DE1519211A1 - Plastic powder for melt coating processes - Google Patents

Description

XHAPSAOK AKTIENGESELISCHAPT
Knapsack near Cologne

K 602

Plastic powder for melt coating processes.

The use of powdered plastics for surface coating of objects according to known melt coating processes, for example according to the fluidized bed or pouring process or by flame spraying or electrostatic spraying is known and is carried out on a technical scale. Thermoplastic or thermosetting plastics are used here Plastics, such as B. polyamides, polyethylene, polymethacrylate, polyvinyl chloride, Celluloaeacetobutyrat or Epoxy resins. A prerequisite for a good fluidized bed coating is a powder quality specially tailored to the sintering process. The plastic does not fall during production already as a powder, it must be pulverized afterwards. After pulverization, the plastic powder should be in fine grain with a grain size of preferably between about 0.1 and 0.2 mm are present in order to be used in the above Procedure to be appropriate.

A previously used process for the production of, for example powdery soft polyvinyl chloride is that one soft polyvinyl chloride granules with the help of liquid Nitrogen cools to about -100 ° C or even lower. At this temperature, polyvinyl chloride is as brittle as glass and can pulverized in normal pin mills to the desired degree of fineness. The supercooled granulate splinters in the process many small parts of different sizes with smooth fractures, similar to breaking glass.

Another known method is, for example, polyamide melted, pressed through particularly fine nozzles and a steam or nitrogen stream arranged at right angles to it

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exposed. Here, ea atomizes similarly to an atomizer. The powder is then placed in appropriate devices collected, the individual grains have a spherical shape.

According to another known procedure, the to be pulverized Plastic exposed to extremely strong shear forces shortly before the softening point and the crushed Material withdrawn by a suction air stream.

Finally, it is known for the production of a plastic powder Dissolve the plastic in a suitable solvent at normal or higher temperature and then dissolve the plastic to precipitate again from the solution. Powder obtained in this way is extremely fine-grained and resembles a powder, which, however, leads to the formation of undesirable agglomerates individual powder particles.

Manufactured according to the known processes described above Plastic powders are characterized by a different size of the plastic particles, which is why they are used in the known melt-coating processes, in particular in the fluidized bed process, is disadvantageous. To become a plastic powder To get a uniform grain size, one would have to sieve the powder produced by known methods or subject to other suitable measures, which means an additional cost. In addition, for example with a single sieving only the coarsest plastic particles can be removed, so that dust is generated the processing of the powder by the smallest powder particles could not be prevented. Another disadvantage which results from the different grain sizes of plastic powders, consists in the fact that in the manufacture of a Plastic coating according to the known melt coating process, which melts the plastic particles in a unit of time thermal energy to be applied to the coarsest particles

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must be tuned in order to achieve a smooth coating. However, if the plastic is heated for too long, a * Depolymerization favors 30 that there is a need to keep heating times as short as possible. Furthermore you can when fusing plastic powders with coarse-grained fractions with an average diameter of 0.3 mm, for example, no coatings of a significantly smaller layer thickness than 0.3 mm can be obtained, since only in the rarest of cases does the The melt viscosity of the plastics is so low that the relatively coarse particles flow into a thin coating. Thin, pore-free plastic layers are, however, general Desirable for cost reasons, especially if it is are built-in parts with defined tolerances.

It has now been found that the application of at bie Kunatstoffpulvern different grain size of between about 0.1 mn to about 0.3 mm Heratoilung of coatings on articles by known üühmeliaübereugoverfahren, in particular · «rfahren when Wirbelsinterv, resulting disadvantages can be overcome, when using a plastic powder whose particles have a uniform size 'and a cylindrical shape, wherein the ratio of diameter to length of each cylinder is about 1: 1 to about 1 t 4.

Plastics such as polyamides, polyethylene, polymethacrylate, cellulose acetobutyrate or polyvinyl chloride are suitable for the production of the aforementioned powders.

The use of plastic powders of the same particle size has a particularly advantageous effect in the known fluidized bed sintering process. The fluidized bed sintering process requires an air flow of a certain flow velocity to whirl up the powder in the whirling container. must be high, so that in the case of using a conventional powder of different particle size, the largest proportions of the powder

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vera be whirled up. This cannot prevent that the finer parts of the powder partly from the vortex container are carried out and thus dust is caused, thereby simultaneously deteriorating the desired liquid-like state of the powder in the fluidized bed can occur. This disadvantage is due to the nature of the plastic powder according to the invention, which consists of particles of the same shape and size and is characterized by good flowability.

Another object of the invention relates to a method for the production of the plastic powder according to the invention, which is characterized in that one of the plastic raw material or a mixture dos raw material with known Additives such as plasticizers, stabilizers, pigments or fillers, for example by extruding or im Spinning process individual threads or bundles of threads with a dem Durohmeraoer dor TuJvertöllohen appropriate thread diameter produces and then the threads or, the thread bundle on cuts a length that is equal to or approximately equal to the thread diameter is.

A modification of the above method is that one is made from the plastic roll material or a mixture of the raw material with known additives, such as plasticizers, stabilizers, pigments or fillers, for example by extrusion or in the spinning process individual threads or bundles of threads with a thread diameter larger than the diameter of the Powder particles are produced, stretching the threads obtained in a known manner until the thread diameter is the Corresponds to the diameter of the powder particles and then cuts the threads or the thread bundle to a length that equal or etv / a equal to the thread diameter. In this way of working, it is advantageous to use e3 with threads or bundles of threads a thread diameter of above 0.3 mm up to preferably about 1.5 mm and then these threads up to

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a lead diameter of between about 0.1 and 0.3 mm stretch egg.

The above-described process for the production of plastic powders The same or approximately the same particle size is compared to the known sieving process, whereby made of a plastic powder the coarsest and finest powder fractions of different particle sizes are sieved out, technically advanced, since electrostatic charging of the powder particles is avoided and, in addition, time and costs are saved.

example

A polyvinyl chloride raw material with the following composition,

Weight ^

Polyvinyl chloride 59.06

S-Polymeriaat K- »fert 55

Polyvinyl chloride 8.05

E-polymer K value 60

Di-2-ethylhexyl phthalate 12.80

Di-n-octyl adipate 11.80

Polymethacrylic acid ester 5.32

Titanium dioxide 0.55

Chromium Oxide Green 0.45

Barium-Cadmium Stabilizer 1.97

100.00 weights ^

which was produced according to the well-known dry blend process, was extruded into threads in an extruder provided with perforated plates, the threads having a diameter of 0.8 mm. The plastic threads of the aforementioned diameter emerging at the extruder head were wound on a winder wound at a speed that was greater than the exit speed of the threads from the extruder, so that the threads have a diameter of originally 0.8

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mm to a diameter of 0.2 mm.

The obtained single filaments with a diameter of 0.2 mm were combined to a thread bundle with parallel threads and in a cutting machine to thread particles cut with a length of 0.2 mm. In this way, one made up of cylindrical particles of the same size became Plastic powder with good trickle and vortex properties, which could be used with success in all known enamel coating processes.

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Claims (1)

Claims 1 · Plastic powder with a grain size of between about 0.1 mm to about 0.3 mm for the surface coating of objects according to the fluidized bed sintering process, characterized in that that the powder particles have a uniform size and a cylindrical shape, the ratio of The diameter to the length of the individual cylinders is approximately 1: 1 to approximately 1 ι 4. 2, plastic powder according to claim 1, consisting of polyamides, Polyethylene, folymethacrylate, cellulose acetobutyrate or Polyvinyl chloride. 3 · Process for the production of plastic powders according to a of claims 1 or 2, characterized in that one of the plastic raw material or a mixture of the raw materials with known additives, such as Y / eichmacher, Stabili- ' Sator, pigments or fillers, for example by extrusion or, in the spinning process, individual threads or bundles of threads with a diameter corresponding to the powder particles Produces thread diameter and then cuts the threads or the thread bundle to a length that is equal to or approximately equal to the thread diameter. 4 · Process for the production of plastic powders according to a of claims 1 or 2, characterized in that from the plastic raw material or a mixture of the raw material with known additives, such as plasticizers, stabilizers, pigments or fillers, for example by extrusion or in the spinning process, individual threads or bundles of threads with a thread diameter that is greater than the diameter the powder is produced, the threads obtained stretch in a known manner until the thread. diameter corresponds to the diameter of the powder particles and then the threads or 3aa ^,! enbündel on a -8th- 009808/1339 ORIGINAL BATHROOM Length that is equal to or approximately equal to the pad diameter. 5 · The method according to claim 4, characterized in that Threads or bundles of threads with a thread diameter of above 0.3 mm to preferably about 1.5 mm and then these threads up to a thread diameter of «Wipe about 0.1 mm and 0.3 mm stretches. 009808/1339