introduced into the cavity (102) of a blow molding die (100), wherein the cavity (102) has a top region (1), a middle region (2), and a bottom region (3), wherein a container shoulder is formed in the top region, and a container bottom is formed in the bottom region. - Blow-molding preforms into containers. - With the blow molding die (100) closed, the middle region (2) is moved relative to the top region (1) and / or the bottom region (3) so that the container is compressed at least in the region for forming the edge, and the container shoulder and / or the container bottom is moved relative to the container body, thereby forming a sharp edge between the container body and the container shoulder and / or between the container body and the container bottom.

11. The molding method according to claim 10, characterized in that, The blow molding die (100) is a blow molding die according to any one of claims 1 to 8.

12. The method according to claim 10 or 11, characterized in that, The edge is formed to have a radius of less than 0.5 mm.

13. The method according to claim 10 or 11, characterized in that, The middle region (2) and the bottom region (3) are moved together toward the top region (1).

14. The method according to claim 10 or 11, characterized in that, The middle region (2) is moved together with the top region (1) toward the bottom region (3).

15. The method according to claim 14, characterized in that, After the middle region (2) and the bottom region (3) move together, the bottom region (3) is moved toward the middle region (2) to form another edge.

16. The method according to claim 10 or 11, characterized in that, During the movement inside the container, the pressure is maintained at greater than 20 bar.

17. The method according to claim 16, characterized in that, During the movement inside the container, the pressure is maintained at greater than 30 bar.

18. The method according to claim 16, characterized in that, The pressure is maintained at 40 bar during the movement inside the container.

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