EP1028838A1

EP1028838A1 - Method for producing multi-layered preforms

Info

Publication number: EP1028838A1
Application number: EP98951147A
Authority: EP
Inventors: Otto Hofstetter; Luis Fernandez
Original assignee: Hofstetter Otto AG
Current assignee: Hofstetter Otto AG
Priority date: 1997-11-04
Filing date: 1998-11-04
Publication date: 2000-08-23
Also published as: CH692573A5; WO1999022926A1; JP2001521837A; CA2303766A1

Abstract

The inventive method for producing multilayered preforms makes it possible to create extremely thin layers, especially a thin surface layer and/or a thin barrier layer. These thin layers are at the most 35 % and 5 % respectively of the overall volume. They are produced using a multi-component injection moulding form tool which is operated in such a way that the plastic component provided for creating the thin layers is conveyed through the innermost jet chamber. Said plastic component has a slightly higher temperature and is therefore slightly viscous. Preforms produced in this way are characterised by a surface layer representing less than 35 vol. % or a barrier layer representing approx. 5 vol. %.

Description

Process for the production of multilayer preforms

The present invention relates to a method

Preamble of claim 1, as well as preforms which are produced by this method.

In particular, the present invention relates to a method which is suitable for producing three-layer preforms with an increased recyclate content and enables preforms to be produced with an improved oxygen diffusion barrier behavior.

Multi-layer preforms have been known for a long time and are used inter alia. in the beverage industry, which uses these preforms to manufacture plastic bottles on site into which the respective drinks are filled. These beverage bottles are preferably made of PET, although they are also made of other thermoplastic

Materials such as PEN, polyamide, polycarbonate, etc. could be made. Such production plants today produce 48 three-layer preforms per work step by sequential injection with an annual capacity of approx. 50 million pieces. In the production of these preforms, new material is first injected into the mold, then cleaned and processed recyclate is introduced and new material is injected again in a third production step in order to free the injector from recycled material. Care is taken to ensure that the tolerance in the metering of the individual injection quantities can be kept as small as possible. This dosing precision is a prerequisite for the production of beverage bottles with a high proportion of recycled material, since the recycled material is not directly filled with the bottles

Beverages may come into contact. This is determined by legal regulations. When blow molding the preforms into PET bottles, it is therefore possible to ensure that the inner layer of recyclate is covered everywhere by a Layer of new material remains covered, which places high demands on the construction of the injection molding tools as well as on the production systems of the preforms. Unfortunately, the injection molding machines known today do not have the high dosage precision required for the production of PET preforms with a high proportion of recyclate. As confirmed by EP 0 '655' 306, the PET bottles used today generally only have a recyclate content of at most 25% for these reasons.

However, for reasons of cost and cost stability, the beverage industry generally strives for a higher proportion of recyclate. In particular, reusable bottles made of PET with 35% recycled material would come very close to the cost of the life cycle assessment for one-way bottles ("break-even point"). An increased proportion of recyclate would therefore also increase the economy of the reusable PET bottles. This cost-effectiveness essentially depends on the strongly fluctuating price for the new PET granulate. If this granulate is cheaper than the recycled material, single-layer preforms made from 100% new material can be manufactured more cheaply; however, if the price rises above this "break-even-point" threshold, three-layer preforms with 35% and more recycled material would be cheaper. A high proportion of recyclate also leads to better price stability, since the large price fluctuations of the

New materials at Vorfor only have a partial impact with recycled PET. This makes it easier to calculate the costs for manufacturers and bottlers.

It has therefore already been proposed (Modern

Plastics International, February 1997, page 29), to use a co-extrusion blow-for tool for the production of PET preforms and to connect product parts manufactured independently of one another. So that Hessen can produce PET bottles with up to 80% recyclate. However, such a procedure requires additional ones Tools and thus proves to be complex and costly.

The beverage industry strives to create legally compliant moldings with a high proportion of recycled material without complex technical measures.

The resulting technical task is therefore to be able to produce preforms with extremely thin layers of new material and without complex constructions in order to be able to increase the proportion of recycled material in these preforms.

In particular, three-layer preforms should be created in a simple manner, which at least one layer as thin as possible, respectively. have a recyclate content of more than 35% by volume, in particular 35 to 65% by volume.

This object is achieved according to claim 1 by a surprisingly simple method for operating a multi-component injection molding tool and in particular in that the supply of components A and B is reversed in contrast to the conventional arrangements and the molding tool is operated in such a way that in a first cycle Step the locking needle is brought into a position in which both the inner nozzle chamber and the outer nozzle chamber are open, the conveyance of the B component by the outer nozzle chamber being stopped and only the A component by the inner nozzle chamber in the mold cavity is injected.

For the production of preforms with a high recyclate content, component A (new material) to be injected as the first component is passed through the inner nozzle chamber to form a thin skin layer, and component B (recycled material) to be injected as a further component klat) passed over the outer nozzle chamber for the formation of a filling layer. When such a three-layer preform is sprayed, in a first cycle step the valve pin is brought into a position I in which both the outer nozzle chamber with the B component and the inner nozzle chamber with the A component are open. At this needle position, the delivery of the B component is interrupted and the A component is injected into the mold cavity. In a second cycle step, the valve pin is brought into a position II, in which the inner nozzle chamber is closed and the outer nozzle chamber is open. At this needle position, the delivery of the A component is interrupted and the B component is injected into the mold cavity. For the next cycle step, the so-called holding phase, in which the B component shrinking due to cooling is supplemented, the position of the closure needle remains unchanged. At the end of the holding phase, the valve pin is brought into its closed position III, in which both the inner and the outer nozzle chamber are closed.

It turns out to be unexpected that the first shot with the A component is free of undesired B material in the next spraying cycle. This surprising effect can be explained by swapping the feed channels. In particular, the special guidance of the individual components, i.e. Guiding the A component through the slightly warmer inner nozzle chamber, a slight reduction in the viscosity of component A (new material) achieved.

Compared to the preforms produced with conventional injection molding methods, preforms with a thinner skin layer (A component) can be formed with the method according to the invention, and the relative proportion of filler material can be increased by refilling the mold cavity with material of the B component during the shark pressure phase. The method according to the invention also allows preforms to be produced with an extremely thin barrier layer (for example made of nylon or the like). These barrier layers have the task of minimizing the oxygen permeability of the molded articles (bottles) and are relatively expensive. In order to produce a preform according to the invention with a thin barrier layer, the supply channels are in turn exchanged contrary to the conventional arrangements and the barrier material to be injected to form the thin barrier layer is passed through the innermost nozzle chamber and the plastic forming the skin layer is passed through an outer nozzle chamber. When such a preform is injected, the shut-off needle is again brought into a position I in a first cycle step, in which both the outer and the inner nozzle chamber are open, and in a first process step the component guided through the outer nozzle chamber is inserted into the Injection molded cavity, while at the same time the delivery of the barrier material passed through the inner nozzle chamber is interrupted. For the next cycle step, the shut-off needle remains in this position I and the barrier material conveyed through the inner nozzle chamber is simultaneous with that through the outer resp. middle filling chamber led filling material introduced into the mold cavity. In this injection phase, both components (filling and barrier material) are conveyed simultaneously, i.e. in the form of hoses lying one inside the other, whereby care is taken to ensure that the proportion of barrier material conveyed remains extremely low, for example, 5% of the total amount of material injected. The filling material and the material forming the skin layer can be identical. However, inexpensive recyclate is preferably used as the filling material. This is achieved in a known and simple manner by controlling the supply of the plasticized plastics. In a third cycle step, the conveyance of the barrier material is stopped again and the filled mold is cavity filled with the amount of filler material required to compensate for the shrinkage. By advancing the valve pin into position III, both nozzle chambers are closed and the injection cycle is ended. In the preforms produced in this way, the thin barrier layer lies in the central wall area of the preform. It shows that preforms resp. Moldings with such a layer arrangement have the required barrier behavior against the oxygen diffusing into these containers.

Further embodiments of the method according to the invention are characterized by the features of the subclaims. The preforms produced by the operating method according to the invention have a recyclate content of more than 35% by volume and possibly a barrier layer content of less than 5% by volume.

The invention will be described in more detail below with the aid of an exemplary embodiment. It shows:

Figure 1: a cross section through a hot runner nozzle and its needle valve;

Figures 2a to 2d: the positions and control of the needle valve assembly;

Figure 3: longitudinal section through a preform produced in a conventional manner;

Figure 4: Longitudinal section through a preform produced according to the invention with a high recyclate content.

Figure 5: Longitudinal section through a preform produced according to the invention with a barrier layer.

Figure 1 shows a section of the structure of a co-injection mold with a hot runner nozzle 34 and a needle valve 36 for two different components A and B. The material plasticized in the extruders reaches the hot runner distributor block 15 through separate channels, is branched therein and fed to the individual hot runner nozzles 34. Each of these hot runner nozzles 34 has a removable nozzle holder 33 and is constructed from a plurality of nozzle inserts lying one inside the other, between which an inner nozzle chamber 3 and at least one outer nozzle chamber 5 are formed, in which the various plastic components are conveyed to the nozzle tip. Heating elements hold both the hot runner

Distribution block 15 as well as the nozzle holder 33 and thus the hot runner nozzle 34 at the required temperature. A pneumatically controlled needle valve 36 controls a movable needle 37 in the nozzle tip area of the hot runner nozzle 34 for releasing or. to shut off the individual components A resp. B and / or C.

In the conventional mode of operation, the closure needle 37 is brought into four positions during a spraying cycle in order to fill a cavity, for example, in three layers. In a first position, the needle 37 is only retracted to such an extent that the cavity has a first component, in particular with original PET or. Raw material that can be filled. In a second position, the needle 37 is withdrawn further, so that the second component, for example recycled PET, can also be pressed into the mold cavity through the inner nozzle chamber 3 before the needle 37 returns to the first position for the holding phase and then completely afterwards is pushed in front to close the nozzle 34. For each injection cycle, the shut-off needle must therefore be brought into four predetermined positions: a) opening the outer nozzle chamber 5, b) opening the inner nozzle chamber 3, c) closing the inner nozzle chamber 3, d) closing the outer nozzle chamber 3.

As shown in FIG. 1, the needle lock 36 is in a recess acting as a pneumatic cylinder in FIG the top plate 13 logs and consists of a first piston 38 guiding the needle 37, over which a second piston 39 is movably inserted. A hermetically sealing cylinder cover 40 closes off this recess in a pressure-tight manner. Suitably arranged pressure lines 41, 43 and 44 allow the individual pistons and thus the needle 37 to be brought into the desired position. The individual pressure lines each have a pressure required for the movement of the needle. The outer pressure line 44 is usually pressurized with 20 bar, the middle pressure line 43 with 10 bar and the inner pressure line 41 with 5 bar. The positioning of the individual pistons 38 and 39 shown in FIG. 1 is generated when the individual pressure lines are under pressure, as indicated above. If the needle 37 is to be retracted in a conventional manner into a first position to release the first plastic component, only the pressure in the middle pressure line 43 needs to be reduced or released. The first piston 38 is thus moved by the pressure of the inner pressure line 41 as far as the stop of the second piston 39. In order to bring the needle 37 into a second position, which opens the supply of the second plastic component through the inner nozzle chamber, the pressure of the outer pressure line 44 is reduced or reduced in an analogous manner. canceled. This leads to the two pistons 38, 39 moving together up to the cylinder cover 40. In order to stop the material supply again, the outer pressure line 44 is initially pressurized again and the two pistons 38, 39 are thus moved together in the closing direction. Only when the middle pressure line 43 is again under pressure can the outer nozzle chamber be interrupted again by the movement of the first piston 38. Pressure-proof seals 51, 52 are provided on the individual for the pneumatic needle lock arrangement 36 to work properly

Pistons and seals 53 are provided on the cylinder cover 40. There is also an axial seal 55 in the nozzle holder 33 provided, which prevents a pressure equalization between the piston arrangement 38, 39 and the nozzle arrangement 33, 34 and thereby the pressurized vapors of the individual hot plastic components of the nozzle needle 37 penetrate through the nozzle holder 33, get on the piston walls or on knock down the nozzle needle and thus impair the mobility of the individual components of the needle valve 36. To block. This is achieved in a known manner with a gas-tight axial seal 55 made of temperature-resistant plastic.

In order to use such a multi-component injection molding tool, multi-layer preforms with an increased recyclate content or. To be able to produce with extremely thin layers, according to the invention, the supply of components A and B is exchanged contrary to the conventional arrangements and operated in such a way that component A with the material to be introduced only in a thin layer (new material or barrier material) in the inner nozzle chamber 3 of the hot - Channel nozzle 34 is promoted, while component B with the recyclate to be introduced in the outer resp. middle nozzle chamber 5 of the hot runner nozzle 34 is promoted. If a molding with a thin outer skin is to be produced from new material and a thin barrier layer, the new material is conveyed in the outermost of three nozzle chambers and the barrier layer material in the innermost nozzle chamber, in such a way that the barrier layer material can be injected simultaneously with the filling material from the middle nozzle chamber . In the production of moldings from a single carrier material and with a thin barrier layer, a first portion of the carrier material is injected into the mold cavity through the outer of two nozzle chambers in a first step and the carrier material and the barrier material are simultaneously processed in a second step. ie in the form of hoses lying one inside the other, injected into the mold cavity. The needle 37 will brought into positions, as will be explained in more detail below with reference to FIGS. 2a to 2d.

FIGS. 2a to 2d show partial sections of the hot runner nozzle 34 with the associated needle valve 36. For the introduction of the original component A conveyed in the inner nozzle chamber 3, the needle 37 is withdrawn to the extent that this inner nozzle chamber 3 is released, as shown in FIG. 2a . By interrupting the conveyance of component B and conveying component A, the required amount of original material A can be introduced into the mold cavity. Since this original material A in the interior of the hot runner nozzle 34 has a lower viscosity than the filling material B in the outer nozzle chamber 5, it is sufficient to introduce only a small proportion of original material A into the mold cavity. This needle position I can be achieved in that the pressure in the pressure lines 44 and 43, above the second piston 39 and. between the first piston 38 and the second piston 39 is reduced to, for example, 0 bar, while the pressure in the pressure line 41 below the first piston 38 is built up to, for example, 6 bar. With the aid of this pressure distribution, both pistons are in their highest possible position and the needle 37 can thereby release the inner nozzle chamber 3.

In a second cycle step shown in FIG. 2b, the needle 37 is brought into a position II, in which the inner nozzle chamber 3 is closed, but the outer nozzle chamber 5 remains open. This is achieved by maintaining the pressure of, for example, 6 bar in the pressure line 41 and increasing the pressure in the pressure line 44 above the second piston 39 to somewhat more, for example 10 bar. In this position, component B (filling material) is passed through the outer nozzle chamber 5 into the

Mold cavity promoted. This material has a higher viscosity than that from the inner nozzle chamber 3 and therefore displaces the previously injected component A in a thin film onto the outer surfaces of the mold cavity without tearing this film. This difference in viscosity allows preforms with a thin outer skin to be produced. In a third cycle step, the filled mold cavity is kept under pressure for a time, ie during the so-called holding phase with the filler material B, in order to compensate for the loss of volume of the material which occurs due to shrinkage processes.

Figure 2c shows the hot runner nozzle 34 and its needle valve 36 in a position III, in which both the inner nozzle chamber 3 and the outer nozzle chamber 5 are closed. This is achieved in that the pressure in the pressure line 41 below the first piston 38 is reduced to, for example, 0 bar and at the same time the pressure in the pressure line 43 between the two pistons is increased to, for example, 6 bar, while the pressure in the pressure line 44 above the second piston 39 is maintained at 10 bar, for example.

Conventionally and with non-interchanged delivery channels for components A and B, the injection cycle is started with a needle position as shown in FIG. 2b in order to introduce component A (new material) into the mold cavity. The closure needle 37 is then brought into position I in order to fill up the mold cavity with component B (filler material). For the holding phase, the needle is brought back into position II in accordance with FIG. 2d in order to supplement the material which has shrunk due to the cooling with the A component and thus to ensure that no B component (recycled material) is used as the first material for the next injection cycle Cavity. To complete the injection cycle, the needle is moved to position III as shown in FIG. 2c. This makes it clear that with the present operating method, the injection cycle is ended by refilling the shrinked filler material with the same component, while conventionally the shrinked material volume is replaced with the component that is to be injected as the first component in the next injection cycle. With the present method, therefore, an increasing amount of B component (recycled material) can be introduced into the mold cavity and surprisingly it turns out that because of the lower viscosity of the A component guided in the inner nozzle channel and due to the interruption of the B component delivery at the beginning of the next Injection cycle only A component gets into the mold cavity and thus the strict requirements of the beverage industry for blow molded moldings with an intact outer or Inner skin can be met.

The longitudinal sections shown in FIGS. 3 and 4 make the difference between the method according to the invention and the conventional method clear. 3 shows one

Longitudinal section through a preform produced in a conventional manner with a threaded part 61 and a container part 62, the sprue pin 63 of which lies in the bottom part 64. From this longitudinal section it can also be seen that both the inner skin 65 and the outer skin 66 (with the exception of the sprue tap) are not penetrated by the filling material B at any point. The deformations in the threaded part 61 of the preform prove to be particularly critical points. This figure also shows how the filling of the filling material volume that shrank during the holding phase with new material A has an effect. In particular, this new material additionally introduced into the bottom part 64 substantially reduces the percentage of recycled material.

In contrast, FIG. 4 shows a longitudinal section through a preform produced according to the invention. This differs essentially in the structure of the floor partly 64, which only has three layers, namely an inner skin, filler material and an outer skin. There is also a significant difference in the thickness of the individual layers. Conventional preforms with a weight of 48.0 g and a total wall thickness of 4.37 mm, which are suitable for 1.5 liter bottles, have an outer skin with a thickness of 1.3 to 1.5 mm. This results in a volume fraction for the internal filling material B of 25 to 33% by volume. In the preform produced according to the invention according to FIG. 4 with the same weight of 48.0 g, the outer material 65, 66 has a thickness of 1.2 to 0.6 mm and the percentage of filler material can be reduced to 37 to 63% by volume through the special manufacturing process. increase.

By swapping the feed channels, preforms with a barrier layer (for example made of nylon, EVH or the like) can also be produced which have an improved barrier effect against oxygen. This will be explained in more detail with reference to FIGS. 2a to 2c. According to the invention, in the production of preforms with a barrier layer, the needle 37 can be brought into position II in a first cycle step (FIG. 2b) in order to fill the cavity with the material used for the skin layer. In a second cycle step, the shut-off needle 37 is brought into a position I (FIG. 2a), and the barrier material (for example nylon) conveyed through the inner nozzle chamber 3 is injected into the mold cavity together with the component guided through the outer nozzle chamber 5. As a result, the barrier material comes to rest in the inner wall area of the preform and enables the molding to be provided with an extremely thin barrier layer of approximately 5% by volume or less.

In a preferred embodiment, the barrier material is passed through the innermost nozzle chamber and sees this Method in a first cycle step to bring the needle 37 into a position I in which both the inner and the outer nozzle chamber are open, but only the material passed through the outer nozzle chamber 5 is conveyed into the mold cavity while the delivery of the material passed through the inner nozzle chamber 3 is stopped. For the second cycle step, the needle 37 remains in this position I and at the same time material is conveyed through the outer nozzle chamber 5 and barrier material through the inner nozzle chamber 3, so that the proportion of the barrier material accounts for approximately 5% or less of the total injected material. To supplement the material shrinkage during the holding phase, the shut-off needle remains in position I and the conveyance of those conveyed through the inner nozzle chamber 3 is increased

Blocking material set. After filling, the needle is moved to position III (Figure 2c) to close the inner and outer nozzle chamber. The preforms produced in this way have a thin barrier layer which lies in the central wall area of the preform.

The advantages of the method according to the invention and of the preforms produced with this method are immediately apparent to the person skilled in the art. In particular, four consecutive needle positions are required in the conventional method per injection cycle, while only two or three needle positions are required with the operating method according to the invention. This simplifies the control of the valve gate. In addition, according to the invention, the shrunk B component is combined with the same

Replaces material and can thus increase the percentage of this component (recyclate), respectively. the percentage of the component guided in the innermost nozzle channel can be reduced. No new and expensive machines or tools need to be purchased to carry out the method according to the invention. Further developments, in particular for influencing the viscosity of the individual components and for controlling the spraying cycle, are within the range of expert knowledge. It goes without saying that not only PET material can be processed with this method, but also all plastics used in injection molding technology, in particular also nylon.

Claims

claims

1. Method for operating a multi-component injection molding tool for producing multi-layer moldings, which multi-component injection molding tool has a hot runner nozzle with a needle valve (36) for releasing or. Shutting off an inner nozzle chamber (3) and at least one outer nozzle chamber (5) of the nozzle body (34), and the needle valve (36) has a movable needle (37) and, arranged movably in a cylinder space, at least one first piston ( 38) and a second piston (39), which pistons (38, 39) can be selectively displaced by a pressure medium, such that the needle (37) coupled to these pistons (38, 39) is in corresponding release or. Barrier positions (I, II, III, IV) can be brought, characterized in that the plastic mass to be injected (new or barrier material) to form a thin layer, in particular a skin or barrier layer (component A or C), through the innermost nozzle chamber ( 3), and the plastic mass to be injected as the filling component (recyclate B or virgin material A) is passed through the at least one outer nozzle chamber (5).

2. The method according to claim 1, characterized in that in a first cycle step, the closure needle (37) is brought into a position (I) in which the innermost nozzle chamber (3) with the A or C component and the at least an outer nozzle chamber (5) with the B or A component is open, only the A or C component being conveyed through the innermost nozzle chamber (3) in this first cycle step and the other components being conveyed through the at least one an outer nozzle chamber (5) is stopped.

3. The method according to any one of claims 1 or 2, characterized in that for the production of a three-layer preform with a B component component (recyclate) of more than 35%, in a second cycle step, the B component by the at least one Outer nozzle chamber (5) is promoted and in a third cycle step, the material that has shrunk during cooling is supplemented by the B component, and to complete the injection cycle, the sealing needle (37) is brought into a position III, in which both the innermost nozzle chamber (3) and the at least one outer nozzle chamber (5) are closed.

4. The method according to claim 3, characterized in that during this second cycle step, the closure needle (37) is brought into a position II, in which the innermost nozzle chamber (3) is blocked and the at least one outer nozzle chamber (5) is open .

5. The method according to any one of claims 1 or 2, characterized in that in order to produce a three- or five-layer preform with a barrier layer made of C material, in a second cycle step both the C component through the innermost nozzle chamber (3) also the B component by the at least one outer one

Nozzle chamber (5) is conveyed, in particular with a C component proportion of approximately 5% or less of the total volume, and that, during this third cycle step, the conveyance of the C component is interrupted in such a way that only material of the B component is conveyed from the outer nozzle chamber (5) into the mold cavity, and in a fourth cycle step the material that has shrunk during cooling is replaced by this B component, and to complete the injection cycle, the closure needle (37) into a position III is brought, in which both the innermost nozzle chamber (3) and the at least one outer nozzle chamber (5) are closed.

6. The method according to claim 5, characterized in that during the second and third cycle step

Locking needle (37) is left in position I.

7. The method according to any one of claims 1 or 2, characterized in that for the production of a five-layer preform with an outer (66) and inner skin (65) made of A material, a barrier layer made of C material, in particular nylon, and a filling material B, in particular a recycled material, the closing needle (37) is brought into a position I in a first cycle step, in which the innermost nozzle chamber (3) with the C-

Component and both the outer nozzle chamber with the A component and the intermediate nozzle chamber with the B component (recycled material) are open, whereby in this first cycle step the delivery of the B and C components is stopped and only the A- Component is promoted by the outer nozzle chamber, that the promotion of the A component is stopped in a second cycle step and the B and C components simultaneously, ie tubular, conveyed and in a third cycle step

Promotion of the C component is stopped and the plastic mass which has shrunk on cooling is supplemented by the B component.

8. The method according to claim 7, characterized in that during the second cycle step, a C-component portion of about 5 vol .-% and a B-component portion of more than 30% of the total volume is promoted.

9. Preform made according to the procedure

Claim 3, characterized in that this one B component content (recyclate) of more than 35 vol .-%.

10. Preform, produced by the method according to claim 5, characterized in that the barrier layer consisting of the C component lies in the central wall area of the preform.

11. Preform, produced by the method according to claim 7, characterized in that this one

Has a barrier layer of C material of less than approx. 5% by volume and a proportion of B material (recycled material) of more than 35% by volume.

12. Preform, produced according to the method

Claim 7, characterized in that the A component and the B component consist of the same material.