Manufacturing process for heat set multilayer containers The technical field of the invention is defined by DE-A 32 01 986 and DE-A 37 37 291. Both documents concern multilayer containers which originate from a stretch-blowing process in a mould, in which process a preform of smaller size is expanded by pressure in a mould to achieve a bottle shaped container. For example Figure 5 and Figure 4 of DE 32 01 986 (Toyo Boseki) gives an impression of possible shapes of a preform and a container. A multilayer preform is also shown in a sectional view in Figure 2 of DE 37 37 291 (Owens Illinois), the blown container from this preform is in full scale shown in Figure 1 of said document. The multilayer structure of Figure 2 of said document comprises a central layer 13 of EVAL, having two tie-layers (Klebeschichten), one on each side, which strengthens the cohesion and reduces delamination trend, which is inherent, if combining a EVAL-layer 13 of this prior art directly to a PET outer layer (items 11 and 12 on each side of the central layer 13 in said document).

It is an object of the invention to improve a method for manufacturing of multilayer containers by giving the containers an improved gas barrier property (reduce the permeability of gases into the container or out of the container), without increasing the weight percentage of a barrier layer in the multilayer preform and the multilayer container and-of course-without increasing cost for manufacture of said container.

According to the invention, the process for manufacturing said multilayer container comprises the providing of a preform, which is stretch-blown. The preform comprises a substantially Nylon containing layer as an inner layer and substantially polyester (PET) layers as outer layers;"inner and outer"being regarded with respect to a wall segment of the preform. In this respect, claim 1 is to be understood as having at least one inner layer comprising said Nylon and at least one layer on each side (outer layers) of said inner Nylon layer. This includes the

understanding of preforms with a three-layer structure, with a four-layer structure and a five-layer structure and it does not necessarily imply that the Nylon layer is the center layer in the wall of the preform. Preferably, the claim comprises a three-layer or a five-layer structure. In a three layer one layer being Nylon and two outer layers substantially comprising PET, in which understanding the two outer layers are the outside layer and the inside layer of the preform, later to define the outside surface and the inside surface of the blown bottle. The amount of Nylon is kept below 10 of weight of the preform and the stretch-blowing according to the invention is provided by leaving the stretch-blown preform after the stretch-blow process at a hot inner surface of the mould to thereby heat set said multilayer container, which is after a cooling step taken out of the mould.

The amount of Nylon, which is a main factor in cost, but also a main factor in providing good gas barrier property and reduced permeability of gases (e. g. oxygen or CO2) is kept at a low percentage, preferably between 4% and 6% of weight of the preform (claim 7). The heat setting occurs at a temperature of above 100°C, preferably between 130°C and 170°C (claim 8) for a stay time, which is sufficient to achieve increased barrier property and improved cohesion of the layer structure, which is no detrimental delamination trend. Visual crystallizing is substantially avoided, to keep the bottle clear. All this without increasing the cost due to a minimum amount of Nylon in the PET multilayer preform. The stay time can be below lsec or above 1,5sec, but depends on the machine speed for manufacturing the bottles (claim 6) and the temperature for the heat setting period.

The inventive concept of manufacturing a bottle with low permeability rate avoids an increased percentage of Nylon, which would yield a reduction of permeability, but also would increase the delamination trend of the different layers.

The heat setting of the PET multilayer container with a Nylon inside layer as barrier layer reduces the permeability factor between about 30k to 40% as compared to a PET multilayer bottle containing the same Nylon layer in the same weight percentage, but having no heat setting phase during manufacture.

The percentage of used Nylon is reduced, achieving the same barrier effect, or if using the same percentage as in prior art, the barrier effect can according to the invention be increased without any detrimental consequences on the bottle cohesion and on the delamination trend.

No tie layers as still necessary in DE-A 37 37 291 are according to the invention necessary for maintaining proper cohesion of the inventive layer structure.

The process can be a one-step blowing process (claim 1) or a two-step blowing process (claim 5). In the two-step process, a first blowing is performed to shape an intermediate container and this intermediate container receives a heat treatment to shrink and is then blown in a second blowing process to arrive at the finally shaped container, which receives heat setting in the second mould. The second mould of the second process is to be understood as the first and single mould of the one-step process of claim 1. Heat setting in the two-step process is further improved by the intermediate heat treating to shrink the intermediate container from its intermediate size and thus in the process the heat setting following the second blow step can be shortened.

According to the invention, a thermally stable multilayer container is provided (claim 10), which has an improved cohesion of layers (less delamination trend between layers) and an increased barrier property (less permeability for e. g. oxygen or CO2). The container is made according to the process of claim 1.

It has a mouth portion which generally has a thread for attaching a cap. It has a body portion and a base portion on which the bottle is standing. Between the body portion and the

mouth portion, there is an intermediate portion which generally is slanted to the inside to connect the broader body to the narrow mouth portion. In the body portion, the heat treated (heat set) multilayer structure provides a good barrier property with low permeability for gases, although small amount of barrier material and small layer thickness of the barrier layer is used, still having good layer cohesion.

Examples of the invention will be given in a non-limiting way.

Figures will not be necessary to understand the invention, since the detailled description of prior art in the introductory part will give the man skilled in the art precise knowledge on preforms, on blowing processes and on multilayer structures of preform and blown bottles. Such prior art will therefore be not described in detail.

The process according to an example will have in a one step blow process the method steps of providing a preform of mainly PET outside and an inner Nylon layer for barrier purposes. This preform is introduced into a mould, which cavity has the shape of the final bottle. Pressure is introduced into the preform, to expand it and bring it into contact with the inside surface of the mould, which is heated to a temperature of 130°C. After contacting the wall, the stretch blown preform will remain for a certain amount of time, called"stay time"at the mould wall to provide heat-setting of the multi layer structure, mainly in the wall portion of the bottle. After heat-setting, the bottle is quickly cooled down by an air stream to avoid deformation. After cooling down it is taken out of the mould, by opening the mould and the process achieves a finished mulilayer bottle with heat set characteristic.

In a second process, which is another example of the invention, a two-step blow process is used. In this two-step process the preform with the multilayer structure and the Nylon barrier layer is introduced into a first mould and stretch blown to yield an intermediate container, which is larger than the final container. The wall of the first preform is cold, in the example it has about 20°C. In the mould or after taking the intermediate container out of the mould a heat process effects shrinkage of the intermediate container, preferably in a recovery oven at 200°C, which is substantially above the temperature which is used for the heat setting in the before mentioned one-step blow process. After bottle shrinkage in said recovery oven at 200°C the shrunk intermediate container is again blown in a second blow step in a second mould. In the second mould the final

container is obtained and heat setting is provided at the inner surface of the second mould, by heating it to about 130°C before the PET is stretchblown against the wall. Since the bottle shrinkage in the recovery oven has already obtained some heat setting to the intermediate container, the time at the inside surface of the bottle can be reduced with respect to the one- step process, it can be one or two seconds, depending on the speed of the machine, which manufactures the bottles. After heat-setting in the second preform, the bottle is quickly cooled down by an air stream to avoid deformation and then taken out of the mould.

The temperature given above as an example can be extended to a full range of temperatres, depending on the structure of multilayer and depending on the speed of the machine. It should be at such temperature, which avoids substantial visual crystalizing and such it should be below 170°C, preferably below 140°C. Although crystalizing at a small scale in the PET can not be avoided at all, visual crystalizing, which results in a whitening can be avoided during heat setting. The speed of the machine and the temperature of the mould for heat setting are adjusted to avoid such visual crystalizing in the container. The amount of Nylon is in a range between 4k and about 6%. Between the Nylon barrier layer and the PET outer layers there is no intermediate tie-layer, which provides adhesion or cohesion of the different material layers. In other words the Nylon-layer and the PET-layer are directly attached to each other and still provide good cohesion.

Examples are given below.

In a first example a five layer preform according a standard process of prior art was stretch-blown. The standard preform had three layers of PET (two outside and one in the middle) and had two layers of Nylon MXD6 between the PET layers. Such preform was biaxially stretch-blown in a cold mould (20°C inner surface temperature) to produce a multilayer bottle. The speed of the machine was adjusted to 1200 bottles per hour and the examples

were taken in a range of Nylon between 4% and 6% of weight of the preform. The measurement results of this bottle, manufactured according to prior art, will be given after explaining the two inventive examples with heat setting after stretch-blowing.

Inventive example 2 has a five layer preform according to example 1 and was blown in a one-step stretch-blowing process.

The mould (the only mould) was set to a temperature of 160°C at the inside surface. The cycle time (speed) of the machine was reduced, it was operated at a speed of 500 bottles per hour, as compared to the aforementioned speed of the machine, to significantly increase the residual time in the (only) mould. At the end of the first blowing step the bottles were quickly cooled down, as mentioned before.

Example 3 is the second inventive example. It is similar to the aforementioned example 2, with the exception that a two step stretch-blowing process was used. In a first stretch-blowing step the intermediate container was created and stretch-blown onto the inside of a first mould, which had a temperature of about 20°C. Bottle shrinkage was obtained in a recovery oven with a temperature of about 200°C. The final blow in a second blow mould took place according to example 2 as given above, but with a temperature of only 130°C at the inside surface of the second mould. Cooling was performed after heat setting time with the"stay time"of about 60k less than in the second example, since the speed of the machine was increased to 800 bottles per hour, with respect to said 500 bottles per hour in example 2.

The speed given above for the manufacturing machine gives an indication of the"stay time", which performs heat setting in the blown container.

The results of the three examples are compared below. The tests were taken for measurement of C02-loss in 30 days and a judgement of quality of the interlayer cohesion.

First example according to prior art: Nylon with 4% of weight with respect to the preform and the parameters given in the general description of this example achieved a C02-loss after 30 days of 3,6%. The inner layer cohesion was judged good. The same parameters as given in the general description of this example were used for variation, in which the weight percentage of Nylon was 6%. In this variation the C02-loss was 3,1% after 30 days.

The interlayer cohesion was just acceptable, but not as good, as with 4% of Nylon.

With heat setting after stretch blowing in the inventive examples (second and third example) improved measurement results were obtained. In the second example 4% of Nylon was used, a loss of only 2,5% CO2 after 30 days and a good layer cohesion was obtained. If 6% of weight for Nylon was used, the loss of CO2 after 30 days was only 2,2%, but the layer cohesion was slightly reduced, but was still acceptable. The maximum temperature of the inside of the only mould in the one step process was 160°C.

In the two step process according to the third example the heat setting took place with 130°C at the inside of the second mould.

The 4% Nylon example achieved 2,1% of C02-loss after 30 days.

The 6% example with respect to Nylon obtained 1,9% of C02-loss after 30 days. The interlayer cohesion was judged good with the 4% Nylon example and was judged acceptable in the 6% Nylon weight.