Cleaning compositions for solid surfaces – auxiliary compositions – Cleaning compositions or processes of preparing – For cleaning a specific substrate or removing a specific...
Reexamination Certificate
2001-06-14
2004-01-06
Boyer, Charles (Department: 1751)
Cleaning compositions for solid surfaces, auxiliary compositions
Cleaning compositions or processes of preparing
For cleaning a specific substrate or removing a specific...
C510S475000, C510S476000, C264S039000
Reexamination Certificate
active
06673759
ABSTRACT:
The invention relates to a cleaning composition for apparatus for processing thermoplastic melts.
When thermoplastics are processed on machinery with screws, long running times are frequently required to change from one thermoplastic to another, since thermoplastic melt from the previously used material remains in the machinery. During a changeover, these residues are gradually discharged and contaminate the moldings or semifinished products thus produced, and these therefore have to be rejected. A material change of this type can extend over hours or days, creating high costs for energy and the raw materials required, taking a considerable amount of time and sacrificing machine utilization. This applies in particular when the materials involved in the change are thermoplastics which differ in their processing temperature and/or in their chemical structure or their composition, or when a change is required from dark to light colors or from an opaque product to a transparent or glass-clear thermoplastic, such as polystyrene.
To accelerate this procedure, it has been usual in the prior art to take the extruder out of operation, disassemble and clean the barrel and screw and then reassemble these after cleaning. Shutting down the extruder and subsequently cleaning not only incurred considerable costs but also led to damage to internal surfaces of parts of the extruder resulting from the use of tools. In addition, during disassembly there is a high risk of damaging add-on parts, e.g. temperature sensors or gaskets.
In order to avoid this awkward procedure, it is also known in the prior art, via DE-A-23 21 883, that a cleaning composition can be used. This is fed into the extruder inlet and conveyed through the extruder until the extruder surfaces are free of residues of material, in particular of encrusted residues of material. This is achieved using a cleaning composition composed of a brittle thermoplastic polymer which is embedded into a second polymer. The cleaning temperature in the extruder is controlled in such a way that this second polymer is liquid or flowable during the cleaning procedure. It thus forms a carrier for the particles of the first polymer. It is important that the brittle polymer can be crushed or comminuted during its passage through the extruder screw. The cleaning action of this composition consists in scrubbing by the crushed or comminuted particles to loosen and remove the deposits in the contaminated zones of the extruder. The second, liquid or flowable, polymer component has the task of conveying the particles of the first brittle polymer through the extruder and of taking up deposits released from the surfaces within the extruder.
A disadvantage of this process is that here, too, damage can result from the use of brittle polymer particles which may also be sharp as a result of comminution, and which are intended to scrub the internal surfaces of parts of the extruder. There is also the risk that the crushed or comminuted brittle polymer particles in this known cleaning composition will remain held in cavities of the extruder or in particular during passage through narrowing connector pieces or adapters, thus clogging the extruder so that it needs to be cleaned by hand anyway. This cleaning composition is also unsuitable for thermoplastics which melt above the temperature at which the first, comminuted, polymer used is brittle, since in that case the polymer particles soften and lose their brittleness and thus their cleaning action.
DE-A-38 02 127 has disclosed a process for cleaning extruders by conveying through the extruder one or more organic or inorganic salts together with one or more organic or inorganic solvents in which the respective salt dissolves. A disadvantage of this process is that the use of the solvents can cause corrosion in the area of the feed zone of the extruder screw. In addition, the solvent vapor produced in the hot extruder requires particular protective and preventive measures. This process can be used to clean vented screws only if the vent aperture has been sealed, since the solvent escapes in the area which is at atmospheric pressure.
It is an object of the present invention, taking into account this prior art, to provide, for apparatus for processing thermoplastic melts, a cleaning composition which can effectively avoid damaging the internal walls of the extruder or clogging during passage through narrowing parts of the extruder, and at the same time achieves a high degree of cleaning action.
We have found that this object is achieved by a cleaning composition which essentially comprises discrete particles capable of plastic deformation and made from a thermoplastic (A) with a melting point above 250° C. and with a crystallinity of not more than 50%, and comprises an amorphous or semicrystalline thermoplastic (B) with a processing temperature below the melting point of the thermoplastic (A), where the proportion of the thermoplastic (A) is from 1 to 95% by weight and that of the thermoplastic (B) is from 5 to 95% by weight, and the total of the percentage proportions by weight of (A) and (B) is always 100% or less.
In the novel cleaning composition, the essentially discrete particles made from the thermoplastic (A) and capable of plastic deformation have a very effective cleaning action, while the amorphous or semicrystalline thermoplastic (B) acts as a liquid or flowable carrier for the particles, which are made from the thermoplastic (A) and/or contamination which has been released, and are capable of plastic deformation. The very effective cleaning action results in a very rapid change from one material to the next, even if the change of material to be undertaken is from dark colors or black to light colors, or from an opaque or colored material to a glass-clear material.
Another particular advantage is that the cleaning action of (A) is not restricted to the use of a polymer (B) having a melting point below the brittleness temperature (Tg). In principle, any polymer (B) whose melting point is below that of the polymer (A) is suitable.
A further advantage is that the particles made from the thermoplastic (A) and capable of plastic deformation can also pass without difficulty through narrowing sections of the extruder, for example adapters or connector pieces. Their capacity for plastic deformation means that in an extreme case they are elongated to give long thin filaments. This means that the cleaning composition can even be injected into cavities with low molding wall thicknesses of, for example, 0.4 mm. Another particular advantage is that in injection-molding machines there is no need to disassemble the nozzle in the machine. Even shut-off nozzles can be left on the machine. The cleaning procedure can also be carried out with hot-runner molds. The cleaning composition can be injected through the hot runner into the cavity, and the change of material in the hot runner can thus be accelerated.
It has also been found that the claimed cleaning composition gives an extremely low wear rate, and experiments using a wear-model method for flowable plastified plastic molding compositions show that the wear corresponds to that for an unfilled, i.e. unreinforced, thermoplastic (“Verschlei&bgr; in der Kunststoffverarbeitung: Phänomene und Schutzma&bgr;nahmen”, Günter Menning, Hanser Verlag 1990, pp. 194-197).
The percentage proportions by weight of thermoplastic (A) and thermoplastic (B) may be from 5 to 30% by weight and, respectively, from 70 to 95% by weight, preferably from 5 to 25% by weight and, respectively, from 75 to 95% by weight and particularly preferably from 7 to 15% by weight and, respectively, from 85 to 93% by weight.
In a preferred embodiment of the cleaning composition, the thermoplastic (A) has been selected from the group consisting of partially aromatic polyamides, polyaryl ethers, in particular polysulfones and polyether sulfones, polyaryl ether ketones, polyether ether ketones, polyphenylene ethers and mixtures of these.
The partially aromatic polyamides may, for example, have been built up from ter
Friel Peter
Gareiss Brigitte
Klenz Rainer
Koch Uwe
BASF - Aktiengesellschaft
Boyer Charles
Keil & Weinkauf
LandOfFree
Cleaning material for extruders does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cleaning material for extruders, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cleaning material for extruders will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3230639