Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
2002-09-04
2004-05-04
Boykin, Terressa (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C264S219000, C428S034700, C528S271000, C528S272000
Reexamination Certificate
active
06730774
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The invention relates to a process for decontaminating polycondensates, such as PET, PBT, PEN or PA and also to an apparatus for carrying out a process of this type. The process and apparatus are used in particular in the treatment of used PET or the like, for example of drinks bottles.
b) Description of the Related Art
Consumer products such as drinks bottles made from PET have been in use for some years, and for some years have also been collected for recycling, sorted, comminuted to give flakes, and subjected to surface-cleaning. A high proportion of PET bottles is nowadays recycled. The sorting process may take place either manually or using machinery and various optical methods, or else be a part of the surface-cleaning process. The surface-cleaning process mostly comprises various washing stages and separation stages, and conmminution of the PET drinks bottles to give flakes. However, surface-cleaned PET flakes can also be produced from PET bottles by a dry-mechanical route.
The initial assumption made by those skilled in the art and by approval bodies was that it is not possible for this collected PET material (RPET) to be reintroduced to the same application (drinks bottles). The reason given for this was contamination of the RPET by a wide variety of substances, for example drinks ingredients, such as flavors, or substances, such as solvents or household or garden poisons, inadvisedly stored in bottles. However, it has now been recognized that it is possible to provide the required removal of contaminants of this type, and various processes for this purpose have been developed. The starting point for the processes developed has been the assumption that the contaminants penetrate uniformly through the PET products. The entire mass of mixed product was therefore fed to a devolatilizing process.
A so-called Stehning method is known in which PET flakes as an end product of known recycling methods form the starting base. Such flakes are extruded in an extruder in differentiated zones in a predetermined temperature range, degassed and finally granulated. In this process it is intended to eliminate the main component of volatile side products or contaminants. Any residual contamination remaining in the product is degraded by means of a solids after-condensation (SSP). A careful and even mixing is to be achieved in the vacuum wobble dryer. The progress of the process occurs in a discontinuous manner.
According to a further method, PET is comminuted, mixed, heated and precompressed in a cutting compressor. This is followed by extrusion and degassing, with the energy input being lower due to the preceding heating. The heated material is drawn into fibers, film, etc.
According to another method, PET is comminuted into flakes, dried and thereafter extruded in a two-shaft extruder and thereafter granulated. The granulate is crystallized and later subjected discontinuously to an SSP treatment.
According to a method in accordance with U.S. Pat. No. 5,876,644, there is a mixing with a fresh melt of polyester-prepolymer after the cleaning, grinding, melting and extrusion of RPET. This mixture is pelletized and further polymerized.
U.S. Pat. No. 5,899,392 discloses a method for the decontamination of finely ground RPET, preferably under heating in hot gas, e.g. nitrogen. RPET flakes are ground into particles which are substantially smaller than 0.25 cm. A decontamination is also to be enabled by placing the finely ground particles in a liquid solution.
U.S. Pat. No. 5,807,932 describes the preparation of RPET which originates from used PET bottles. The RPET flakes are molten in the extruder, with the contamination which is originally evenly concentrated on the surface of the flakes is distributed evenly over the entire melt, as a result of which the optional subsequent decontamination from the melt is made more difficult.
WO-98/44029 discloses a decontamination of RPET from bottles (RPET flakes) in an inert gas stream of high temperature, with a solid phase after-condensation inevitably occurring during said decontamination and leading to an increase of the mean molecular weight or the intrinsic viscosity of the polymer material. In order to prevent this increase of the mean molecular weight, the volatile side products which are emitted during the solids phase after-condensation are continuously supplied to the gas stream in an equilibrium quantity, so that said solids phase after-condensation is pushed back. Although it is achieved in this way that the mean molecular weight of the treated RPET material remains substantially unchanged during the decontamination, this is gained with an additional complexity of the machinery involved.
U.S. Pat. No. 5,597,852 discloses a method for preparing solid polyester material in which there is also a step for removing volatile components and reaction products. An increase in the mean molecular weight and a rise in the intrinsic viscosity of the RPET molecules also occur inevitably in this case. At the same time, however, this step also includes the sintering of the previously comminuted and thereafter healed material. In a second step, the sintered material, which is relieved of volatile components, is mixed with new material. By sintering the material particles, the bare surface is reduced in the entirety, so that any escape of the contaminants close to the surface from the sinter block is made more difficult. It was also not recognized here that in the decontamination of RPET flakes from PET vessels, the primary goal is to remove the contaminants from the zone directly below the surface of the flakes.
U.S. Pat. No. 3,804,811 also discloses a method for preparing previously cleaned polyester material, in which the RPET material which is cut into flakes or other parts is subjected to a heat treatment in a furnace. No RPET material is processed which originates from PET vessels, especially PET beverage bottles. The sole purpose is to increase the mean molecular weight or the intrinsic viscosity of the RPET material and thus its tensile strength.
According to a so-called URRC method, the PET flakes are wetted at first with NaOH and thereafter treated in a rotary tubular kiln at high temperature over a number of hours. Layers close to the surface of the flakes are removed by caustics in this case. This represents a certain departure from the aforementioned methods, but one must consider in this case a certain material loss by the etching in addition to a disposal problem for the residual matter.
The complexity in respect of process and equipment of this state of the art for the purpose of decontaminating RPET is high.
OBJECT AND SUMMARY OF THE INVENTION
The invention is therefore based on the primary object of providing a method for the decontamination of RPET which avoids the disadvantages of the state of the art and can be performed continuously. The solution of this object occurs in accordance with the invention for a process for decontaminating polycondensates, such as RPET or similar polymers, comprising the steps of beginning, where appropriate, with presorting, cleaning, and comminuting the contaminated material to give flakes or the like, followed by a further decontamination step and during this decontamination step, subjecting flakes to continuous and adequate passage of a hot gas stream (excess gas). A further object of the invention is to provide a suitable apparatus for the decontamination of RPET to perform the method just described. This occurs in an apparatus in accordance with the method of the invention comprising a device for comminuting objects of a polycondensate into flakes and a device for cleaning the flakes as well as a further device for decontamination, with the device for decontamination being provided downstream with an extruder for melting and granulating the decontaminated polycondensate, wherein the device for the further decontamination is a shaft reacher for after-condensation in solid phase in which a removal of the contaminants occurs without prior homogenizatio
Borer Camille
Christel Andreas
Hersperger Thomas
Boykin Terressa
Buehler AG
Reed Smith LLP
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