Preform made of a thermoplastic material, and apparatus and method for manufacturing the preform
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- アクタスマヒル
- Filing Date
- 2023-07-10
- Publication Date
- 2026-07-01
AI Technical Summary
Existing preform manufacturing methods result in residual heat causing premature solidification, leading to sink marks and inefficient material consumption due to uneven temperature distribution and wall thickness, which affects the quality and efficiency of blow molding processes.
A preform design with a thin wall thickness at the rounded end and optimized melt spaces and flow channels that allow for controlled cooling and even melt distribution, ensuring efficient thermal energy transfer and stable stretching during the blow process.
This design prevents premature solidification, reduces material consumption, and enhances the quality of the blow-molded containers by maintaining holding pressure and achieving uniform wall thickness, thereby improving production efficiency and reducing material waste.
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Abstract
Description
Technical Field
[0001] The present invention relates to a method and an apparatus for manufacturing a preform so as to form a preform round end shape advantageous for a subsequent blow process.
[0002] The present invention ultimately results in a significant saving of raw materials, and in addition, quality improvement is achieved in the finished product.
[0003] The present invention also relates to a preform or preform having an improved bottom shape.
Background Art
[0004] A preform is an injection-molded semi-finished product made of at least one thermoplastic material, and these semi-finished products are used in a blow molding machine for the production of plastic containers to be stretch blow molded.
[0005] For the production of the preform described according to the present invention, the plastic raw material is plasticized and subsequently pressed into a single-cavity or multi-cavity mold tool (die) at high pressure.
[0006] According to the prior art, preforms corresponding to FIG. 1 are made, and these preforms, as a shape (geometry), substantially consist of a neck region (neck area), a shaft region, and a bottom round end (bottom dome), and the inside is hollow by incorporating a core in the mold tool. The neck region is shaped such that it is possible for the neck region to be configured to be re-closable, for example, using a screw-on cap. However, the neck region does not undergo further changes during the blow process. In contrast, the shaft region and the bottom round end are blown into a hollow body at a high temperature, whereby the plastic is stretched and significantly cured during this process. The preform region to be deformed thus cooperates with the core shape and is responsible for the resulting bottle quality.
[0007] Typically, the mold tool is the largest investment in a production system. Therefore, it is important that the mold tool operates efficiently. That is, the outer shell of the preform is in direct contact with the intensively cooled mold steel, whereby the preform rapidly solidifies there, is demolded without damage and without mechanical deformation, and thereby the mold tool is prepared for the next production cycle without time loss.
[0008] Also, during the solidification process of the preform with shrinkage, and thus during the solidification process of the preform that causes material chipping, in order to compensate for this lack and thereby avoid unwanted sink marks in the molded part, it should be noted that the holding pressure is maintained throughout the entire preform via the sprue during the injection molding process.
Prior Art Documents
Patent Documents
[0009]
Patent Document 1
Patent Document 2
Patent Document 3
Summary of the Invention
Problems to be Solved by the Invention
[0010] In a normal high-speed production cycle, a lot of residual heat remains inside the wall of the preform, and this residual heat causes reheating, whereby the preform softens and crystallizes again, which renders the preform unusable.
[0011] Therefore, it is extremely advantageous to cool the preform more intensively after demolding, within a simpler molded part, and within a so-called cooling sleeve during multiple production cycles.
[0012] The preform as shown in Fig. 1 meets the current state of the art. In this preform, as described, it is inevitable that the wall thickness of the preform has a similar wall thickness, particularly in the regions of the rounded ends and the shaft of the preform. If the wall thickness is thinner in the bottom region or the neck region, causing the material to solidify prematurely, the shrinkage during the cooling stage cannot be avoided even by the holding pressure of the melt acting on the entire preform including the neck region. This results in unwanted sink marks in important regions of the preform.
[0013] Thus, the preform shape (preform geometry) according to the invention, shown in Fig. 2 and the advantages of which are explained in the following paragraphs, cannot be produced in known injection molding methods or can only be produced in known injection molding methods considering corresponding measures to maintain the required holding pressure. The reason is that, according to this invention, a much thinner wall thickness is achieved at the rounded ends of the preform than in the subsequent shaft region. At this time, the aim is to eliminate premature solidification and avoid sink marks in these thin-walled regions.
[0014] For the subsequent blow process, there is a further criterion that the temperature distribution (temperature profile) between the preform rounded end and the shaft should make a sudden temperature jump of approximately 50°C to 80°C for optimal results, but this cannot be achieved at all today according to the prior art. This means that in most cases, the gentle temperature transition results in the inability to stretch the material in the bottom region optimally into the bottle body during the stretch blow process, thereby causing unnecessary material consumption. This also means that although the wall thickness at the preform rounded end will be more strongly optimized to be thinner, during the injection molding process, due to the rapid solidification in the thinner region, the holding pressure within the shaft or neck cannot be maintained, thereby causing the aforementioned sink marks, and the neck will no longer form a tight system in its mating with the lid member.
[0015] The central problem of the present invention is to provide a method and an apparatus for manufacturing a preform having a much more favorable wall cross-section at the preform rounded end. The advantage is that the infrared heater of the subsequent blow molding machine can more efficiently provide thermal energy to bring the plastic within this region to a temperature at which it can be stretched more rapidly through this enlarged surface where the wall thickness is reduced. Thereby, during the stretch blow process, the material can be directly drawn from the preform rounded end optimally for the bottle bottom or the bottle body, which enables an obvious saving of raw materials.
Means for Solving the Problem
[0016] The preform according to the present invention can be cooled more efficiently within a mold tool (hereinafter also simply referred to as a tool), because there is a relatively thin wall thickness between the melt space and the flow channels, and these flow channels have a relatively large surface area. An exception to the more efficient cooling is the region of the melt space, because here the cooling within the mold tool is reduced, so that the melt receives a higher residual heat than the remaining preform regions. The melt is injected directly through the sprue into a relatively large melt space, where it is injected so as to be collected in a washbasin or a tub, and subsequently is guided (along the flow path) into the remaining preform body in a controlled manner. Thereby, the melt space ensures a continuous filling of the preform with the melt and, during the holding pressure phase, by its design supports an even distribution of the melt into the subsequent thinner wall thickness regions. The melt passes through the melt space so as to pass through a sprue or a shield and is evenly guided into the corresponding flow channels or directly into the thinner wall thickness regions of the round ends of the preform. Due to the optimal design of the melt space, the flow channels can also be omitted, matching the respective bottle bottom shape. In the final cooling of the robot system, a relatively high cooling efficiency is likewise achieved, because within the cooling sleeve of the extraction robot system, a relatively large cooling surface with a reduced wall thickness can be utilized for the round ends of the preform, which counteracts re-softening and the associated quality degradation. The cooling sleeve of the robot system is based on protrusions and respective optional webs (strip parts) formed at the outer round ends of the preform by the melt space and the optional flow channels, and can better receive the preform during the transfer from the mold tool to the robot system. The round ends of the preform have a relatively large contact surface with the cooling sleeve, which ensures a more efficient cooling of the preform.
[0017] In addition, due to the special preform round-end design, it can adapt to the shape of each container bottom. During the blow process, the stretching rod hits the preform round-end at the inner sprue area upon contact, cooling the sprue area uncontrollably and thereby preventing optimal stretching of the bottom area. According to the present invention, by means of protrusions and webs around the inner sprue area generated by the inner melt space and optional vertical and / or horizontal flow paths in the tool, matching the structural bottle bottom specifications, an optimized stretching of the preform round-end can be achieved using a conforming stretching rod shape. Also, in the tool, when a corresponding relatively large melt space located inside is utilized, each inner flow path can be omitted. The melt space is located immediately after the sprue in the future preform body, that is, the melt is collected here and then evenly distributed into the remaining preform. In this case, the melt is directly led into the thinner wall thickness area through the melt space without using the flow path. This results in better forming around the sprue area or the bottle bottom area in the blown bottle, thereby avoiding sudden wall thickness differences and material accumulations that would otherwise cause so-called stress fractures at the bottle bottom, especially in the case of gas-containing beverages.
[0018] Using the protrusions and optionally incorporated webs, the surface of the inner and / or outer preform round-ends can be enlarged throughout the bottom area. This has the advantage that the infrared heater of the subsequent blow molding machine can more efficiently provide thermal energy through the enlarged surface, enabling better stretching of the material from the preform round-ends. The stretching rod of the blow molding machine can better influence the wall thickness of the bottle bottom through better guidance or centering, as well as an accurately determined design of the inner protrusions and the webs, thereby enabling accurate axial stretching of the preform.
[0019] Regarding the production of this type of preform, three solutions are proposed below, which are used in the bottom plate of the mold tool and / or the core of the mold tool.
[0020] In the first variation, in the area of the base plate of the mold tool, for example, the shaping of the outer preform rounded end can be configured as follows: that is, in the transition part of the sprue to the preform bottom, most of it is actually a thin wall, but there is at least one melt space and two or more optional flow paths in the axial and / or vertical directions, and these are designed so that they do not solidify prematurely, thereby enabling the holding pressure on the preform shaft to be maintained. The melt space around the sprue area is designed to guide the melt in an optimal state into each flow path or into the wall thickness area of the thin wall of the preform rounded end in order to ensure the even distribution of the melt.
[0021] The size of this melt space depends on the preform size, weight, shape (geometry), and the quality requirements of each blown bottle. The preform rounded end formed by the melt space and the flow path can appear as protrusions or webs on the outside in the preform, and as long as they are distributed as symmetrically as possible in the circumferential part, they will not have an adverse effect on the subsequent blowing process. Also, they can act rather to stabilize in the stretch blow process and later in the bottle. Furthermore, in Embodiment Variation 1 and Embodiment Variation 3, the protrusions and the optional webs can be seen from the outside in the finished product, visually indicating savings (savings of raw materials).
[0022] Channels that serve the purpose of influencing the bottle shape are known from the prior art, for example, from the above-mentioned Patent Document 1 (WO 2010 / 069042 A1) and the above-mentioned Patent Document 2 (US 5,455,088). Both documents describe channels that have an impact on the bottle body and the bottle bottom. These channels start directly in the preform sprue and end inside the preform shaft. The advantage for both of the above-mentioned embodiments is that, according to the present invention, the melt space is first filled, and only then is the melt distributed into the thinner preform round end region or into each channel, thereby ensuring an even filling of the preform.
[0023] In addition, in order to support the shape stability of the preform during the holding pressure phase, the axial channels can be connected to each other in the vertical direction. Furthermore, all of these channels end in the region of the preform round end, without weakening the wall thickness of the future bottle foot at this time. This allows for a more even axial stretching and a good temperature distribution at the preform round end without creating a large wall thickness jump between the preform sprue and the outflow to the cylindrical preform body.
[0024] An alternative second variation that the present invention describes here is that in the core of the mold tool, for example, the shaping of the inner design of the preform can be configured as follows, that is, most of the inner preform rounded ends are actually thin-walled, but at least one inner melt space and two or more optional flow paths in the axial and / or vertical directions are designed so that they do not solidify prematurely, thereby enabling the holding pressure on the preform shaft to be maintained. Due to the core cooling being adapted or reduced at the preform rounded ends, the melt space and the flow paths can support the preform shaft with the melt for a longer time during the holding pressure stage, thereby avoiding sink marks. What is important in the design of the flow paths is to avoid undercuts, for example as in the above-mentioned Patent Document 3 (WO 2016 / 059135 A1), so as not to endanger the demolding of the preform, because the preform will become non-demoldable here due to undercuts. These flow paths appear as webs on the inside at the completed preform rounded ends, and these webs will not adversely affect the subsequent blow process as long as they are distributed as symmetrically as possible in the circumferential part, but rather act to stabilize in the stretch blow process and later in the container. Furthermore, the inner protrusions and the webs formed by the melt space and the flow paths of the tool cannot be seen from the outside in the completed product, which is a major difference from the first and third solution approaches. If the bottle bottom design permits, the flow paths can be omitted and only one inner melt space in the tool can be utilized.
[0025] A third variation for optimizing the preform according to the invention in the bottom region is to implement a combination of the melt space and the outer and inner flow channels at the rounded end of the preform. For this purpose, in the mold tool, the bottom plate and the core are fitted together. Thereby, the inner / outer melt space and the axial and / or vertical flow channels can be created simultaneously. In particular, in the case of CSD (carbonated soft drink) applications where a large internal pressure acts, by means of a defined preform rounded end design, or by creating a combination of the melt space and the axial / vertical outer flow channels and / or the corresponding inner flow channels, a more stable bottle bottom can be achieved with a relatively low weight.
[0026] Hereinafter, the present invention will be described in detail based on embodiments in relation to the accompanying drawings.
Brief Description of the Drawings
[0027]
Figure 1
Figure 2
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Figure 12
DETAILED DESCRIPTION OF THE INVENTION
[0028] The accompanying drawings should support the description of the manufacturing process of the preform round end region hereinafter.
[0029] All structural details and method details described below can be realized according to the present invention, individually or in any combination thereof. All device features can also be utilized within the framework of the method, and all method features can be implemented in the device.
[0030] Figure 1 shows a preform (1) manufactured according to the prior art. At this time, the wall thickness (10) at the round end (6) of the preform under the sprue (7) has the same wall thickness (10) as the shaft region (5). The preform according to FIG. 2 optimized for the blow process, with the wall thickness (9) reduced in the bottom region (6), can only be realized injection-technologically with limitations due to the risk of solidification of the melt, because at that time the holding pressure counteracting the shrinkage of the preform (2) during the cooling process can no longer act in the important regions.
[0031] In the present invention, three solution variations are shown such that the preform (2) of FIG. 2 can be manufactured. At this time, all three methods provide, at the periphery of the described preform rounded end portion (6), at least one inner / outer melt space, an optional outer axial / vertical (vertical direction in a preform having a longitudinal axis arranged horizontally in the drawing, i.e., the lateral direction with respect to the axial direction) flow path, and / or an optional inner axial / vertical flow path, provided that these do not have an adverse effect on the desired blow result during the blow deformation of the preform (2). Conversely to the adverse effect, in Variation 1 and Variation 3, in the preform, the formed protrusions and the optional webs can be seen from the outside and, despite the material being saved, suggest increased strength. Furthermore, due to the adapted container bottom shape within the tool, the outer / inner flow paths can be completely omitted and production is possible with only the outer or inner melt space. The melt reaches directly into the melt space from the sprue, and the melt space is not arranged at the material supply part of the tool but is always arranged as a material distribution center immediately behind the sprue region, so as to form a protrusion (FIG. 12) with a diameter of at least 2 mm to 30 mm in the future preform rounded end portion. The hot melt stream is not cooled immediately here but is first evenly guided into the connecting thin-walled region, comparable to a stud or a shield, and is then cooled in a controlled manner by the adapted tool cooling until the holding pressure process is completed.
[0032] However, in order to produce a preform (2) as shown in FIG. 2 using conventional injection molding technology, a mold tool cavity as shown in FIG. 11 having a melt space and an optional flow path is configured as follows: that is, through the thin wall portion (9) at the rounded end portion (6) of the preform, at least one protrusion (8), two, preferably five, outer axial webs (strip portions) (11), and / or one outer vertical web (strip portion) (12) are configured to be formed. At this time, this structural design supports the maintenance of the holding pressure in the bottom region (6) of the preform (2) during the injection molding process, as considered in FIG. 2. The surface contour of the preform (2) continues in the region of the web, while in the region of the recess, the contour descends inward or outward, so that a smaller wall thickness (9) is generated in the region of the recess.
[0033] The rounded end portion (6) of the preform has a uniform wall thickness in the sprue region and has a protrusion (8) formed by the melt space (3) in the tool and ensuring continuous distribution of the melt, and the melt is led into the preform shaft (5) through the recess in the mold tool cavity through flow paths that appear as webs (11, 12, 13, 14) in the preform.
[0034] The axial flow path ideally leads directly into the shaft of the preform or, depending on the bottom design of the container to be manufactured, terminates freely definable between the sprue (7) and the shaft region (5). Thereby, the forward movement of the melt is compensated again, and unwanted seam lines are avoided. The vertical flow paths, which can be seen as webs (12, 14) in the preform, connect at least two axial flow paths (11, 13), which can be seen as webs (11, 13) in the preform, so that the melt is led into the preform shaft (5) through these flow paths simultaneously during the pressure holding phase. In addition, the vertical flow paths support the bottom stability of the bottle in order to compensate for uncontrolled stretching caused by different wall thicknesses between the melt space and the respective flow paths in the subsequent blow process. It is also possible to utilize only one vertical flow path, which can be seen as a web (12, 14) in the preform, in order to obtain more material in a specific bottle bottom section for the purpose of supporting the shape stability of the bottle bottom.
[0035] At this time, the important thing is not that these faces (the faces in the region of the thin-walled part) must have an excessively large length in the axial direction, but that the radial cross-sectional face in the region of the thin-walled part ensures the desired sudden heat conduction for the blow process through a short length (both in the axial and radial directions). This has the advantage that the implementation of the thin-walled part can often be carried out circumferentially in the divided molded part of the preform round end. Furthermore, the flow paths, which can be seen as webs (11, 12, 13, 14) in the preform, are relatively short in this embodiment, which simplifies the thermal and hydrodynamic design of these flow paths in the sense that early solidification in the flow paths and the formation of seam lines become less with shorter lengths.
[0036] However, in order to form the plurality of axial channels narrower, it is also possible to incorporate at least one additional vertical channel into the mold cavity as a connecting element between the plurality of axial channels, which are illustrated by webs (11, 12, 13, 14) in FIGS. 2, 3, and 4, and these webs then support the shaping of the preform (2) during the holding pressure phase. However, at the same time, it is also possible to create only one outer vertical channel and / or only one inner vertical channel.
[0037] The preform (2) in FIG. 3 shows a second solution variation, in which the webs are incorporated into the inner contour of the preform (2), where these webs cannot be seen from the outside in the blown bottle, and at least two, preferably six, axial inner webs (13), as well as at least one vertical inner web (14), are incorporated into the preform rounded end (6) to ensure the holding pressure during the injection process through the melt space (3) in the preform bottom region.
[0038] In contrast, FIG. 4 shows a combination of outer and inner webs. The webs (11, 13, and 14) continue the original surface contour of the preform (2). The protrusion (8) in the preform is generated by the melt space (3) in the tool and is ensured in the simultaneous and parallel incorporation of the inner / outer channels visible as webs (11, 13), where the outer and inner channel contours match in terms of shaping such as width and length and conform to the surface contour of the preform (2), thereby enabling an optimal supply of the preform (2) with melt. Thereby, sink marks in the shaft (5) and the neck region (4) are prevented during the holding pressure phase.
[0039] The flow path (15) in Fig. 5 marked with an arrow indicates how the melt flows through the sprue into the melt space (3), which can be seen here as the protrusion (8), and from there through five flow paths of sufficient width and length (which can be seen here as webs) into the preform shaft, thereby maintaining the holding pressure. First, the melt collects in the adjacent melt space (3), which has a larger diameter (Fig. 12) than in the sprue (7), keeping the melt at a constant temperature like in the tank, thereby preventing premature cooling of the melt from causing sink marks in the neck region (4) or even in the shaft region (5) before the injection molding process or the holding pressure is completed.
[0040] Figs. 6 and 7 illustrate webs with various inner and outer contours in different embodiments. Various shapes of the protrusion (8), axial webs (11, 13), and vertical webs (12, 14) can be clearly seen.
[0041] Fig. 8 shows the stretching rod (16) during the stretching process in the entry position. When the stretching rod (16) enters the preform (2), it hits the inner protrusion (8) and the vertical web (14) of the inner preform rounded end (6). The inner contour of the axial / vertical web can match the outer contour of the stretching rod shape to ensure that the preform (2) can be accurately stretched axially. This has the advantages that the preform sprue of the container is always exactly centered and that the wall thickness difference at the bottom of the container caused by a displaced sprue (7), the so-called off-center (where the preform sprue is displaced from the center of the axial container center) is avoided.
[0042] In an injection molding mold, it is possible to create inner / outer melt spaces and axial / vertical inner or outer flow paths into the bottom plate according to FIG. 9 or into the core according to FIG. 10. FIG. 11 shows a complete mold cavity having inner and outer melt spaces (3). This melt space (3) can be generated by the respective recesses or enlargements of the future wall thickness of the preform (2) and by adaptation within the bottom plate (17) and / or the core (18).
[0043] FIG. 12 shows two different shapes of protrusions (8) without inner / outer webs. The outer / inner diameters of the outer / inner protrusions (20, 21) are in the range starting at the transition to the thin wall thickness region (9) of the preform round end and ending at the transition to the preform shaft (5), with values ranging from a minimum of 2 mm to a maximum of 30 mm. In this case, the thin wall thickness region is designed to have a constant wall thickness a between the protrusion and the transition to the preform shaft. This wall thickness can be implemented as constant according to the size of the inner / outer protrusions, or it can also be implemented to have a wall thickness a that tapers or increases until reaching the transition of the preform shaft. The inner protrusion (20) in this example leads directly into the thinner wall thickness region (9) of the preform round end.
Explanation of reference numerals
[0044] 1 Preform according to the prior art 2 Preform with an optimized thin-walled bottom region 3 Melt space 4 Neck region 5 Shaft region 6 Preform round end 7 Sprue 8 Protrusion 9 Reduced wall thickness at the preform round end 10 Normal wall thickness for the injection molding process 11 Axial flow path in the outer contour of the preform 12 Vertical flow path in the outer contour of the preform 13 Axial flow path in the inner contour of the preform 14 Vertical flow path in the inner contour of the preform 15 Flow path 16 Extension rod 17 Bottom plate 18 Core 19 Inner space of the preform 20 Inner protrusion 21 Outer protrusion
Claims
1. A preform made of a thermoplastic material for manufacturing a blow-molded container, wherein the preform has a tubular intermediate region (5), a closed bottom (6), and a neck region (4) located on the opposite side of the bottom in the direction of the longitudinal axis of the preform and limiting the internal space (19), and the wall thickness in the bottom region (6) is dimensionally smaller than that in the intermediate region (5), at least in each region, The bottom portion (10) has, in the surface region, at least one inner / outer projection and optional outer or inner webs (11, 12, 13, 14) having a certain wall thickness, wherein the webs start from the central portion of the bottom portion (6) and extend toward the intermediate region (5). A preform characterized by the following.
2. The protrusions and the optional webs (13, 14) are arranged on the inside with respect to the internal space (19) of the preform (2). The preform according to claim 1, characterized by the following:
3. The protrusions and the optional webs (11, 12) are arranged on the outside with respect to the internal space (19) of the preform (2). The preform according to claim 1, characterized by the following:
4. The aforementioned webs (11, 12, 13, 14) are arranged on the inside and outside with respect to the internal space (19) of the preform (2). The preform according to claim 1, characterized by the following:
5. The material of the aforementioned preform is injection molded. The preform according to claim 1, characterized by the following:
6. The sprue (7) is positioned in the central area on the outside of the bottom portion (6). The preform according to claim 1, characterized by the following:
7. The wall thickness in the bottom region (6) is approximately 20% to 70% less in each region than in the intermediate region (5). The preform according to claim 1, characterized by the following:
8. The aforementioned protrusion and the optional inner and outer webs are configured as additional reinforcements for the bottle bottom without reducing the wall thickness in the bottom (6) region. A preform according to any one of claims 1 to 7, characterized by the above.
9. An apparatus for manufacturing a preform (2) made of a thermoplastic material by injection molding technology for manufacturing a blow-molded container, wherein the apparatus comprises an outer mold and a core disposed within the cavity of the outer mold, and in the apparatus, the outer mold comprises a bottom and a neck region located opposite the bottom in the direction of the longitudinal axis, In the bottom region, the distance between the core and the inner surface of the outer mold is determined to be smaller than the distance between the core and the intermediate portion of the outer mold, at least in each region, and Starting from the center of the bottom, at least one hole for the molten material space and optionally a groove-like flow path extend, the hole being fabricated in the mold tool following the material supply section and immediately after the sprue, and being larger in diameter than the sprue, the hole being formed by the core or bottom plate, thereby having an inner or outer molten material space within the mold cavity, and the hole being seen as an inner or outer projection in the molded preform. A device characterized by the following.
10. The hole for the molten material space and the optional flow path extend from the center of the rounded end in the core. The apparatus according to claim 9, characterized by the following:
11. The hole for the molten material space and the optional flow path in the outer mold extend from the inner central portion. The apparatus according to claim 9, characterized by the following:
12. The aforementioned interval is approximately 20% to 70% smaller in the bottom region than in the intermediate region. The apparatus according to claim 9, characterized by the following:
13. A molten material space is provided in the bottom region. The apparatus according to any one of claims 9 to 12, characterized by the above.
14. A method for manufacturing a preform made of a thermoplastic material for manufacturing a blow-molded container, having a tubular intermediate region, a closed bottom, and a neck region located on the opposite side of the bottom in the direction of the longitudinal axis and limiting the internal space, The wall thickness in the bottom region is determined to be smaller than that in the intermediate region, at least for each region. The bottom portion has at least one molten material space and an optional flow path in the surface region, the flow path starting from the central part of the bottom portion and extending toward the intermediate region.
15. At the end of the injection molding process, a holding pressure is generated. The method according to claim 14, characterized by the above.
16. The molten space is filled with plasticized plastic. The method according to claim 14, characterized by the above.
17. During the injection molding process, after material is supplied via the sprue, the larger diameter molten space and then the space between the core and the outer mold are filled with thermoplastic plastic. The method according to any one of claims 14 to 16, characterized by the above.