WO2000034023A1

WO2000034023A1 - Method for producing multi-component preforms and preforms produced according to this method

Info

Publication number: WO2000034023A1
Application number: PCT/EP1999/009529
Authority: WO
Inventors: Karl Hehl
Original assignee: Karl Hehl
Priority date: 1998-12-07
Filing date: 1999-12-06
Publication date: 2000-06-15
Also published as: DE19856356A1

Abstract

The invention relates to a method for producing multicomponent preforms which are drawn into fillable plastic hollow bodies in a succession of steps. At least two materials are plasticised on an injection moulding machine. The first material is injected into a first mould cavity (14) which corresponds to the proportion of the entire form of the preform (10) made up by said first material. The first intermediate form (21) moulded in this way is then combined with a second cavity (23)to form a second mould cavity (15), which is partially delimited by the intermediate form (21). The resulting mould cavity (15) corresponds to the proportion of the entire form of the preform (10) made up by the second material. Once the second material has been injected into the second mould cavity (15), the finished preform (10) can be removed. One of the injected materials forms a barrier layer, so that the barrier layer can be positioned as required during the construction of the preform.

Description

Process for the production of multi-material preforms and preform produced thereafter

description

Relation to related applications

The present application claims the priority of the German patent application 198 56 356.6, filed on December 7, 1998, the disclosure content of which is hereby expressly made the subject of the present application.

Field of the Invention

The invention relates to a method for the production of preforms consisting of several materials on an injection molding machine for processing plastics and other plasticizable materials according to the preamble of claim 1 and a preform produced according to the preamble of claim 7.

State of the art

For the production of preforms, which can later be biaxially stretched into hollow plastic bodies, different materials with different properties are preferably used. These materials can be different types of PET, but also other types of material such as PEN, polycarbonates or barrier materials such as nylon, EVAL, which are joined together in the preforms in a multi-component technique so that their respective advantages come into play. Different materials, for example, have different barrier properties, thermal stability, tendency to crack due to aging (stress cracking) or can be formed by new goods or recycling material. In this respect, the different load areas during manufacture and use as well as official regulations determine the use of the respective materials. For the bottle body itself, one application limit is the washing temperature or the hot filling temperature. The second limit is the barrier properties. Thirdly, in the beverage sector, recycling material must not come into contact with the filling material at the moment. A minimum layer thickness of new goods is required between the recycling material or barrier layer and the filling material.

It is therefore desirable, depending on the part of the preform, to improve the barrier properties, the thermal properties, the stress cracking or the layer covering. For example, nylon layers are added for increased barrier properties, which reduce the permeability and thus increase the storage time of the filling material, for example by reducing the transfer of CO ₂ to the outside and of oxygen in the hollow plastic body. The thermal properties can be improved by selecting materials with a higher glass transition temperature and higher thermal stability. To reduce stress cracking, materials with a higher viscosity have to be selected. To achieve a sufficient coverage of recycling material, it should be applied evenly.

Previous multi-component processes take place e.g. in that a suitable spraying sequence of the material components is carried out in the same spraying process and the following materials are injected into the still hot soul of the preceding material, so that the materials are at the appropriate place of use. For example, WO 97/40972 proposes to press different materials through two concentrically arranged ring outlet gaps in a ring nozzle, so that there is a homogeneous structure with a suitable connection between the two materials. The problem is, however, that there is no exact arrangement of the layers and thus the barrier layer. This leads to reduced process reliability and above all to problems with molds with several mold cavities, since a uniform production from mold cavity to mold cavity is not guaranteed. A similar co-extrusion is for laminates e.g. known from US 4,808,482 A.

In order to improve the arrangement of the individual materials themselves, it has already been proposed in WO 95/00325 on which the preamble of claim 1 is based to inject individual layers into defined mold cavities. In a first Step, a preform is created, which is then placed in a second mold cavity and delimits part of this second mold cavity there, so that a second layer can be injection molded on. According to page 7, lines 12 to 22, the injection of the usually relatively thin barrier layer is avoided. This layer of barrier material is instead applied by dipping, spraying or brushing, since the person skilled in the art presumably assumes that the barrier layer cannot be produced reliably by injection molding at all.

To achieve improved properties of the preform, it is known to use parts of the preform such as e.g. prefabricate the threaded area and insert it as an insert into the mold cavity for the preform. This increases the manufacturing effort. The barrier layer is applied in a similar manner in accordance with US Pat. No. 4,646,925. First, an inner layer and a molded part made of barrier material are injection molded. This molded part is placed over the lower part of the intermediate molding forming the inner layer and connected to the inner layer. Both parts are inserted into a new mold cavity, in which case the additionally injected outer layer rolls the barrier layer over the core layer like a condom (column 2, lines 62 to column 3, line 25). There is no direct injection of the barrier layer onto the preform, so that after the injection process the barrier layer is already in its final position.

EP 0 035 035 A1 also addresses the problem of the improved arrangement of the materials, in which both a preform is produced by injection molding by injecting simultaneously from both the bottom and the threaded area. However, this document remains silent about the arrangement of barrier layers.

From the older, post-published EP 0 894 604 A1 it is known to produce a multilayered object such as a preform in successive steps by injection molding. Up to 3 layers are sprayed on top of each other (column 14, lines 21 to 25). However, only two materials or combinations of materials are preferably injected (column 13, lines 28 to 31; column 17, lines 50 to 53). The mention of barrier material and its arrangement, however, is limited to the introduction to the description, column 2, lines 9 to 15 and lines 39 to 49, where the common way of introducing the barrier layer is to jointly inject it with another material. However, the sole injection of the barrier layer is not mentioned there or in the description of the exemplary embodiments.

It can therefore be assumed that until shortly before the priority of the present application, experts assumed that a barrier layer could not be reliably produced by injection alone. It was erroneously assumed that when another material was injected onto the still warm barrier layer due to the spraying process that had just taken place, unauthorized damage to the relatively thin layer could occur, and not only in the area of the sprue but also in the area of the later wall . If the barrier layer in the floor area is still tolerable due to the material thickness still present there even in the finished bottle, it is not acceptable in the wall area.

Summary of the invention

Based on this prior art, the present invention is based on the object of achieving an exact positioning of the barrier layer in the preform.

This object is achieved by a method having the features of claim 1 and by a preform produced thereafter having the features of claim 7.

The method ensures that a guaranteed distribution of the layers is achieved in the case of fillable plastic hollow bodies produced from the preform. The required materials and thus also the barrier layer can be arranged specifically at the desired location. By injecting the different materials into defined mold cavities, almost 100% positioning is achieved. Depending on the requirements, uniform properties or properties that improve the respective weak points are created across the blown hollow body. shadow achieved. If necessary, it is consciously accepted that high flow velocities with a small flow channel diameter are necessary in order to achieve the improved properties. It turned out that, despite these high flow rates, the barrier layer does not erode. Since the individual layers are not produced together, but in succession and are also thinner than the entire preform, the cycle times for producing the entire preform can be reduced. Higher tool costs are consciously accepted. Nevertheless, the manufacturing systems are nowhere near as complex and complex to construct and operate as conventional systems, especially if they have appropriate nozzles for injecting into the hot soul.

Whereas previous applications were still more or less satisfactorily covered with the existing processes, the new process shows clear advantages, particularly in the production of plastic beer bottles. Beer is very sensitive to defects in storage and very sensitive to oxygen, so a reliable barrier layer is essential here. Any bottle that does not meet these high requirements is rejected. By injecting the barrier layer, these requirements are met.

In an embodiment according to claims 7-10, weak areas of the preforms can be replaced not only in layers but also in sections by appropriately suitable materials. For example, materials with higher glass transition temperatures or better stress-cracking behavior can be used for threads and floors.

Brief description of the figures

1 shows a side view of an injection molding machine for the production of preforms with a vertical clamping unit and two injection molding devices, FIG. 2 shows a top view of the injection molding machine according to FIG. 1,

3, 4 is an enlarged vertical section through the mold clamping unit with the mold closed and open, Fig. 5 is an enlarged, horizontal section above the parting plane of the

Shape with a view of the removal device,

6 shows an enlarged section in a view according to FIG. 3 in the region of FIG

7 shows a section through the opened mold during production,

8 shows a section through the open mold with the removal device retracted,

Fig. 9 is an illustration of FIG. 5 with four workstations within the

10, 11 is an enlarged section through the mold in the region of the cavity for producing the intermediate molding with the mold closed and opening,

Fig. 12 is an enlarged section through a shape through the cavity

Production of the preform, FIG. 13 an illustration according to FIG. 9 using a third injection molding device,

14, 15 is a schematic representation of a preform consisting of two or three layers,

16, 17 is a schematic representation of a preform with a different material in the threaded area or with a different material in the bottom.

Detailed description of preferred embodiments

The invention will now be explained in more detail by way of example with reference to the accompanying drawings. However, the exemplary embodiments are only examples which are not intended to restrict the inventive concept to a specific arrangement.

1 shows an injection molding machine for processing plastics and other plasticizable materials, which is used here for the production of multi-material, that is to say multi-material preforms 10. Such preforms can be biaxially stretched in the following process steps, for example by blow molding, to fill plastic hollow bodies that can be filled. The in particular in FIGS. 1 and 2 shown injection molding machine has two mold carriers 11, 12 (Fig. 3, 4), between see which at least one mold 13 with at least one mold cavity 14, 15 is received. A closing unit 17 is provided for the cyclical closing and opening of the mold 13 (Fig. 3,4). If necessary, several clamping units can also be provided which open and close molds 13 with the various mold cavities 14, 15. A part 13a of the mold is located on the movable mold carrier 11, while in the vertical mold clamping unit F there is a stationary mold part 13b in FIGS. 3, 4 at the bottom of the stationary mold carrier 12. In order to be able to rotate the molded part 13a with the dome inserts 25 attached to it, the molded part 13a on the movable mold carrier 11 can be rotated in bearings 33.

Injection molding devices 18, 19 (FIGS. 1, 2), 20 (FIG. 13) inject into the mold cavities 14, 15 of the mold 13, which in the exemplary embodiment are arranged horizontally in a machine base 26. The injection molding devices are supported indirectly via bars 27, 28 on the mold clamping unit. Due to the indirect support via sliding devices 41, 42, the injection molding devices can, if necessary, be moved parallel to the respective sprue channel 31, 32. A fixed arrangement without such displacement devices is also possible.

Instead of the vertically standing mold closing unit, it would also be possible to use a horizontally closing mold clamping unit F, in which case another removal device H must then be provided. In the removal device H, which can be seen in particular in FIGS. 5 and 9, a cake-sheet-like removal part 36 moves horizontally into the parting plane and removes the preforms 10 there. The movement of the removal part 36 takes place via piston-cylinder units 39 which are driven hydraulically or pneumatically could be. The removal device H is fastened to the mold clamping unit on the guide bars 35 of the mold carriers 11, 12. The removal part slides on rails 38 during its movement. A swivel motor 40 is provided on the removal device H for tilting the removal part 36 about its longitudinal axis.

The preforms are produced on this injection molding machine as follows. First, the respective desired materials are filled into the injection molding devices 18, 19 and plasticized there. The at least two materials plasticized in this way are injected into the mold cavities 14, 15, so that the preform 10 subsequently can be taken. The plasticized first material is injected from the injection molding device 18 via the sprue 31 into the first mold cavity 14. This mold cavity 14 is formed by the cavity 37, the mold cavity 14 being delimited on the inside by the dome insert 25. The mold cavity 14 thus delimits the space occupied by the first material. It therefore corresponds to the proportion of the first material in the overall shape of the preform 10. A first intermediate molding 21 is formed in this first mold cavity 14.

The intermediate molding 21 is then brought together with a second cavity 23 to form a second mold cavity 15. This bringing together can take place either by moving a molded part as in the exemplary embodiment, here the part 13a is rotated, while the second cavity 23 remains stationary. Alternatively, the intermediate molding can remain in place while the cavities e.g. be moved on a rotary table machine. The second mold cavity 15 created in this way precisely defines the space which is occupied by the second material after the injection of the second material by the injection device 19 via the sprue 32. The mold cavity 15, which is partially delimited by the intermediate molding 21, thus determines the proportion of the second material in the overall shape of the preform 10. After the plasticized second material has been injected, the preform 10 can then be e.g. can be removed by the removal device H. This process can be continued with other materials or with one of the first two materials in several cavities until a preform made of e.g. two, three, four, five or more layers are created.

The figures 5-8 show a manufacturing process for a preform 10 consisting of two materials, two work stations being provided in the mold clamping unit F. 5 shows a top view of the lower part 13b of the mold. On the right are the cavities 37 for producing the intermediate form 21, while on the left the cavities 23 for producing the preform 10 can be seen. The parts of the thread mold 34 can also be seen. The mold is closed in FIG. 6, with injection to the right in the picture in the mold cavity 14 for the production of the intermediate ring 21 with the injection molding device 18. In the same cycle klus, the second material can be injection molded on the left of the intermediate preforms previously produced (on the right in the picture) in order to produce the preform 10. After the injection cycle, an image according to FIG. 7 results when the mold is open. On the right mandrel insert 25 there is the intermediate molding 21, which was removed from the mold and was produced in the cavity 37. The preform 10 is located on the left-hand dome insert. To produce the preform 10, the molded part 13a is rotated with the mold open so that the intermediate molding 21 is in the next step in the cavity 23, where it also delimits the mold cavity 15. When the mold is closed, the thread forms 34 are brought together along their conical surfaces, so that the thread region 10a can be formed. 8, the removal part 36 is moved into the opened mold 13, so that the preforms 10 can be transferred from the dome inserts 25 to the removal part 36, for example using scraper plates. One of the injected materials can be a barrier material, although so far this has usually been arranged in the preform between other materials.

FIG. 9 differs from the illustration according to FIG. 5 in that there are now four work stations, although only two injection molding devices 18, 19 are used for injection. The dashed areas of shape 13b illustrate the hot runner blocks. Accordingly, the injection molding device 18 injects into the cavities 24, 37 and the injection molding device 19 into the cavity 23. In principle, the intermediate stations can be provided as cooling stations or, like the upper station in FIG. 9, as a transfer station to the removal part 36, but one and the same material can also be supplied to two stations in order to build up the preform 10. In this embodiment e.g. A barrier material can be injected into the mold cavity 23 via the injection molding device 19.

10-12 show the production of a preform on an enlarged scale. 10, the mold is closed and the mandrel insert located on the molded part 13a plunges into the cavity 37 to form the mold cavity 14. The intermediate molding 21 is injected there via the sprue 31, which is removed from the cavity 37 in FIG. 11 when the mold is opened with the dome insert. This intermediate blank 21 is then transferred into the cavity 23, wherein not only the shape for the threaded region 10a is established when the mold is closed, but also at the same time Mold cavity 15 is created, which is then filled with the second material. FIG. 12 clearly shows the two-layer preform, the intermediate preform 21 still being recognizable on the inside.

In the embodiment of FIG. 13, a third injection molding unit 20 is additionally provided, which in FIG. 13 covers the cavities 23 below with a third material, e.g. can load the barrier material.

14-17 show different designs of preforms 10 produced by the method. Thus, FIG. 14 shows a two-layer preform, the outer layer 10 being made from one and the same material together with the thread region. The outer layer may e.g. are recycling material, while the intermediate form is made of new goods. Basically, one of the two materials can be a barrier material.

A three-layer preform is shown in FIG. The outermost and most recently applied layer is also made of the same material as the remaining preform in the threaded region 10a. Another material, e.g. arranged a barrier material that was introduced by injection molding. The intermediate moldings 21 and 22 can be clearly seen.

The preform 10 can be built up not only in layers but also in sections. For example, FIG. 16 shows that the threaded area 10a is made of a different material, while FIG. 17 shows that the bottom 10b is made of a different material than the remaining preform 10. Since the barrier layers are usually most needed in the wall area, In this way, barrier material can be specifically injected into these areas.

The transition areas can be designed to be correspondingly positive or non-positive. Adhesion promoters can be used here. Either the contact areas must be dimensioned accordingly or, which is a further advantage of injecting into defined mold cavities, the mold cavity itself is designed in such a way that there is a positive connection between the individual materials. The materials themselves can not only be joined together, but also influence each other when spraying, so that there is an intimate connection due to intermolecular binding forces.

In principle, the use of several intermediate moldings is possible, the intermediate mold always delimiting part of the following mold cavity. This limitation does not only have to be made by the intermediate molding 22 produced last, it can also be made using a plurality of intermediate moldings if these have not been completely covered. As already indicated, it is advisable to build the preform from the inside out and from the bottom up, i.e. from the bottom to the thread area. The main reason for this is that the thread area should preferably be removed from the mold last.

With such a method, preforms can be produced in which no delamination occurs between the barrier layer and the outer layers. Due to the precise positioning, moisture can no longer penetrate from the surface to the barrier layer, so that detachment is avoided. It is also fundamentally conceivable to first produce the barrier layer and then to overmold it with another material from both sides. Another advantage of the method is that the corresponding materials can also be used appropriately from other points of view. On the one hand, as much barrier material as possible should be used since the barrier properties also increase. On the other hand, the barrier material is usually very expensive. The more recycling material is used, the cheaper it is to manufacture. Finally, rinses in the sprue area can completely remove thin layers. All of this must be taken into account when dimensioning the layers. The preform can, however, also be manufactured in such a way that it is precisely measured which layer thickness the final plastic hollow body will have. Corresponding calculations can be used to determine easily how the individual areas of the bottle deform later, so that appropriate layer thicknesses can be used in a targeted manner during the manufacture of the preform.

It goes without saying that this description can be subjected to various modifications, changes and adaptations which range from equivalents to the appended claims.

Claims

claims

1. A method for producing preforms (10) consisting of several materials, which are stretched to fillable hollow plastic bodies in subsequent steps, on an injection molding machine for processing plastics and other plasticizable materials, the injection molding machine comprising:

- Two mold carriers (11, 12), between which at least one mold (13) with at least one mold cavity (14, 15) for forming the preforms (10) is accommodated, - at least one clamping unit (17) for cyclically closing and opening the

Shape (13),

- At least two injection molding devices (18, 19, 20) for plasticizing the materials and injecting the plasticized materials into the mold cavity (14, 15), the method comprising the following steps: a) plasticizing a first material in a first injection molding device (18) and Plasticizing a second material in a second injection molding device (19), b) injecting the plasticized first material into a first mold cavity (14), which corresponds to the proportion of the first material in the overall shape of the preform (10), for molding a first intermediate molding (21 ), c) bringing the intermediate molding (21) together with a second cavity (23) to form a second molding cavity (15), which is partially delimited by the intermediate molding (21) and the proportion of the second material in the overall shape of the preform (10) corresponds to, d) injection of the plasticized second material into the second mold cavity (15), e) removal of the pref ormlings (10), characterized in that one of the injected materials forms a barrier layer.

2. The method according to claim 1, characterized in that in step d) a further intermediate molding (22) is formed, which is placed in at least one further cavity (24) to form at least a third molding cavity, which is partially delimited by the further intermediate molding (22) and corresponds to the proportion of a third material or the further partial proportion of one of the first two materials in the overall shape of the preform (10), a material lying inside the preform forming a barrier layer.

3. The method according to claim 2, characterized in that the first intermediate molding (21) partially delimits the third mold cavity.

4. The method according to any one of claims 1-3, characterized in that the preform (10) from the bottom (10b) to the threaded region (10a) is built up in sections.

5. The method according to any one of claims 1-4, characterized by the production of an adhesive bond in step d) between the materials.

6. The method according to any one of claims 1 to 5, characterized in that the mold cavity (14, 15) is designed in the transition region between the materials so that there is a positive connection.

7. preform, characterized in that it is produced by a method according to claims 1-6.

8. Preform according to claim 7, characterized in that the bottom (10b) is made of a first material and the rest of the preform (10) is made of other materials.

9. Preform according to claim 7 or 8, characterized in that the threaded area (10a) is made of a different material than the rest of the preform.

10. Preform according to one of claims 7 to 9, characterized in that the materials in the preform (10) are joined together positively or non-positively.