WO2005018912A1

WO2005018912A1 - Method for producing a preform for plastic bottles

Info

Publication number: WO2005018912A1
Application number: PCT/EP2004/007053
Authority: WO
Inventors: Robert Siegl
Original assignee: Alpla-Werke Alwin Lehner Gmbh & Co. Kg
Priority date: 2003-07-21
Filing date: 2004-06-30
Publication date: 2005-03-03

Abstract

The invention relates to a method for producing a preform for plastic bottles, especially for PET bottles. Said preform is preferably produced by an injection moulding process, provided with a friction-reducing coating, and transported to a storage container or a blowing machine. The preform is transported through a coating chamber (9, 10, 11) wherein sections of the surface thereof are provided with a friction-reducing coating, a region around the opening and the inside of the preform being excluded from the coating. The coated preform is transported to the storage container or to a blowing machine for further processing, directly after the coating, without an intermediate drying process, and forms a sliding layer in the blow cavity, that prevents the material from adhering to the blow cavity, aids the forming of the blow-moulded part, and positively influences the wall strength in the corners and at the edges.

Description

Process for producing a preform for plastic bottles

The invention relates to a method for producing a preform for plastic bottles, in particular for PET bottles, according to the preamble of patent claim 1.

When manufacturing plastic bottles, for example PET bottles, there are two basic manufacturing processes. In a first method, the plastic bottles are inflated immediately after the production of a preform from the still warm preform according to the cavity of a blow mold. The second method provides that the production of the preforms and the production of the plastic bottles from the preforms take place completely separately from one another in terms of space and time. In this second method, the preform is first produced in an injection molding process. After cooling, the preform is temporarily stored for later use. For this purpose, the preforms usually manufactured in ϊvfehrf ach tools are filled into containers, for example, which enable easy transport and storage. In the later actual manufacturing process of the plastic bottles, the preformers are reheated and the plastic bottles are inflated or stretch-blown therefrom.

The plastic used to manufacture such plastic bottles, polyethylene terephthalate or PET, has relatively poor sliding properties. This makes it difficult to transport the preforms produced in the injection molding process, which is usually carried out via conveyor belts and slide rails. In the actual blow molding machine, the preforms are separated via conveyor belts and slide rails and transported to the blow molding stations. During transport and especially when storing the preforms, they come to rest against each other. Due to the poor surface properties, the preforms almost stick together. When filling into the transport and storage container, the available volume becomes very low due to the poor sliding properties of the preforms badly used. In addition, damage, scratches, adhesion spots or the like can occur in the surfaces of the preforms during transport and when filling the preforms into the container. These surface defects are then visible on the fully inflated plastic bottles. These surface defects do not usually affect the mechanical properties of the bottle walls; however, they are often optically unacceptable. The poor sliding properties also mean that during the blowing process the plastic does not slide optimally over the surface of the blow mold, and corners and edges that are difficult to access either cannot be formed or the wall thickness at these points is too small.

It is already known from the prior art to provide the preforms with a friction-reducing coating. The preforms are coated in an immersion bath. Then the preforms are placed around the coating. to dry. After drying the coating, the Preformlinge be WEI ¹ * ter transported and stored. " During dip coating, a relatively large amount of coating material is applied to the preform. Part of the coating also drips off "<". Therefore, the preforms have to remain in the coating station for a relatively long time, if one does not want to risk contaminating the transport routes. The drying of the coating also takes a certain time and leads to an increase in the manufacturing costs for the preforms.

A method is also known in which the preforms are provided with a coating shortly before or only after being placed in the storage container. For this purpose, the coating is poured or sprayed over the preforms from a viewing device arranged above the transport plane of the preforms. The coating then dries inside the storage container. This form of coating leads to relatively uneven results. Shaded areas of the preforms are, for example, not coated at all or only inadequately.

In the known methods it can happen that the coating also gets into the area of the opening of the preforms and even into the preforms. This is particularly undesirable in the case of bottles for foodstuffs since the coating can impair the taste of the contents. The fact that the coating can also reach areas in which it can come into contact with the subsequent filling material also severely limits the selection of the coatings. In particular, it must be ensured that the coatings cannot cause any health problems.

The object of the present invention is therefore to remedy the disadvantages of the prior art methods described. A method for producing preforms for plastic bottles, in particular PET bottles, is to be modified in such a way that the transportation and filling of the preforms are facilitated and damage to the surfaces of the preforms can be avoided. It should be ensured that no coating materials are deposited in areas that can come into contact with the filling material in the later plastic bottle. The new process is intended to enable the production of bottle geometries: «whose edges and corners have so far either not been able to be formed at all or only with an insufficient wall thickness.

The solution to these problems consists in a process for the production of preforms for plastic bottles, which has the process steps specified in the characterizing section of patent claim 1. Further developments and / or advantageous embodiments of the invention are the subject of the dependent claims.

The invention proposes that the preform, which is preferably produced in an injection molding process, is transported through a coating chamber in which its surface is provided with a friction-reducing coating in some areas prior to its further processing or storage. An area around the opening and the interior of the preform is left out of the coating. The coated preform is transported without an intermediate drying process, immediately after coating to the storage container or for further processing to a blow molding machine. The risk of damaging the surface of preforms is reduced by the friction-reducing coating. The coating ensures that the preforms can slide against each other. This has advantages when separating the preforms and when transporting them on belts or in rail systems. Because of their improved sliding properties, the preforms are also finished in a more orderly state in the storage container. This prevents oversized voids between the preforms and the volume of the storage container is better utilized. The entire manufacturing process for the preforms is simplified and shortened in time by transporting the preforms further immediately after coating. A drying step can be dispensed with in the method according to the invention. The area around the opening of the preform is left out during the coating. This prevents areas • from being coated that come into contact with the filling material in the plastic bottle produced later. The selection of the coating materials that can be used increases, which can result in cost advantages. Due to the improved sliding properties of the preform, the pre-bubble produced in the subsequent stretch blow molding process can slide better into the edges and corners of the blow mold and also reaches areas that were difficult or impossible to reach with the previous methods. As a result, more complex bottle geometries can now also be produced.

The arrangement of the coating chamber is advantageously chosen such that the preform can be transported through the coating chamber in an upright state with the opening oriented upwards. The preforms usually have an approximately cylindrical shape and are closed on one side. Following a circumferential flange, a short collar section protrudes, which is equipped with the opening of the preform. The longer section of the preform extends below the circumferential flange. When aligning and transporting the preforms, they align with the opening upwards due to gravity. In the coating chamber, only the section below the flange is covered by the coating. The flange forms a barrier to that Coating material. This ensures in a simple manner that the collar section and the interior of the preform do not come into contact with the coating material.

The coating can be applied, for example, by dipping, painting or else using an electrostatic process. However, it is particularly preferred to coat the preform in a spray. The spray can be concentrated in a very narrow space. It also allows very small amounts of coating to be applied to the surface of the preform. The part of the spray that is not applied is suctioned off and recycled. This largely prevents contamination of the environment or of the transport means for the preforms with the coating material.

The coating applied to the preforms in the processes known from the prior art takes on a solid physical state over time. This usually requires a separate drying step. In the method according to the invention, the preform is provided with a coating which has a liquid aggregate state even after the preforming has cooled to ambient temperature. Liquid films as coatings have the advantage that they are better distributed on the surface and lead to a more homogeneous coating. The liquid coating of the preforms is automatically pressed against the blow mold during the blowing process. Part of the coating remains in the blow mold, where it forms a lubricating film that also wets those areas of the bottle that were not optimally wetted on the preform.

Because of the liquid physical state of the coating, it can also flow at a later time into areas that are less well coated or into areas that are subject to greater mechanical stress in the short term. The distribution process is a dynamic process that is retained over time. This is particularly advantageous when the preforms are stored for a long time. The good sliding properties of the liquid films are retained over a longer period of time. The layer thickness of the coating can be chosen to be very small, particularly in the case of liquid films. It is advantageously about 2 μm to 100 μm. The friction-reducing coating materials used are advantageously essentially materials from the group comprising oils, esters, polyols, silicone oils and mixtures of these and their emulsions. The materials mentioned are known for their high level of friction reduction and can be applied very easily to the surface of the preform in the desired thickness in a spray coating process.

For reasons of higher throughput, several preforms are advantageously coated at the same time. The size of the spray can be easily adapted to the requirements. ^~ -

The method according to the invention for the production of preforms for plastic bottles, in particular PET bottles, can be combined very simply with the known blowing or blowing stretching methods, in which a finished plastic bottle is produced from a preform produced according to the invention. The blow or blow stretching process can directly follow the production of the preform or it can be spatially and / or temporally separated from the production of the preform.

A preform according to the invention for the production of plastic bottles, in particular PET bottles, has an essentially cylindrical shape that is closed on one side. The preform has a collar section which adjoins a circumferential flange and is provided with an opening. The body section of the preform extending below the flange is provided with a friction-reducing coating which has a liquid physical state at ambient temperature. Further advantages of the invention result from the following description of an exemplary embodiment variant of the invention with reference to the schematic drawings. In a representation that is not to scale,

Fig. 1 shows an embodiment of a pref ormHngs; and

Fig. 2 shows a coating head of a coating chamber for preforms.

A preform shown in FIG. 1 is provided with the reference number 1 as a whole. It has a cylindrical shape that roughly resembles the shape of a test tube. A circumferential flange 4 divides the preform 1 into a collar section 5 and into a cylindrical body section 3 with a closed bottom 3. The collar section 5 is provided with an external thread and has an opening 8 which leads into the interior of the preform 1. The preform 1 is manufactured in an injection molding process and usually consists of polyethylene terephthalate PET. It is a preliminary stage for a PET bottle, which is manufactured from the preform 1 in a blow or stretch blow molding process. Despite their relatively smooth surfaces 6, the manufactured preforms 1 have poor sliding properties. This makes it more difficult to separate the preforms 1, which adhere almost to one another when touched. The poor sliding properties also prove to be disadvantageous for yours

Transport via conveyor belts or hanging in slide rails to a storage container or in a blow molding machine. When the preforms 1 are stored in a storage container, large cavities are formed due to their poor sliding properties, which lead to inadequate filling of the storage container. The almost adhesive properties of the surfaces 6 of the preforms 1 can also result in damage which becomes apparent in the later PET bottle and is often optically unacceptable. The poor sliding properties also prove to be disadvantageous for the stretch blow molding process, since they make it difficult or block the bubble to slide into corners and edges that are difficult to reach.

The invention remedies these disadvantages of the preforms of the prior art in that the surface 6 of the body section 2 with a low-friction Coating is provided. For this purpose, the preforms 1 are transported through a coating chamber while they are still hot in the injection molding process. As an essential component, the coating chamber u comprises a coating head, which is provided with the reference number 10 in FIG. The coating head 10 has a coating channel 9 which is U-shaped in cross section and through which the preforms 1 are transported in a hanging state. In this case, the preforms 1 are supported, for example, on the underside 7 of the radially circumferential flange 4 on two rails spaced apart from one another. It can also be provided that the preforms 1 slide with the underside 7 of the flange 4 directly along the upper sides 11 of the coating head 10 delimiting the U-shaped coating channel 9.

A spray of the low-friction coating material is generated in the U-shaped coating channel 9. For this purpose, 9 spray nozzles can be provided in the walls of the U-shaped coating channel, for example. The spray is restricted to the U-shaped coating channel 9 of the coating head 10. A small proportion of the spray mist is deposited on the upper sides 11 that delimit the recess and promotes the sliding properties of the preforms 1 resting on the underside 7 of the flange 4 collar section 5 running above the radial circumferential flange 4 does not come into contact with the coating material. The circumferential flange 4 forms a barrier for the spray mist and prevents it from being able to get into the interior of the preform 1 through the opening 8. The preform hangings 1 are practically coated in the viewing chamber during their transport. An interruption in transport or a deposit of the preforms 1 for a drying process or the like is canceled. The size of the coating grains and the coating head 10 is selected such that several preforms 1 can be coated at the same time.

For the friction-reducing coating, materials are advantageously used which, even after the preform 1 has cooled, form a liquid aggregate. have condition. Suitable materials are, for example, oils, esters, polyols, SiHcon oils, mixtures of these and their emulsions

The coating of the preforms has a thickness of approximately 2 μm to approximately 100 μm. The friction-reducing coating reduces the risk of damage to the surface of the preforms 1. The coating of the surface 6 of the body section 2 ensures that the preforms 1 slide against one another. This has advantages when separating the preforms 1 and when transporting them on belts or in rail systems. Because of their improved sliding properties, the preforms 1 also settle into the storage container in a more orderly state. This prevents oversized cavities between the preforms 1, and the volume of the storage container is better utilized. The entire manufacturing process for the preforms 1 is simplified and shortened in time by the preforms 1 being transported on immediately after coating.

Claims

claims

1. A process for the production of a preform for plastic bottles, in particular for PET bottles, in which the preform is preferably produced in an injection molding process, provided with a friction-reducing coating and transported to a storage container or to a blow molding machine, characterized in that the preform is transported through a coating chamber in which its surface is partially provided with the low-friction coating, an area around the opening and the interior of the preform being left out of the coating, and the coated preform immediately after coating to the storage container or to Further processing is transported to a blow molding machine.

2. The method according to claim 1, characterized in that the preform is transported in the upright state, with the opening oriented upwards through the coating chamber.

3. The method according to claim 1 or 2, characterized in that the preform is provided with a coating which has a liquid physical state after cooling the preform to ambient temperature.

4. The method according to any one of the preceding claims, characterized in that the preform is coated in a spray.

5. The method according to any one of the preceding claims, characterized in that the coating of the preform has a layer thickness of about 2 microns to about 100 microns.

6. The method according to any one of the preceding claims, characterized in that the preform is essentially coated with a material from the group comprising oils, esters, polyols, SiHcon oils, mixtures of these and their emulsions.

7. The method according to any one of the preceding claims, that a plurality of preforms are coated individually or simultaneously.

8. A method for producing a plastic bottle, in particular a PET bottle, in a blow or blow stretching process from a preform, which is manufactured according to one of the preceding claims.

9. Preform for the production of plastic bottles, in particular PET bottles, with an essentially cylindrical shape that is closed on one side and a collar section that adjoins a circumferential flange and that is provided with an opening, characterized in that the section extending below the flange Body portion of the preform is provided with a friction-reducing coating, which has a liquid physical state at ambient temperature.