DE2419330A1 - PROCESS FOR THE MANUFACTURING OF FLOWABLE COATING POWDERS OF FINE PARTICLE SIZE - Google Patents

Description

PATENT LAWYERS ___

Dlpl.-Ing. P. WIRTH Dr. V. SCHMIED-KOWARZIK Dlpl.-lng.G. DANNENBERG Dr. P. WEINHOLD Dr. D. GUDEL

281134 β FRANKFURT AM MAIN

TELEPHONE (0611) _{287 (J] 4 GB} . ESCHENHEIMER STRAS3E 39

Union Carbide 'Corporation

270 Park Avenue

New York, N.Y. 10017 / USA

Process for the production of flowable coating powders fine particle size

The coating industry must profoundly change its minds because of the environmental problems associated with the use of conventional solvent-based coating preparations. In the past The most common coatings were preparations of pigmented or unpigmented carriers, which for easier application with Solvents were diluted. After application to the 'surface the solvent was allowed to evaporate, often to the atmosphere, leaving a dry, uniform coating. Over time, the development led to organosols, plastisols, Emulsions, dispersions, 100% reactive solid coatings, waterborne coatings, with significant efforts being made in the past two decades and on ringing of powder coatings, the main impetus of which was given by the invention of fluidized bed technology. the initial powder coatings efforts were done by immersing a preheated object in

a bed of powder particles, which are usually 50-150 ~ ^r - 409845/0999.

Hicron and were swirled by a gas stream. At the When immersed in the fluidized bed, the powder particles adhere to the surface of the object and converge on it, as a result of which a uniform coating, usually of a thickness greater than 0.125. mm and often up to 2.5 mm. The relatively large particles preclude the formation of thin coatings from 0.005 to 0.05-0.075 mm thick, which are often desirable. There were many attempts have been made to apply such thin coatings, and / or recent efforts - on the electrostatic Spray coating of particles on the earthed to be coated Object and subsequent heating to melt the particles and form a uniform coating. This method is widely used because of many advantages found and brings e.g. improved film properties, the absence of volatile solvents, the elimination of Water pollution problems, the elimination of preheating of the substrate, a practically 100% utilization of the "material, decreased capital expenditures and the ease of changeovers with it. In making the powder for such use however, many difficulties arose because the conventional milling and spray-drying methods used so far did not Powders with the desired physical properties could result in the achievement of thin films by electrostatic Allow spray draw process. Occurred in the past Lubricities in the production of particles with the correct. Shape, the desired fine particle size and the desired

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Particle size distribution on the. To achieve the desired Film thicknesses were necessary. Known methods include dry blending, melt treatment, wet treatment, spray drying and combinations and modifications of these methods.

There has now been a method of making powder coatings by spray precipitation of a solution of the polymer in a precipitating agent for the resin and subsequent recovery of the found fine powder particles. This process enables the production of powders with particles of one diameter between 3-20 microns and spherical shape, which is applied to a substrate by electrostatic spraying processes and therein to a continuous, smooth, shiny coating can be cured to a thickness of 0.005 mm; thicker coatings can be obtained by applying the powder more heavily.

In the process according to the invention, a solution of the resin is used as Mist of fine droplets is sprayed and these are brought into contact with an anti-solvent or precipitating agent, whereupon the resin particles precipitate in fine particle size. The resin solution can contain any additive customary in powder coatings, such as pigments or dyes (e.g. titanium dioxide, cadmium red. Soot, phthalocyanine blue, toluidine red, iron oxide, calcium carbonate, barium sulfate), stabilizers (e.g. dibutyltin dilaurate, Ethylene oxide, alkylated phenols and bisphenols, barium cadmium powder, Epoxy resins), plasticizers (such as dioctyl phthalate, 2-ethylhexyl phthalate, diisobutyl adipate, diisooctyl azelate), dispersants, Flow regulators (such as the 75/25 copolymer of 2-ethylhexyl acrylate and ethyl acrylate and the

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77.5 / 22.5 mixed polymer of n-hexyl acrylate and isodecyl acrylate), Crosslinking agents (such as polyols, polycarboxylic acids, hydroxycarboxylic acids, Polyamines, hydroxylamines and other active hydrogen compounds) etc. These can be soluble or in the resin solution to be insoluble; those skilled in the art are the types of additives as well as theirs Commonly used quantities.

The resin solution can contain 3-50 Gb% resin; it preferably contains 5-30 Geuf.-Jb and in particular 5-20 wt .- / £. Optionally, concentrations above 50 wt -.% Are used, but in this case we obtain larger particle sizes. It has been found that smaller and more spherical powder particles are usually obtained by reducing the concentration of resin in the solution. "-. - ~

The process can form fine particle size powders from any thermoplastic or thermoset resin that can be dissolved in a solvent to form a virtually clear solution and precipitated by an anti-solvent. Such resins are, for example, vinyl halide polymers such as polyvinyl chloride, copolymers of vinyl chloride with vinyl acetate, ethyl acrylate, ethyl methacrylate, acrylic acid, 2-hydroxyethyl acrylate, maleic acid, vinyl alcohol, glycidyl methacrylate, styrene, hydroxypropyl acrylate, acrylate and vinyl methacrylate ,. "Vinyl ethyl ketone, ethylene, methacrylic acid, etc. The polymers and copolymers of all ethylenically unsaturated monomers with the polymerizable ^ C = C ^ group can also be used; examples of these are the polymers and copolymers of the above monomers. This list. is not exhaustive, and those skilled in the art are familiar with many others as appropriate, """" 409845/0999

Ethylenically unsaturated monomers familiar. Furthermore, the known polyesters, polyamides, epoxy resins, polyurethanes, etc. can be used in this method. If necessary, mixtures of two or more resins in the solution can also be used. The preferred resins have a glass transition temperature above about 45 ^° C., since the powders produced from them usually have better storage properties and a lower tendency to block. Resins with lower glass transition temperatures can also be used, but the powders generally have to be stored with appropriate cooling. The resins should also be insoluble in the anti-solvent or precipitant medium so that powders can be made by the process of the invention. ·

For the formation of the resin solutions, the usual known solvents can be used be used, which convert the special, in powder form. The dissolving resin can be dissolved at room temperature or at an elevated temperature. Suitable solvents are e.g.

Acetone, methoxyethyl acetate, diethyl ether of diethylene glycol, diacetone alcohol and all other solvents for the particular resin used. The particular resin solvent or solvent mixture used will necessarily depend on the particular resin to be dissolved; this solvent is just- *; if practically completely soluble in the anti-solvent. You can also use some anti-solvent or precipitating agent in the resin solution, as will be described below. Meanwhile, '■' ■ amount varies irr Abhänigigkeit from special 'resin solvent, the resin concentration in the Harzlösurrg and the precipitating ·

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Usually it can be any amount up to the one causing the precipitation

of the resin in the resin solution can be used. Through this the ...

may have a lower precipitant in / powder-forming reaction— amount to be used. The amount to be used in this manner can be easily determined by simple small-scale tests will. ·. . -

The anti-solvent or precipitating agent is any solvent soluble with the resin solvent in which the resin itself is practically insoluble. This phenomenon is known, and it is also known that a solid can be precipitated from a solution thereof by adding an anti-solvent to the solution. The precipitating agent may be a single anti-solvent or a mixture thereof The particular resin solvent and precipitant will vary. Usually, the ratio of precipitant to resin solution can vary from 0.5: t to "50:} or more. The special Uer-. ratio in a given case depends on the resin, solvent and precipitating agent, as well as concentration and temperature. Compounds suitable as precipitating agents are, for example, water, isopropanol, ethanol, methanol, butanol, heptane, decane, benzene, etc .:. . ...., -_. . -.--. ^'::. -. -. '. "" ..-

The following table shows examples of resin solvent combinations and precipitants for different types of resin:

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Table 1 '' \ · ·.

Resin, Resin Solvent, Precipitant Vinyl _:. Acetone '. Water ^ Vinyl - acetone, hed'tan - - ■ - Polyester diethyl ether of isopropanol / water Diethylene glycol mixture. Polyurethane dimethylformamide. 'Isobutanol " Polyethylene cn. -Chlonaphthalene - isopropanol

This list is an illustration and is not intended to be a complete listing of the mixtures that are suitable according to the invention. ■ ... ^v ■

The fine particles made by the process of the present invention can be as small as 3 microns or less. Usually the powders are mixtures of particles as large as 1-20 microns. According to the method according to the invention, larger particles can optionally also be produced by using spray orifices of suitable size, these particles then having a size of up to. 400 microns or more. Although larger sized particles can be used satisfactorily in fluidized bed or electrostatic spray applications, the smaller particles have the advantage of allowing the formation of film coatings as small as 0.0075 mm. Thus, the preferred powders for thin film coatings by electrostatic spraying are those having particles between 3/4 microns in size. In the present Ahmeldung the term means "thin film ^lr a continuous, smooth coating of" about 0.0050 to 0.075 mm thickness. '

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The powder particles are usually spherical; this means that they are rounded and have no sharp corners or edges * The spherical shape is preferred for many reasons, namely mainly due to the lower tendency towards charge dissipation in the electrostatic spray process. Experience has shown " that the sharp corners formed by conventional grinding processes and catalysts cause rapid dissipation of the electrostatic charge imparted to a particle to a reduced effectiveness in the electrostatic spray process.

- The Sprühausfällung can at any temperature from etma -3O ⁰ C to 150 C, are performed, whereby room temperature are usually preferred. The particular temperature depends, of course, essentially on the boiling points of the solvent and precipitant used. In some cases it may therefore be advisable to either cool or heat the resin solution and / or the precipitating agent. Under, over or atmospheric pressure can be used. In the spray precipitation process according to the invention, neither temperature nor pressure are decisive factors. .

The spraying of the resin solution can be airless or with any gas or gaseous medium. Air, nitrogen, carbon dioxide, water vapor, acetone vapors, isopropanol vapors, Fluorocarbon barrier or any other gaseous medium used that does not interfere with the spray precipitation. Such gaseous media are known.

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The factors influencing the particle size include the type or nature of the resin, the viscosity of the resin solution, the Concentration of the resin in the resin solution, the surface tension the resin solution, the special combination of the resin solvent and precipitating agent used, the opening capacity the 'spraying or evaporation device, the gas pressure when carrying out the spraying and the intimacy of the contact Resin solution droplets with the precipitating agent. These can can easily be adjusted by a person skilled in the art in each particular case to achieve the best desired particle size »

The device used to form the spray can be any known fog or 'spray material forming device. Many of these are commercially available and include paint spray guns and sliver atomizers »In some In some cases it may be desired to spray the resin solution to impart electrostatic charge; this can be done by means of a known electrostatic spray device.

The reactor in which the spray precipitation occurs can take many different forms. The essential feature in this part of the process is a reactor in which the resin solution spray material can be brought into intimate contact with the precipitating agent, see above _; that the precipitation of the resin from the resin solution spray is present in a fine size. The term "spray precipitation ¹¹ or variants thereof" refers to a method by which a spray material of a resin solution is brought into contact with a precipitating agent, see above

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that the resin is precipitated and a fine particle powder is formed u / ird. . ·

A simple orphan to carry out the process according to the invention consists in spraying the resin solution with a spray gun into the precipitation solvent contained in a reactor. During this process the precipitation solvent is stirred thoroughly. In a modification the " Resin solution 'sprayed into the reactor while the precipitant from falling liquid film on the inner reactor surfaces and introduced; with this modification can-also soil, Fibers, tubes or rods be present in the reactor, their surfaces are also covered with the falling liquid film of the precipitant. Another modification is made by introducing part or "all of the precipitant into the reactor in the form of "a spray material" using one or more spray nozzles for atomizing or spraying the precipitant in addition to the spray nozzle (s) for the resin solution. Particularly advantageous is a system in which the resin solution spray material is electrostatic Charge and imparting the opposite charge to the precipitation spray material; in these cases, droplets of the " one material attracted by the droplets ^ the other and the spray precipitation takes place largely on the fly. The expert combinations of the above procedures and other measures are also familiar. . ■ "'

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After extensive spray precipitation, the mixture obtained can be precipitated and then sieved to remove the larger, unwanted particles for recycle. Then the fine ones are grounded Particles in the usual way, e.g. by filtering or centrifuging, obtained, whereupon the powder can be dried and flaked by conventionally known methods.

The powder coatings produced by the process according to the invention can be used in conventional powder coating processes to produce thin, glossy coatings. So they can used in fluid bed systems or electrostatic spray systems will. The produced by the method according to the invention * Powder coatings with a fine particle size are extremely Mostly suitable for use in electrostatic powder spray coating processes. The powder is deposited onto a substrate by means of an electrostatic spray device and then melted or cured at an elevated temperature to form a uniform, smooth, shiny, thin coating which ■ often only has a thickness of 0.005G mm. Through stronger application or multiple coating of the substrate with the powder. thicker coatings can also be obtained. ..- "- ■

The following examples illustrate the present invention without limiting it. ·. example 1

There was a pigmented resin preparation from 2100 g acetone, 900 g of a copolymer of vinyl chloride and .Vinylacetat having a viscosity at 25 ^Q C. of 23 to (20 fa copolymer in

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Methyl ethyl ketone), which contained 14 % polymerized vinyl acetate, 454 g titanium dioxide, 3.78 g "Nuodex NA" as pigment wetting and dispersing agent, 151.32 g dioctyl phthalate, 3.78 g "Carstab T-17""as heat and Light stabilizer was prepared and sprayed with a spray gun into a 75:25 water-isopropanol precipitant mixture in a reactor; during the spray precipitation the mixture in the reactor was stirred thoroughly and vigorously. The resulting precipitate was passed through a series of sieves to remove large particles The effluent recovered from the 200 mesh sieve was finally filtered and the powder particles air-dried at room temperature. The dried cake was crushed in a Waring blender to a fine, powdery, flaky mass. The powder yield was about 20 % of the particles were between about 5-50 microns in size and were generally spherical in shape with rounded edges.

This process was used to produce additional quantities of powder coatings with a fine particle size; the powders were combined and used to coat steel panels using a Ransburg electrostatic spray gun at 90,000 volts (-) and 18.1 kg air pressure. The coated plates were heated for 3 minutes in an oven at 23O ⁰ C. and bildentsn smooth, glossy color coatings.

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A pigmented resin preparation was produced according to Example 1 and then diluted with 9000 g of acetone. The preparation was precipitated by spraying as above and provided a yield of about 20 % of a dry powder coating material with a particle size between 5-30 microns. "The particles were more uniformly spherical than those of Example 1. 9 e- is ρ is 1 ' 3

A pigmented resin preparation was produced according to Example 1 and diluted with 1,8000 g of acetone *. The preparation was spray precipitated as above and provided about 30 % yield of a dry powder coating material having a particle size between about 3-25 microns which was more spherical than the materials of the previous examples. ..,, ....; ,, Example 4 . -. ; - · '

A resin preparation was produced according to Example 1, but without titanium dioxide, and then diluted with 9000 g of acetone.This was precipitated in the above manner by spraying and provided a yield of about 30 % of a dry powder coating material with a particle size between 3-20 Kicronj the particles had a uniform spherical shape.

B β i 3 QL B 1 ' 5'"" ■ "" ... ".; / ' In this example, the concentrations of the solvent components in the water / isopropanol mixture were varied in order to have the effect on the powder produced The resin preparation was prepared as in Example 1, but without pigment, diluted with 9000 g of acetone and precipitated as in Example 1 by spraying into the solvent mixture. The ratio of '

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Water to isopropanol in the precipitant solution was from pure water to pure isopropanol varied using the following ratios: 100: 0,, 80: 20, 70:30, 50:50, 30:70, 20:80 and 0: 100. In all cases the powder particles were between 3-25 microns in size and were generally spherical.

When using isopropanol and high isopropanol concentrations * Functions of the precipitation solvent remained as determined the fine resin powder particles in suspension in the precipitation solvent. With increased water concentration and with water alone, the fine resin powder particles showed an increased tendency to "float to the surface" in spite of the fact that the The density of the resin was greater than the density of the precipitation solvent. Presumably this was a result of the trapped air on the surface of the solid particles and the greater affinity of the air for "wetting" the particles than the precipitation agent.

Example 6

200 parts of a vinyl chloride / vinyl acetate / glycidyl methacrylate terpolymer (11 ^{% viscosity at 25 °} C. / a 20-5% solution in methyl ethyl ketone), 2 parts of adipic acid, 0.6 parts. of a 75/25 2-ethylhexyl acrylate / ethyl acrylate copolymer as a flow control additive, 550 parts of acetone and 400 parts of heptane were stirred to form a solution. As in Example 1, the preparation was precipitated by spraying in about 19 ι of a 9: 1 heptane / isoprcpanol mixture as a precipitation solvent. This gave about 150 g of fine powder particles between 3 and 50 microns in size with a uniform spherical shape.

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Example 2

As in Example 1, an acetone solution of a commercially available. Vinyl chloride / vinyl acetate copolymers produced and using isopropanol as the precipitation solvent precipitated by spraying. The spray precipitation reactor consisted of a container about 0.6 mm in diameter and about 0.9 m high, which is expediently vented to the atmosphere, but is practically completely closed

one

The beginning of the spray precipitation was / small amount of filling agents present that was sufficient to cover the reactor floor »During the spray precipitation the precipitation solvent was through Openings were introduced in an annular tube which was led around the reactor head, so that «I a falling or A descending liquid film of the precipitation solvent formed on the inner reactor walls. As the precipitation solvent flowed down the walls, the resin preparation became sprayed through a suitable opening in the reactor} at Beruh »»

ft

After the resin preparation droplets with the precipitant, the resin fell into a powder form with a fine particle size. After the spraying, the powder was collected and dried as in Example 1; the yield was 75 % of theory The powder particles had a size of 5-30 microns and were uniformly spherical.

Example B _-

According to Example 4, a pigmented resin preparation was produced and precipitated by spraying according to the method and apparatus of Example 7. In doing so, however, precipitation solvent was additionally sprayed into the reactor

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Spray gun used. Thus, the precipitation took place in flight, whenever the resin preparation droplets and the precipitant droplets came into contact with one another; Any resin that did not precipitate in this way precipitated on contact with the precipitating agent on the walls or the bottom of the reactor. A spherical powder coating material having a particle size and size distribution similar to that of the material obtained by Example 7 was obtained; the yield was about 70 % of theory.

Example 9_

Example 8 was repeated with the omission of the falling liquid film of precipitant on the reactor walls. A spherical fine powder similar to that in Example 8 was obtained in a yield of around 70 % of theory.

Example 10

As the epoxy resin, the reaction product of epichlorohydrin and bisphenol-A with an average molecular weight of about 1400 was dissolved in acetone to form a 15% solution and precipitated as in Example 7 by spraying in water. A fine spherical powder with a particle size between about 3-20 microns in diameter was obtained in a yield of about 70 % of theory.

All powders produced in the above examples could be used in can be satisfactorily applied by electrostatic spray or fluidized bed processes.

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There was a 5 / o solution prepared 11O ⁰ C. Polyethylene in oC-chloronaphthalene bsi. This was precipitated by spraying in isopropanol at room temperature from the hot solution at 110 ° C. using air as the atomizing gas. The precipitated, powdery polyethylene was filtered off, recovered and extracted by slurrying and filtering three times in succession to remove all of the OQ-chloronaphthalene. A spherical, fine powder with a somewhat larger particle size than in the preceding examples was obtained in a yield of about 60 %. This powder could be easily and satisfactorily applied by electrostatic spray coating methods.

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Claims (3)

Claims 1.- A process for the preparation of flowable powder over powder of fine particle size, characterized in that a solution of the polymer sprayed in the form of a mist or fine droplets, this mist or the fine droplet with a precipitating agent for the polymer in the solution brings into contact, whereby the polymer precipitates in fine particle size, and The fine powder particles formed wins. 2.- The method according to claim 1, characterized in that Gie polymer concentration in the solution between 3-50 Geui .-% lies. 3.- The method according to claim 1 and 2, characterized in that an aqueous precipitating agent used u / ird. The patent attorney: 409845/0999