MXPA99007601A - Ball-shaped polyester particles, production thereof and use of same for powder lacquers - Google Patents

Abstract

The invention concerns homogeneously tinted polyester particles of an average size<50&mgr;m, having a monomodal granulometric distribution per particle (=d90-d10/d50)=2,5. At temperatures<200°C, these particles can be molten to form a continuous coating. The invention also relates to the process of production of same and their use as powder lacquers. In the preferred embodiment, the particles contain units of formulae (1) -CO-X-CO and (2) -O-D-O-, in which X represents a substituted or non-substituted aromatic residue C6 to C14 or an alkylene, polymethylene, cycloalkane or dimethylene-cycloalkane group or an alkandiyle group in a straight or branched chain, possibly unsaturated, and D represents an alkylene, polymethylene, dimethylene-cycloalkane group or an alcandiyle group in a straight or branched chain, possibly unsaturated.

Description

DYEED SPHERICAL POLYESTER PARTICLES. PROCESS FOR PREPARATION AND USE FOR POWDER COATINGS DESCRIPTIVE MEMORY The present invention relates to homogenously dyed spherical polyester particles with particle sizes of < 50 μm, which form a continuous coating at temperatures < 200 ° C, to the procedure for its preparation and to its use as powder coatings. Powder coatings generally consist of a crosslinkable film-forming polymer, additives such as, for example, flow improvers or devolatilization auxiliaries and, in the case of dyed powder coatings or coatings, pigments and if you want, fillers. Powder coatings are traditionally prepared by subjecting the aforementioned components to intensive blends in an extruder at a temperature above the softening temperature of the film-forming polymer, but below the interlacing temperature and then, by a process of grinding, bring the resulting extruded material to an average particle size of about 40 to 70 μm. The grinding process leads to the fact that the powders of irregular structure, (means those powders having an average particle size notably less than 30 μm), can not be further processed, by means of the electrostatic spray techniques used in the coating process powdered. For example, EP-A-0 459 048 mentions that the powder coating compositions have a particle size of less than 15 μm and can not be processed by means of the electrostatic spray technique. The ground powders that were used in the prior art have an average particle diameter of about 40 to 70 μm and typically result in a layer thickness of 40 to 70 μm. The grinding technology produces, in particular, a very wide distribution of particle size. In addition, an extension of this distribution is observed increasing the fineness of the powders. The amplitude of a particle size distribution is characterized using not only the d50 parameter, for which only 50% of the particles are greater than or less than the d50 value, but also using two additional parameters: d10 designates the size of particle for which 10% of the particles are smaller than their limit value. Correspondingly, d90 designates the particle size for which 90% of the particles are finer than the d90 value. The amplitude of the particle size distribution is generally characterized because it forms a quotient defined as the interval and is calculated according to the following formula: interval = d90-d10 / d50. The relationship is, therefore: the smaller the interval, the narrower the particle size distribution. A powder consisting of spheres identical in size will have a range of 0. For the ground powders of the prior art, with an average particle size d50 of 50 μm, a range of 3-4 is typically obtained. Based on economical aspects , (lower consumption of material) but also because of the technical advantages (greater flexibility of the coating) a relatively low layer thickness is desirable for the powder coatings. A relatively low layer thickness can be achieved only by reducing the particle size of the powder. Another critical factor is that the powders have a very narrow particle size distribution, since otherwise there are difficulties in processing, especially with a very high content of fine particles. Therefore, there has been no lack of attempts in the past to obtain a reduction in particle size of powder coatings by means of new technologies without incurring the aforementioned disadvantages in powder processing capacity. The objective is, in general, prepare particles with an almost ideal spherical shape, since said powders exhibit substantially more favorable flow behavior than irregularly ground powders. And it has been tried, for example, to prepare almost spherical particles by sprinkling molten polymer materials. However, the results presented in WO 92/00342 indicate, that this leads only to moderate success. The particles obtained by means of this technique, although they have a smoother surface than the ground powders, are still far from the ideal structure of a sphere.

Another method that has been investigated for the preparation of spherical particles is the spraying of polymers from a supercritical solution, as described, for example in EP-A-0 661 091 or EP-A-0 792 999. This method is also It has substantial disadvantages. For example, in the cited acations it is mentioned that, due to the sudden evaporation of the supercritical "solvent", a powder having a porous structure is obtained. If these powders are used to prepare films there is - in comparison with non-porous powders - an increased presence of bubble formation and therefore of defects in the coating, since the porous structure means that a large amount of gas has been trapped. in the dust and must be removed in the course of the process of forming the film. Moreover, the use of supercritical solvents is technically complex because, for example, an operation is required under high pressures. One method to produce spherical particles that differs in this principle is the production of a dispersion. Physical laws establish that in a dispersion, the perfect spherical shape is the preferred geometry of the particles obtained. Under appropriate conditions it is possible to prepare spherical particles having a very narrow particle distribution. Accordingly, there has been no lack of attempts in the past to obtain polymer particles that can be used as binders in coating systems, preferably in liquid and highly solid coating systems, by preparing them under dispersion (Keith Barett, Dispersion Polymerization in Organic Media, John Wiley & Sons, London, 1975). GB-1 373 531, for example, describes the preparation of stable dispersions of polycondensation polymers, such as polyesters. The possibility of using polymer particles from non-aqueous dispersion processes based in particular on polyesters, such as a powder coating, is discussed in DE-C-21 52515. In this part, an existing polymer is brought to dispersion at a temperature < 200 ° C and coloration is obtained by adding pigments, preferably after the dispersion has cooled below the "solidification point" of the polymer particles. The resulting particles are described as substantially spherical "aggregates" of primary polymer particles, having a particle size of 0.05 to 20 μm and pigment particles. The aggregates are described as secondary particles, and have a particle size of about 10 to 90 μm or 100 to 300 μm and are obtained by spraying the dispersion. In the described process, pigments are added at room temperature or at only slightly elevated temperature, which means that the pigment particles only adhere without cohesion to the polymer particles; Experience has shown that this leads to problems in relation to the powder process, since the pigment separation of the polymer binder is carried out. The possibility of adding pigments at a relatively high temperature prior to the solidification of the binder is described as difficult and not preferable, because there may be some change in the particle size.

Furthermore, methods for defining how to prepare the powder coating systems which are interlaced at desired low temperatures between 20 and up to 200 ° C are not indicated. All the interlacing systems mentioned have an interlacing temperature that is above the temperature required for the dispersion. Furthermore, the use, as described in DE-C-21 52 515, of a polymer that has been condensed to high molecular weights as a starting material for the preparation of the dispersion, has the following disadvantages: the already considerable viscosity of polymers, which in the case of polymers used commercially is in the range of 3000 to 20, 000 mPas (at 200 ° C) which makes it difficult to achieve a good division of the molten material and obtain a homogeneous particle size distribution. The object of the present invention, consequently, is to provide homogeneously stained spherical polyester particles, which have a very small particle size and a narrow particle size distribution, with which there is no separation of the pigments from the polymeric binder in the course of the powder process, and which can be processed and, if desired, interlaced even at low temperatures to form a continuous coating, and therefore, are suitable for use as powder coatings. The present invention accomplishes this objective and provides non-porous, spherical and homogenously dyed polyester particles that can be interlaced as desired, having an average particle size.50 μm and a monomodal particle size distribution (d90-d10 / d50) < 2.5, which can be melted at temperatures < 200 ° C to form a continuous coating. The novel polyester particles, spherical, homogeneously dyed, which can be entangled if desired, are prepared by: a) dispersing the starting materials for a polyester binder in a high boiling inert heat transfer medium at a temperature which at least it is as high as the softening temperature of the starting materials, in the presence of at least one polymeric dispersion stabilizer, preferably organic, and b) then heating the reaction mixture to a temperature in the range of 120 to 280 ° C. , with the simultaneous removal of the secondary condensation products, until the polyester has the desired molecular weight; c) Subsequently, on the temperature scale of 140 to 220 ° C, add dyes, pigments and / or fillers and also, if desired, additional additives; d) subsequently, cooling the reaction mixture, in the case of a crosslinkable functional polyester, to a temperature in the range of 60 to 140 ° C and adding at least one polyfunctional crosslinking agent or epoxy resin, and e) subsequently reducing the temperature to a scale that is below the softening temperature of the polyester and separating the resultant particles of spherical polyester dyed homogeneously. The starting materials used are preferably oligoesters having a viscosity less than 1000 mPas (measured at 200 ° C), in particular < 500 mPas, which consists of units of the formulas (D and (2) -CO-X-CO -ODO-, (1) (2) wherein X is a substituted or unsubstituted C6 to C14 aromatic radical or an alkylene, polymethylene, cycloalkane or dimethylenecycloalkane group or a straight or branched chain alkanediyl group, saturated or unsaturated and D is an alkylene, polymethylene, cycloalkane or dimethylenecycloalkane group or a straight or branched chain, saturated or unsaturated alkanediyl group. To save time it is preferred to first prepare all the oligoesters of the composition described above in the melt by heating the carboxylic acid components, such as terephthalic, isophthalic, adipic or fumaric acid to name but a few, in the form of acid or as esters of low molecular weight alkyl, together with the diol components, for example ethylene glycol, diethylene glycol, neopentyl glycol or bi-hydroxymethylcyclohexane, in the melt in the presence of a transesterification catalyst, such as manganese acetate or zinc salts or tin salts, until that most condensation products are wet or until the lower alkanols have been distilled off, respectively. However, in the course of this operation, no significant increase in the viscosity of the melt is observed. At 200 ° C the viscosity is still < 1000 mPas. An oligomeric mixture of this kind can be converted directly, for example, into a novel dispersion at elevated temperature by the combination with the heat transfer oil and the dispersant. This method is preferred for large-scale industrial preparation. However, it is also possible to cool the mixture of oligomers for the purpose of storing it and heating it again later. In general, it is also possible to carry out the preparation of the oligomers in the effective dispersion. In a practical embodiment of the novel process, starting materials preferably as a mixture of oligomers are mixed in step (a) in an inert high boiling heat transfer medium, the mixture is heated to an elevated temperature which must be supported on the softening temperature of the starting materials, reasonably in the range from 150 to 280 ° C, and then at least one dispersion stabilizer or a dispersion stabilizer mixture is incorporated with heat transfer media (dispersion media) ) which have proven to be particularly suitable and which are aliphatic heat transfer oils having a boiling point on the scale of 150 to 300 ° C. Said heat transfer oils are - in the technical sense - free of aromatic structural groups; in other words, they contain less than 2% by weight, preferably less than 1% by weight, of aromatic constituents. Due to the low polarity of these oils, which are marketed, for example, by Exxon Chemical under the trade names of © Isopar, © Exxsol or © Norpar, the polyesters do not dilate.

This is a problem that occurs in some cases for aromatic oils, which in principle are equally suitable for the dispersion process. The general rules for the design of appropriate polymer dispersion stabilizers are provided in "Keith, Barett, Dispersion Polymerization in Organic Media, John Wiley & Sons, London, 1975"on pages 45 to 1 10. The main requirements are the solubility of the polymer dispersion stabilizer in the dispersion medium used, and the polar or reactive groups that allow a strong interaction with the particles to be dispersed. In the novel process, it is preferred to use amphiphilic copolymers or inorganic compounds with modified surface.

Examples of the latter are the surface-modified phyllosilicates with trialkylammonium salts, especially bentonite with surface modified with trialkylammonium salts, or amphiphilic copolymers consisting of a polar polymer unit, for example poly-N-vinyl pyrrolidone and a polymer unit non-polar, for example long chain α-olefins such as 1-eicosene. These amphiphilic copolymers are sold by the ISP company Global under the trade name of © Antaron and have been found particularly appropriate. As described, for example in EP-B-O 392 285, the Antaron has already been used successfully at relatively low temperatures to stabilize the polyurethane dispersions. It has been found that Antaron can also be used to advantage, however at temperatures above 300 ° C and results in excellent dispersion stability. The content of the dispersion stabilizer is, according to the invention, of the scale of 0.1 to 6% by weight based on the polyester starting materials, preferably in the range of 0.3 to 4% by weight and, in particular, on the scale of 0.5 to 2% by weight to obtain particles having the desired size. In the next step (b) the reaction mixture is further heated to a temperature in the range of 120 to 280 ° C, in particular to 200 to 250 ° C, with the resulting condensation by-products extracted in parallel. The temperature is maintained until the polyester has reached the desired molecular weight, which is located on the scale Mn = 500 to 20,000, preferably on the scale of 1,000 to 10,000. Of decisive importance for molecular weight is the duration of the reaction, which can be monitored by taking samples. To increase the functionality of the polyester, it is possible to add polyfunctional components to the interlacing systems, after the required molecular weight has been reached, subsequent to step (b). For example, polyfunctional carboxylic acids or alcohols, for example trimellitic anhydride, are added at the same reaction temperature, and heating is continued for a time to ensure that the added components are incorporated. After the termination of the condensation in step (b) it is also possible to add additives such as flow aids or devolatilization aids, for example, to optimize the polyester-coating properties since optimum surface quality is desirable. the finishes of the powder coating). This is carried out by cooling the mixture to 160 or 200 ° C and adding the desired additives at the same time that the reaction mixture is stirred. The addition of additives can be carried out separately or in combination with the addition of dyes and pigments. Additives that are customary in powder coating technology, such as flow improvers or defoamers, can be added as described above without negatively impacting the dispersion stability in the particle formulation.

Subsequent to (c), at a temperature markedly above the softening point of the polyester, preferably on the scale of 140 ° C to 220 ° C, fillers are added, for example calcium carbonate, barium sulfate, titanium dioxide, mica, talc, dolomite or wollastonite, and dyes and / or pigments for dyeing the polyester particles. To establish the color, it is possible to use all customary commercial organic and inorganic pigments or dyes, which are stable temperature at least up to 200 ° C or up to the curing temperature of the powder coating system. The dyes or pigments that meet these requirements are listed, for example in "David A. Bate, "The science of powder coatings" Volume 1, SITA Technology, ISBN 0 947798005. If desired, it is also possible to use mixtures of different pigments or dyes to establish the color. In an embodiment which is preferred according to the invention, the dyes, pigments and / or fillers, before they are added to the reaction mixture, are dispersed in the presence of dispersion stabilizer amounts which are sufficient for the dispersion, preferably in the the heat transfer medium used, and the dispersion is preheated to the temperature of the reaction mixture. In this form, it is possible to achieve intensive and highly homogeneous coloration of the same polyester particles that adhere even if the powders are further processed.

The reaction mixture is subsequently cooled to a temperature in the range of 60 to 140 ° C, in particular 80 to 120 ° C, and in the case of a crosslinkable functional polyester, at least one polyfunctional crosslinking agent or a resin is added. Epoxy By this method, it is possible to avoid the entanglement reaction to the point where the coatings obtained from the powders having the gel times used for 2 to 5 minutes at the firing temperature (eg 180 ° C). Therefore, novel powder coatings are not different in terms of firing temperatures and gel times from conventional systems obtained by extrusion and grinding. The novel polyesters can both exhibit thermoplastic behavior and contain functional groups that are subsequently interlaced. Accordingly, the carboxyl groups of functional polyesters can be entangled, for example, with epoxides. Examples of the customary compositions of said polyesters are presented in the following monograph: "David A. Bate," The science of powder coatings "Volume 1, SITA Technology, ISB 0 947798005, with explicit reference thereto. Examples of typical raw materials that can be used for functional polyesters are the following dicarboxylic acids, or their low molecular mass esters: terephthalic, isophthalic, adipic, sebacic, phthalic, and fumaric acid Examples of the diol components that can be employed they are ethylene glycol, diethylene glycol, neopentyl glycol, hexaneidol, and bihydroxymethylcyclohexane.In the abovementioned literature, a review of the crosslinking agents used for functional polyesters and the required additives, for example, flow improvers is presented.As examples of the crosslinkers typical are triglycidyl isocyanurate (®Araldite PT 810), resin s epoxies that are based on bisglycidyl bisphenol A or, in addition, β-hydroxyalkylamides (e.g. ® Primid XL 552). The content of the crosslinking agent is usually from 2 to 20% by weight, preferably from 5 to 10% by weight, preferably from 5 to 10% by weight, based on the polyester component, but for the hybrid epoxy / polyester systems mentioned above , can reach up to 50% by weight. Following the addition of the interlacing agent, the temperature of the reaction mixture is reduced to a temperature which is below the softening temperature of the polyester, preferably < 60 ° C. In this process the polyester is obtained in powder form. The resulting homogenously stained spherical polyester particles are separated from the supernatant reaction solution, and purified if desired. The polyester particles obtained by means of the described process are transparent and can be prepared with any desired molecular weight, for example on the scale from Mn = 500 to Mn = 50,000. The performance is > 95%, in general even greater than > 98%, especially if the reaction is conducted relatively on a large scale.

There really are no cases of adhesion in the reactor that would lead to a reduction in performance. By means of the novel processes it is possible to obtain homogeneously stained spherical polyester particles, having an average particle size (d50) < 50 μm, preferably < 40 μm and in particular < 30 μm and a particle distribution of monomodal particle size (d90-d10 / d50) < 2.5, in particular < 2.0 and, preferably < fifteen. The polyester particles obtained are also notable for the fact that after application to an appropriate surface they can be melted at temperatures below 200 ° C, and in particular at temperatures in the range of 120 to 200 ° C, preferably 160 at 200 ° C, to form a continuous coating, which in the case of interlaced polyesters can also be cured at these temperatures. Due to its narrow particle size distribution, the novel polymer spherical particles are extremely suitable for processing by means of customary powder coating technology techniques., and result in homogenously dyed coatings that have a very good surface. Compared with the known powders, when the novel polyester powders are processed for the powder coat finishes, there is no separation of the pigment particles from the polymer particles. The coatings produced in this way, therefore, offer a highly homogeneous uniform coloration, and an excellent cover dust. Compared with conventional powders, which normally give a layer thickness of 50 to 70 μm, it is possible to use the polyester powders described herein to produce layers having thicknesses of <; 50 μm preferably coatings having thicknesses in the range from 50 to 40 μm, in particular from 10 to 35 μm. The following examples are intended to illustrate the invention: EXAMPLES EXAMPLE 1 Prepare an oliomer mixture as starting material for the preparation of a crosslinked polyester powder coating. 4090 g of dimethyl terephthalate (21.06 moles), 888.4 g of dimethyl isophthalate (4.58 moles), 2814 g of neopentyl glycol (27.05 moles) and 1.5 g of manganese (II) acetate tetrahydrate as a catalyst are weighed into a round-bottomed flask of four necks 101. The flask is connected to a compact column (1 = 10 cm) equipped with a distillation accessory. The reaction mixture is then brought to 150 ° C under an inert gas environment. At this temperature, all the monomers have melted. Subsequently, at this temperature, the esterification begins. The temperature is controlled so that the maximum temperature does not exceed 75 ° C. The internal temperature is increased from 150 ° C to 225 ° C over the course of 4 hours to remove as much of the methanol as possible from the reaction mixture. 6181.1 g of the oligomer mixture and 1448.8 g of methanol are isolated (theoretical: 1640 g of methanol).

EXAMPLE 2 Prepare an oliqomer mixture for thermoplastic polyesters. 2475 g of dimethyl terephthalate (12.75 moles), 2250 of dimethyl isophthalate (11.59 moles), 450 g of neopentyl glycol (4.33 moles), 2500 g of ethylene glycol (40.28 moles), 252 g of diethylene glycol (2.37 moles) are weighed and 1485 g of manganese (II) acetate tetrahydrate in a four-neck round bottom flask 101. Under an inert gas atmosphere, the reaction mixture is heated to a temperature of 150 ° C. At this temperature all the monomers have melted. The methanol formed is distilled via a compact column (1 = 10 cm) with a distillation bridge. The temperature is controlled so that the maximum temperature does not exceed 75 ° C. The reaction mixture is heated to a temperature of 225 ° C to remove as much as possible, the amount of methanol from the reaction mixture. 1555 g of methanol (theoretically 1557 g) were distilled off. Upon cooling to room temperature, a highly viscous oligomer mixture of 6240 g was given.

EXAMPLE 3 Prepare dyed interlacing powder coatings From 225 g of the oligomer mixture prepared in Example 1, 180 g of Isopar P and 45 g of Isopar L as a heat transfer oil, 88 mg of antimony trioxide as the esterification catalyst, and the amount of Antarctone V were weighed. 220 (ISP Global) indicated in Table 1, as a dispersant (Antarcton 1), in a reactor 11 with a water separator, and the mixture was heated under an inert gas environment. As soon as all the components have melted (internal temperature approx. 150 ° C) the stirrer is switched on and the mixture is heated with vigorous stirring to the boiling temperature of the heat transfer oil (approximately 230 ° C). The reaction mixture is held at this temperature for 1 hour, during which small amounts of methanol and neopentyl glycol are separated. Subsequently, 16.5 g of trimellitic anhydride are added and the mixture is boiled for a further 30 minutes. Few ml of the distilled material are obtained. Subsequently, the heat bath is removed and the dispersion is allowed to cool slowly. When the internal temperature is in the range between 200 and 160 ° C, the dispersion prepared in advance, preheated to the same temperature and containing the amounts mentioned in Table 1, of pigment, dye and dispersant (Antarón 2) is added. ) and auxiliaries ®BYK 360 P (3.4 g, BYK Chemie) as a flow improver and 0.9 g of benzoin as a devolatilizing aid, in Isopar L. This dispersion is obtained by heating all components to approximately 100 ° C under shear conditions. The mixture is subsequently allowed to cool to a temperature of 100 to 120 ° C and, within this temperature range, 15.7 g trigicidyl isocyanurate (TGIC) is added. After cooling to room temperature, the powder is isolated by filtration, washed with low boiling hydrocarbons and dried. Spherical powders of highly free flow are obtained, which have the particle sizes established in Table 1 and which can be processed by means of the electrostatic spray techniques used to finish powder coatings. Curing at 180 ° C for 20 minutes produces coatings that have good adhesion and excellent surface quality. The film thicknesses obtained are listed in Table 1 below.

TABLE 1 EXAMPLE 4 Prepare thermoplastic powder coatings 300 g of oligomer mixture of example 3, 150 g of Isopar P and 150 g of Isopar L as heat transfer oils are weighed, and also Antarón of V 220 (see quantities in Table 2) as a dispersion stabilizer and 100 mg of antimony trioxide as esterification catalyst in a 1 l reactor with a water separator. The reactor is connected to the water separator. The reaction mixture is subsequently heated by vigorously stirring at an internal temperature of 217 ° C (commencement of the boiling of the heat transfer oil). Distillation begins at approximately 20 ° C below the boiling point of the heat transfer medium (t = 0 minutes). The distillation is continued for 4 hours at an internal temperature of 217 to 218 ° C. During this time, approximately 82 ml of a mixture of ethylene glycol, neopentyl glycol and diethylene glycol are distilled by azeotropic distillation with the heat transfer medium. The majority of the distillates consist of ethylene glycol. Subsequently the heat bath is removed and the mixture is allowed to cool when shaken. On the temperature scale between 200 and 160 ° C the amounts of pigment or dye indicated in Table 2, dispersed in little or Isopar L, are added. The mixture is cooled to room temperature while stirring. The polyester powder is separated from the heat transfer oil by means of filtration. To remove adhesion heat transfer oil, the polyester particles are washed 3 times with isohexane and subsequently dried at 30 ° C / 0.1 mbar for 3 hours. Stained spherical particles are obtained having average particle sizes and particle size distributions established in Table 2. The dust yield is considered between 95 and 98% theory.

TABLE 2 The powders were electrostatically sprayed on metal surfaces and melted at 180 ° C for 10 minutes. Homogeneous coatings are obtained with good adhesion of excellent surface quality. The layer thicknesses are listed in table 2.

Claims (22)

NOVELTY OF THE INVENTION CLAIMS

1. - Polyester particles having an average particle size of < 50 μm, which are homogenously stained and spherical, having a monomodal particle size distribution with an interval (= d90-d10 / d50) < 2.5 and can be melted at temperatures of < 200 ° C to form a continuous coating.

2. Polyester particles according to claim 1, which have a molecular weight Pm in the range of 500 to 50,000.

3. Polyester particles according to claim 1 or 2, which have a monomodal particle size distribution with a range (= d90-d10 / d50) < 2.0.

4. Polyester particles according to at least one of claims 1 to 3, which can be used to produce coatings having a thickness in the scale of < 50 μm.

5. Polyester particles according to at least one of claims 1 to 4, which consist of units of formulas (1) and (2) -CO-X-CO -ODO-, (D (2) wherein X is a substituted or unsubstituted C6 to C? 4 aromatic radical or an alkylene, polymethylene, cycloalkane or dimethylene cycloalkane group or a saturated or unsaturated straight or branched chain alkanediyl group and; D is an alkylene group, polymethylene, cycloalkane or dimethylene cycloalkane or a straight or branched chain, saturated or unsaturated alkanediyl group 6.

The use of polyester particles according to at least one of claims 1 to 5, for powder coatings.

Process for preparing homogeneously stained spherical polyester particles having a range of (d90-d10 / d50) < 2.5 by means of: a) dispersing the starting materials for a polyester binder in an inert heat transfer medium from aita boiling which contains mostly 2% aromatic components at a temperature which is at least as high as the softening temperature of the starting materials, in the presence of at least one polymeric dispersion stabilizer, which is an amphiphilic copolymer or a anorganic compound with modified surface, and b) subsequently heat the reaction mixture to a temperature in the range of 120 to 280 ° C, with the simultaneous removal of the secondary condensation products, until the polyester has a molecular weight on the scale of 500 to 20,000; c) the subsequent addition of fillers, dyes and / or pigments, and if desired, additional additives at a temperature in the range of 140 to 220 ° C; d) in the case of crosslinkable functional polyesters, the subsequent cooling of the reaction mixture at a temperature in the range of 60 to 140 ° C and the addition of at least one polyfunctional crosslinking agent or an epoxy resin, and the further reduction of the temperature on a scale that is less than the softening temperature of the polyester and separating the resultant particles from homogenously dyed spherical polyesters.

8. The process according to claim 7, further characterized in that compounds are used as starting materials comprising units of formulas (1) and (II) CO-X-CO -ODO- (1) (2) in where X is an aromatic radical from Ce to C? substituted or unsubstituted or an alkylene, polymethylene, cycloalkane or dimethylenecycloalkane group or a straight or branched chain, saturated or unsaturated alkanediyl group and D is an alkylene, polymethylene, cycloalkane or dimethylenecycloalkane group or a straight or branched chain alkanediyl group, saturated or unsaturated.

9. The process according to claim 7 or 8, further characterized in that the starting materials are heated in step (a) at a temperature in the range of 150 to 280 ° C.

10. The method according to at least one of claims 7 to 9, further characterized in that the heat transfer medium used has a boiling point in the range of 150 to 300 ° C.

11. The process according to at least one of claims 7 to 10, further characterized in that the content of the interlacing agent is in the range of 5 to 20% by weight, based on the starting materials.

12. - The method according to at least one of claims 7 to 11, further characterized in that fillers, dyes or pigments, before being added, are dispersed in step (c) in the heat transfer medium used, in the presence of sufficient quantities of dispersion stabilizer, and this dispersion is preheated to the temperature of the reaction mixture.

13. The process according to at least one of claims 7 to 12, further characterized in that the dyes or pigments that were added in step (c) are stable at temperatures of up to 200 ° C.

14. The process according to at least one of claims 7 to 13, further characterized in that an amphiphilic copolymer is used as dispersion stabilizer.

15. The method according to at least one of claims 7 to 14, characterized in that ®Antaron V is used 220 as a dispersion stabilizer.

16. The process according to at least one of claims 7 to 15, further characterized in that subsequent to step (b) and after the required molecular weight has been reached, polyfunctional components are added to increase the functionality of the polyester.

17. The process according to at least one of claims 7 to 16, further characterized in that after concluding the condensation in step (b), the reaction mixture is cooled to 160 ° C to 200 ° C and suitable additives are added to optimize the coating properties of the polyester.

18. The conformity method according to at least one of claims 7 to 17, further characterized in that the polyesters obtained have a molecular weight Pm in the range of 500 to 50,000.

19. The process according to at least one of claims 7 to 18, further characterized in that polyester particles are obtained in powder form.

20. The process according to at least one of claims 7 to 19, further characterized in that the polyester particles obtained have a monomodal particle size distribution with a range (d90-d10 / d59) of < 2.5.

21. The process according to at least one of claims 7 to 20, further characterized in that the obtained polyester particles can be used to produce powder coating finishes having a coating thickness of < 50μm 22.- Polyester spherical particles, homogenously dyed, having an average particle size of < 50μm, which have been prepared by means of the process according to one or more of claims 7 to 21.