DE1446788B2 - Process for coating objects - Google Patents

Description

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Thermoplastic polymers, such as polyethylene, but in any case will be the pigment and the can be premixed as a smooth, uniform coating on polymerizate before the mixture is fluidized Objects are applied by siert. It's a major benefit for the cooker heated object in a fluidized bed by fine adjustment to exclude this premixing stage and divided polymer is immersed. For coloring 5 only to color the polymer that is currently in a Until now, pigment was used for the coating process specified in tablet form, Given lying thermoplastic polymer, very many objects can be used successfully with and the substances were coated in a Banbury thermoplastic polymer, Mixer or a roller mill, or which is where the heated object is placed in a fluidized bed of Mixture was dipped into finely divided polymer through a suitable nozzle. Wood, presses, To ensure good dispersion of the pigment in the tall, glass and even paper objects, such as paper polymer to obtain. The pigmented polymer cup can be above the softening point of the Posat is then heated to a powder suitable as a fluidized bed and immediately immersed in the fluidized bed ground. . · ■■■ -; · .... ". Polymer particles melt and adhere

It has now been found that a surprisingly good 15 as a layer of very uniform thickness on the

Pigment dispersions in the finished polymer hot object.

coating can be achieved when the pulyeri- If the object is removed from the fluidized bed,

ized pigment directly in a fluidized polymer bed dis- so the surface has not adhered due to

Pergiert and the heated object then completely melted polymer particles

while maintaining the conditions for a rough appearance. You can have a smooth coating

dense fluidized bed is immersed in the bed. Though produce in which the layer just lasted that long

The density and / or particle size of the additive is not heated to the softening point of the polymer,

be the same as with the fluidized bed polymer as is necessary to make this outer layer of poly-

need, a uniform distribution of merizate particles is obtained.

of additive in the whole fluidized bed. 25 The finely ground polymer begins to flow draw, first to form a dense polymer fluid bed by placing a gas in a suitable container, then add the powdered pigment and the polymer flows through a layer of polymer. To that finally the conditions of a dense fluidized bed polymer to flow well and the To maintain until the overall color of the layer object to coat, the particle size should be becomes uniform. The present invention is particularly about 0.05 to 0.6 mm, preferably about 0.1 to this is advantageous for pigmentation, but can be 0.2 mm. The container size should be a 10-also for the installation of similar solid additives, such as anti-up to 50% expansion of the fluidized bed. Oxidizing agents are added to the polymer coating. The polymer is used by monitoring the gas will. - '-. speed kept in suspension. The gas

The coating method of the present invention varies depending on the speed of objects with a mixture of powder density and particle size of the polymer and can shaped polymers and powdery too easily due to visual observation of the flow types can be regulated by immersing the heated objects. The Verin according to the invention a fluidized bed generated by a gas stream should drive with a dense fluidized bed with a good mixture consists in that the polymer 40 formed boundary or surface is carried out first Brought to flow, then the additive, especially the, in contrast to solid-in-gas dispersion Pigment, added to the fluidized bed and nen, as in a cloud chamber with high gas after whose uniform distribution of the opposing speeds would be obtained, stand being immersed in the mixture. It was The finely divided polymer is placed in a vessel Already known, fine-grained material of various 45 brought with a porous or sintered base plate. Kind of in a fluidized bed, in particular the holes in the plate should be as large and as numerous is generated by forcing in air, with sufficient that the polymer cannot penetrate the plate to mix with each other (cf. the German patent specification flows through when the bed is at rest, 669 206, the Swiss patent specification 115 696 but that evenly distributed by the bed cross-section and the magazine "Kunststoffe", 1957, pp. 64 to 68). 50 divided gas to pass freely. If the gas pressure is too low

In all of these processes, the bed seems to be of no essential nature Means used for agitation, in order to only cook a sufficient change in volume, the gas mixing increases to effect the solid materials. speed, so the bed comes to flow, The citation of the means shows that it is not close and the volume increases considerably, but remains of the present invention wherein simply the Mi- 55 has a well-defined surface. If the gas is too high The speed of the pigment and the polymer appear powdery clouds of dust by the fluidizing effect of the gas and poly over the fluidized bed and the polymer is with merisats is effected. The use of auxiliary the gas entrained from the vessel, The medium or cyclizing agent is in a fluidized bed. Any harmless gas can be used for this purpose undesirable that in coating processes 60 to make the substance flow, and air should be used. works quite satisfactorily. If there is a risk of oxy-

In addition, the present invention is particularly suitable for using inert gases such as nitrogen

the other thing is that a powdered pigment becomes vigorous with it.

the finely divided polyethylene through the first

subsequent fluidization of the polymer and then 65 many thermoplastic polymers are used

by adding the pigment to the fluidizing, e.g. B. according to high and low pressure processes

rungsbett can be mixed. State-of-the-art polyethylene, blends of polyethylene

the technology does not suggest this possibility, with polyisobutylene, polystyrene, acrylonitrile and sty-

Roll copolymers, polyacrylic acid esters, polyamides and the like. In general, to achieve the best results solid resins used, d. H. Polymers of monoolefins with 2 to 8 carbon atoms per Molecule, preferably polyethylene and solid copolymers of ethylene with other monoolefins.

The present method is particularly favorable when used on ethylene polymers produced by the low-pressure process were prepared, the polymer being formed in solution and therefrom by evaporating the solvent or cooling the solution was precipitated by direct or indirect heat exchange. It's quite light and flaky and can Grind lightly in a Banbury mixer or micropulverizer, making the intermediate step the tablet production is omitted and the precipitated polymer directly into finely divided powder is transferred, which is applied directly to the finished article in a fluidized bed process.

Excellent results have been obtained with a high density ethylene polymer made in Was polymerized in the presence of a chromium oxide-containing catalyst. The ones to be preferred Solid polymers can be prepared according to the process disclosed in US Pat. No. 2,825,721 Mono- (l) -olefins are produced which have 2 to 8 carbon atoms per molecule and do not are branched closer than in the 4-position to the double bond.

Solid ethylene polymers can also be produced by low-pressure processes using catalyst systems containing a Group 4 metal halide and an organometal or an organometal halide.

The preferred Äthylenpolymeri-; Sates are by a density of at least 0.94, preferably at least 0.955 g / cc at 25 ° C and a softening temperature of at least 115 ° C preferably at least 120 ° C.

The method according to the invention can advantageously be used with any organic powder that can be converted into powder form or inorganic solid pigment, z. B. carbon black, titanium dioxide, chrome yellow, zinc oxide, iron blue pigments, etc. The particle size of the pigment should be about 0.01 to 0.1 mm, preferably less than 0.075 mm. The pigment loading can be varied widely. Satisfactory pigment dispersions can be obtained by fluidized bed mixing can be obtained at loads as low as 0.25% to as low as 5% and higher. The cheapest Pigment loading is about 3 to 5 percent by weight.

The desired amount of pigment can be pulverized and poured directly into the fluidized bed. There is no separation or layer formation, and the pigment is evenly distributed in the fluidized bed, so that the resulting coatings are perfectly uniform.

The powdered pigment should be added slowly to the fluidized bed and sufficient time should pass in order to achieve thorough mixing through the flow process. A few minutes, in general 2 to 10 minutes, mixing results in a uniform dispersion of pigment in the fluidized bed. The correct mixing time can be determined on the basis of visual observation, since at the end of the process Mixing throughout the bed the color appears evenly. As the bed in general looks lighter than the finished coating, the amount of pigment used must be based on the amount of pigment in the finished coating Coating desired pigment concentration can be calculated, not according to the appearance of the fluidized bed. The pigment concentration in the finished coating is the same as that in the fluidized bed.

Claims (2)

Patent claims: 1. Process for coating objects with a mixture of powdered polymers and powdery additives by immersing the heated objects in a fluidized bed generated by a gas stream Mixture, characterized in that first the polymer is brought to flow, then the additive, especially a pigment, is added to the fluidized bed and after the even distribution of which the object is immersed in the mixture. 2. The method according to claim 1, characterized in that a particle for the addition Size from 0.01 to about 0.1 mm and for the polymer particles from about 0.05 to 0.6 mm be used.