The invention concerns a container for packaging products, which has a wall made of a thermoplastic material that contains at least one constituent that can be released at least from certain regions of the container into the interior of the container.
The invention also concerns an installation for producing preforms from a thermoplastic material, which has an injection-molding machine with cavities for the preforms. The invention also concerns a method for producing containers from a thermoplastic material, in which the plastic is produced in a reactor and then shaped into preforms by an injection-molding machine, and in which the preforms are formed into containers by blow molding, and then at least a portion of the inner surface of the containers is coated by a plasma coating process.
Containers of this type can consist, for example, of PET and can be used to package beverages or other liquids. Especially in the case of the packaging of beverages or other foods, there are strict requirements on the purity of the materials that are used. These requirements conflict with the likewise desired use of recycled materials for reasons of environmental protection, since materials of this type often contain impurities.
A well-known compromise solution between these different requirements is first to produce multilayer preforms by injection molding and then to form them into containers by blow molding. The multiple layers are formed in such a way that at least one inner layer made of a recycled material is covered by outer layers made of fresh material, so that the product to be packaged does not come into contact with the recycled material. However, the production of suitable preforms requires the use of expensive special injection-molding machines, and this results in a high product price.
Another problem with respect to the selection of materials for the containers is that the plastics that are used generally are not gastight. This allows especially oxygen to penetrate the container and carbon dioxide to escape from carbonated beverages, for example, soft drinks, mineral water, or beer. To improve the barrier properties of the containers, multilayer containers are also widely used, in which a special barrier layer made of a barrier material that is different from the primary material is applied. Here again, the production of the corresponding preforms is expensive. In addition, the combination of different materials leads to recycling problems, because the different materials often cannot be easily separated.
Another method for improving the barrier properties consists in plasma coating the container material. This coating can be applied on both the interior and exterior surface. Especially coating with silicon oxides has proven effective.
PCT-WO 95/22413 describes a plasma chamber for coating the inner surface of PET bottles. The bottles to be coated are raised into a plasma chamber by a movable base and connected at their mouths to an adapter. The inside of the bottles can be evacuated through the adapter. A hollow lance for supplying process gas is also inserted into the inside of the bottles through the adapter. Microwaves are used to ignite the plasma.
The same publication also describes the arrangement of a plurality of plasma chambers on a rotating wheel. This helps achieve a high production rate of bottles per unit time.
EP-OS 10 10 773 describes a feeding device for evacuating the inside of a bottle and supplying it with process gas. PCT-WO 01/31680 describes a plasma chamber into which the bottles are introduced by a movable lid that has first been connected with the mouths of the bottles.
PCT-WO 00/58631 also already describes the arrangement of plasma stations on a rotating wheel and the assignment of groups of vacuum pumps and plasma stations for an arrangement of this type to help provide favorable evacuation of the chambers and the interiors of the bottles. It also mentions the coating of several containers in a common plasma station or a common cavity.
Another system for coating the inside surfaces of bottles is described in PCT-WO 99/17334. This document describes especially an arrangement of a microwave generator above the plasma chamber and means for evacuating the plasma chamber and feeding it operating agents through the floor of the plasma chamber.
In most of the previously known plasma coating methods, silicon oxide coatings, which have the general chemical formula SiOx and are produced on the surface of the containers by the plasma, are used to improve the barrier properties of the thermoplastic material. In addition, the barrier layers produced in this way can contain carbon, hydrogen, and nitrogen components. Barrier layers of this type prevent oxygen from penetrating the bottled liquids and prevent the escape of carbon dioxide from carbonated liquids.
Plasma coating is often performed on containers that were produced by blow molding preforms that have first been heated to a suitable temperature. Preforms of this type typically consist of a thermoplastic material, for example, PET (polyethylene terephthalate). After suitable thermal conditioning, the preforms are formed into containers by the action of blowing pressure. These containers are used, for example, as bottles for bottling liquids. In accordance with DE-OS 100 33 412, blowing stations are arranged on a rotating blowing wheel. The blowing wheel rotates continuously, and the blowing stations, which are arranged on the blowing wheel and rotate with it, receive the preforms to be shaped and deliver the finished containers. Moreover, blowing wheels that move in a timed cycle are also already known.
Until now, no one has succeeded in producing containers and in designing equipment for producing containers and preforms to achieve an optimum combination with respect to fulfilling the partly conflicting requirements on economical production of the containers, a high level of environmental friendliness, and a high level of protection of the packaged products from both penetration of unwanted substances and the escape of product constituents.
Therefore, the objective of the invention is to provide a container of the aforementioned type which simultaneously fulfills economic, ecological, and qualitative requirements.
In accordance with the invention, this objective is achieved with a container that is made of a thermoplastic material that contains the constituent that can be released in a concentration that is above the concentration that is allowable for the packaging of the products, such that at least a portion of the inner surface of the wall of the container is coated in such a way that a release rate of the constituent in the direction of the interior of the container is realized which, at most, is equal to a release rate that would be realized with the use of a thermoplastic material which has a concentration of the constituent that can be released that is near the allowable limit but which does not have an inner coating.
A further objective of the present invention is to design an installation of the aforementioned type in such a way that economical production is possible.
In accordance with the invention, this objective is achieved by coupling the injection-molding machine with a reactor for producing the thermoplastic material.
A further objective of the present invention is to develop a method of the aforementioned type that allows economical, ecological, and qualitatively superior production of containers.
In accordance with the invention, this objective is achieved by connecting the reactor directly to the injection-molding machine and feeding the plastic produced by the reactor from the reactor to the injection-molding machine in the form of a melt.
The container of the invention makes it possible to use a relatively inexpensive material and nevertheless to prevent or at least greatly reduce the unallowable release of undesired substances from the container material into a product contained inside the container. The container of the invention especially allows the use of recycled material without the need for the expensive production of multilayer preforms. Furthermore, it is possible to produce the thermoplastic material used for the production of the containers by modified methods or with the use of catalysts other than those that are presently used, since the formation of undesired byproducts or residual catalyst substances is now of only secondary importance.
The installation of the invention and the method of the invention make it possible to avoid high-cost and high-energy intermediate steps in the production of the containers. The direct coupling of the reactor and the injection-molding machine makes it possible to avoid a cooling operation for the material produced in the reactor, granulation of the material, and subsequent reheating and plastication of the granulated material.
Environmentally friendly container production is supported by producing the thermoplastic material at least partly from recycled material.
To make it possible to produce the containers inexpensively, it is proposed that the plastic have an acetaldehyde content of at least 10 ppm. It is also possible for the acetaldehyde content to be at least 50 ppm, and typically 60-100 ppm.
Inexpensive production of the containers is also helped if the plastic contains a catalyst as one of its constituents.
Qualitatively superior container production in high quantities is assisted by the application of the surface coating as a plasma coating.
In the case of food or beverage packaging, it has been found to be especially advantageous if the surface coating is applied as at least one layer of a silicon oxide of general formula SiOx.
A typical application consists in shaping the container as a bottle.
In regard to material selection, it is advantageous for the plastic to consist at least partly of PET.
To promote optimum product properties, even when the product is subjected to loads, it is proposed that the surface coating be applied to the surface with the use of an adhesion promoter.
If the wall consists of a single-layer material, this also contributes to inexpensive production of the containers.
To adapt continuous material production to discontinuous material consumption, it is proposed that at least one temporary storage tank for molten thermoplastic material be installed between the reactor and the injection-molding machine.
Simple mechanical control of the filling and emptying of the temporary storage tank is realized by the reciprocating motion of a piston.
A large field of application is opened by designing the reactor as a device for the production of PET.
To further improve the properties of the material with respect to gas permeation and to promote the binding of volatile material constituents within the material, it is proposed that the reactor have a mixing device for supplying a scavenger.
To make it possible to adapt to different production capacities of the reactor and of injection-molding machines coupled with the reactor, it is proposed that at least two injection-molding machines be coupled with the reactor.
Production flexibility can be increased by coupling injection-molding machines that are different from one another to the reactor.
The number of possible applications can be increased by connecting a mixing device for admixing plasticated recycled material at a coupling between the reactor and the injection-molding machine.
Embodiments of the invention are schematically illustrated in the drawings.
The individual functional components involved in the production of containers are described below.
The view in
The workpieces to be treated (5) are fed to the plasma module (1) in the region of an input (6) and further conveyed by an isolating wheel (7) to a transfer wheel (8), which is equipped with positionable support arms (9). The support arms (9) are mounted in such a way that they can be swiveled relative to a base (10) of the transfer wheel (8), so that the spacing of the workpieces (5) relative to one another can be changed. In this way, the workpieces (5) are transferred from the transfer wheel (8) to an input wheel (11) with increased spacing of the workpieces (5) relative to one another compared to the isolating wheel (7). The input wheel (11) transfers the workpieces (5) to be treated to the plasma wheel (2). After the treatment has been carried out, the treated workpieces (5) are removed from the area of the plasma wheel (2) by an output wheel (12) and transferred to the area of an output line (13).
In the embodiment shown in
Rotary distributors (20, 21), by which the plasma stations (3) are supplied with operating agents and power, are located in the center of the plasma wheel (2). Especially ring conduits (22) can be used for distribution of the operating agents.
The workpieces (5) to be treated are shown below the cylindrical chamber walls (18). For the sake of simplicity, lower parts of the plasma chambers (17) are not shown in the drawing.
The microwave generator (19) is located in the upper region of the plasma station (3). The microwave generator (19) is connected by a guide (25) and an adapter (26) to a coupling duct (27), which opens into the plasma chamber (19). Basically, the microwave generator (19) can be installed directly in the vicinity of the chamber lid (31) or coupled with the chamber lid (31) at a predetermined distance from the chamber lid (31) via a spacing element and thus installed in a larger surrounding area of the chamber lid (31). The adapter (26) acts as a transition element, and the coupling duct (27) is designed as a coaxial conductor. A quartz glass window is installed in the area of the opening of the coupling duct (27) into the chamber lid (31). The guide (25) is designed as a waveguide.
The workpiece (5) is positioned in the vicinity of a sealing element (28), which is located in the vicinity of the chamber floor (29). The chamber floor (29) is formed as part of a chamber base (30). To facilitate adjustment, it is possible to mount the chamber base (30) in the area of the guide rods (23). An alternative is to mount the chamber base (30) directly on the station frame (16). In an arrangement of this type, it is also possible, for example, to design the guide rods (23) in two parts in the vertical direction.
In the position shown in
In the illustrated embodiment, the coupling duct (27) has a cylindrical shape and is arranged essentially coaxially with the chamber wall (18).
A typical treatment operation is explained below for the example of a coating operation. The workpiece (5) is inserted into the plasma station (3) with the sleeve-like chamber wall (18) in its raised position. After completion of the insertion operation, the chamber wall (18) is lowered into its sealed position, and then both the cavity (4) and the interior of the workpiece (5) are evacuated, simultaneously at first.
After sufficient evacuation of the interior of the cavity (4), the lance (36) is inserted into the interior of the workpiece (5), and partitioning of the interior of the workpiece (5) from the interior of the cavity (4) is carried out by moving the sealing element (28). It is also possible already to start moving the lance (36) into the workpiece (5) synchronously with the start of evacuation of the interior of the cavity. The pressure in the interior of the workpiece (5) is then further reduced. Moreover, it is also possible to carry out the positioning movement of the lance (36) at least partly at the same time as the positioning of the chamber wall (18). After a sufficiently low negative pressure has been achieved, process gas is introduced into the interior of the workpiece (5), and the plasma is ignited by means of the microwave generator (19).
In particular, it is intended that the plasma be used to deposit both an adhesion promoter and the actual barrier layer, which consists of silicon oxides, on the inner surfaces of the workpiece (5).
The adhesion promoter can be applied, for example, as the first step of a two-step process before the application of the barrier layer in the second step. However, it is also possible, in a continuous process, to produce at least a portion of the barrier layer that faces the workpiece (5) as a gradient layer even as at least a portion of the adhesion promoter is simultaneously being applied. A gradient layer of this type can be produced in a simple way during the duration of an already ignited plasma by varying the composition of the process gas. This sort of change in the composition of the process gas can be achieved abruptly by changing the valve controls or continuously by changing the mixing proportions of components of the process gas.
A gradient layer is typically formed in such a way that the portion of the gradient layer that faces the workpiece (5) contains at least a preponderance of the adhesion promoter, while the portion of the gradient layer that faces away from the workpiece (5) contains at least a preponderance of the barrier material. In at least a portion of the gradient layer, a transition of the given components occurs continuously according to a predeterminable gradient variation. Similarly, it is possible to produce both the adhesion promoter layer and the barrier layer itself as gradient layers.
The interior of the plasma chamber (17) and the interior of the workpiece (5) are initially evacuated together to a pressure level of about 20 mbars to 50 mbars. The pressure in the interior of the workpiece (5) is then further reduced to about 0.1 mbar. During the treatment process, a negative pressure of about 0.3 mbar is maintained.
After a coating operation has been completed, the lance (36) is withdrawn from the interior of the workpiece (5), and the plasma chamber (17) and the interior of the workpiece (5) are ventilated. After ambient pressure has been reached inside the cavity (4), the chamber wall (18) is raised again to allow the coated workpiece (5) to be removed and a new workpiece (5) to be inserted for coating. To allow lateral positioning of the workpiece (5), the sealing element (28) is moved at least partly back into the chamber base (30).
The chamber wall (18), the sealing element (28), and/or the lance (36) can be positioned by means of various types of drive equipment. In principle, it is possible to use pneumatic drives and/or electric drives, especially in the form of linear drives.
As
To allow the introduction of compressed air, a connecting piston (50) is installed below the transport mandrel (49). It supplies compressed air to the preform (41) and at the same time creates a seal relative to the transport mandrel (49). However, in a modified design, it is also possible to used fixed compressed air lines.
The preform (41) is stretched with a stretching rod 51 (see
In the embodiment shown in
After the mold halves (45, 46), which are arranged in the vicinity of supports (59, 60), have been closed, the supports (59, 60) are locked relative to each other by a locking device (80).
As shown in
To be able to shape a preform (41) into a container (42) in such a way that the container (42) has material properties that guarantee a long storage life of foods, especially beverages, packaged in the containers (42), specific process steps must be followed in the heating and orientation of the preforms (41). Furthermore, advantageous effects can be realized by following specific dimensioning specifications.
Various plastics can be used as the thermoplastic material. For example, it is possible to use PET, PEN, or PP.
The preform (41) is expanded during the orientation process by supplying compressed air. In a preblowing phase, gas, for example, compressed air, is supplied at a low pressure level, and in a subsequent main blowing phase, gas is supplied at a higher pressure level. During the preblowing phase, compressed air at a pressure of 10-25 bars is typically used, and during the main blowing phase, compressed air is supplied at a pressure of 25-40 bars.
To allow the closest possible arrangement of the transfer wheel (69) and the input wheel (75) relative to each other, the illustrated arrangement is found to be especially effective, since three guide pulleys (74, 76) are positioned in the area of the corresponding expansion of the heating line (64), specifically, the smaller guide pulleys (76) in the area of the transition to the linear paths of the heating line (64) and the large guide pulley (74) in the immediate region of transfer to the transfer wheel (69) and to the input wheel (75). As an alternative to the use of chain-like conveying elements (73), it is also possible, for example, to use a rotating heating wheel.
After the blowing of the containers (42) has been completed, the containers (42) are removed from the area of the blowing stations (43) by an extraction wheel (77) and conveyed by the transfer wheel (68) and an output wheel (78) to the output line (72).
In the modified heating line shown in
A stationary mold part (96) of an injection-molding mold (87) with cavities (88) is arranged in the area of a mounting plate (86). The cavities (88) are connected with the inside of the sleeve (84) by a melt channel (89). A connecting channel (90) of a holding pressure unit (91) also opens into the melt channel (89). The feeding of the plasticated plastic to the cavities (88) is coordinated by control devices (not shown).
A movable mounting plate (93), on which a movable mold part (97) of the injection-molding mold (87) is mounted, can be positioned along sidepieces. When the mounting plates (86, 93) are moved towards each other, the two tool parts (96, 97) of the injection-molding mold (87) together bound the cavities (88).
The movable mounting plate (93) is positioned by means of an adjusting mechanism (94), which is operated by a locking cylinder. The adjusting mechanism (94) can be designed with the use of toggle mechanisms.
In accordance with the embodiment in
In particular, the drawing in
In the embodiment shown in
The mouth section (102) can be provided, for example, with an external thread (112), which makes it possible to close the finished container (42) with a screw cap. However, it is also possible to provide the mouth section (102) with an external bead to create a working surface for a crown cap. Furthermore, there are many other conceivable designs that allow a closure device to be placed on the container.
The drawing in
In the shoulder region (106), the thickness of a preform wall (114) can increase from the neck region (103) towards the wall region (105). In the direction of the longitudinal axis (108) of the preform, the preform (41) has a preform length (115). The mouth region (102) and the neck ring (104) extend in the direction of the longitudinal axis (108) of the preform with a common mouth length (116). The neck region (103) has a neck length (117) in the direction of the longitudinal axis (108) of the preform. The neck region (103) of the preform (41) preferably has a constant wall thickness along its length.
The wall region (105) of the preform (41) has a wall thickness (118), and the base region (107) has a base thickness (119). The dimensions of the preform (41) can be further specified on the basis of its inside diameter (120) and its outside diameter (121), which are measured in the approximately cylindrical wall region (105).
In the bottle-shaped container (42) shown in
The container (42) has a container mouth length (131) and a container neck length (132), and at least the container mouth length (131) is generally the same as the mouth length (116) of the preform (41).
To carry out a so-called two-step container production process, the preforms (41) produced by the injection-molding machine (81) are first sent to an intermediate storage location (135), in which they cool to ambient temperature. The preforms (41) are then further conveyed from the intermediate storage location (135) to a blow-molding machine (136), which is equipped with the blowing stations (43) described earlier. To carry out a so-called one-step process, either the intermediate storage location (135) is completely eliminated, or the intermediate storage is relatively brief without cooling of the preforms (41) to ambient temperature.
After the preforms (41) have been shaped into containers (42), the containers (42) are transferred from the blow-molding machine (136) to the plasma module to receive the required surface coating.
The constituents that can be released into the interior of the container can also arise, for example, by decomposition of the material of the container by aging or by external influences. In general, the use of the inner coating of the container also makes it possible to use materials that would be attacked or destroyed by the action of the contents of the container. Finally, the use of the inner coating makes it possible to use materials with high concentrations of harmful substances, which otherwise could not be used for packaging the intended products. A preferred use is the packaging of liquid foods, with which the use of uncoated container materials would lead to contamination of the foods or deformation of the containers.
Number | Date | Country | Kind |
---|---|---|---|
102 42 086.6 | Sep 2002 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/IB03/04003 | 8/19/2003 | WO | 11/7/2005 |