Technology of barrier of high level against the action of UV-Vis light

Applications of barrier of all kinds have gained increasing importance in the PET industry. To date have been imposed three different solutions to achieve a barrier effect satisfactory in PET bottles.

One of these three applications of proven efficiency is technology multilayer, also called coinyección. The manufacturing process begins with the injection of the base, the PET material. Then introduces the barrier material through the still hot soul, which builds a central barrier layer. This manufacturing process requires heavy investments and highly skilled staff, as well as expensive quality controls.

Other solutions to obtain a barrier effect is based on the manufacture of preforms monolayer with an addition of TIO2 in the premium PET subject. The manufacture of these preforms can be processed in standard systems without much effort, so the operator of the machine does not need large additional knowledge. The handicap of this application is located in a high percentage of addition of TIO2 and a weight limit of ~ 28 grams for a barrier to acceptable visible light.

The third method is called method of coating. In this case, the (usually in the market today) finished containers either preforms them (in rare cases) are coated with plasma inside or outside. This method of manufacture, however, entails expensive production processes.

However, there are other solutions to achieve a barrier effect in PET preform. An example is the technology of sobremoldeo, which, unfortunately, has been driven into a corner in the last few years. The process begins with the injection of the inner layer. Below are applied additional layers through several passes in parallel.

Within the sector, the process of sobremoldeo for the manufacture of preforms is difficult and costly. Then a little explain the reasons for this bad reputation: this technology is to be effective, all layers must have a very small wall thickness. The problem is that, because of pressure differences, there is a risk that the core deviates from the central axis, so the distribution of thickness is not guaranteed. In addition, after the first cycle of the body of her preform has to go into another cavity to inject the next layer, something which until now was through movement of rotation.

Netstal Maschinen has managed to put into practice the process of sobremoldeo in a profitable, reliable and reproducible way.

Thanks to the innovations introduced in the mould and the machine, it is now possible to produce preforms with a thickness of less than 1.2 mm wall after the first cycle. As the raw material has been included in the developments, it has able to eliminate the risk of delamination. Addition, the new system provides for lateral row of nuclei displacement during the change of cavity, which enabled us to eliminate costly Rotary movements.

These advances open the door to a number of barrier and other applications. In the future you could combine materials for filling hot, but it is also possible to use Oriented Polypropylen (OPP) with materials barrier. As additional feature to create various chromatic effects, you can use materials that adhere to the layer base. Also, now the outer layer could be recycled, there is no contact with the contents of the package.

This article explains the use of the sobremoldeo in the manufacture of preforms for dairy products with the necessary anti-luminic barrier. The product in question, called PRElactia (Preform for light measurement by carbontitanium addition), was already presented at the K 2007 in Düsseldorf fair.

In order to reflect the UV light, PET containers should be white and also include some amount of dioxide of titanium (TIO2). This compound is generally added at a concentration close to 12%. The addition of a grey or black ink would increase the absorption of UV light and would use less amount of TIO2 (a very abrasive and rather expensive additive), with what the pieces that lead the molten material would suffer less wear. However, it seems clear that bottles of milk in grey or black would not be welcomed in the market of dairy products. The sobremoldeo system provides the perfect solution to this problem and, therefore, is a technology that should be seriously considered.

How is the procedure of manufacturing through sobremoldeo? Below we explain broadly all the steps of the process of sobremoldeo. In this case a moulding machine was used by injection of the SynErgy, model 2 c 2400 - 2150/900 series with two groups of injection. Novapet detected the technical and economic potential of this procedure quickly and decisively promoted the development in regards to raw materials. This resulted in a material which, on the one hand, presents fluid characteristics that make it very suitable for preforms with thin layers. This raw material, called the Dairy2 complex, was created specifically for the manufacture of preforms PRElactia and it is a ready to use, material added to that during the polymerization is only 5.5% of TIO2.

It has also created a liquid ink color anthracite for the inner layer, while the outer layer is still white. Thanks to this ink, a grey surface metallic in the interior of the bottle, the key to a perfect absorption of light is obtained after the process of soplado-estirado.

The mold created especially by the Molmasa company for the process of sobremoldeo has a very efficient design and does not work with the aforementioned rotation movements. The transport of the nuclei is based on the principle of displacement, so that all the plate moves with a corresponding to a row of cavities career. Thus, the kernel comes first into the cavity of the first layer, and then in the second cycle, to the adjacent cavity where the second layer is applied. When the first part concludes, the mold opens and the ranks of nuclei move parallel to the adjacent row with cavities of larger.

The body of her it preforms, which in the first cycle is injected without neck and with a thickness of less than 1.2 mm wall, presents at the moment three small holes in the background. These holes are due to the support of the core, which during the phase of filling the cavity serves to prevent diversion of the kernel. This solution, whose patent is in the pipeline, will ensure a uniform wall in the first layer thickness.

Once the rows of kernels have transferred to the second cycle, the nuclei which have just become free are entered again into the cavity to the first layer. The bodies of preforms them, which are still gray and they are now in the second phase, is coated with a layer of glossy white of ~ 2 mm of thickness. Now is the time the neck and the thread form and fill the three holes of the Fund mentioned above.

Also the system of valves, covering alternatively with molten material the two outer rows has been enhanced (only used in the second cycles). Finally opens the mold and they expel preform them completed. The result is preform perfect two layers without variations in the thickness of wall.

To realize such innovative ideas also need interested buyers, so that the application was submitted to the PDG Plastiques company, headquartered in France. This company, which already is responsible for manufacture dairy products to neighboring LSDH containers, quickly relied on the success of this system. PDG has many blow molding machines, so that it could quickly turn into bottles preform them produced PRElactia and then undergo a verification. Six months later, after evaluating under more stringent conditions 1,000 full of UHT milk bottles, it was shown its superiority to the monolayer bottles (not found even a single bottle with corrupted milk). The first stone of a fruitful collaboration was placed, so that at the end of 2007 PDG commissioned the first Netstal machine for the manufacture of preforms PRElactia.

To hold the final product with the hands, and despite the grey inner layer, immediately drew attention to the bright white color of the bottle. In this case, unlike what happens with the multilayer method, not appreciated the translucency of the dark layer. If you cut the bottle, it is clear the perfect adaptation of the materials together. Especially surprising light measurements, which confirm an absorption and reflection of 99.99% with a light of up to 700 nm.

The use of the sobremoldeo to obtain an anti-luminic barrier is a solution clearly winning. In addition to providing a technically perfect product, is revealed as clearly superior to other procedures.

In this respect, it's worth mentioning the following advantages:

-Optimal anti-luminic barrier with a minimal amount of TIO2.

-Bottle of bright white (like when using mixtures).

-Maximum stability of process in the manufacture of preforms.

On the other hand, this method also convinces in economic terms:

-The weight of the bottle of milk of 1 litre has been reduced to 22 grams which represents 30%, without prejudice to its properties and with a ratio of 30-50% less of additives as the TIO2. As a result, the wear of the plastificador group has been reduced significantly.

-No longer a film obturator is needed because the neck is formed by moulding by injection.

-Preforms PRElactia costs about 25% less.

With this innovation, in addition, Netstal and its partners have achieved pave the way for the PET for use with dairy products. Currently there is no solution to match.