MXPA00004574A - Method for producing reactive coating powder compositions - Google Patents

Abstract

The invention relates to a method for producing coating powder preparations by expanding a composition containing a low-molecular inert compound, said low-molecular inert compound being liberated. One or several base resins and one or several hardeners for the base resins or one or several self-hardening resins and optionally, other usual coating constituents are transformed into a flowable state together or separately by heating. The low-molecular inert compound is dissolved under pressure in at least one of the base resin or hardener constituents either before it is combined with the other constituents or in the pre-prepared mixture. The whole mixture is homogenised and the mixture with all the constituents is expanded with cooling.

Description

PROCEDURE FOR THE PREPARATION OF REAGENT POWDER COATING COMPOSITIONS DESCRIPTIVE MEMORY The invention relates to a preparation process for powder coating materials that use an inert compound of low molecular mass as an auxiliary. From the large number of known powder coating preparation processes, the processes that find particularly wide application are those in which the already formulated powder coating material is extruded in the form of a paste-type foundry and brought to the desired particle size. , after cooling of the molten and coarse grind, by means of fine grinding and subsequent sieving. The following particular process steps are common for color powder coating materials: 1. The components of the powder coating material are subjected to a deep initial mixing in dry form as solids in the required proportions. 2. The mixture is melted in an extruder at a very low temperature in order to avoid premature entanglement, and is thoroughly mixed. In the course of this mixing, the binder and hardener are plasticized and wet the pigments and fillers. 1. The optionally colored extruded material is rolled into a thin layer, cooled and milled to give coarse granules. 2. The granules are milled in a mill to give the finished powder coating material. In general, the inevitable fine fraction of < 10 μm in the milling process is removed in a subsequent sieving procedure. The resulting powder typically has an average particle size of 40 to 70 μm. (Compare Ullmanns Enzyklopadie der technischen Chemie, Volume 15, page 680, 1978, Verlag Chemie Weinheim and the monograph "The Science of powder coatings" Volume 1 and 2 (Editor D.A. Bate, London 1990)). In the case of these procedures there may be difficulties and / or subsequent laborious operations, especially considering the extrusion and grinding procedures. In the case of highly reactive binder mixtures, the extrusion process can take place very slowly so that partial gelation occurs, which no longer allows the use of the product for coatings. By limiting the residence time in the extruder, on the other hand, it results in a non-optimal dispersion of the pigments in the binder. In carrying out the coating with powder coating material, this poor dispersion leads to a relatively poor coating capacity which must be compensated by a relatively high proportion of pigments. The extrusion step also imposes a limitation with respect to the binders that can be used, because it is possible to operate only within a certain viscosity scale. For example, the newly developed crystalline resins, which above the melting point have a very low functional viscosity and give rise to outstanding powder coating materials, can not be processed in an extruder. The use of resin mixtures having very different viscosities is also of very limited viability in an extruder, due to the poor homogenization of said systems. The broad particle size spectrum that is formed in the course of milling is on the scale, for example, from 0.1 to 500 μm and requires additional sieving and milling procedures for specific applications. Furthermore, the fine powders that are produced are disadvantageous for health and for processing reasons. Processes for preparing powder coating materials are also known, in which the powder coating foundries are sprayed (DE-A-22 33 138, EP-A-0 537 233). The casting of the basic resin and hardener components can lead to thermal stress of the powder coating composition. The reduction of the contact time between the basic resin and the hardener in the molten state is possible only at a great technical cost. It is also known to use inert compounds of low molecular mass in the form of compressible fluids as auxiliaries for the preparation of powders and powder coating materials. In this way according to EP-A0 157 827, WO 95/34606 and EP-A-0 720 999 the components of the powder coating composition are dissolved in a supercritical fluid and the resulting solution is sprayed with pressure release.

The cooling induced by the pressure release process causes the formation of the powder particles. This release of pressure can be carried out spontaneously or as a function of time, continuously or in stages. It is possible to obtain particle sizes from 5 to 150 μm but also very fine particles in the scale of 1 to 5 μm or less, using the appropriate nozzles. A disadvantage of these methods is that the components concerned are in many cases of only slight solubility in supercritical fluids. High pressures and large amounts of gas are necessary in order to dissolve the solids in the supercritical fluid. EP-A-0 669 858 and EP-A-0 661 091 relate to preparation processes for coating powders, in which the solid starting substances are designed to be insoluble in the supercritical fluid under processing conditions. One of the purposes of this is to avoid losses due to the transportation of the starting material out of the pressure release vessel. According to EP-A-0 669 858, the solid starting substances are mixed homogeneously in the supercritical fluid and then this mixture is relieved from its pressure, while according to EP-A-0 666 091 the components in dust are melted and the liquid material is dispersed in a suitable fluid. With procedures of this type there can be problems in terms of the homogeneity of the mixtures. Processes are also known in which the powder preparation takes place from solvent-containing compositions, using compressible fluids, by means of pressure release of the solution and simultaneous evaporation of the solvent, the examples being EP-A-0 711 586 and JP 8-104 830. The solvents used must be partially miscible with the solid components and must have a high velocity of volatility. The use of organic solvents and the efforts involved to recover those solvents make these procedures disadvantageous. In order to avoid high pressures and quantities of gas, and also the use of organic solvent and the associated expense for its recovery, a procedure according to WO 95/21688 has been developed, in which the compressible fluid is dissolved under pressure in the mixture of substance that is going to be treated and then the solution is relieved of its pressure. For this purpose, the solid components are melted and a suitable fluid is dissolved under pressure in them. This process relates to the preparation of particles and powders, the examples being starting materials for the production of emulsifiers and detergents, and also pharmaceutical active ingredients. Where mixtures of different substances are processed by this process, these mixtures are first of all prepared and then inserted into the process. The preparation of reactive powder coating materials is not recognized. A mixture of different powder coating components comprising basic resins, hardeners and pigments / fillers and also additives of additional coatings can lead to undesired chemical reactions between the base resin and the hardener which influence the properties of the powder coating compositions. in an unsuccessful way The object of the invention is to provide a process that makes it possible to prepare powder coatings continuously or in batches and in a simple manner while avoiding strong thermal stresses. Additionally the object of the present invention is the preparation of homogeneous powder coating formulations by gas spraying containing smelters without premature chemical reaction between the powder coating components. The process is designed to yield homogeneous powder coating particles with an adjustable average particle size in the range of 10 to 80 μm and with a narrow particle size distribution and to allow the use of supply materials within a scale of wide viscosity. further, the processing of powder coating compositions with a low interlacing temperature should be possible. At the same time, the laborious removal of solvents and the use of high pressures compared to conventional procedures, will be avoided. It has been discovered that this object can be achieved by the process forming the subject matter of the invention, ie a process for preparing powder coating formulations by pressure release of a composition comprising an inert compound of low molecular mass, with release of the inert compound of low molecular mass as a gas or vapor, which is characterized in that one or more basic resins and one or more hardeners for the basic resins or one or more basic self-healing resins and, if desired, conventional coating components additional, as additives and, in the case of colored powder coating materials, pigments, inks and, if desired, fillers, are converted together or separately in a flowable form by heating, the inert compound of low molecular mass is dissolved under pressure at least one of the components of basic resins or hardeners used, either If these components are combined with the other components or in the mixture already prepared, the complete mixture is homogenized, and then the mixture of all the components is released from pressure, with cooling and formation of a powder having a particle size. medium between 10 and 200 μm and a narrow particle size distribution. In the process of the invention the components, especially the basic resin and the hardener, can be brought in a flowable form separately from one another by heating. This procedure prevents a reaction of premature binding. The pigments, fillers and additives can be converted to a flowable melt as a mixture with basic resin component or hardener. It is suitable that these components are mixed with the binder, because in many cases the hardener is used in relatively small amounts. However, it is also possible to carry out the initial mixing of pigments, fillers and additives with the hardener component. The separate liquefaction of the basic resin and the hardener leads to a very short contact time in the mixing section of the process, which contributes to a substantial reduction of any premature interlacing reaction. The supply of inert compound of low molecular mass before or simultaneously with the operation of the mixture of hardening and basic resin components takes place under conditions such that said compound is dissolved under pressure, at least partially, in the mixture or at least in one of the components of the mixture. In the course of the subsequent pressure release, the inert compound of low molecular mass is released and the mixture falls below the solidification temperature of the powder coating formulation. The simultaneous increase in volume of the inert compound of low molecular mass leads to the formation of essentially spherical particles which have a narrow particle size distribution and which can then be isolated. In the case of particularly particularly very reactive substances, the process of the invention can be varied by supplying the inert compound of low molecular mass under pressure before the mixing of the individual components before and / or during the melting of the individual components. In particular it is possible, in the case of powder coating compositions in which the basic resin component and the hardener have a very different viscosity, to dissolve the inert compound of low molecular mass in one of the starting components, such as the resin basic, for example, and then mix this solution with the second component. This variant of the procedure makes it possible on the one hand to reduce the temperature required to heat this component, in which the melt viscosity is reduced and the mixing operation can be carried out at a lower temperature. This is advantageous in the case of highly thermally reactive systems. Alternatively, it is possible in this way to reduce the viscosity of the component before mixing. This is particularly important in the case of powder coating systems with very different viscosities of basic resin components and hardeners, because in these systems the homogeneous mixing of these components in the conventional powder coating preparation process it's hard. In the process of the invention it is possible to bring in line the viscosity of both components by first dissolving the inert component of low molecular mass in the higher viscosity component and being able thereby to adapt the viscosity before the mixing operation. This leads to a better homogenization in the subsequent mixing operation and results in a powder coating having improved service properties. The mixing operation required in the process of the invention may proceed so that, for example, the basic resin and hardener components forming the powder coating composition, and any additives, pigments and fillers, are mixed in a static mixer. with simultaneous addition of the inert compound of low molecular mass. A further possibility is to mix the basic resin and hardener components, with or without the addition of additives, in a static mixer after the separate dissolution of the inert compound in the respective component. In a variant of the process it is also possible to briefly melt the complete powder coating mixture, which consists of basic resin (s), hardener (s), additives, any pigments and fillers, in an extruder, and then dissolve the inert compound of low molecular mass in the mixture under pressure. This can be done using again, for example, a static mixer, which allows a better dispersion of the pigments in the powder coating mixture. In the case of this variant, the residence time in the extruder, in order to avoid premature reaction, is preferably less than 5 minutes. There is another variant of the process in which portions of powder coating waste, especially oversprayed powder coatings from the spray process, are transported to the powder coating components and, if necessary, additives, pigments and / or Extenders before or during their mixing with one another and / or with the inert compound of low molecular mass and are manufactured together with the components mentioned according to the invention by pressure release, with cooling. According to a further embodiment of the invention, the basic resin and hardener components can be used as powder coating overspray or overcoated powder coating mixtures. As a base resin and overcoated powder coating hardener or powder coating overspray mixtures having different compositions can be used. The compound of low molecular mass which is inert towards the basic resin and hardener components is added to the powder coating components, before or after they are mixed, under pressure and temperature conditions that are below or above. the critical pressure and the critical temperature of a gaseous compound of low molecular mass, such as to give a pressurized solution of the compound of low molecular mass in the initial charge of substance or mixture of substances. This operation can occupy, for example, an average time period in the range from 0.1 seconds to 5 minutes, preferably from 1 second to 1 minute, more preferably less than 1 minute, in particular less than 30 seconds. Mix, which is preferably saturated with the compound of low molecular mass, is relieved from its pressure rapidly in a suitable pressure-releasing device. According to the invention, the pressures and temperatures in the mixer are established so that the inert compound is released in the course of the pressure release operation and brings the cooling to such a degree that it is possible to fall below the temperature of solidification of the powder coating formulation to be treated. The powder coating formulation is solidified. Due to the large increase in volume with the release of the inert compound, the solidified powder coating formulation is obtd as a fine powder. After the particles have been separated, they can be fractionated if desired. The mass ratio between the low molecular mass compound and the powder coating formulation or the individual components in this case is preferable between 0.05: 1 and 8: 1, particularly preferably between 0.1: 1 and 2: 1 and, in particular between 0.02: 1 and 1: 1. Thus, in the course of pressure release, the substance mixture at least reaches and preferably falls below its solidification temperature, which in the case of powder coatings is usually between 25 and 70 ° C, is advantageous if certpressure and temperature conditions exist before the pressure release operation. The adapted solidification temperature is the glass transition temperature of the mixture under atmospheric pressure, which can be determined with the help of differential evaluation calorimetry (DSC). Because the glass transition temperature is decreased by the dissolution of the inert lower molecular mass compound according to the invention, it is also possible to spray the mixture below the solidification temperature. Differential evaluation calorimetry (DSC) can be carried out, for example, as described in Schwarzl, Polymermechanik 1990, page 273. A preferred temperature scale is the scale of 20 ° C below and 100 ° C above the solidification under atmospheric temperature. The selection of a suitable inert compound takes place judiciously after having determined the solidification temperature of the substance mixture at atmospheric pressure and the resulting temperature scale for the operation of the mixer. Examples of suitable inert compounds in this context are low molecular weight compounds which are soluble in at least one component of the powder coating formulation and which within the temperature range for the operation of the mixer have reduced temperatures of 0.5 to 2. , preferably 0.7 to 1.7. The reduced temperature is the ratio of the temperature at which the mixture is operated at the critical temperature of the compound of inert low molecular mass in [Kj. The pressure under which the mixing operation is carried out is preferably between 0.5 MP and 60 MPa, with particular preference between 0.1 MPa and 35 MPa and, in particular, between 0.3 MPa and 20 MPa. As an inert compound it is possible in principle to use any substance of inert low molecular mass or any mixture of substances, especially if it meets the above conditions in relation to the reduced temperature and the absolute pressure at the operating temperature of the mixer and is soluble in at least a component of the powder coating formulation. Preferred examples of compounds of low molecular mass which are inert towards the basic resin components and hardeners are carbon dioxide, dinitrogen oxide, ammonia, nitrogen, noble gases, sulfur hexafluoride, halogenated hydrocarbons such as, for example, chlorotrifluoromethane, monofluoromethane , trifluoromonofluoroethane, trifluoromethane, alkanes, such as methane, ethane, propane, n-butane, i-butane, n-pentane and i-pentane, for example, alkenes, such as ethene, propene and butene, for example, ethers, such as dimethyl ether and diethyl ether, for example, amines, such as dimethylamine, for example, alcohols, such as methanol, ethanol and isopropanol, ketones, such as acetone, methyl ethyl ketone and methylisopropyl ketone, esters, such as ethyl acetate and also mixtures of these. Particular preference is given to using carbon dioxide. For a powder coating formulation with a solidification temperature under atmospheric pressure of 45 ° C it is possible, for example, at a mixer temperature of 80 ° C to operate with carbon dioxide (critical temperature: 304.3 K, temperature reduced in temperature of mixer 1.16). For a powder coating formulation having a solidification temperature under atmospheric pressure of 65 ° C it is possible at a mixer temperature of 150 ° C to use methanol (critical temperature: 313.65 K, critical pressure 7.89 MPa, temperature reduced in temperature of mixer: 0.82) as an inert compound. A static mixer is preferably used to mix the individual components of the powder coating formulation and the inert, low molecular mass component. The temperature of this mixer can preferably be regulated. Alternatively, the formation of a homogeneous mixture can also be achieved with stirring or stirring devices or any other device that serves for homogenization, for example an ultra sound source or a rotor-stator apparatus. Additionally, homogeneous mixtures can also be produced by suitable flow guidance, for example by means of tangential flows, jet streams according to the water jet principle, or by impact flow. The mixing action can be improved by means of pressure pulsations imposed. The subsequent pressure release, for example at atmospheric pressure, can take place in several ways. The pressure can, for example, be released spontaneously within a very short period of time, for example in a nozzle, or the pressure release is carried out as a function of time inside the pressure vessel, for example in a period of time. between a few seconds and a number of hours. If necessary, the solution can be released by filtration, before the release of pressure, of mechanical impurities originating from the powder coat overspray, for example, which does not dissolve in the inert compound. The filtration can be carried out batchwise, for example by means of screens, cloths, filter fibers or concretion plates or, preferably continuously, by means of, for example, in-line cartridge filters. The release of spontaneous pressure from the solution or mixture of powder coating formulation and inert compound can take place, for example, by spraying in an environment which is preferably at atmospheric pressure. The intention here is to cool the powder particles formed below their glass transition temperature / solidification temperature, which can take place, for example, using the evaporation enthalphy of the inert liquefied or supercritical compound. It is also possible to choose the ambient temperature which is below the glass transition temperature of the powder coating composition. This can be achieved by indirect cooling of the spray vessel or by direct cooling. In the case of direct cooling, the spray vessel can be cooled by introducing gases, or liquid gases, in the form of jets. The cooling medium can in this case be applied in the area of the pressure release device, in the cover, in the base or in the wall or walls of the spray container. The spraying can take place by means of a spray device connected to the pressure vessel, examples being a blower nozzle, a solid cone nozzle, a hollow cone nozzle, a double substance nozzle, a plate with holes, a capillary valve, manual or automatic, a nozzle / deflection plate system or a rotating disc or a rotating bell. The spraying is preferably carried out vertically. The separation of the particles formed from the gas stream takes place in a known manner by means, for example, of a centrifuge. According to the invention, the resulting powders can be used directly without additional treatment as a powder coating material. If desired, the particles can be separated by subsequent screening, for example on metal meshes, in a class size suitable for a particular application. Through an appropriate choice of processing parameters such as temperature, pressure, flow rate, nozzle type, nozzle diameter, viscosity, concentration of the pressurized solution, for example, it is possible to influence the particle size of the coating particles powdered. The particles generally have a diameter of 1 to 150 μm. Particle sizes from 1 to 100 μm are preferred, with particular preference being given to an average particle size below 50 μm. The process of the invention can also be carried out directly, in the form of a powder coating process. In this case the above described spray of the pressurized solution takes place directly in the direction of a substrate to be coated. After atomization, the powder coating particles formed are cooled below their glass transition temperature before being impregnated onto the surface of the substrate. After coating, the powder coating particles are caused to melt, flow, and if appropriate, are entangled. According to the process of the invention it is possible to process all heat-sealing powder coating compositions or all thermoplastics in which the inert compounds of selected low molecular mass are soluble under suitable temperature and pressure conditions. By "basic resin" is meant the film-forming component of a powder coating material. Suitable examples are basic resins which are customary and are used for powder coating materials and mixtures of these resins, examples being polyester resins, (meth) acrylic copolymers, epoxy resins, phenolic resins, polyurethane resins and siloxane resins. The basic resins possess, for example, glass transition temperatures of 30 to 120 ° C, preferably of less than 80 ° C and, for example, average number (Mn) molar masses of 500 to 20,000, preferably less than 10,000. It is also possible to use unsaturated resins, which are suitable, for example, for radiation curing systems. The crystallizable and semi-crystalline polymers can also be used, for example. As curing component it is possible to use hardeners which are familiar to the person skilled in the art for the basic resin component, examples being amines, phenolic resins, polyfunctional oligomeric epoxides, polyfunctional epoxides of low molecular mass such as triglycidyl isocyanurate, for example, and hydroxyalkylamides. For radiation curing systems it is also possible to use customary initiators. The hardening components possess, for example, molar masses in average number (Mn) of 100 to 10,000, preferably less than 2,000. The selection of the basic resins and hardeners depends on the functional groups that react with each other, and is familiar to the person skilled in the art. In this context it is possible, if desired, to combine several reactive groups with one another. The basic resins and hardeners can on average contain at least two functional groups per molecule. The weight ratio of basic resin to hardener is in general, for example, from 98: 2 to 50:50. Preferably it can be between 96: 5 and 70:30. It is possible that two or more basic resins and two or more hardeners are present in the mixture. As additives it is possible to mix the usual powder coating additives, examples being leveling agents, devolatilizing agents, anti-oxidants, light stabilizers, leveling agents, adhesion promoters, lubricants, catalysts, rheology control agents, and additives to adjust the structure of coating surface. The process of the invention is suitable for the preparation of color and transparent powder coating materials. To produce color powder coating materials it is possible to use all organic or inorganic pigments and inks which are known to the person skilled in the art. By adding fillers such as barium sulfate or calcium carbonate, for example, it is possible to increase the covering capacity of the coating and modify the mechanical and optical properties. The good dispersion of the pigments and / or fillers according to the invention leads to color powders of excellent hiding capacity. The powder coating materials prepared according to the invention can be used, for example, as anti-corrosion coating materials as a decorative industrial coating, for example in the field of facade coatings, office furniture, electrical equipment and automotive accessories. . The thickness of the coating layer can be, for example, between 15 and 200 μm. The process of the invention offers considerable advantages in particular for coatings of <50 μm, which are difficult to carry out with conventional powder coating materials because it allows the preparation of powders having an average particle size of < 40 μm, which is necessary in order to achieve these low coating thicknesses and lead in an excellent way to processing by the usual methods for powder coating materials. The powder coating materials prepared according to the invention are equally suitable as fillers or as a coating for resistance to falling stones, and as base coatings or top coatings. The powder coating materials prepared according to the invention are also used as transparent powder coating materials for example in the automotive sector and, for example, with coating thicknesses of 30 to 150 μm. The powder coating material prepared according to the invention is applied by customary powder coating application techniques, examples being spray application, embedding techniques (such as triboelectric spraying, spray assisted by ESTA, fluidized bed compression assisted by ESTA, and coating procedures by stripes). The methods of the invention make it possible to prepare powder coating materials in a simple manner. The melting by means of temperature-tension bonding of basic resin components and hardeners and extrusion can be avoided. With the process of the invention, finely divided and homogeneous powder coating mixtures can be prepared without laborious milling processes. This is achieved by virtue of the homogeneity of the mixture of powder coating components that can be obtained with the process of the invention, and by the narrow particle size distribution that is achievable, and the morphology similar to a sphere of the powder coating particles resulting. A particular advantage of the process is that the inert compound of low molecular mass can be supplied before and / or during the melting of the individual components. In this way there is only a very slight temperature tension of the basic resin and hardener components. The process additionally allows the contact time between the basic resin and hardener components during the mixing operation to be substantially reduced, to avoid premature reaction of the individual components with one another, especially in the case of components of highly reactive powder coating. The process allows the use of supply materials that can vary greatly in viscosity, and the possibility of predispersing pigments and / or fillers in the resin without side reactions. The attached drawings show illustrative embodiments of the method of the invention. "According to the example described in figure 1, the binder component (s) and the hardening component (s) are melted separately and each of them is thermally conditioned in a separate storage vessel (1), with or without the added mixture of the additives, pigments, fillers in one or both of the reserve vessels, the separately melted components are supplied by pump devices (2) to the mixing point.The inert component is passed at the same time to the mixing point, which from a reservoir (3) is compressed by a compressor device (4) and then supplied to the mixing point.In addition, a heat exchanger (5) is equipped to regulate the temperature of the inert compound. from the mixing point is a mixer (6) preferably of adjustable temperature, in which the homogeneous mixture is produced.After passing through the mixer (6) passes the solution / mixture, for aspersion, au n Pressure release device (8), for example a high pressure nozzle, valve, capillary, or plate with holes, which is integrated in the head of a spray tower (7). In order to avoid a drop in pressure in the mixer (6) during the spraying operation, the inert compound and the individual components of the powder coating formulation are continuously dosed. In the course of the pressure release the inert compound escapes as a gas and the coating composition to be formed in powder is separated into solid particles. The dimensions of the spray towers (7) are such that the particles having an equivalent diameter of >100 μm are preferably deposited by sedimentation. The particles are collected in a discharge vessel (10) or can be discharged continuously with a suitable device. The gas stream that has been released from the relatively large particles leaves the spray towers (7) at the upper end and is supplied to a centrifuge (9). The dimensions of the centrifuge are such that particles having a size of more than 1 μm are deposited preferentially. The particles are collected in a discharge vessel (10) which is mounted at the lower end of the centrifuge, or are discharged continuously from this vessel using a suitable device (safe, screw, fluidized bed with overflow, etc.). Particles having a size below 1 μm can be filtered out of the gas stream left by the centrifuge (9) with the aid of a fine filter, for example an electrofilter. The inert compound can be recovered and supplied back to the reserve vessel (3). An additional exemplary embodiment of the method is shown in Figure 2. This embodiment differs from the embodiment shown in Figure 1 in that one of the two reactive components is first of all brought into contact with the inert compound from the reservoir (3). ) in a mixer (6). Preferably, the component (s) of the powder coating formulation having the highest viscosity is initially mixed with the inert compound. The solution / mixture of inert compound and relevant powder coating component (s) can have a considerably lower viscosity than that of the pure powder coating component (s). The additional component (s) of the powder coating formulation, to which the inert component may have been added if desired, is subsequently added to this mixture / solution to an additional mixing point, and mixed thoroughly in a mixer ( 6). Examples of this variant are the simpler deep mixing and the additional reduction in the contact time of the reactive powder coating components during the mixing and / or dissolving operation. Furthermore, it is therefore possible to avoid casting the relevant powder component (s). The addition of an additional component is not completely ruled out. Pressure release, particle formation, separation, fractionation by particle size, and particle discharge are not different from the modality shown in Figure 1.

EXAMPLE 1 In a unit corresponding to Figure 1, 20 kg of a glycidyl methacrylate copolymer customary for the preparation of powder coating materials are charged as a melt at a temperature of 136 ° C to a reserve vessel. 5 kg of Additol VXL 1381 (anhydride hardener) as hardener component is discharged as a melt at a temperature of 10 ° C to an additional storage vessel. The two components are supplied by dosing pumps to a static mixer (SMX type, Sulzer, length 200 mm). The mass flow of the binder is 10 kg / h and that of the hardener is 2 kg / h. In the static mixer, carbon dioxide is added to the powder coating formulation and is at least partially dissolved. The temperature of the carbon dioxide is chosen so that the temperature in the static mixer is 105 ° C. The solidification temperature of the powder coating mixture is determined by differential thermal analysis as 87 ° C. The pressure is 110 bar. The mass flow of carbon dioxide is 7 kg / h. After the mixture has passed through the static mixer, the pressure release takes place in a usual commercial high pressure nozzle with an outlet diameter of 0.8 mm. The nozzle is integrated in the top of a spray tower. The temperature in the spray tower in the course of the spray operation is 39 ° C. This is clearly below the solidification temperature of 87 ° C of the powder coating formulation produced. The carbon dioxide released in the course of the pressure release is extracted by suction using a fan, together with the fine fraction of the powder that has been formed, and is passed through a centrifuge. The gas extracted by suction from the centrifuge is passed through an ultrafine filter paper before passing through the suction fan. After a spray time of 45 minutes, a total of 10 kg of a powdery powder coating formulation are removed from the spray towers (1 kg), the centrifuge (8.95 kg) and the ultra-fine filter (approximately 50 g) . The average fraction obtained from the centrifuge has a mean particle size of 22 μm. This product is applied to a steel panel using the ESTA technique in a coating device. After curing at 130 ° C, a homogeneous, firmly adhering coating having an average coating thickness of 35 μm is obtained.

EXAMPLE 2 In a unit corresponding to Figure 2, 20 kg of a glycidyl methacrylate copolymer customary for the preparation of powder coating materials are charged as a melt at a temperature of 136 ° C to a reserve vessel. 5 kg of Additol VXL 1381 as hardener component are charged as a melt at a temperature of 100 ° C to an additional storage vessel. The binder is supplied with a dosing pump to a first static mixer (SMX type, from Sulzer, length 70 mm). The mass flow of the binder is 10 kg / h. In the first static mixer, the carbon dioxide as an inert compound is mixed with the binder and dissolved at least partially. After passing through the first static mixer, the hardening component is added with a mass flow of 2 kg / h to the solution / mixture of binder and inert compound, which now has a low viscosity, and the resulting mixture is deeply mixed in a second static mixer (SMX type, from Sulzer, length 200 mm). The temperature in this mixer is 123 ° C. The pressure is 105 bar. The mass flow of carbon dioxide is 8.2 kg / h. The temperature in the spray tower is 44 ° C. After a 30-minute spray time, 0.75 kg of a powdered powder coating formulation is removed from the spray tower, 5.23 kg from the centrifuge and 0.02 kg from the ultrafine filter. The average particle size of the average fraction recovered from the centrifuge is 34 μm. The properties of the coating film produced with this product are not different from those in Example 1.

Claims (14)

NOVELTY OF THE INVENTION CLAIMS

1. - A method for the preparation of reactive powder coating formulations by releasing pressure of a composition comprising an inert compound of low molecular mass, with release of the inert compound of low molecular mass, characterized in that one or more basic resins and one or more hardeners for the basic resins, or one or more basic self-healing resins, and, if desired, additional customary coating components, are converted together or separately into a flowable form by heating, the inert compound of low molecular mass is dissolved under pressure at least one of the components of basic resins or hardeners used, either before these components are combined with the other components or in the mixture already prepared, the complete mixture is homogenized for a time of 0.1 seconds and 5 minutes , and then the mixing of all the components is released from pressure, with cooling.

2. The process according to claim 1, further characterized in that the mass ratio of the low molecular weight compound to the powder coating formulation is 0.05: 1 to 8: 1.

3. The process according to any of the preceding claims, further characterized in that the operation of mixing the powder coating formulation with inert compound is carried out on a temperature scale of up to 20 K below or 100 K per above the solidification temperature of the powder coating formulation at atmospheric pressure.

4. The process according to one of the preceding claims, further characterized in that the pressure under which the mixing operation is carried out is between 0.5 MPa and 60 MPa.

5. The process according to one of the preceding claims, further characterized in that the mixing time of the components with the inert compound is less than 1 minute.

6. The process according to one of the preceding claims, further characterized in that the inert compound of low molecular mass is dissolved before mixing in the component of higher viscosity.

7. The process according to one of the preceding claims, further characterized in that the basic resins used are polyester resins, (meta) acrylic copolymers, epoxy resins, phenolic resins, polyurethane resins and / or siloxane resins.

8. The process according to claim 7, further characterized in that the basic crystallizable and / or semicrystalline resins are used.

9. The process according to one of the preceding claims, further characterized in that the over coating of powder coating is used in addition to the basic resins and hardeners. The process according to one of claims 1 to 8, further characterized in that the basic resins and the hardeners are used in the form of powder coating overspray or powder coating overspray mixtures. 11. The process according to one of the preceding claims, further characterized in that the carbon dioxide is used as an inert compound of low molecular mass. 12. The process according to one of the preceding claims, further characterized in that it is carried out in the form of a powder coating process, with release of pressure taking place directly in the direction of a substrate to be coated. 13. The powder coating formulation obtainable by the process of one of claims 1 to 11. 14. The powder coating formulation according to claim 13, which consists of particles with a sphere-like morphology and a narrow particle size distribution and an adjustable average particle size of less than 100 μm.