Energy efficiency in the production of PET foil thermoformed

Since its introduction, by gneuss kunstsofftechnik about a year and a half ago, the multiple system of rotation (MRS) of the extruder has been tested in many lines for the production of PET sheet for thermoforming of packaging. In contrast to conventional systems, the innovative system MRS enables processing of the scales highly contaminated PET bottle post consumption directly to the plate, without the previous steps of the crystallization and drying. This system need only go through the stage of filtration, and does not require an additional melt pump. Vacuum system extracts, not only the moisture, but all substances and pollutants in an efficient manner. Its simple and compact design reduces the complexity of the line and provides the maximum availability with minimum maintenance.

Extrusion Gneuss drum.

The design of the extruder MRS is based on the extruder monotornillo, widely tested and reliable, to which a special degassing section has been added. The molten polymer is introduced in a straitjacket of larger diameter in the extruder. The shirt contains eight or ten (depending on the size of the model) extrusores-barrera small, parallel to the main screw axially. Installed in these small extrusores barrier are the screws satellite, which are led by a gear placed in the main shirt. Satellite screws rotate in the opposite direction to the main screw, while rotate axially with it. This greatly increases the area of exchange of the melt. The placed extrusores-barrera inside the shirt of the SMR are open approximately 30%, to allow the optimal transfer of mass cast within the straitjacket that the evacuation can be carried out without restrictions.

Thanks to this patented design, this large area with a very high surface area of Exchange, the system offers a capacity of desvolatilización until now never reached and with levels of only 30 mbar vacuum, a vacuum level easily attainable with a simple ring of water pump. Compared to a conventional mono extruder screw, the area of exchange of the mass cast in the MRS is 4.5 times higher and in comparison with one of double screw is 3 times higher. The renewal of the perhaps most important surface is a factor of 50 and 25 times higher respectively.

The first MRS extruder was provided for processing PET without presecado, which was originally conceived (sheet, fibre, sunchos, extruded) system.

The hydrolytic degradation in the PET process is reversible. The moisture in the PET shortens the length of the molecule chain which leads to low mechanical properties and correspondingly to a reduced level of quality of the final product. In the section of the extruder degassing, the water molecules that are present within or on the PET are removed or extracted by vacuum (diffusion process). The viscosity of the mass can then be controlled with changes in the level of vacuum. Therefore, it is possible to maintain constant viscosity, even when the level of humidity varies, regulating the gap, in response to changes of viscosity that are detected by the measurement carried out by a viscometer online.

After leaving the section of desvolatilización, the polymer becomes a conventional extruder section monotornillo, which gets enough pressure to carry the following processes (e.g., filtration, head, etc.) does happen no hidrolítico process.

The importance of the films for thermoforming of packaging industry is growing rapidly. This is due in part to its excellent mechanical, in part to be a relatively simple process characteristics and partly to lower material costs, particularly if used post consumer bottle flake. Thanks to the new processes, it is possible to transform this impure material to the point that could directly manufacture a blade with him, and this plate can be used in direct contact with foodstuffs.

With the correct process technologies the prints, with excellent thermoforming, reducing weight and therefore saving material characteristics can be finer. In addition, the stability of temperature of the packaging of PET is significantly better than the other polymers made: to be able to warm up food in the container (for example in a microwave oven).

Another advantage of the packaging of PET is good transparency and high brightness, so that before the product has the best possible presentation. And as a manufacturer of thermoforming of PET packaging: "the packaging is part of the decision to purchase".

A manufacturer of sheet for thermoformer and thermoformed containers can, with the help of MRS extruder, eliminate successfully much of the energy consumption that represent the steps of precristalizado and predrying material before being subjected to the extrusion.

MRS extruder plasticised and desvolatiliza material, the RSFgenius filtered it with a fineness of 56 to 75 microns; the viscometer online measuring viscosity immediately before the head and controls command to the vacuum pump in section devolatilización of the extruder, to maintain the viscosity within a narrow range. In this way the quality of the sheet and its thickness can maintain at a consistent high level of quality.

Line of blade thermoformed of 1000 kg/hour.

A smaller line of this kind is running in Brazil, with a MRS 110 extruder. This line is also used for the production of sheet for thermoforming of packaging for fruit, with a capacity of slightly smaller production of 600 kg/h.

In this line, a mixture of remolida cuts away, the remolida scale and Virgin material are processed without presecado and with an extremely simple technology of vacuum, without necessity of purifying the gas and high maintenance requirements.

The MRS concept means that you there is no crystallization or presecado., which allows to reduce the requirement for space at 25% and the energy requirement by 15 to 25%. Not to mention the reduced maintenance and that the time required for drying and the crystallization of the material before the process considerably restrict the flexibility of the entire operation.

In the production of sheet of PET using post consumer bottle flake, the effect of desvolatilización of the extruder MRS is not only useful to remove moisture, is also useful to decontaminate the melt, allowing the process to achieve "without any objection" approval of the food and Drugs Agency (FDA) American.

Line of PET sheet of 600 kg/h.

Compared to a conventional extruder of a single screw, with which the residual level of humidity is reduced to less than 50 PPM, the specific energy requirement of the MRS extruder is around 20% lower than high energy costs necessary to heat the material with hot air before extrusion.

With a twin screw extruder process would avoid the need for the presecado of the material (although actually, material need be predrying approximately 1,000 PPM) much of the savings from the energy of this system with respect to the conventional monotornillo with crystallization and the presecado is cancelled because of the vacuum (less than 5 mbar) higher required, and the need for an additional to the coarse filtration Filter changer or even a bomb of molten mass, due to restrictions in the pressure behind the twin screw extruder.

Specific energy consumption of the MRS technology is therefore about 15% to 25% less than for conventional technologies. The additional advantages over the single screw extruder are not having to carry out drying and crystallization, which gives greater flexibility and, of course, less maintenance. With regard to the extrusion machines with twin screws, the MRS has the advantage that the necessary vacuum is much smaller, which means much lower cost of maintenance.

Thanks to the high level of surface of the extrusion MRS system renovation, the desvolatilización of the melt is highly efficient. Diffusion process increases drastically, due to the rotating multitornillos. Therefore, it is possible to produce PET foil with high quality for thermoforming directly from scales of bottle without any presecado.

As MRS extruder avoids the need for the presecado and crystallization, the MRS system of extrusion offers an extremely attractive economic alternative technologies for the PET process. Both the maintenance and operation of the extruder MRS have been already tested in practice for more than a year, in all the various applications of the range.