MXPA98000958A

MXPA98000958A - Continuous processing of coating compositions, in po

Info

Publication number: MXPA98000958A
Application number: MXPA/A/1998/000958A
Authority: MX
Inventors: H Decker Owen; T Daly Andrew; T Grundowski Leo; R Wursthorn Karl; R Houda Frank; W Ernst Carl
Original assignee: Morton International Inc
Priority date: 1997-06-25
Filing date: 1998-02-03
Publication date: 1999-02-01

Abstract

The present invention relates to systems, apparatus combinations and methods for producing a powder coating wherein a stream of a powder coating precursor including at least one resin and at least one additional powder coating ingredient is contacting an effective process fluid to reduce the viscosity of the powder coating precursor to allow processing of the powder coating precursor at a lower temperature.

Description

CONTINUOUS PROCESSING OF COATING COMPOSITIONS, POWDERED REFERENCE TO RELATED APPLICATION This application is a continuation request in part of US Application Serial No. 08 / 684,112, filed July 19, 1996. The co-pending patent application is hereby incorporated by reference and becomes a part of this , including but not limited to those portions that specifically appear in the future.

BACKGROUND OF THE INVENTION This invention relates generally to powder coatings and, more particularly, to the continuous processing of powder coatings. Due to the increasing interest of environmental aspects, much effort has been devoted to the problem of reducing the pollution caused by the evaporation of solvents from the paints, these efforts have given rise to the development of new technologies of coatings that eliminate, or at least decrease, the emission of vapors of organic solvents into the atmosphere. Since the mid-1950s, powder coating technology has been one of the most successful developments in terms of reducing or eliminating solvent vapor emissions. The use of compositions for powder coatings can be extremely desirable when these compositions are essentially free of organic solvents as traditionally present in liquid paint systems. Therefore, the economic and social benefits of these reductions in air pollution, energy requirements and fire risks and health can be achieved through the use of powder coatings. A common technique for applying a powder coating to an object makes use of electrostatic spray equipment for coating the powder. In this application, a powder for the coating is dispersed in a stream of air and passed through a high-voltage field, whereby the coating particles acquire an electrostatic charge. These charged particles are attracted and deposited on the object to be coated, which, in general, is at room temperature. Subsequently, the object is placed in an oven and heated, by means of which the powder melts / hardens to form the desired coating on the object. U.S. Patent No. 5,009,367 to Nielsen, U.S. Patent No. 5,027,742 to Lee et al., And "HIGHER SOLIDS COATINGS ABOVE 80% BY VOLUME" filed at Water-Borne & Higher Solids Coatings Symposium, March 10-12, 198-Q, refers to the spraying of materials using supercritical fluids. In addition, based on U.S. Patent No. 5,158,986 to Cha et al., U.S. Patent No. 5,334,356 to Baldwin et al., And the article entitled, "NEW ROLES FOR SUPERCRITICAL FLUIDS," which appears in Chemical Engineering, March 1994 (pp. 32-35), feed fluids, including CO / supercritical, are known to an extruder to form an extruded figure of a fluid and poly-rich plastic material. As described, this extruded material can be further processed to form a foamed, supermicrocellular material, such as in the form of a sheet. Traditionally, the manufacture of a powder coating consists of mixing, by melting, a resin, a hardening agent, plasticizers, stabilizers, auxiliaries for the fluid, pigments and extenders. Whereas, dry mixing is commonly used to make PVC powders under non-manageable conditions for the formation of very fine powders, melt mixing involves high speed mixing, high intensity of dry ingredients in a Henschel mixer or the like , and then heating the mixture to an elevated temperature (for example, about 84-123 ° C) in a continuous mixer, such as a single or double screw extruder, to achieve complete dispersion of the other ingredients in the resin as the resin melts, forming a molten mixture. The molten mixture is then cooled to quench the reaction and crushed. In general, this processing is then followed by a sequence of operations which may include grinding, screening, separation and filtration, followed by another screening. However, this manufacturing and processing of coating powders is subject to a number of disadvantages or difficulties. For example, high-temperature processing of the ingredients in a melt extruder may result in premature reaction of the resin with the hardening agent or degradation of at least some of the polymer resins. In addition, the particles that are produced as a result of the crushing and grinding operations are usually irregularly substantially non-spherical in shape. These irregularly shaped particles can have an undesirable effect on the uniformity and continuity of any resulting coating formed on a substrate surface as a result of the application and hardening of this powder coating.

In addition, the particles produced by the conventional manufacturing process tend to vary greatly in size. Accordingly, various techniques for separating particles such as screening and separation by means of cyclone may be necessary to separate undesirable large and small particles from the powder particles having the desired size distribution. Dust particles, which have undesirable sizes, then usually must be classified in a lower range or, otherwise, it may be necessary to get rid of them. In the past, various methods have been proposed to overcome or reduce some of the problems already identified. U.S. Patent No. 5,207,954 to Lewis et al., Discloses a method for making a powder composition of co-reactable, thermoset particulates from a first copolymer of an olefinically unsaturated monomer having at least one functional group and at least one second copolymer of an olefinically unsaturated monomer having at least one functional group, which reacts with the functional group of the first copolymer. Aqueous dispersions containing the coreactive polymers are described as spray-dried to produce copolymer particles having a substantially uniform and spherical shape. U.S. Patent Nos. 4,582,731 and 4,734,541 both to Smith, describe the methods and apparatuses for the deposition of these thin films and the formation of powder coatings through a molecular spraying of solutes dissolved in organic and supercritical fluid solvents. The examples describe the application of single-component films to substrate surfaces. These patents do not appear to describe coating materials composed of multiple components or materials, or the processing thereof. US Patent No. 5,290,827 to Shine refers to a process for preparing a homogeneous mixture of otherwise thermodynamically immiscible polymers, instead of resins with or without curing agent. According to the description, the polymer blends are dissolved under pressure in supercritical fluid solvents and then spread through a fine nozzle. As the supercritical fluid solvent evaporates, the polymer mixture is described as being deposited as a substantially homogeneous mixture. U.S. Patent No. 5,399,597 to Mendel et al., Describes a batch process for preparing powder coating materials, by means of which it is sought to reduce or avoid at least some of the problems already identified. According to the process thereof, a first and second different organic materials and a supercritical fluid are mechanically agitated in a first container. The contents of the first container are then discharged to a second container, maintained at a lower pressure than the first container and in which substantially all of the first and second organic materials are collected. This batch processing can have some drawbacks. For example, batch processing may undesirably result in long cycle times which, for example, may cause unwanted polymerization of fast curing powder coating compositions. In addition, batch processing can lead to inconsistencies in the product, such as inconsistencies in the properties of the product, such as viscosity and particle size, due to variations in process conditions such as pressure and mixing time during the course of a batch process. Furthermore, processes in large batches usually need to use large processing containers. Large process vessels can in turn cause undesirable time consumption to properly clean between processes for or with different product compositions. further, in this batch processing it can be difficult to maintain the high pressure seals as commonly required to contain supercritical fluids in the processes. Furthermore, U.S. Patent No. 5,399,597 emphasizes that, with the process described therein, the solubilization of the components in the supercritical fluid is undesirable as this sobilization will inevitably result in the loss of material upon transfer from the process vessel. to the recipient that receives the product. The patent shows how to avoid these undesirable results through the choice of materials that are not suitable in the supercritical fluid under the operating conditions.

SUMMARY OF THE INVENTION A general objective of the invention is to provide improved processing for preparing powder coatings. A more specific objective of the invention is to overcome one or more of the aforementioned problems. The general objective of the invention can be achieved, at least in part, by the production of a powder coating by a method wherein a stream of the powder coating precursor is brought into contact with a fluid, which is the medium of the invention. process, effective to reduce the viscosity of the precursor stream for the powder coating, to allow processing of the precursor stream for the powder coating at a lower temperature. The precursor stream for the powder coating includes at least one resin and at least one additional ingredient for the powder coating. The fluid of the process medium includes a material of the process medium in the form of a fluid that is selected from the group consisting of supercritical fluids and liquefied gases. In a particular embodiment, the process medium fluid is effective to plasticize at least one of the resins and the additional ingredient for the powder coating. In another particular embodiment, the process medium fluid is an effective supercritical fluid to totally or partially dissolve at least one of the resins and the additional ingredient for the powder coating. The prior art does not provide the systems, combinations of apparatus and methods for the continuous process production of the powder coatings, particularly the production of powder coatings having greater uniformity in one or more properties or characteristics such as particle size, shape, color, brightness and hardening speed. The invention further comprises a method for producing a powder coating wherein the raw materials for the powder coating are fed and processed in a continuous extruder. The raw materials for the powder coating that are fed and processed in the continuous extruder include at least one resin and at least one additional ingredient for the powder coating, the extruder processing being effective to disperse the at least one ingredient additional with the at least one resin to form an extruded product. The method of the invention includes the step of adding a process medium fluid comprising a process medium in the form of fluid that is selected from the group consisting of supercritical fluids and liquefied gases to a process stream of at least one of the following: a.) the raw materials fed to the continuous extruder; b.) the raw materials processed in the continuous extruder; and c.) the extruded product of the continuous extruder. The addition of the fluid • of the process medium is effective to reduce the viscosity of the selected process stream to allow processing of the process stream at a lower temperature. The invention still comprises a method for producing a powder coating, wherein a premixed combination of raw materials for the powder coating is extruded to form an extruded product. In one embodiment, the premixed combination of the raw materials for the powder coating includes at least one thermosetting resin and at least one hardening agent for the at least one thermosetting resin. A stream of the extruded product is then fed through a pump to the molten material to form a stream of the extruded product at an increased pressure. The stream of the extruded product is then spray dried to form the powder coating. According to this method, at least one of the mixture of the raw materials for the powder coating undergoes extrusion and the stream of the extruded product under increased pressure makes contact with a process medium fluid selected from the group consisting of supercritical fluids and liquefied gases. The process medium is effective to reduce the viscosity of the materials of the process stream, selected to allow processing at a lower temperature. The invention also encompasses systems for producing a powder coating. According to one embodiment, the system for producing the powder coating of the invention includes a continuous extruder, wherein the raw materials for the powder coating including at least one resin and at least one additional ingredient for the coating in powder are fed and processed to disperse the at least one additional ingredient with the at least one resin to form a precursor stream for the extruded coating. The system also includes a source of a medium process material. The process medium achieves a fluid state within the processing system and is effective to reduce the viscosity of the precursor stream to the powder coating, to allow processing of the precursor stream for the powder coating at a lower temperature . The system also includes the means for adding this process medium material in at least one of the following: a.) The raw materials fed to the continuous extruder; b.) "the raw materials processed in the continuous extruder, and c.) the extruded product of the continuous extruder, and the means for forming and separating the powder coating from the average process material. means for forming and separating the powder coating from the process medium can take various forms including: spray drying (including spray drying in a recovery booth), the formation of a foam or friable mass suitable for the subsequent grinding or the like reduction in a desired powder form, and the sprinkling in a solution The invention also comprises a system for producing a powder coating which includes a continuous extruder, a pump for molten material, a source of a material process medium The continuous extruder, the raw materials for the powder coating, including at least one thermosetting resin and at least one hardened agent For the at least one thermosetting resin, they are fed and processed to disperse the at least one hardening agent with the at least one thermosetting resin to form a precursor for the powder, extrudate and melt coating. The precursor for the extruded and melted powder coating is processed by the pump for molten material, to form a precursor stream for the powder coating of increased pressure. The source of a medium process material contains a process medium material which, within the processing system, is in a fluid state and is effective in reducing the viscosity of the precursor stream for the powder coating to allow processing the precursor stream for the powder coating at a lower temperature.

The system further includes means for adding this processing medium material to the raw materials for powder coating in the continuous extruder and a spray dryer to form and separate the powder coating from the process medium. When used in the present, references to a "supercritical fluid" should be understood to refer to a material that is at such a temperature and pressure that it is at, above, or slightly below its critical point. When used in the present, the "critical point" is the point of transition at which the liquid and the gaseous state combine with each other and represents the combination of the critical temperature and the critical pressure for a given substance. The "critical temperature", when used in the present, is defined as the temperature over which a gas can not be liquefied by an increase in pressure. The "critical pressure" when used in the present is defined as that pressure which is sufficient to cause the two phases to appear at the critical temperature. When used in the present, references to a "liquefied gas" should be understood to refer to a material that is liquid but that under normal conditions of temperature and pressure is gas.

The term "generally spherical particles", when used in the context of this invention, comprises particles having real spherical shapes up to those which have almost spherical shapes. The almost spherical forms include ovoid-shaped particles; particles that have bulbous, open or closed protuberances; these protuberances may or may not be of a generally spherical shape and particles having cell portions therein. These cell portions may be extended or contained internally and / or externally on the main surface of the particle and may be opened or closed.

The term "cellular", when used in the context of this invention, means that it has at least some hollow portions or portions. Other objects and advantages will be apparent to those skilled in the art from the following detailed description taken in conjunction with the appended claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a simplified schematic flow diagram of a processing system for a powder coating according to an embodiment of the invention. Figure 2 is a schematic, simplified flow chart of a processing system for powder coating according to an alternative embodiment of the invention. Figure 3 is a simplified, schematic flow diagram of a processing subsystem for the powder coating according to one embodiment of the invention. Figure 4 is a simplified, schematic flow diagram of a processing subsystem for the powder coating according to another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION With reference to Figure 1, a system, generally designated by the reference number 10, is schematically shown for the processing of a powder coating according to the invention. The system 10 includes a source 12 of raw materials for the powder coating, as described below, from which a fluid stream 14 of raw materials is passed to a feed system of the raw materials 16 to form a fluid stream 20 containing a premixed combination of the raw materials for the powder coating containing the resin. The fluid stream 20 is fed to a continuous extruder 22, such as a twin-screw extruder, wherein the premixed combination of raw materials for the powder coating are extruded. In practice, the residence time of materials within this extruder is usually less than about 2 minutes and usually within 30-45 seconds. The system 10 also includes a source 24 of a process medium. As described in more detail below, the process medium consists of one or more materials that arrive at a fluid state, i.e., a supercritical fluid or a liquefied gas, within the processing system. This process medium fluid is effective to reduce the viscosity of the precursor materials for the powder coating or at least selected components of a precursor composition of the powder coating, especially the resin for the powder coating. In practice, this reduction in viscosity can be achieved through the plasticization, solubilization or partial solubilization of at least the particularly selected components of a precursor composition of the powder coating. It will be appreciated that these materials for the process medium can be added in different ways, such as by the original addition of the material in the fluid state, ie, the material is originally added as a supercritical fluid or a liquefied gas, or by the addition of the material in a form that subsequently reaches the desired fluid state. For example, a liquefied gas can originally be added to the material that will later reach a state of supercritical fluid in the processing system, as may be desired. A fluid stream 26 of a process medium is passed through a pressure-raising device 30, such as a pump or compressor, to form a fluid stream 32. With the opening of the valve 34a, at least one part of the fluid stream of the process medium 32 known as the fluid stream 32a, is passed and added to the materials to be processed in the continuous extruder 22. For example, the fluid stream 32a of the process medium can be inject directly into the barrel part of the continuous extruder with double helix. As the materials to be processed in the continuous extruder are subjected to complete mixing, the admission of the process medium fluid by these materials may be more significant in this processing position. As a result of the input of the process medium fluid and in comparison with similar processing without the input of the process medium, lower viscosities are observed, with the subsequent reduction of the processing temperature. It will be appreciated that, with sufficient reduction of the viscosity, the product of the process can be atomized or otherwise isolated as a friable or frothy dough which is easily reduced to a powder product. For example, the product outside the extruder may be suitable for further immediate processing such as milling to form the desired powder product. It will also be appreciated that in this processing, the mass of the material to be processed can serve to form the required joints in and for the processing apparatus, thus avoiding the problems associated with the high pressure operation of the prior art, as identified before. If necessary or desired and as shown in the embodiment of the invention illustrated in Figure 1, a fluid stream 60 of the extruded product, such as in the form of a molten material, is passed to a pump for molten material. 62 through which the precursor for the powder coating, extruded is processed to form a fluid stream of the precursor for the powder coating 64 of increased pressure to facilitate and allow the desired post-processing, as described below. This pump for molten material can, for example, take the form of a diaphragm pump, an extruder or, in a preferred embodiment of the invention, a gear pump. In practice, gear pumps are well suited to handle the high torques resulting from the use of highly viscous materials such as resins, fillers, etc., as commonly present in powder coating compositions. further, it will be appreciated that the detrimental reduction of viscosity within the extruder can result in poor mixing and reversal of flow within the extruder. To avoid this detrimental reduction in viscosity, it may be necessary or desirable to limit the amount of the process medium fluid that is added to the extruder. However, the addition of another process medium fluid may be desirable where, for example, the viscosity of the materials to be processed is not sufficiently reduced to easily allow the subsequent atomization of the precursor material for the powder coating through of a spray nozzle or an air-operated nozzle, such as to assist in the atomization, or static mixing or reduction of the particle size of the suspended solids, such as through a MICROFLUIDIZER process apparatus. Microfluidics International Corporation of Newton, MA, for example, as described hereinafter. In this way, although in the system described in the above the process medium is described as being added to the materials to be processed in the continuous extruder 22, it will be appreciated that this process medium can, if desired, be further added. or alternatively, in other places within the system. For example, otherwise or in addition to the addition step of at least a part of the process medium to the materials to be processed in the continuous extruder 22, a part of the fluid stream of the process medium 32, designated as the fluid stream 32b can, with the opening of a valve 34b, if desired, be passed and added to the fluid stream of the powder pressure precursor 64 increased to form a fluid stream of the powder coating precursor, designated 66, which contains the additional process medium fluid. In general, the fluid stream of the precursor for the powder coating 66 is in the form of a fluid solution. The fluid stream of the precursor for the powder coating 68 is then passed to one or more continuous fluid mixers 70, such as the static in-line mixers, causing greater mixing in the various components of the precursor for coating in powder and, as desirable, facilitates the reduction of the viscosity of the streams of materials to be processed to form a fluid stream 72. The fluid stream 72 is directed to a receiving vessel 74, such as through a nozzle of spray or air-operated nozzle 76 and can be released to desirably reduce atmospheric pressure. In one embodiment of the invention, the high pressure continuous in the system resulting from the inclusion of the pump for molten materials described in the above 64 ensures that the fluid stream 72 can adequately pass through the nozzle 76. As a result of this release to reduce the atmospheric pressure in a desirable manner, the supercritical fluid process medium and the process gas or both contained in the fluid stream will gasify very rapidly, preferably immediately. Gasification of the process medium fluid in a desirable manner results in foaming or atomization of the precursor material for the remaining powder coating. If desired, an external atomizing force such as high pressure air may at this point be injected into the nozzle to facilitate further atomization and the formation of precursor material particles for the remaining powder coating. From the receiving vessel 74, a fluid stream 80 of the material for the powder coating is passed to a final processing step 82, where, if necessary or desired, the material for the powder coating can also be crushed or sieved. to produce particles for the powder coating of suitably desired dimensions. In practice, this grinding and sieving will usually only be necessary when more than about 1 to 2 percent of the material for the powder coating discharged from the receiving vessel 74 is greater than the desired particle size range. In addition, by subsequently combining the additives such as silicas and aluminum oxide recovered, to improve the powder flow, eliminate cake formation in the powder composition or both, or the additives to produce desired special effects such as the metallic coating, for example, It can be done if desired. A fluid stream 84 of finished powder coating particles is passed to a collecting container for the final product 86 for subsequent packaging and handling. Again in relation to the receiving vessel 74, a fluid stream 88 of volatiles is formed therein which includes the recovered process medium. If desired, this fluid stream 88 can be passed to a recovery unit 90, such as a condenser and / or separator, whereby the material of the process medium is collected and passed as a fluid stream 92 to a pressure-elevating device 94, such as a compressor or pump for liquids, to form a fluid stream 96 to return it to the source of the process medium? -eleven . In this way, the invention provides simple and effective removal of the process medium fluid from the precursor for the powder coating. As a result, although the presence and use of the fluid in the process medium according to the invention may advantageously facilitate the processing and preparation of the powder coatings, in a convenient form the fluids of the process medium will not adversely affect the characteristics and properties of the powder coatings thus processed. Although in the system as described above the fluid of the process medium has added to either or both of the materials that are processed in the continuous extruder 22 and the precursor for the powder coating resulting from a continuous extruder, it will be appreciated that this fluid of the process medium can, if desired, be additionally or alternatively added at yet other points within the system. For example, with the opening of a valve 34c, a part of the fluid stream of the process medium 32 designated as the fluid stream 32c, can, if desired, be passed and added to the raw materials in the raw material feeder system , continuous 16. This addition of the fluid of the process medium with the raw materials that are processed, can be especially advantageous together with those temperature-sensitive raw materials which allows the processing, as occurs inside an extruder, at processing temperatures only relatively low. In this way, in practice, extrusion processing at or below the temperature of the softening point of the resin can be significant, with reductions in the processing temperature of at least about 5.5 to 11 ° C or more, preferably at least about 11 to 22 ° C or more, below the temperature at which the comparable composition without the fluid of the process medium could be processed, can be particularly significant and desirable, as described below. The introduction of the fluid in the process medium with the raw materials can serve to reduce the viscosity of the flow of the materials to be processed before the materials are extruded. As a result of this reduced viscosity, the amount of work that is introduced into the materials to be processed during this extrusion process can be substantially reduced, thus reducing the temperatures that are reached within this extruder. As a result, raw materials that have relatively low hardening temperatures can now be practically used in the formulations for powder coating. Else, or in addition, with the opening of a valve 34d, a portion of the fluid flow of the fluid in the process medium 32 designated as the fluid stream 32d, may, if desired, be directed towards and externally applied to the joints and valves as they may be present in the pump for the molten materials 62 to help keep these surfaces free of the materials for the powder coating to be processed. It should be appreciated that this fluid application of the process medium can serve to prevent undesired hardening of the thermosetting resins in areas such as the joint areas in the pump. The process means useful in the practice of the invention are, in general, effective in reducing the viscosity of the precursor materials for the powder coating or at least the selected components of a precursor composition of the powder coating, especially the resin for the powder coating. In practice, this reduction in viscosity can be achieved through the plasticization, solubilization or partial solubilization of at least the particularly selected components of a precursor composition of the powder coating. In particular, in one embodiment of the invention, this reduction in viscosity as a result of the addition of the fluid from the process medium is carried out without. no significant solubilization of the resin or other component in the composition. For example, in epoxy and polyester powder coating resins, a fluid from the process media, carbon dioxide, can serve to plastify the composition containing the resin. Also, in this processing, the fluid of the process media can be added in small enough quantities to achieve the desired processing benefits, such as the softening of the resin and the reduction of temperature, without significantly dissolving these resinous materials. As a result, the amount of fluid in the process medium, needed, can be substantially reduced thereby improving the economics of this processing. In another embodiment, this reduction in viscosity as a result of the addition of the fluid in the process means is associated with this significant solubilization of the resin or other component of the composition to form solutions of low viscosity which, for example , they can be sprayable to form regular spheres. As already described, the process medium of the invention may consist of one or more materials that reach a fluid state, i.e., a supercritical fluid or a liquefied gas, within the processing system. In some of the particular embodiments of the invention, at least one or more of these materials of the process medium reaches a supercritical fluid state within the processing system. In some particular embodiments of the invention, at least one or more of these materials of the process medium reaches a fluid state of liquefied gas within the processing system. Although in some embodiments at least one or more of these process medium materials reach a supercritical fluid state within the processing system and at least one or more of these medium, process materials reach a fluid state of liquefied gas within of the processing system. Examples of compounds that can be used as fluids for the process medium are provided in Table 1. Others will be apparent to those skilled in the art. TABLE 1 EXAMPLES OF FLUIDS IN THE MEANS OF PROCESS In addition, almost supercritical liquids demonstrate characteristics of solubility and other properties similar to those of supercritical fluids. The solute can be liquid at supercritical temperatures, although it is a solid at lower temperatures. In addition, it has been shown that fluid "modifiers" can often significantly modify the properties of the supercritical fluid, even at relatively low concentrations, greatly increasing the solubility of some compounds. These variations are considered within the concept of a supercritical fluid when used in the context of this invention. The reduction of the viscosity by the addition of the fluid of the process medium, according to the invention, can have significantly beneficial processing advantages. For example, in one embodiment, the addition of the fluid from the process medium is effective to form a powder coating precursor material that can be sprayed through a nozzle to produce the powder coating material that does not require grinding processing or sieved.

In another embodiment, the addition of the fluid from the process medium is effective to reduce the processing temperature of the materials to be processed. For example, the addition of the fluid from the process medium can be effective to reduce the processing temperature in the double-screw extruder in the continuous system. In this way, by adding a fluid in the process medium according to the invention, the extrusion temperature of the precursor for the powder coating based on epoxy resin can be reduced, for example, from about 84 ° C. or more at about 38.4 ° C. As a result of using these lower processing temperatures, the range of the compositions increases as now materials unsuitable for use at the higher processing temperatures of the prior art can be used. In practice, this fluid vision of the process medium allows the processing temperature to be reduced below, preferably about 5.5 to 11 ° C below, in some cases more preferred at least 11 to 22 ° C below. the softening temperature of the specific resin of the composition for the powder coating during the preparation. Further, to be effective in reducing the viscosity of the precursor materials for the powder coating or at least the selected components of a precursor composition for the powder coating, especially the resin for the powder coating, the Process medium contacted with the precursor for the coating, preferably, will be a composition or form that facilitates the subsequent removal of the material from the process medium prior to the formation of the final powder coating particles. For example, the process medium, supercritical fluid, will usually evaporate in a gas when exposed to atmospheric or reduced pressure.

It should be appreciated and understood that the means for forming and separating the powder coating from the process medium can take various forms depending on the specific processing needs. In this way, the means for forming and separating the powder coating from the material of the process medium according to the invention may include: spray drying (including spray drying in a recovery booth), the formation of a foam or friable mass suitable for subsequent grinding or reduction similar to a desired powder form, and sprinkling in a solution. In relation to this, although the addition of a material of the process medium according to the invention can serve to reduce the viscosity of the material being processed, the viscosity of the material is therefore less. less certain materials to be processed can be sufficiently high so that the processing of these materials through a spray nozzle can still be difficult. Again in relation to figure 3, a processing subsystem 300 for forming and separating a powder coating from a process stream according to one embodiment of the invention is illustrated schematically. More specifically and as shown, a process stream 302, such as the fluid stream described above 72, is passed through a wall of the container 304 and exits through a heated nozzle 306 to form a spray 310 of powder coating particles. It will be appreciated that the nozzle 306, which includes the conduit for the flow of the process materials 312 adjacent to the discharge of the nozzle 314, may be in various forms including, for example, a nozzle heated by means of a hot oil or 316 electric coil, for example. This heating of the nozzle can serve to increase the solubility of the process medium in the material to be processed, thus reducing the viscosity of the material to be processed sufficient to allow the atomization of the process material and the obtaining of the spherical particles with the spraying of the material to be processed. In this processing subsystem, the heat is usually applied at the point of atomization or formation of the particles for the powder coating. Although alternative methods of reducing increased or increased viscosity, such as by the addition of a co-solvent, are described in greater detail below, it will be appreciated that this addition of a cosolvent may be undesirable due to increased costs associated with this, for example, the cost of the co-solvent itself and the need or desire to recycle and process this co-solvent. In this way, it will be appreciated that this processing system where the heat is usually applied at the point of atomization or the formation of the particles for the powder coating, may offer or provide certain processing advantages. Now in relation to FIG. 4 schematically illustrates a processing subsystem 400 for forming and separating the powder coating from a process stream according to an alternative embodiment of the invention. More specifically, and as shown *, a process stream 402, such as, for example, the fluid stream of the extruded product described above 60, the fluid stream of the precursor for the powder coating 64 or the fluid stream 72 is made passed to a mill, grinder or the like 404. If necessary or desired, a fluid stream 406 of cryogen such as liquid nitrogen, is added to the mill 404 and a fluid stream 410 of the material for the powder coating is passed from the mill 404. It will be appreciated that this addition of a cryogen may be desired or necessary to allow or facilitate the easy grinding of materials such as powder coating compositions based on thermoplastic resin, such as that commonly associated with commercial crushing. of these materials. The trituration of the process streams for the powder coating, according to the invention, is described in greater detail together with the following examples. In addition, the process medium which are used in the practice of the invention are preferably relatively inexpensive, recyclable, non-toxic and non-reactive with the ingredients of the composition for the powder coating. The carbon dioxide either as liquefied gas or as a supercritical fluid is a fluid for the preferred process medium for use in the practice of the invention. The solvency of supercritical carbon dioxide is similar to that of a lower hydrocarbon (eg, butane, pentane or hexane) and, as a result, one can consider supercritical carbon dioxide as a substituent for the hydrocarbon diluent portion of a formulation of solvent-borne coating, conventional. In practice, these process media are added in the range from about 0.01 to about 99 or more parts of the process medium, to the base resin. For example, supercritical and liquid CO is usually added in relative amounts from about 10 to about 90% by weight of the resin. Also, it should be appreciated that sometimes it may be desirable to employ one or more co-solvents in addition to the process medium. For example, the inclusion of a co-solvent may be desired wherein the addition of the process medium, such as liquefied or supercritical CO, does not in itself reduce the viscosity of the precursor materials for the powder coating or so less the selected components of a precursor composition of the powder coating, especially the resin for the powder coating to a desired degree or required for further processing. The addition of a co-solvent may also be desired to more or completely dissolve the selected components of the powder mixture for the coating. The co-solvent (s) suitable for the practice of this invention, usually includes (n) any solvent or mixture of solvents that are miscible with the fluid of the process medium and is (n) a good solvent for a powder component. In addition, the desired co-solvents are usually significantly unreactive with the composition materials for the powder coating and are relatively easy to remove, such as by drying or extraction processing, from the powder coating precursor. . The solubility parameters must be taken into account in the choice of solvent. It must be recognized that some organic solvents, such as cyclohexanol, have utility as both conventional solvents and process media. When used herein, the term "co-solvent" does not include solvents in the supercritical or liquefied gas state. Suitable co-solvents include organic solvents such as tetrahydrofuran, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, mesityl oxide, methyl amyl ketone, cyclohexanone and other aliphatic ketones.; esters such as methyl acetate, ethyl acetate, alkyl carboxylic esters, methyl t-butyl ethers, dibutyl ether, methyl phenyl ether and other aliphatic or alkyl aromatic ethers; glycol ethers such as ethoxyethanol, butoxyethanol, ethoxypropanol, propoxyethanol, butoxypropanol and other glycol ethers; glycol ether ester such as butoxyethoxy acetate, ethyl ethoxy propionate and other glycol ether esters; alcohols such as methanol, ethanol, propanol, 2-propanol, butanol, amyl alcohol and other aliphatic alcohols; aromatic hydrocarbons such as toluene, xylene and other aromatics or mixtures of aromatic solvents; and nitroalkanes such as 2-nitropropane. Commonly, co-solvents suitable for this invention must have the desired solvency characteristics as already mentioned, and likewise, the proper balance of the evaporation rates to ensure good dust formation. A review of the important structural relationships for choosing the solvent or mixture of solvents is given in Dileep et al., Ind. Eng. Chem. (Product Research and Development) 24, 162, 1985 and Francis, A.W., J. Phys. Chem. 58, 1009, 1954. Usually, in practice these co-solvents are a in relative amounts from about 0 to about 50% by weight of the total mass of the composition. As already described, the reduction of the viscosity as a result of the addition of the fluid of the process medium is associated with it in one embodiment of the invention the significant solubilization of the resin or other component of the composition to form solutions of low viscosity. . For example, a supercritical carbon dioxide process medium fluid and a co-solvent such as tetrahydrofuran or methyl ethyl ketone, for example, may be effective to dissolve the resin for the powder coating or other resin for the coating composition. . Figure 2 schematically illustrates a system, generally designated by the reference numeral 110, for the processing of a powder coating according to another embodiment of the invention. As will be described in more detail in the following, system 110 establishes the addition of a co-solvent and a supercritical fluid process medium. The system 110, similar to the system 10 described above, includes a source 112 of raw materials for the powder coating from which a fluid stream 110 of raw materials is made raisins to a raw material feeder system 116 for forming a fluid stream 120 containing a premixed combination of the raw materials for the powder coating. The fluid stream 120 is fed to a continuous extruder 122 where the premixed combination of the raw materials for the powder coating is extruded, as described herein. As in the system 10, described in the foregoing, the system 110 further includes a source, here designated 124, of a process medium. In a particular embodiment of the invention, a fluid stream 126 of this process medium is passed through a pressure-elevating device 130, such as a pump or compressor, so that the process medium reaches a supercritical state. , forming a fluid stream 132. In particular, this supercritical fluid is effective to plasticize at least the selected components of a precursor composition of the powder coating. With the opening of a valve 134a, at least a part of the fluid stream of the supercritical fluid process means 132 designated as the fluid stream 132a, is passed and a to the materials to be processed in the continuous extruder 122. The system 110 further includes a source 135 of at least one co-solvent, such as those described herein and desirably in the form of a liquid. This addition of the co-solvent may be desired where, for example, the a process medium fluid is unable to provide only the desired amount of plasticization to at least the selected components of the precursor composition for the powder coating. In a particular embodiment of the invention, the process medium is a supercritical fluid, such as C02, and a co-solvent, such as tetrahydrofuran and methyl ethyl ketone, is a, for example, suitably selected from the list of solvent materials provided in the above.

As identified and described in the commonly assigned patent application series No. 08 / 662,104, filed on June 14, 1996 as an application for continuation of serial patent application No. 08 / 354,308 filed on December 12, 1994, the description of which is fully incorporated herein by reference, this addition of the co-solvent may result in the formation of dust particles of the cell coating is, generally spherical as may be desirable in the formation of thin film coatings. In a particular embodiment of the invention, a fluid stream 136 of the co-solvent is passed through a pressure boosting device 140, such as a pump or compressor, to form a fluid stream 142. The fluid stream 142, or parts thereof, then they can be suitably directed so that the co-solvent is added to the desired process streams. For example, with the opening of a valve 144a, at least a portion of the fluid stream of the co-solvent 142, referred to as the fluid stream 142a, is passed and added to the materials to be processed in the extruder. co-ntinuous 122. As with the system already described 10, the extruder forms an extruded product stream, herein designated as the fluid stream 160. The fluid stream 160 of the extruded product, such as in the form of a molten material , is passed to a pump for molten materials 162 through which the precursor of the extruded powder coating is processed to form a fluid stream of the precursor for the powder coating 164 of increased pressure. As already described, this pump for the molten material can, for example, take the form of a diaphragm pump, an extruder or, in a preferred embodiment of the invention, a gear pump. With the opening of a valve 134b, a portion of the fluid stream of the supercritical fluid process medium 132, designated as the fluid stream 132b, is passed through. addition to the fluid stream of the precursor for the powder coating 164 of increased pressure. Further, if desired, with the opening of a valve 144b, a portion of the fluid stream of the co-solvent 132, referred to as the fluid stream 132b, is passed and added to the fluid stream of the precursor for the powder coating 164 of increased pressure. This addition of one or more of the supercritical fluid and co-solvent process media forms a fluid stream of the precursor to the powder coating, designated 166, which contains something or liquid co-solvent process medium and / or additional supercritical fluid. As already described, this addition of more than the liquid cosolvent process medium and the supercritical fluid can be desired where, for example, the viscosity of the materials to be processed has not been reduced sufficiently to easily allow atomization Subsequent precursor material for the powder coating through a nozzle. In general, the fluid stream of the precursor for the powder coating 166 is in the form of a fluid solution. The liquid stream of the precursor for the powder coating 166 is then passed to one or more continuous fluid mixers 170, such as in-line static mixers, resulting in further mixing of the various components of the precursor for the powder coating and, conveniently, facilitates the reduction of the viscosity of the currents of materials to be processed to form a fluid stream 172. The fluid stream 172 is directed to a receiver vessel 174, such as through a nozzle of spray or air-driven 176, and released at atmospheric pressure. As a result, the process medium contained in the fluid stream will immediately be gasified and will cause foaming and atomization of the precursor material for the remaining powder coating.

If desired, an external atomizing force, such as high pressure air, can be injected at this point into the receiving container to facilitate further atomization and particle formation of the precursor material for the remaining powder coating. From the receiving vessel 174, a fluid stream 180 of the material for the powder coating is passed to a final processing step 182 where, as already described, if necessary or desired, the material for the powder coating also it can be crushed or sieved to produce powder coating particles of appropriately desired dimensions. In addition, as also described above, the subsequent mixing of the additives can also be done, if desired. A fluid stream 184 of the finished powder coating particles is passed to a collecting container of the final product 186 for subsequent packaging and handling. Again, in relation to the receiving vessel 174, from there a fluid stream 188 of volatile is formed which includes the recovered fluid process media and the cosolvent. This fluid stream 188 is passed to a recovery unit 190, such as a condenser and / or separator, whereby the material of the process medium is separated from the co-solvent. The process medium is passed as a fluid stream 192 to a pressure-raising device 194, such as a liquid compressor or pump, to form a liquid stream 196 to return to the source of process medium 124. The cosolvent it is passed as a fluid stream 198 to the source of the process medium 135. Although in the system as described above, the fluid of the process medium and the co-solvent have been described as being added to either or both of them. the materials to be processed in the continuous extruder 122 and the powder coating precursor resulting from a continuous extruder, it will be appreciated that this fluid from the process medium and the co-solvent can, if desired, be additionally or alternatively added in still other points of the system. For example, with the opening of a valve 134c, a portion of the fluid stream of the process medium 132, referred to as the fluid stream 132c, may, if desired, be passed and added to the raw materials in the material feeder system. continuous raw 116. In the same way, with the opening of the valve 144c, a part of the fluid stream of the co-solvent 142, referred to as the fluid stream 142c, can, if desired, be passed and added to the raw materials in the raw material feed continuous system 116. Alternatively or in addition, with the opening of a valve 134d, a part of the fluid stream of the process medium fluid 132, referred to as the fluid stream 132d, can, as described in the foregoing, be directed in and externally applied to those joints and valves such as those that may be present in the pump for molten materials 162. In the same way, with the opening of a valve 144d, a part of the fluid stream of the co-solvent 142, referred to as the fluid stream 142d, can, if desired, be directed and externally applied to those gaskets and valves as they may be present in the pump for molten material 162, to help maintain these free surfaces of the materials for the powder coating to be processed. Examples of the powder coating raw materials suitable for use in the present invention include thermoplastic and thermosetting base resins. The thermoplastic resins suitable for use in the coating powders of this invention must melt and flow to form a thin film in a few minutes at application temperatures from 200 ° C to 300 ° C without significant degradation. Examples of thermoplastic resins suitable for use in the practice of the invention include polyamides, polyesters, cellulose esters, polyethylene, polypropylene, polyvinyl chloride or PVC, polyvinylidene fluoride or PVF, polyphenylsulphone and polytetrafluoroethylene or PTFT. It should also be appreciated that as a result of the processing temperatures usually below which the resins are subjected in the practice of the invention, the thermoplastic resins such as polyphenylsulfones and PTFE are particularly suitable for processing in accordance with the invention. The plasticization of PVC has been the conventional way to reduce its melt viscosity so that it flows sufficiently when heated to form a continuous film. The nylon-11 and nylon-12 resins are representative of the polyamides and the cellulose acetate butyrate is an example of the cellulose esters contemplated for use in this invention. All suitable thermoplastic resins are available commercially from various suppliers. The thermostable resins. which are suitable for this invention include epoxy resins, polyurethanes, silicones, polyesters (including unsaturated polyesters), acrylics and hybrids such as epoxy-acrylic, polyester-acrylic and epoxy-polyester. The transition temperature of the glass (T ") of these resins should be quite high so that the particles do not melt together or sinter at temperatures that are likely to be encountered during transport and storage. Preferably, the Tv is at least about 50 ° C. Epoxy resins are those which contain aliphatic or aromatic structures with oxirane functionality and are exemplified by the diglycidyl ether condensation polymers resulting from the reaction of epichlorohydrin with bisphenol in the presence of an alkaline catalyst. Bisphenol A is the most commonly used, but bisphenols B, F, G and H are also suitable. By controlling the operating conditions and varying the proportion of the reagents, products of various equivalent weights can be made. For the purpose of this invention, the epoxy equivalent weight (PEE) can be from about 600 to about 2000 and the hydroxyl equivalent weight can be from about 300 to about 400. These are available to a wide variety from providers. The GT epoxy bisphenol A series of Ciba-Geigy, including 7004, 7013, 7014, 7074 and 7097 are examples of useful epsxid resins in this invention. Shel Chemical Co. also supplies suitable epoxy resins under the tradename EPON. Dicyandiamide, modified and substituted dicyandiamides, solid dicarboxylic acids and their anhydrides are examples of the various agents that can be used to cure epoxy resins. A hardener in solid form is preferred for convenience in the formulation of the epoxy resin-based powders as well as in the formulation of other resin-based powders of this invention. Hydroxy functional polyesters are predominantly hydroxyl in their functionality; its acid number is preferably about 15 or less, and, even more preferably, from about 1 to 2. The hydroxyl number, on the other hand, is preferred from about 25 to about 50, as reported traditionally. The Tv preferably exceeds 50 ° C, due to its effect on the blocking problem these are condensation products of polybasic carboxylic acids and polyhydric alcohols. Examples of the carboxylic acids useful for the preparation of these polyester resins are phthalic acid, tetra- and he-ahydrophthalic acids and their anhydrides, adipic acid, sebasic acid, terephthalic and isophthalic acids, 1,3- and 1,4-acids. cyclohexane-dicarboxylic and trimellitic anhydride, esters of those acids and mixtures of two or more. Ethylene-, diethylene-, propylene- and trimethylene glycol exemplify bifunctional alcohols, along with other dihydric alcohols such as hexanediol, 1,3-, 1,2- and 1,4-butanediols, neopentyl glycol, 2-butyl-2- ethyl-l, 3-propanediol, 2-methyl-1,3-propanediol, 1,4-cyclohexanediol, trimethylolpropane and mixtures of two or more. The condensation of acids and alcohols is a well-known reaction and various well-known processes can also be carried out. The temperature for convenience is from about 180 ° C to about 300 ° C; an azeotropic distillation with a solvent or a stream of an inert gas through a molten mixture of the reactants can be used to improve the removal of the water formed by the condensation; and a catalyst such as para-toluenesulfonic acid or dibutyltin oxide can be used. An ester exchange reaction catalyzed by a carboxylate or lead oxide, zinc acetate, hydroxide or lithium carboxylate can be used at temperatures of 200 ° C to 300 ° C. the hydroxy functional polyesters are commercially available under the tradenames RUCÓTE 107, CARGILL 3000, CARGILL 3016 and CRYLCOAT 3109. The hydroxyl functional polyesters are hardened by the hydroxyl groups with aminoplasts [sic] and with aliphatic and aromatic isocyanates. The hardening of the isocyanate forms resins that are technically polyurethanes but are often sold as polyesters. The aminoplasts are oligomers that are the product of the reaction of the aldehydes, particularly formaldehyde with amino- or amino group-carrying substances exemplified by melamine, urea, dicyandiamine and benzoguanamine. It is preferred in many cases the use of aminoplast precursors such as hexamethylol melamine, dimethylol urea and their etherified forms, that is, modified with alkanols having from 1 to 4 carbon atoms. Hexametoxymethylmelamine and tetramethoxyglycoluril exemplify these etherified forms. Thus, a wide range of commercially available aminoplasts and their precursors can be used to combine with the linear polyesters of this invention. The cross-linked agents that are commercialized by American Cyanamid under the trade name CYMEL are particularly preferred. In particular, the alkylated melamine-formaldehyde resins CYMEL 301, CYMEL 303 and CYMEL 385 are useful. Of course, it is possible to use mixtures of all the above N-methylol products. The aminoplast hardening agents are usually provided in an amount sufficient to react with at least one half of the hydroxyl groups of the polyester, ie to be present at least one half of the stoichiometric equivalent of the hydroxyl functionality. Preferably, the crosslinking agent is sufficient to react substantially completely with all the hydroxyl functionality of the polyester, and crosslinking agents having nitrogen crosslinking functionality are provided in amounts from about 2 to about 12 equivalents of the hydroxyl functionality of the polyester. . This usually results in an aminoplast that is provided between about 10 and about 70 phr. The hardening of the hydroxyl functional polyester with an aminoplast is carried out in about 20-30 minutes at temperatures within the range of about 120-200 ° C (about 250-400 ° F). The acid catalysts can be used to modify the hardening of the polyester with an aminoplast resin by reducing the necessary temperature or by raising the reaction rate or both. When it is desirable to reduce the speed to ambient storage temperatures, the acid catalyst can be blocked with an amine. The volatile amines that can escape from the hardening film when the catalyst is not blocked by heating are suitable for this purpose. It is particularly desirable for the purpose of this invention to retard the complete hardening of the composition until the coated metal substrate has traveled about three quarters of the length of the furnace for hardening. In a particular embodiment, the residence time before complete hardening was about 33 seconds. An amine-blocked dinonylnaphthalenesulfonic acid sold by King Industries under the trade name and number NACURE 1557 is an example of the block acid catalyst contemplated for use in curing the aminoplast of the powder coating composition of this invention. Hardening can be delayed by the addition of free amines such as triethlonamine. The diisocyanates harden the hydroxy-functional polyester resin by forming urethane linkages between the polymer chains at the hydroxyl group sites. the aliphatic diisocyanates are exemplified by hexamethylene diisocyanate (HDI), di-cyclohexylmethane diisocyanate (marketed under the brand DESMODUR W by Miles Chemical), and isophorone diisocyanate (IPDI). Toluene diisocyanate (TDI) is an example of a suitable aromatic diisocyanate. The low-temperature reactivity of the free diisocyanates can be attenuated by adding them with b1-linked agents selected from phenol, cresols, isononylphenol, amides such as e-caprolactam, oximes such as methyl ethyl ketoxime and butanone oxime, active compounds containing the methylene group as be isopropylidene diethyl dimalonate malonate and acetoacetates and sodium bisulfite. The addition products have a weak bond that breaks at an elevated temperature to regenerate the blocking agent and the free diisocyanate which can react with the polyester in the desired form. Examples of the block diisocyanates include isophorone diisocyanate blocked with caprolactam and hexamethylene diisocyanate blocked with caprolactam. Examples of commercially available hardening agents of this type are the products 24-2400, 24-2430 and 24-2450 marketed under the trademark CARGILL. An excess of about 10 to 20%, preferably 5 to 10% by weight of the diisocyanate can be used beyond the stoichiometric amount. The reaction of the polyester with the diisocyanate is carried out in the absence of moisture at a temperature from about 80 ° C to about 200 ° C and, when using the block diisocyanate, the temperature is preferably at least about 120 °. C and more preferably near 200 ° C or higher. Dibutyltin dilaurate and triethylenediamine are examples of catalysts that can be used to promote the hardening of the diisocyanate. The use of block isocyanates for the hardening of the coatings is described in a document presented by T. A. Potter, J. w. Rosthauser, and H. G. Sche elzer in the Water Borne & Higher-Solids Coatings Symposium in New Qrl ans on February 5-7, 1986; the document is incorporated herein by reference. Functional carboxylic polyesters are also suitable for the purposes of this invention. These can be made from the same polyfunctional acids and glycols as are the hydroxyl functional polyesters, but with an excess of acid. The acid number is from about 18 to about 55. These are exemplified by products sold under the trade name CRYLCOAT 130, CRYLCOAT 3010, URALAC 3400, URALAC 3900 and GRILESTA V7372, which have a Tv of 60 ° C and an acid number of 32-35, and which is commercialized by Ems-Chemin AG. Rapid hardening is achieved with polyepoxidic hardening agents such as triglycidyl isocyanate (TGIC). Unsaturated polyesters suitable for use in the practice of the invention include the ethylenically unsaturated reaction products of a di or polyfunctional organic acid and a di or polyfunctional alcohol. Usually, the acid is unsaturated. These polyester resins usually work best in combination with a second copolymerizable resin such as diallyl phthalate. it may also be necessary to incorporate initiators. A hybrid resin system is usually considered a mixture of functional carboxyl polyester and an epoxy resin. The polyester has conveniently had an equivalent weight of 550-1100 and the epoxy resin has an equivalent weight of 600-1000. Zinc oxide is effective as a catalyst at 1-5 parts per 100 parts by weight of the resins to improve the rate of hardening and the physical properties of the product. Other systems of hybrid resins such as the epoxy-acrylic and polyester-acrylic mixtures mentioned in the foregoing are also suitable for this invention. Preferred acrylic resins for the coating powders are copolymers of the acrylates and / or alkyl methacrylates with glycidyl methacrylates and / or acrylates and olefinic monomers such as styrene. Functional glycidyl acrylic resins are sold by Mitsui Toatsu Chemicals, with the trade name ALMATEX (for example, PD-7610, PD-7690, PD-6100). The ALMATEX PD-7610 resin, for example, has an epoxy equivalent of 510-560 and a melt index of 50-58. Solid dicarboxylic acids having, for example, 10 or 12 carbon atoms are used to cure functional glycidyl acrylic resins. A polymer terminated in carboxy can also be used as an agent-crosslinker for these acrylic resins. The hydroxyalkyl acrylate and methacrylate copolymers are also suitable for this invention. The silicone resins suitable for use in this invention should be sold at room temperature and preferably have a Tv of at least about 45 ° C. The organic portions of the silicone resins are aryl, particularly phenyl or short chain C 1 -C 4 alkyl. For a good thermal resistance, the methyl and phenyl groups are the organic portions of choice. In general, higher thermoresistance is provided for more phenyl groups. Examples of these silicone resins are phenylsilicone SY-430, marketed by Wacker Silicone, Conshohocken, PA, having an average molecular weight of about 1700, MK methylsilicone also marketed by Wacker and methylphenylsilicone 6-2230 marketed by Dow Corning. For stability at higher temperature, the silicone resins useful in the invention have a degree of substitution as described in Silicones in Protective Coat ngs, above about 1.5 or less, usually between about 1 and about 1.5. Specifically, the degree of substitution is defined as the number of average substituent groups per silicon atoms and is the sum of the mole percent multiplied by the number of substituents for each ingredient. Self-condensing silicone resins are used at high end-use temperatures, for example, on a rotisserie grill or a part of the automobile exhaust. This requires siloxane functionality (Si-O-H), and the silicone resins that are used herein have an -OH content between about 2.5 and about 7.5 weight percent of the silicone resin. Silicone resins suitable for use in the invention are described in "Silicones in Protective Coatings" by Lawrence H. Brown in Treatise on Coatings Vol. 1, Part III "Film-Forming Compositions", pp. 513-563, R.R. Meyers and J.S. Long, eds., Marcel Dekker, Inc. New York, 1972, the teachings of which are incorporated herein by reference. Suitable silicone resins are also disclosed in U.S. Patent Nos. 3,170,890 and 4,879,344, 3,585,065 and 4,107,148, the teachings of which are incorporated herein by reference. In addition, crystalline resins are also used, such as the crystalline polyester PIONEER PIOE? TER 4350-55. Suitable additives for inclusion in the compositions of the coating powders include antioxidants, light stabilizers, pigments and dyes, processing aids, anti-blocking agents and anticorterization agents. Examples of antioxidants include, but are not limited to: hindered phenols, phosphites and propionates. Examples of hindered phenols are 1, 3, 5-trimethyl-2,4,6-tris- (3,5-di-tert-butyl-4-hydroxybenzyl) benzene; octadecyl-3- (3, 5-diter-butyl-4-hydroxyphenyl) -propionate; tetrakis [methylene-3 (3 ', 5' -diter-butyl- '-hydroxyphenyl) -propionate] methane); 4, 4 '-butylidene-bis (5-methyl-2-t-butyl) phenyl; and 2, 2'-ethylidene-bis- (4,6-di-butylphenol). Examples of the phosphite antioxidants are tris (2,4-tert-butyl-phenyl) phosphite; bist2, 4-di-t-butyl-phenyl) pentaerythritol diphosphite; and 2,2'-ethylidene-bis (4,6-di-t-butylphenyl) fluorophosphite. Examples of the propionate antioxidants are dilauryl thiodipropionate and distearyl thiodipropionate. Phenol 100 [sic] IRGANOX 1010 and HIRGAFOS 168 phosphite are commercially available antioxidants. Antioxidants can be used in amounts ranging from about 0.01 to about 2.0% by weight of the powder.

Light stabilizers and UV absorbers are exemplified by benzophenone stabilizers, such as those sold under the trade name CYASORB-UV 2018 (American Cyanamid), hindered amine compounds, including those marketed by Ciba-Geigy with the trade names TINUVIN 144, TINUVIN 292, TINUVIN 944, TINUVIN 622LD and TINUVIN 770 (N, -diphenyl-N, N-di-2-naphthyl-para-phenylenediamine), and UVINUL M40 and UVINUL 490 from BASF , particularly those containing the tetraalkyl-piperidinyl functionality, and the UV absorbers marketed by Ciba-Geigy under the tradename TINUVIN 900 and BY American Cyanamid under the name CYANOX 3346. Examples of anti-blocking agents (agents for dry flow) they are recovered silica, clay, talc, recovered alumina and precipitated silica. Commercial examples of anti-blocking agents are sold under the trademarks AEROSIL and CABOSIL. The flow leveling agents (anticrater) are sold under the tradenames TROY EX486 and RESIFLOW P-67 (a low molecular weight acrylic resin). Other additives are often used to degas the films and are sold under the tradename URAFLOW B (benzoin), OXUMELT A-1 and OXIMELT A-2. The deleterious effects of the surfactants and other additives such as chain switches and the final coating film can be avoided and these additives not be included in the powder coating compositions processed according to the invention. It should be understood, however, that at least in certain specific embodiments, it may be desirable to use a surfactant that improves the solubility of the selected resin in the medium of the selected process fluid. For example, fluorocarbons, fluoroethers, and siloxanes can serve as useful surfactants in combination with a medium carbon dioxide process fluid. It should be appreciated that the systems of the invention, such as the continuous processing systems described in the foregoing, can be easily purged to clean between processes by or with different product compositions. In this way, these systems can have more desirable commercial application and utility. It should also be appreciated that an advantage of the continuous processing of the materials for the powder coating according to the invention is the facilitation of achievement of steady-state processing conditions such as temperature, pressure and time under the conditions. A wide variety of powder coating materials can be prepared according to the invention, and include: a.) Powder coating materials identified and described in the commonly assigned patent applications mentioned in the above series No. 08 / 662,104 filed on June 14, 1996 and series No. 08 / 354,308 filed on December 12, 1994, the descriptions of which are hereby incorporated by reference in their entirety, and include cell coating powder particles, generally spherical and as they may be those produced by the dissolution of the ingredients of a coating powder in a supercritical fluid with a cosolvent as described herein. These materials for powder coating are described herein with an extremely narrow particle size distribution. Specifically, with the exception of a smaller number of fines that have particle diameter smaller than 2, the particle sizes of these powdered materials are all within the range of about 2 to about 40 microns, with approximately 96%. of the volume of the powder with a particle size of 20 microns or less and about 75% of its volume has a particle size between 2 and 20 microns. In this way, these powder coating particles range in size from less than 2 to about 40 microns with an average particle size of about 4.4 microns and an average size from about 6 to about 7 microns, where the particle size measurement is made with a particle size analyzer COULTER LS, where an Fraunhofer optical model (PIDS included) and a LS 130 fluid module are used; b.) The materials for powder coating identified and described in U.S. Patent No. 5,399,597, published March 21, 1995, the disclosure of which is hereby incorporated by reference in its entirety, includes both round and flake types described herein as being produced by a method of: providing a first container connected via pipe to a second container; load the first container with the initial materials; supplying C02 to the first container and maintaining this C0¿ in this first container at a temperature and pressure such that the C0.¿ consists of a supercritical fluid; shake the initial materials and the supercritical fluid; transfer C0Z and initial materials through a spray nozzle having an orifice diameter from about 0.001 inches to about 1 inch; and then discharging the CO and the initial materials to a second container that has been maintained at a lower pressure than the first container; c.) The materials for the powder coating identified and described in the U.S. Patent No. 4,582,731, published on April 15, 1986 and the U.S. Patent No. 4,734,227, filed March 29, 1988, the descriptions of which are hereby incorporated by reference in their entirety, include particles with a narrow size distribution, which have average sizes in the range from 0. 3 microns to about 3 microns; d.) Materials for powder coating that include crystalline resins such as PIONNER PIOE? TER 4350-55 and a hardening agent; and e.) the highly reactive powder coating system, such as epoxies hardened by primary amines, suitable for application on temperature sensitive substrates such as wood plastics and pre-assembled articles that contain or include heat-sensitive components. In general, the powder coatings that are prepared according to the invention are suitable for application to a wide range of substrate materials including metallic and non-metallic substrates. For example, these powder coatings can be applied to various metal substrates that are inert to the coating material. These metal substrates can usually include various structural metals such as iron, steel and aluminum, for example. Suitable non-metallic substrates can include wood and paper-based substrates including particulate boards and cartons, glass, ceramics, plastics and rubber, for example. The present invention is further described in detail together with the following examples that illustrate / simulate various aspects involved in the practice of the invention. It should be understood that, it is desired that the changes that arise within the spirit of the invention be protected and in this way the invention is not considered limited by these examples.

EXAMPLES Comparative Example 1 (EC 1) and Example 1 (Ex. 1) An acrylic acid-ethylene resin was processed in a co-rotating 27 mm extruder with a double-stranded nozzle according to the conditions identified with the Table 2 below with the processing of Example 1 prepared according to the invention with the addition of COz in the processing extruder while in the EC 1 the resin is processed through the extruder without the addition of this process medium fluid. TABLE 2 The powder coating compositions thus formed were then granulated, the granules of the respective powder coating composition were then cryogenically ground in a Retsch Ultra Centrifugal Mili mill. More specifically, the respective granules were immersed in liquid nitrogen and fed to the mill where the entire product was crushed, the mill included a 12-barrel rotor and a 1.0-mm orifice sieve. The yield of the product was the percentage- of the amount of the resin originally provided that formed the product that was ground to less than 250 microns (60 mesh), see TABLE 3, below.

TABLE 3 Analysis of the results As shown in TABLE 3, a significantly higher yield was obtained when the powder coating based on thermoplastics was processed according to the invention. In addition, the grinding of the granulates of the conventionally prepared thermoplastic composition (EC 1) tend to give rise to considerable elongation instead of fracturing, with the particles forming "tails". It will be appreciated that the appearance or presence of these glues may result in fluidization and poor handling during the application of this composition to the powder coating. In contrast, the thermoplastic composition prepared according to the invention (Ex. 1) appeared to have a superior tendency to fracture rather than tear and form a glue, as a result, this prepared composition can facilitate handling and application.

Comparative Example 2 (CE 2) and Example 2 (Ex. 2) In this Comparative Example and Example, the formulation for the powder coating, hybrid (i.e., a formulation containing epoxy resin and carboxyl functional polyester resin and specifically identified in TABLE 4, below) was extruded through a laminar nozzle and then crushed into the form described in the following. More specifically, the hybrid formulations were processed in a co-rotating 27 mm extruder and discharged through a laminar nozzle under the conditions identified in the following TABLE 5, with the processing of Example 2 made in accordance with the invention. with the addition of C02 to the processing extruder.

TABLE 4 TABLE 5 The sheets of the composition for the powder coating thus formed were then flaked. The flakes of the respective powder coating composition were then fed to the mill with the entire product to be crushed, the yield of the product was the percentage of the amount of the resin originally supplied to form the product that was passed through a 40 mesh screen. The extrusion temperature was measured using an optical pyrometer. The flowability of the material for the powder coating resulting from Example 2 was also compared to the powder coating material resulting from the EC 2 in the following manner: 1. A cylindrical granulate of 12.7 mm in diameter and 6.0 mm in length was compressed from the material that was being tested. 2. The granulate was then compressed using as little pressure as possible and released, immediately, onto a heated electric plate (212 ° C) for hardening, set at an angle of 35 °. 3. the granulate was allowed to melt, within 5 minutes after the granulate contacted the plate, the length of the molten fluid was measured using a steel ruler. The length of the respective molten fluids for EC 2 and Ex. 2 are provided in Table 6 below.

TABIA 6 Analysis of the results From the great drop in pressure in the fusion pressure it is evident that the addition of the CO in Ex. 2 is reducing the viscosity of the resin that is processed, which in turn reduces the pressure in the nozzle as the material with lower viscosity can more easily exit through the laminar nozzle. In addition, the superior performance obtained in Ex. 2, compared to that obtained in EC 2, shows that the material processed according to the invention is more easily processed. The flow data confirm that the reduction in temperature associated with the practice of processing the invention (for example, the addition of CO¿, as a process medium during extrusion) will reduce the degree of the hardening reaction or swelling of the resin in the extruder and results in a product having better flow characteristics, which in turn usually results in a more uniform coating.

Example 3 (Ex. 3). PROCESSING OF CRYSTALLINE MATERIALS According to the invention, the formulation containing crystalline thermoset polyester (identified in the following TABLE 7) was processed by an extruder under the conditions defined in TABLE 8 below. TABLE 7 TABLE 8 Analysis of the results . This example demonstrates that the invention allows and facilitates extrusion processing of crystalline materials. It should be noted that common conventional extrusion processing is not useful in relation to crystalline materials, in conventional extrusion processing, it is considered that the crystalline material melts, the viscosity of the material rapidly decreases making the material difficult or incapable of be handled or processed. In contrast and in accordance with the invention, in theory, the addition of the fluid in the process medium reduces the viscosity of the process stream and thus allows the material to be processed through the extruder.

In this way, the continuous processing of the powder coating compositions according to the invention can provide various advantages in which they include, for example: a.) Provides better product consistency, b.) Provides better processing of fast hardening compositions, c.) simplifies, reduces or eliminates the grinding processing necessary to shape the final powder product; d.) facilitates the formation and maintenance of the necessary joints in and for the processing apparatus, thus avoiding the problems associated with the high pressure operation of the prior art, as identified in the foregoing.; e.) provides the desired processing flexibility where, for example, the process medium can be added in 1 or more sites, as desired; f.) provides simple and effective removal of the fluid in the process medium from the precursor to the powder coating; g.) allows processing, as may occur within an extruder, at relatively low processing temperatures to allow and facilitate the use of temperature sensitive raw materials; h.) prevents unwanted hardening of thermosetting resins in areas such as pump joint area; i.) allows the use of the process medium without significant solubilization of the resin or other component of the composition; j.) allows the use of the process medium having associated therewith the significant solubilization of the resin or other component of the composition as it may be to form solutions of low viscosity which, for example, can be pulverized to form regular spheres; k.) allows processing with co-solvents; and 1.) provides a more easily friable cellular extrudate, capable of being reduced with greater control in particle size than the product of the conventional flake extruder. The invention described herein in illustrative form can be practiced properly in the absence of any element, part, step, component or ingredient that is not specifically described herein. The detailed description mentioned above is provided for clarity of understanding only, and no unnecessary limitation should be understood from this, as modifications within the scope of the invention will be obvious to those skilled in the art.

Claims

CLAIMS In a method for producing a powder coating, the step of: contacting a stream of the precursor for the powder coating consisting of the ingredients for the powder coating including at least one resin and at least one ingredient for the additional powder coating with an effective process medium fluid to reduce the viscosity of the precursor stream for the powder coating to allow processing of the precursor stream for the powder coating at a lower temperature, this process medium fluid consists of An average process material consists of an average process material in the form of a fluid that is selected from the group consisting of supercritical fluids and liquefied gases. The method of claim 1, wherein the precursor stream for the powder coating is processed in a continuous extruder to one. temperature no higher than the resin softening temperature. The method of claim 2, wherein the precursor stream for the powder coating is processed at a temperature of at least about 5.5-11 ° C below the softening temperature of the resin. The method of claim 2, wherein the precursor stream for the powder coating is processed at a temperature of at least about 11-22 ° C below the softening temperature of the resin. The method of claim 1, wherein the process medium fluid consists of a supercritical fluid, The method of claim 1, wherein the process medium fluid consists of a liquefied gas. The method of claim 1, wherein the process medium fluid consists of carbon dioxide. The method of claim 1, wherein contacting consists of the steps of: adding the material of the process medium to the precursor stream for the powder coating in a continuous extruder, and extruding the ingredients for the powder coating with the material of the process medium. The method of claim 1, wherein the precursor stream for the powder coating consists of the extruded product of a continuous extruder. The method of claim 1, wherein the precursor stream for the powder coating consists of feeding to a continuous extruder. 11. The method of claim 1 consists of: adding the material of the process medium to the precursor stream for the powder coating in a continuous extruder, extruding the ingredients for the powder coating with the material of the added process medium, and putting in contact the extruded product of the continuous extruder with the fluid of the additional process medium. 12. The method of claim 1 further comprises the step of contacting at least the precursor stream for the powder coating or the precursor stream for the powder coating after contact with a co-solvent. The method of claim 1, wherein at least one resin of the ingredients for the powder coating is a thermoplastic resin. The method of claim 13, wherein the thermoplastic resin is selected from the group consisting of polyphenylsulfones and PTFE. 15. The method of claim 1, wherein at least one resin of the ingredients for the powder coating is a thermostable resin ^ 16. The method of claim 1, wherein after the step of contacting, the current The precursor for the powder coating thus brought into contact is spray-dried to form particles for the powder coating. 17. The method of claim 16, wherein the powder coating particles are spherical in shape. 18. The method of claim 17, wherein the powder coating particles formed into spheres have a size in the range from less than 2 to about 40 microns. 19. The method of claim 1, wherein the precursor stream for the powder coating is processed in a continuous extruder to form a cell mass, this method further consists of the step of: crushing the cell mass to form particles of the powder coating. The method of claim 1, wherein after the step of contacting, the method further comprises the step of heating the precursor stream for the powder coating contacted with the fluid of the process medium. 21. The method of claim 20, wherein the step of heating is to pass the precursor stream for the powder coating contacted with the fluid of the process medium through a heated nozzle. The method of claim 1, wherein the resin is crystalline. In a method for producing a powder coating wherein the raw materials for the powder coating include a resin and at least one additional ingredient for the powder coating are fed and processed in a continuous extruder to disperse the at least one ingredient additional with the at least one resin to form an extrudate, the step of: adding a fluid of the process medium consisting of a material of the process medium in the form of a fluid that is selected from the group consisting of supercritical fluids and liquefied gases at a process stream of at least one of the following a.) the raw materials fed to the continuous extruder; b.) the raw materials processed in the continuous extruder; and c.) the extruded product of the continuous extruder, this addition being effective to reduce the viscosity of the selected process stream to allow processing of the process stream at a lower temperature. 24. The method of claim 23, wherein the precursor stream for the powder coating is processed in the continuous extruder at a temperature no higher than the softening temperature of the resin. The method of claim 24, wherein the precursor stream for the powder coating is processed in the continuous extruder at a temperature of at least about 5.5-11 ° C below the softening temperature of the resin. 26. The method of claim 24, wherein the precursor stream for the powder coating is processed in the continuous extruder at a temperature of at least about 11-22 ° C below the softening temperature of the resin. 27. The method of claim 23 further comprises the step of adding a co-solvent to the process stream which consists of at least one of the following: a.) The raw materials fed to the continuous extruder; b.) the raw materials processed in the continuous extruder; and c.) the extruded product of the continuous extruder, 28. The method of claim 23 wherein the fluid of the process medium consists of carbon dioxide. The method of claim 23 further consists of the step of statically mixing the extruded product of the continuous extruder. The method for producing a powder coating, the method consists in the steps of: extruding a premixed combination of the powder coating raw materials including at least one thermosetting resin and at least one hardening agent for the at least one a thermosetting resin, to form an extruded product; feeding a stream of the extruded product through a pump for molten material to form an extruded product stream under increased pressure; and spray drying the stream of extruded product under increased pressure to form the powder coating, wherein at least one of the combination of the raw materials for the powder coating which is subjected to extrusion and the stream of the extruded product under pressure Increased contact with a fluid of the process medium selected from the group consisting of supercritical fluids and liquefied gases, the process medium being effective to reduce the viscosity of the materials of the selected process stream to allow processing at a temperature lower. The method of claim 30, wherein the precursor stream for the powder coating is processed in a continuous extruder at a temperature no higher than the softening temperature of the resin. The method of claim 30, wherein the precursor stream for the powder coating is processed in a continuous extruder at a temperature of at least about 5.5-11 ° C below the softening temperature of the resin. The method of claim 30, wherein the precursor stream for the powder coating is It is processed in a continuous extruder at a temperature of at least about 11-22 ° C below the resin softening temperature. The method of claim 30, wherein the fluid of the process medium consists of carbon dioxide. The method of claim 30 further comprises the step of applying an additional amount of the process medium fluid to the joints in the molten material pump to keep these joints free of the powder coating materials being processed. 36. The method of claim 30 further comprises the step of statically mixing the fluid of the process medium with the stream of the extruded product at an increased pressure. 37. A system for producing a powder coating, the system consists of: a continuous extruder wherein the raw materials for the powder coating including at least one resin and at least one additional ingredient for the powder coating are fed and processed to disperse the at least one additional ingredient with the at least one resin to form a precursor stream of the coating, extruded; a source of a material, for the process medium, which reaches a fluid state within the processing system, the fluid of the process medium being effective to reduce the viscosity of the precursor stream for the powder coating to allow the processing of the precursor stream of the powder coating at a lower temperature; means for adding this material from the process medium to at least one of the following: a.) the raw materials fed to the continuous extruder; b.) the raw materials processed in the continuous extruder; and c.) the extruded product of the continuous extruder, and the means for forming and separating the powder coating from the material of the process medium. 38. The system of claim 37, wherein the material source of the process medium consists of a source of fluid that is selected from the group consisting of supercritical fluids and liquefied gases. 39. The system of claim 38, wherein the material of the process medium consists of carbon dioxide. 40. The system of claim 37, wherein the means for forming and separating the powder coating from the material of the process medium consists of a spray dryer. 41. The system of claim 37, wherein the means for forming and separating the powder coating from the material of the process medium consists of the means for crushing a cell mass. 42. The system of claim 37 further consists of a lift pump for increasing the pressure of the extruded precursor stream for the coating and increasing the amount of fluid of the process medium accepted by the precursor stream of the coating. 43. The system of claim 37, wherein the means for adding this material to the process medium consists of the means for adding the raw materials processed in the continuous extruder. 44. The system of claim 43, wherein the means for adding the material of the process medium further comprises the means for adding the material of the process medium to at least one of the following: raw materials fed to the extruder continuous and the extruded product of the continuous extruder. 45. The system of claim 43 further comprises the means for statically mixing the extruded product. 46. The system of claim 37 further comprises the means for heating a process stream containing the powder coating and the material of the process medium prior to forming and separating the powder coating from the material of the process medium. 47. The system of claim 37, wherein the means for forming and separating the powder coating from the material of the process medium consists of a heated nozzle. 48. A system for producing a powder coating, the system consists of: a continuous extruder wherein the raw materials for the powder coating include at least one thermosetting resin and at least one hardening agent for the at least one thermosetting resin and are fed and processed to disperse the at least one hardening agent in the at least the thermosetting resin to form a precursor for the extruded and melted powder coating; a pump for molten material through which the precursor for the powder, extruded and melted coating is processed to form a precursor stream of the powder coating of increased pressure; a source of a process medium material, the process medium material in a fluid state within the processing system and effective to reduce the viscosity of the precursor stream of the powder coating to allow processing of the precursor stream for the powder coating at a lower temperature; the means for adding this process medium material to the raw materials for the powder coating in the continuous extruder; and a spray dryer for forming and separating the powder coating from the process medium. The system of claim 48, wherein the middle process material consists of carbon dioxide. The system of claim 48 further comprises the means for adding this process medium material to at least one of the following: the raw materials fed to the continuous extruder and the extruded product of the continuous extruder. The system of claim 48, wherein the pump for molten materials consists of a gear pump.