MXPA99009183A - Spherical particles of a coating composition - Google Patents

Abstract

Spherical particles of a copolymer composition comprising a crosslinker and/or coating additive(s), the particles being especially useful for coating varioussubstrates;and an improved process for making such particles comprising forming the copolymer and unreacted crosslinker and/or other additives in a coating matrix.

Description

SPHERICAL PARTICLES OF A COATING COMPOSITION BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a method for - producing spherical particles of copolymers and one or more coating additives and / or crosslinkers, the particles being useful for coating substrates; and the particles themselves.

State of the Art This invention is an improvement in the process described in U.S. Patent Nos. 4,056,653 and 3,933,954. The improvement comprises the formation of substantially spherical particles containing the coating copolymer and other additives typically employed in coatings of such a copolymer. The problem solved by the improved process is how to produce spherical particles having various components, in addition to the copolymer, to REF: 31231 from a wide range of copolymers than those suggested by the cited patents. The application of such particles to a substrate (eg, in a fluidized bed) produces coatings ready to be crosslinked by means recognized in the art, on durable surfaces, aesthetically pleasing, resistant to chemical attack and delamination. To date, spherical particles such as those described have not been known. The careful selection of the particulate components and the time / temperature profile used during the formation of the particles ensures the easy and rapid application of all the coating components necessary for the substrate, from the matrix of spherical particles that contain them, in a simple fluidized bed immersion step.

BRIEF DESCRIPTION OF THE INVENTION This invention relates to an improved process for producing substantially spherical particles of a copolymer, comprising the steps: i) the shear stress, under pressure, and at an elevated temperature, of a surfactant and the components of a crosslinkable copolymer, to form a homogeneous aqueous suspension of particles; ii) stirring the suspension under pressure at a temperature above the melting point of the copolymer, to make the substantially spherical particles; iii) cooling and stirring the suspension, at a temperature below the melting point of the copolymer; wherein the improvement comprises: a) the addition to the components in step (i) of at least one member selected from the group consisting of one or more coating additives and the crosslinker; b) the use of a time / temperature profile in steps (i) and (ii) to prevent a significant degree of crosslinking during the formation of the particles; c) the optional addition of an additional surfactant to step (i) in an amount sufficient to form substantially spherical particles of a crosslinkable combination of copolymer, one or more coating additives and the crosslinker. By "substantially spherical" it is meant that the particles comprise a uniform and smooth radius of curvature, by 'time / temperature profile' it is understood that lower temperatures can be employed for longer times and higher temperatures for shorter times, all within of the temperature and time intervals discussed hereinafter. The time / temperature balance is important to avoid the significant reaction (i.e., more than about ten percent) of the crosslinker with the copolymer before such crosslinking is desired, which is after the application of the particles to the substrate which is going to be coated. Under certain conditions, however, up to 40 percent of the crosslinker may be allowed to react. It is more preferred that no more than about 5% react. A preferred process of this invention employs as the coating polymer a copolymer of an olefinically unsaturated compound and a carboxylic acid. Still another embodiment comprises the addition to step (i) of one or more additives selected from a pigment, an anti-corrosion agent, a catalyst, ultraviolet light stabilizer, antioxidant, flow agent, leveling agent and the like.

Yet another embodiment comprises the use in step (c) of a surfactant selected from at least one member of the group consisting of ionic and nonionic surfactants. The preferred ionic surfactants are formed in themselves by the reaction of one or more of ammonium hydroxide, triethanolamine, morpholine and dimethylethanolamine with the integral carboxyl functional group to the copolymer Preferred nonionic surfactants are polyoxypropylene-polyoxyethylene block copolymer, alkylphenol thioxylates, and ethylene-propylene glycol oxide polymers. Ionics can be employed, as is readily suggested to one of skill in the art having this description as a guide.In its compositional aspect, this invention relates to a substantially spherical particle of a coating composition comprising a copolymer and at least a member selected from the group consisting of pigment, r eticulator, surfactant, catalyst, ultraviolet light stabilizer, antioxidant, flow agent and leveling agent. Preferred crosslinkers are melamine and those containing epoxide functional group such as bisphenol A diepoxide (blocked or unblocked) and triglycidyl isocyanurate. Preferred copolymers are selected from. group consisting of poly (ethylene / methacrylic acid) and poly (ethylene / acrylic acid) not functionalized or with hydroxyl functional group. Typically, a cross-linker is employed in the stoichiometric range of about 1: 0.05 to 1: 1.5 with respect to the acid group in the base resin. Preferably, the range is between 1: 0.1 to 1: 1. The acid range in the base resin before crosslinking is between about 1 and 30 weight percent of the ethylene. Preferably, the range is between 4 to 20 percent. The hydroxyl functional group in the base resin before crosslinking is between about 0 to 30 weight percent of the ethylene. Preferably, the range is between 2 to 10 percent. The ionic surfactant is about 0 to 15 weight percent of the resin, preferably between about 0.01 to 5 weight percent. In addition, the nonionic surfactant is about 0 to 25 weight percent of the resin. Preferably, the range is from about 0.1 to 10 percent.

The relationship of time and temperature is important to ensure that the resin does not react / cross-link prematurely. The temperature range is maintained at approximately 60-180 ° C; preferably, between 90 and 150 ° C. Time at temperature is another variable, and depends on the crosslinker. For the preferred reticulators, the time at that temperature is in the range of 10 seconds to 1 hour; preferably, between 1 minute to 30 minutes. More preferably, the time is "between 2 to 15 minutes." A minimum of about 2 minutes is needed to ensure that the ammonium hydroxide or other ionic surfactant-forming components react with the acid-containing copolymers. that can be incorporated into the spherical particles by the process described, the following guidelines are offered, as will be easily appreciated by someone of experience in the art.Antioxidants such as antioxidants based on cinnamate and phosphite can be employed, in general at levels from about 0 to 5% by weight The standard ultraviolet light absorbers and the free radical scavengers can be employed at-levels of from about 0 to 3%, leveling agents from 0 to 2%, and anti-bubble agents to 0 to 5% Specifically with respect to the pigment, the composition may contain up to 50% by weight of pigment based on the weight of the film-forming components of the coating composition. Any organic and inorganic pigments can be used including phthalocyanine blue; carbon black; metal oxides such as titanium dioxide, zinc oxide, and iron oxide; metallic powders; metal hydroxides and mica flakes.

DETAILS OF THE INVENTION The Aspects of the Process The substantially spherical particles having a rough surface can be prepared by a method comprising the shear stress in a zone of shear stress of a shear device under positive pressure: water, one or more surfactants and copolymer. Preferably, the copolymer is selected from one or more α-olefins of the formula R-CH = CH 2, wherein R is a hydrogen radical or an alkyl radical having from 1 to 8 carbon atoms, copolymerized with one or more acids α, β-ethylenically unsaturated carboxylic acids of 3 to 8 carbon atoms, said copolymer being a direct copolymer of the α-olefins and the unsaturated carboxylic acid in which the carboxylic acid groups are randomly distributed over all molecules, and in which the α-olefin content of the copolymer is at least 50 mole percent, based on the α-olefin-acid copolymer. The unsaturated carboxylic acid content of the copolymer is from 0.2 to 25 mole percent, based on the α-olefin acid copolymer, and any other monomeric component optionally copolymerized in said copolymer. The shear stress is carried out at a temperature above the melting point but below the point of thermal degradation of the polymer to form a homogeneous suspension wherein the polymer particles have an average particle size of less than 1-0. 0 microns in diameter, the suspension containing at least 0.01% by weight of surfactant and up to 40% by weight of said polymer; after completion of the shear stress, the suspension is maintained with agitation at a temperature above the melting point of the polymer for at least 0.5 minutes until essentially all the polymer particles have become spherical; while stirring continues, cooling the suspension to a temperature below about 80 ° C in a period of at least 0.3 minutes, the pressure being maintained sufficient to maintain the water in the liquid state; simultaneous with or subsequent to the cooling of the suspension by reducing the pressure of the suspension cooled to atmospheric pressure; and separating the polymeric particles. The process of this invention should be broadly understood to employ ionic surfactants prepared therefrom and / or non-ionic surfactants and / or external surfactants such as ammonium lauryl sulfate, and the like. The particles of spherical shape have an average diameter of 10 to 100 microns, whose surface can be rough, dimpled and covered with hemispherical bulges of approximately 0.1 mm in diameter. To prepare the spherical coating composition of this invention, a slurry mixture of water, surfactant and / or ionic and / or nonionic copolymers (including terpolymers) is prepared, along with any other additives typically employed in the coatings. of the desired type. The process can be continuous or performed in a batch operation. In continuous operation, the suspension is maintained external to the shear device. In batch operation the suspension, after the shear operation, is generally maintained in the shear device although this is not necessary. The suspension of the particles is cooled from a temperature above the melting point of the polymer to a temperature below the melting point of the polymer. Sufficient pressure is maintained throughout the system to prevent boiling of the surfactant (s). The water, ammonia, the polymeric mixture together with the arrangement of the selected coadditives is constantly stirred in regions of the process where turbulent flow conditions do not exist, which prevents the separation of the ingredients in layers. The particles are separated from the surfactant (s) by conventional techniques such as filtration or centrifugation. The wet particles (dust) are then dried by conventional methods. The raw materials used in this invention, such as water, surfactants, copolymer components, additives such as pigments, one or more crosslinkers and the like, are fed into the shear device either premixed or as separate streams. When the polymer is fed separately into the shear device, it can be continuously extruded in molten (injected) form as a batten or monofilament to the shear zone. The concentration of surfactant should be sufficient to prevent coalescence of the particles formed in the shear device. The concentration of the polymer can be in the range of about 0.5 to 50% by weight, based on the weight of the suspension. An amount of polymer below 40% is preferred since the viscosity of the suspension increases rapidly as the concentration of polymers approaches that at which the mixture could behave like a wet cake instead of a liquid. The particles of this invention are generally less than 100 microns in size. The suspension is removed from the shear zone and is fed with agitation, firstly through a high temperature retention zone where the particles are subjected to shear stress and then through a cooling zone. Simultaneously, or after the flow, the pressure is reduced to atmospheric pressure, the suspension is passed to a receiver, and the particles are separated from the aqueous ammonia. Suitable olefins include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 3-methyl-1-butene, and 4-methyl-1-pentene and the like. Ethylene is the preferred olefin. The concentration of the α-olefin in the copolymer is preferably greater than 80 mol percent. Examples of α, β-ethylenically unsaturated carboxylic acids are acrylic acid, methacrylic acid, ethacrylic acid, itaconic acid, maleic acid, fumaric acid, monoesters of carboxylic acids, such as methyl acid maleate, methyl acid fumarate, ethyl and maleic anhydride. Although maleic anhydride is not a carboxylic acid since it does not have hydrogen coupled to the carboxyl groups, it can be considered an acid for purposes of the present invention, because its chemical reactivity is that of an acid. Similarly, other α, β-monoethylenically unsaturated anhydrides of carboxylic acids may be employed. Preferred unsaturated carboxylic acids are methacrylic and acrylic acids. The concentration of the acid monomer in the copolymer is preferably 1 to 10 mol percent. More than one olefin can be used to provide the hydrocarbon nature of the copolymer base. The scope of the base copolymers suitable for use in the present invention is illustrated by the following examples of two components: ethylene / acrylic acid copolymers, ethylene / methacrylic acid copolymers, ethylene / itaconic acid copolymers, ethylene / copolymers methyl acid maleate, and ethylene / maleic acid copolymers, etc. Examples of three component copolymers include: ethylene / acrylic acid / methyl methacrylate copolymers, ethylene / methacrylic acid / ethyl acrylate copolymers, ethylene / itaconic acid / methyl methacrylate copolymers, ethylene / methyl acid maleate copolymers / ethyl acrylate, ethylene / methacrylic acid / vinyl acetate copolymer, ethylene / acrylic acid / vinyl alcohol copolymers, ethylene / propylene / acrylic acid copolymers, ethylene / styrene / acrylic acid copolymers, ethylene / copolymers / methacrylic acid / acrylonitrile, copolymers of ethylene / fumaric acid / methyl vinyl ether, ethylene / vinyl chloride / acrylic acid copolymers, ethylene / vinylidene chloride / acrylic acid copolymers, ethylene / vinyl fluoride / methacrylic acid copolymers , and ethylene / chlorotrifluoroethylene / methacrylic acid copolymers, in addition to the third monomeric component of the stable copolymer I have previously, the additional third monomeric components can be an alkyl ester of an α, β-ethylenically unsaturated carboxylic acid of 3 to 8 carbon atoms, where the alkyl radical "has 4 to 18 carbon atoms." Particularly preferred are the terpolymers obtained from from the copolymerization of ethylene, methacrylic acid, and the alkyl esters of methacrylic acid or acrylic acid with butanol The concentration of this optional component is from 0.2 to 25 mole percent, based on the weight of the copolymer, preferably 1 at 10 mol percent Representative examples of the third component include n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, n-butyl methacrylate, isobutyl methacrylate, methacrylate sec- butyl, tert-butyl methacrylate, n-pentyl acrylate, n-pentyl methacrylate, isopentyl acrylate, isopentyl methacrylate, n-hexyl acrylate, n-hexyl methacrylate , 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, stearyl acrylate, stearyl methacrylate, n-butyl ethacrylate, 2-ethylhexyl ethacrylate. Also, the third component includes mono- and di-esters of dicarboxylic acids of 4 to 8 carbon atoms, such as n-butyl acid maleate, sec-butyl acid maleate, isobutyl acid maleate, t-butyl acid maleate , 2-ethylhexyl acid maleate, stearyl acid maleate, n-butyl fumarate acid, sec-butyl acid fumarate, isobutyl acid fumarate, t-butyl acid fumarate, 2-ethylhexyl acid fumarate, fumarate stearyl acid, n-butyl fumarate, sec-butyl fumarate, isobutyl fumarate, t-butyl fumarate, 2-ethylhexyl fumarate, stearyl fumarate, n-butyl maleate, sec-butyl maleate, maleate isobutyl, t-butyl maleate, 2-ethylhexyl maleate, stearyl maleate. Preferred alkyl esters contain alkyl groups of 4 to 8 carbon atoms. The preferred ones contain 4 carbon atoms. Representative examples of the most preferred esters are n-butyl acrylate, isobutyl acrylate, butyl methacrylate, isobutyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate. The copolymers after the polymerization but before the ionic crosslinking (if desired) can also be modified by various reactions to result in the modification of the polymer which does not interfere with the crosslinking. The halogenation of an olefin acid copolymer is an example of such polymer modification. Preferred base copolymers are those obtained by the direct copolymerization of ethylene with a monocarboxylic acid comonomer. The melt index of the polymer is generally in the range of 0.1 g / 10 minutes to 3000"'g / 10 minutes, preferably 10 to 2000 g / 10 minutes.The temperature of the polymer, such as this is fed to the stress device - Cutting depends on the particulate polymer used, and includes temperatures as low as approximately 90 ° C and as high as 228 ° C. The polymer feed temperature within the required range has essentially no effect on the final product. water will be ~ above the melting point of the polymer.The maximum temperature available at reasonable pressure, for example, approximately 35.15 kg / cm2 (500 psi) is 240 ° C. Temperatures of approximately 90 ° C to 150 ° C have proven to be useful in the production of particles of the required size.The pressure of the system throughout the process must be greater than the vapor pressure of the suspension to prevent the boiling of the phase l The specific shear rate used has little effect on particle size, with the proviso that the water / surfactant / polymer suspension remains in the shear zone for a sufficient time for the polymer particles to reach the size of balance. This size is determined by the interactions of the constituents. The size at equilibrium is quickly reached at high rates of shear stress but s-e requires prolonged exposure of the suspension to shear stress when the shear rate is low. After the completion of the shear, the suspension passes or is removed from the area of the shear stress. In the batch process, the suspension can be maintained in the shear device although it can be placed in another vessel, provided that the temperature of the suspension is maintained above the melting temperature of the polymer. In the continuous process, the suspension is maintained external to the shear device. It has been found that the retention time at high temperature is necessary for the surface tension to pull the molten particles towards the spherical shape. The water / surfactant / polymer suspension is sufficiently stirred to prevent separation of the polymer and the aqueous layer and to minimize particle-to-particle contact. It is undesirable that the particles become agglomerated. Separation of the suspension in two layers can also be "prevented by maintaining the turbulent flow during retention." If the product does not become substantially spherical during the retention time, additional retention time can be used at the same or at a temperature The suspension is cooled to a temperature below the melting point of the polymer, for example, approximately 70 to 80 ° C with agitation, preferably slight, to prevent the separation of the ingredients in the aqueous layer and the agglomeration of the particles. The cooling of the suspension allows easy isolation of the product by filtration or other means.The cooling of the suspension can be done in such a way that the surfaces of the particles are formed with varying degrees of surface roughness. can be reduced simultaneously with or immediately after cooling op It can be _located at any speed, time or convenient place after high temperature retention, provided that the product is maintained in a simple phase. Details of an additional process can be found in US Patent No. 3,933,954, and details of the additional particles can be found in US Patent No. 4,056,653.

Utility of the Spherical Particles of This Invention A method for employing the spherical particles of this invention is in a fluidized bed for coating substrates as follows: heating the substrate at a temperature sufficient to thicken or make the particles adherent polymeric after contact with the substrate; ii) maintaining the temperature of the particles in a fluidized bed, below that to which the particles become sticky; iii) covering substantially uniformly all surfaces of the substrate; iv) optional heating of the coated substrate to the level of the coating and curing of the polymer if it is thermosetting; and v) controlling the coating thickness, per unit time, in this manner: a) to obtain relatively thin coatings of up to about 150 microns, the substrate is heated such that the coating temperature is within the tackiness temperature gradient but below Tm, and the particle sizes are maintained so that at least 80% by weight is between 10 to 80 microns; b) to obtain thicker coatings, the substrate is heated above the tack or tack temperature gradient, particle sizes larger than those described immediately above, or both, are used. The build-up in coating thickness is believed to result primarily from substrate heating profiles above the polymer adhesion temperature gradient. By "adhesion temperature" (Tt) is meant the temperature of the substrate sufficiently high to cause the polymer particles to adhere to it.The "adhesion temperature gradient" comprises a temperature range whose lower limit is the temperature of adhesion and whose upper limit is approximately 75 ° C higher, with the condition that it remains below the Tm (melting temperature). One of skill in the art will appreciate that Tm has relevance with respect to crystalline and semi-crystalline polymers, not amorphous polymers. Accordingly, when an amorphous polymer has been selected as the coating, the important considerations, as far as temperature is concerned, are Tt and the adhesion temperature gradient. It is preferred to control the coating thickness to obtain thicknesses of 150 micrometers or less on galvanized steel, treated or untreated, a substrate having a curved shape with --- hollows; a substrate which is an automobile body or component thereof; wherein the polymer is semicrystalline thermoplastic or semi-crystalline thermoset or amorphous thermoplastic or amorphous thermosetting. When the polymer is thermosetting, the substrate to be coated is immersed in the fluidized bed at a temperature that is controlled to effect polymer adhesion, but without substantial crosslinking while the substrate is within the bed. It is preferred to coat a substrate of a vehicle body or component thereof having a curved shape and a recess, comprising: i) applying a coating to the substrate by immersing the heated substrate within a fluidized bed of particles and adhesion of the particles substantially uniformly to all surfaces of the substrate, to produce a coating with an average thickness not exceeding about 150 microns; ii) the optional application of a pigmented base coat to the substrate coated in step i); and iii) the optional application of a non-pigmented top coat to the substrate coated in steps i) and ü) • A preferred base coat comprises water borne or solvent borne polymer; a clear, preferred topcoat comprises water borne, carried by solvent or powder. The invention also optionally refers to the pre-treatment or post-treatment of the substrate coated with a surface preparation-dresser and / or the post-treatment with a colored base coat and / or a light base coat. The substrate can be any object that is substantially chemically stable at the operating temperatures of the coating process. It is preferred that the object be dimensionally stable at the operating temperature (s), to avoid any dimensional changes such as those caused by melting or wrapping. The substrate can be coated with one or more other coating layers prior to coating by this process. For example, a metallic layer such as zinc (galvanized), a corrosion resistant layer and / or a primer can be used. The preferred substrates are metals and plastics. Preferred metals are iron, steel, galvanized steel, electrogalvanized steel (one and two sides), phosphate treated steel, electrogalvanized steel which is treated with phosphate, aluminum, and phosphate treated aluminum. Preferred plastics are compacted fibrous structures and composites. The temperature of the substrate as it enters the fluidized bed of the polymer particles is within the adhesion gradient when a thick coating is desired. Generally speaking, the temperature of the substrate will decrease toward the temperature of the fluidized bed, when the substrate is in the fluidized bath. The temperature of the fluidizing gas in the fluidized bed is below the adhesion temperature, to avoid agglomeration of the polymer particles before their contact with the hot substrate.

The coating is applied in a fluidized bed of particles that are fluidized by the passage of a gas through the particles, to form a reasonably uniform fluid mass. It is preferred that the particles in the fluidized bed are not electrostatically charged to a degree that will cause their adhesion to the substrate, when the substrate is below the adhesion temperature. A coherent and substantially continuous coating will usually have a thickness of at least about 5 microns. Preferred coatings are from about 5 to 150 micrometers thick, preferably not greater than about 75 micrometers and more preferably not greater than 60 micrometers. Thicker coatings of between 150 to 300 microns are less preferred. Preferably, about eighty percent by weight of the coating particles are in the described size range, preferably from about 20 microns to 60 microns. It is more preferred that at least 90 weight percent of the polymer particles be in these size ranges. Substantially none of the particles will be greater than 200 to 250 microns. The particle size of the polymer is measured by the general technique described by Heuer et al., Part. Charact., Vol. 2, pages 7 to 13 (1985). The measurement is performed using a Vario / LA Helos analyzer "available from Sympatec, Inc., 3490 US Route 1, Princeton, NJ 08540, USA using volume percent measurement. After removal of the fluidized bed, the coated substrate can be removed. heated above the gradient of adhesion temperature of the polymer at the coating level and the cure is effected if it is a thermosetting polymer.This is carried out in a typical heating apparatus such as a convection or infrared oven. If the polymer is thermosetting, it is preferred that the substantial cure does not take place - before the leveling has taken place The time required for the leveling will depend on the particle size, the distribution, the thickness, the temperature used and the viscosity of the polymer.The higher temperatures and the lower polymer viscosities favor faster leveling. Mixtures produced by the present process are useful for imparting chemical resistance, and other desirable properties such as will readily occur to one of skill in the art. These can act as primers for a subsequent coating layer and / or provide pleasing aesthetic properties such as color, smoothness and the like. To provide such advantages, it may be useful to include with or within the polymeric particles other materials typically used in polymeric coatings such as fillers, reinforcers, pigments, crosslinkers, surfactants, colorants, antioxidants, leveling agents, antiozonants, UV absorbers, stabilizers and the like. In many cases, the coating attributes depend on the good adhesion of the polymeric coating to the substrate. Such addition can often be improved by commonly known methods such as the use of a primer, the cleaning of the surface of the substrate, the chemical treatment of the substrate surface and / or the modification of the chemical constitution of the coating to be applied. The particles of this invention are useful in many applications, such as the coating of wire-shaped material, automotive, truck and vehicle bodies, instruments, ceramic parts, plastic parts, and the like. For example, for automotive bodies, the spherical particles can be applied directly on the metal surface or a primer can be applied first. One or more coating layers of typical finish coatings such as a so-called basecoat (usually colored) and then a clear coating, they can be applied. 'Care must be taken to ensure adequate adhesion between the various coatings, and between the polymeric coating and the metal body. In general, the temperature of the substrate (and the composition to be coated thereon) will decrease toward the temperature of the fluidized bed, when the substrate is in the fluidized bed. Preferred operating conditions include substrate temperatures of about 20 ° C or more above the Tt, not significantly exceeding about 40 ° C or more above the Tt (but below the Tm). The temperature of the substrate as it enters the fluidized bed (at a temperature above the adhesion temperature) together with the selection of the appropriate size of the coating particles, governs to a large extent the coating thickness, regardless of the time, after a critical minimum immersion time in the fluidized bed.

EXAMPLES The following representative ingredients in the indicated weights can be incorporated by the process of this invention into spherulized particles of the coating composition.

Typical Formulation Table MATERIAL FUNCTION! WEIGHT Nucrel® Binder 100 .00 Cardura E Binder 19. .50 Bisphenol A Epoxy Binder 5.00 TBPB Catalyst 0. .60 Ti02 Pigment 3. .25 BaS04"Pigment 3., 25 Carbon Pigment 0. .07 Nalzih® 2 Pigment 2. .60 Cyasorb® 531 UV Absorber 0., 77 Irganox® 1010 Antioxidant 1., 30 Irgafos® Antioxidant 0. .13 Benzoin Antiforming of holes 0.65 Modaflow 2100 Flow and Leveling 0.80 Total 137.92 MATERIAL NAME CHEMICAL Nucrel Poly (ethylene-co-methacrylic acid), 10% methacrylic acid, 850 M.I. Cardura E Tetracarboxylic acid glycidyl ester Bisphenol A 4, 4 '- (1-methylidene) -bis-1, 1'-epoxy oxypropyloxirane-2, 3 TBPB "Tetrabutylphosphonium bromide Ti02 Titanium dioxide BaS04 Barium sulfate Carbon Dust carbon black Nalzin® 2 Zinc-phosphorus oxide complex Cyasorb® 531 2-hydroxy-4-n-octoxybenzophenone Irganox® 1010 Tetrakis (methylene (3,5-di-t-butyl-4-hydroxy) hydroxycinnamate) methane Irgafos® 168 Tris (2,4-di-t-butylphenyl) phosphite Benzoin Benzoylphenylcarbinol Modaflow 2000 Poly (ethylacrylate-co-2-ethylhexylacrylate) / silica EXAMPLE 1 The ingredients in the Table, in the proportions shown, were mixed to form a uniform mixture in an extruder; 200 grams of this mixture was added to a 1500 ml autoclave equipped with a shear device to which 2.6 grams of concentrated ammonia, 20 grams of polyoxypropylene-polyoxyethylene surfactant and 777 grams of deionized water had been added. The mixture was subjected to shear at 125 ° C for 5 minutes, then allowed to cool by mixing. The material was isolated by filtration and then dried to a powder consisting of substantially spherical particles.

EXAMPLE 2 The Nucrel (950 parts) and the Nalzin® 2 pigment (50 parts) were mixed in a uniform mixture in an extruder; 200 grams of this mixture was added to a 1500 ml autoclave, equipped with a shear device, to which 13 grams of concentrated ammonia and 787 grams of deionized water had been added. This mixture was subjected to shear at 125 ° C for 3 minutes, then allowed to cool by mixing. The material was isolated as in Example 1.

EXAMPLE 3 The procedure of Example 2 was repeated, except that the residence time was 120 minutes.

EXAMPLE 4 Nucrel (1000 parts) and titanium dioxide (100 parts) were mixed until a uniform mixture was obtained in an extruder; 200 grams of this mixture was added to a 1500 ml autoclave, equipped with a shear device to which 40 grams of polyoxypropylene-polyoxyethylene surfactant, 2.6 grams of concentrated ammonia and 757 grams of deionized water had been added. This mixture was subjected to shear at 110 ° C for 3 minutes, then allowed to cool by mixing. The material was isolated as in Example 1.

EXAMPLE 5 Nucrel (1000 parts) and calcium carbonate (100 parts) were mixed until a uniform mixture was obtained in an extruder; 200 grams of this mixture was added to a 1500 ml autoclave, equipped with a shear device to which 40 grams of polyoxypropylene-polyoxyethylene surfactant, 2.6 grams of concentrated ammonia and 757 grams of deionized water had been added. This mixture was subjected to shear at 110 ° C for 3 minutes, then allowed to cool by mixing. The material was "isolated as in Example 1.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (10)

RE IVINDICATIONS Having described the invention as above, the content of the following claims is claimed as property:

1. Improved process for the production of substantially spherical particles of a copolymer, comprising the steps of: i) subjecting a surfing agent and the components of a crosslinkable copolymer to shear under pressure and at an elevated temperature to form an aqueous suspension homogeneous particle; ii) stirring the suspension under pressure at a temperature above the melting point of the copolymer to make the particles substantially spherical; iii) cooling and stirring the suspension, at a temperature below the melting point of the copolymer; characterized in that the improvement comprises: a) adding to the components in step i) at least one member selected from the group consisting of coating additive and crosslinker; b) the use of a time / temperature profile in steps i) and ii) to prevent a significant degree of crosslinking during the formation of the particles; c) optionally adding a further surfactant to step i) in an amount sufficient to form substantially spherical particles of a crosslinkable combination of copolymer, coating additive and crosslinker.

2. A process according to claim 1, characterized in that the copolymer is derived from an olefinically unsaturated compound and a carboxylic acid.

3. A process according to claim 2, characterized in that the olefinically unsaturated compound is selected from the group consisting of olefins of the formula R-CH = CH2, wherein R is a radical selected from the subgroup consisting of hydrogen and alkyl radicals having 1 to 8 carbon atoms, and the carboxylic acid is selected from the alpha, beta-ethylenically unsaturated carboxylic acids having from 3 to 8 carbon atoms.

4. A process according to claim 1, characterized in that it comprises the addition, in step i, of one or more coating additives selected from the group consisting of pigment, ultraviolet light stabilizer, antioxidant, flow agent and agent. leveling.

5. A process according to claim 1, characterized in that it comprises the use in step c) of a surfactant selected from at least one member of the group consisting of ionic and nonionic surfers.

6. A substantially spherical particle of a coating composition, characterized in that it comprises a copolymer and at least one member selected from the group consisting of pigment, crosslinker, surfactant, ultraviolet light stabilizer, antioxidant, flow agent and leveling agent.

7. A particle according to claim 6, characterized in that it comprises a crosslinker.

8. A particle according to claim 6, characterized in that the copolymer component is selected from thermoplastic polyolefin polymers and copolymers, poly (meth) acrylates, polyesters, and polynyl chloride, and thermosetting polymers selected from the group consisting of polyesters. ter / epoxy containing acid, hydroxy acrylate / isocyanate block, hydroxyacrylate / melamine-formaldehyde and acrylate containing epoxy / acid.

9. A particle according to claim 8, characterized in that the copolymer is selected from the group consisting of polyethylene / methacrylic acid) and poly (ethylene / acrylic acid), not functionalized and functionalized with hydroxyl.

10. A particle according to claim 6, characterized in that the -polymer is selected from the group consisting. of acrylic ester and methacrylic ester reacted with glycidyl methacrylate; and the crosslinker is a diacid selected from the group consisting of dodecandioic acid, valeric acid, succinic acid and cyclohexanedioic acid.