MXPA99007354A - Coatings of curable polyes with radiationsultravioleta without fog, containing resins cristali - Google Patents

Abstract

The present invention relates to an ultraviolet curable powder coating composition comprising a mixture of particles of a non-crystalline unsaturated polyester base resin, a crystalline unsaturated cross-linked resin copolymerizable with the base resin, and a photoinitiator , which shows a reduced or eliminated clouding in the cured coating formed with it when cured at low temperatures required by certain heat-sensitive substrates. This is achieved by the incorporation into the powder composition of a recrystallization or cloudy inhibitor comprising a crystalline epoxy resin. When this powder mixture melts for curing, the crystalline crosslinker resin visually appears to separate and recrystallize from the melted powder less completely than it does in the absence of the recrystallization or cloudy inhibitor. This prevents the development of visible clouding on the coating surface when curing the composition with ultraviolet radiation

Description

COATINGS OF CURABLE POLYES WITH NON-FABRIC ULTRAVIOLET RADIATIONS CONTAINING CRYSTALLINE RESINS FIELD OF THE INVENTION This invention relates to powder coating compositions curable with ultraviolet (UV) radiation. More particularly, this invention relates to curable UV-curable powder coating compositions containing crystalline resins adapted to prevent clouding in the coating formed when cured at low temperatures. BACKGROUND OF THE INVENTION Powder coatings have achieved considerable popularity in recent years compared to liquid coatings and that for several reasons. Powder coatings have virtually no harmful fugitive organic solvents, and, therefore, produce few volatile substances during curing or no volatile substances. This eliminates the problems of solvent emission and creates a healthier environment for workers employed in coating operations. Dust coatings also improve hygiene at work, since they are in dry solid form and are not associated with difficult-to-handle liquids that adhere to workers' clothing and coating equipment. They are relatively non-toxic and easy to sweep in the event of a spill and do not require special spill containment and cleaning equipment. Another benefit is that they are virtually 100% recyclable. The oversprayed powder is usually recovered and fed back to the original powder feed circuit during the coating operation, resulting in high coating efficiency and minimal waste. However, despite these advantages, traditional heat-setting powder coatings have not been suitable for the coating of heat-sensitive substrates, since the temperatures at which these powders must be cured are usually higher than what they are. It can resist the heat-sensitive substrate. With the increasing desire to coat heat sensitive parts with powder coatings and obtain the aforementioned benefits, the development of powders allowing polymerization or curing at low temperatures has recently been emphasized. A class of recently developed low temperature curing powder coatings for heat sensitive substrates are powder coatings curable with ultraviolet radiation. Such ultraviolet radiation curable powders can be formulated to melt and flow and cure and produce desired smooth glossy coatings at much lower temperatures than would have been possible with traditional thermofixing chemistry, which is primarily due to the curing reaction initiated. only by ultraviolet radiation instead of heat. The mechanism of curing by ultraviolet radiation also allows the production of the powders in traditional fusion-mixing equipment and storage at room temperature without causing an unwanted prior reaction. Curable powders with ultraviolet radiation are typically prepared from solid unsaturated non-crystalline base resins, solid unsaturated non-crystalline crosslinking resins, solid photoinitiators, flow additives, other performance enhancing additives, as well as optional pigments and inert fillers. It is also common to replace some or all of either the base or the crosslinker resin with a crystalline material, as presented, for example, in EP 0 636 669 of DSM. An ultraviolet curable powder coating promoted by currently preferred DSM employs a mixture of a non-crystalline base resin and a crystalline crystalline crosslinker resin. Specifically, it comprises a stoichiometric mixture of an amorphous (non-crystalline) unsaturated, relatively polar polyester base resin, solid, with maleate fumarate unsaturations and a glass transition temperature (Tg) of about 125 ° F (the glass transition temperature of the base resin is sufficiently high for a desired blocking resistance but still sufficiently low for a desired melt-flow behavior at low temperature), and a relatively non-polar, relatively incompatible crystalline divinyl ether urethane reticulator resin, solid, with a melting point (Tm) of about 195-230 ° F (the melting point) of the crystalline resin is found above the glass transition temperature of the base resin and is also found above the traditional melt processing temperatures to avoid the destruction of the intact crystal structures during processing and the correlated loss of Fusion processing efficiency and blocking resistance), together with a solid photoinitiator, age Control of flow, and optional pigments. The presence of crystalline ingredients, in particular, is highly desired because the powders exhibit a low melt viscosity and excellent flow behavior during the initial melting stage of the coating process, allowing the powders to be easily agglomerated in smooth melted coating films. that with subsequent curing with ultraviolet radiations develop exceptionally smooth coatings with a desired glossy appearance. However, one drawback with the use of crystalline materials, particularly crystalline crosslinker resins, which have such high melting points (Tm) is that to obtain cured coatings with desired smooth glossy appearance, the coating must be cured with UV radiation at higher temperatures. to the melting point of the crystalline component. If the temperature of the melted coating after the flow falls below the melting point to the point at which the crystalline component visually recrystallizes in the coating before curing with UV radiation, which may occur during the transfer of the coated part of the melt to the curing operation with UV radiation and / or as a possible result of the fact that the coated part has a variable mass, the cured coating will have an undesirable clouding on the surface with a corresponding loss of gloss and smooth appearance. The cloudy is believed to result from the fact that the crystalline resin component separates and igrates towards the surface of the coating where it is believed to recrystallize from intact crystal structures. This negatively affects the coating giving it a matt, uneven, cloudy appearance, characteristic of crystalline resins. While it is desirable when making low-gloss coatings, it becomes a problem when it comes to controlling the overcast and obtaining films with higher brightness at low temperatures. In addition, with an increased demand to coat heat-sensitive parts that can only withstand temperatures near the melting point of the crystalline ingredient, there is a need to provide a UV-curable powder coating that does not form cloudy which can be cured at such high temperatures. low and produce a bright, smooth, uniform finish, without cloudy on the part. The limitations of the curable powders with traditional UV radiation containing a crystalline resin can be better observed when attempting to coat frames of assembled electric motors housing various heat-sensitive components, including working parts and electrical circuit related to said parts. To avoid damage to these components, melt-flow and cure temperatures must remain at levels only slightly above the recrystallization point. To further complicate this issue, these engine frames tend to have a variable mass. During the coatingAs the powder melts under the desired conditions for curing, the higher frictions create thermal sinks and cause the temperature of the melted coating in this section to fall below the point at which the crystalline ingredient is recrystallized while in other sections the coating temperature is conserved above the point of recrystallization. As a result, coatings cured from there have an unacceptable mottled appearance due to cloudy appearance in the heavier sections, instead of having a smooth shiny coating consistent throughout the part. To overcome the problem of cloudy and mottled, it is possible to use non-crystalline resins alone that are recrystallized. However, in order to achieve adequate flow at low temperatures proper to heat-sensitive substrates, the glass transition temperature of non-crystalline resins must be greatly reduced, which can make the powders physically unstable and susceptible to blocking or sintering during storage at room temperature. Blocking powders are extremely difficult to measure and spray during coating operations and result in inconsistent spray patterns and coating defects. The reduction of the amount of crystalline resin, especially crystalline crosslinker resin, to levels at which recrystallization does not occur (i.e., below 10% by weight in resin systems) has also been attempted, but at such low levels. Low, the powders present a limited flow at low temperatures and produce incompletely cured coatings with very textured appearance. It would be desirable to provide a coating composition of ultraviolet curable powders containing crystalline resins adapted to prevent clouding in the coating formed when cured at low temperatures. SUMMARY OF THE INVENTION Accordingly, it is a primary object of the present invention to provide a UV curable powder coating composition, containing crystalline resins, which does not suffer from the aforementioned drawbacks. It is another object of the present invention to provide an ultraviolet curable powder coating composition containing crystalline resins adapted to prevent clouding in the coating formed when cured at low temperatures. It is a related object of the present invention to provide UV reversible curable powder coating composition containing crystalline resins adapted to prevent speckle and to provide visually consistent gloss and smoothness in the coating formed with this composition when cured over a wide range of high and low temperatures. It is a further object of this invention to provide a powder coating composition with UV ratios of the aforementioned property which can be melt processed, with stable storage both chemically and physically, which has a low flow viscosity when melted for curing and which it has the ability to melt-flow and cure at low temperatures suitable for temperature sensitive substrates, all this without affecting the smooth, glossy character, and overall quality of the coating film produced with this composition. According to an aspect prior to this invention, there is provided an ultraviolet radiation curable powder coating composition, which flows at low temperatures, stable in storage, melt processable, containing crystalline resins that have a low cloudy or no overcast in the coating formed therewith when cured at low temperature, comprising a mixture of film forming particles of: A) an unsaturated base resin; B) an unsaturated crosslinker resin copolymerizable with the base resin; and C) a photoinitiator, wherein the combination of components A) plus B) comprises a mixture of at least one crystalline resin and at least one non-crystalline resin, and the improvement where the powder coating composition comprises D) an inhibitor of recrystallization or cloudy for the crystalline component that visually appears to inhibit its recrystallization in the coating after melting of the powder composition for curing and which reduces or eliminates clouding in the coating formed when cured at low temperatures that normally cause such clouding.

In accordance with a preferred aspect of this invention, it provides a melt-processable, storage-stable, ultraviolet curable powder coating composition containing crystalline resins that can melt-flow at low temperatures suitable for the preservation of sensitive substrates. heat, for example, within a range of 170 ° F-300 ° F, and showing a reduced or no cloudy overcast in the coating formed with them when cured at low temperatures, eg, about 170 ° F or less , which comprises a mixture of film-forming particles of: A) an unsaturated, non-crystalline polyester base resin having a glass transition temperature of about 90 ° F, preferably a non-crystalline unsaturated polyester having unsaturated polyester resins; maleate or fumarate; B) a crosslinking resin functionalized with crystalline vinyl ether copolymerizable with the base resin having a melting temperature greater than 180 ° C, preferably a urethane oligomer terminated with crystalline vinyl ether; C) a photoinitiator; and the improvement where the composition contains D) a crystalline epoxy resin serving with a recrystallization or cloudy inhibitor having a glass transition temperature greater than 180 ° F, preferably a crystalline epoxy oligomer compatible with A) and with B), where the incorporation of component B) reduces or eliminates clouding in the formed cured coating. DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Throughout this specification, all parts and percentages specified herein are given by weight unless otherwise indicated. Here, the base resin A) plus the crosslinker resin B) plus the recrystallization inhibitor or cloudy D) are considered as the * Resin System "and is equal to 100. The levels of the other components are calculated as parts relating to 100 parts of the resin system ('phr'). Here also 'glossy' or 'high gloss' refers to brightness levels of 50 or more on a Gardner Brightness scale of 60 °. Furthermore, in this document, the expression "non-crystalline" (also "amorphous") refers in general terms to resins that do not show any point of crystallization or melting or only a trace of said point of crystallization or melting as determined. by differential scanning calorimetry (DSC) While the term 'crystalline' includes crystalline materials as well as semicrystalline materials and defines in general terms resins with a point of crystallization or melting that can be observed by DSC. Finally, the "recrystallization temperature" or "recrystallization point" refers to the temperature at which the crystalline resin component visually appears separately and is recrystallized from the powder composition after it has been melted for curing, in accordance with the evidenced by the visual development of a cloudy in the coating. The base resin A) preferably consists of at least one unsaturated polyester resin having at least one site of ethylenic unsaturation per molecule. The unsaturated polyester resins can be prepared conventionally by condensation of one or more of the polyfunctional ethylenically unsaturated carboxylic acids (or their anhydrides) having carboxyl functionalities of two or more with one or more polyhydric alcohols having hydroxyl functionalities of 2 or more. While the unsaturation is typically provided by the carboxylic acid it is also possible to supply it through the alcohol. In addition, the ethylenic unsaturation can be provided in the polymer structure or at the end of the chain. If supplied at the end of the chain, ethylenically unsaturated monocarboxylic acids (or their esters) are used in the condensation reaction. In addition, the fact that the unsaturated polyester ends in carboxyl or hydroxy will depend on the proportion -OH / -COOH used in the monomer mixture. While these saturated reactivities generally do not participate in the curing reaction that continues through the unsaturated groups, they are frequently used to achieve the desired chemical and mechanical properties. Examples of suitable polyfunctional ethylenically unsaturated carboxylic acids (or their anhydrides) include maleic anhydride, fumaric acid, itaconic anhydride, citraconic anhydride, meconic anhydride, aconitic acid, tetrahydrophthalic anhydride, nadic anhydride, dimeric methacrylic acid, etc. maleic anhydride, fumaric acid, or mixtures thereof are generally preferred due to economic considerations. Examples of monofunctional acids used for chain end unsaturation include acrylic acid, methacrylic acid, etc. Frequently, aromatic and polyfunctional saturated acids are used in combination with the polyfunctional unsaturated acids to reduce the density of the ethylenic unsaturation and to provide the desired chemical and mechanical properties to the coating. Examples of suitable saturated aromatic polycarboxylic acids (or their anhydrides) include adipic acid, succinic acid, sebacic acid, malonic acid, glutaric acid, cyclohexanedicarboxylic acid, dodecanedicarboxylic acid, ophthalmic anhydride, isophthalic acid, terephthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, trimellitic acid, pyromellitic anhydride, etc.

Examples of suitable polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, propanediol, butanediol, neopentyl glycol, cyclohexanedimethanol, hexanediol, 2-n-butyl-2-ethyl-l, 3-propanediol, MP diol, didecanediol, bisphenol A, hydrogenated bisphenol A, trimethylol propane, pentaerythritol, etc. The unsaturated polyester resins can be formulated so that they already have a crystalline or amorphous micro structure. According to this invention, it is preferable that the resin system of ultraviolet curable powders contain at least about 10% by weight of reactive crystalline material to provide a desired low flow viscosity when melted for curing. It is well known in the art that some acid and alcohol monomers can provide crystallinity to unsaturated polyesters. For example, symmetrically substituted linear monomers or cyclic monomers or their mixtures are usually used to form crystalline polyesters. Examples of typical dihydric alcohols that promote crystallinity include ethylene glycol, butanediol, hexanediol and cyclohexanedimethanol. Examples of typical dicarboxylic acids known to do the same include terephthalic acid, adipic acid, dodecanedicarboxylic acid, and cyclohexanedicarboxylic acid. Typically, only the unsaturated base resins A) are of interest in powder coatings. Solid unsaturated polyester resins typically have a weight average molecular weight (Mw) within a range of about 400 to 10000, and preferably within a range of about 1000 to 4500. The unsaturated polyesters typically have a degree of unsaturation, unsaturation preference of fumarate or maleate, between about 2 and 20% by weight, and preferably between about 4 and 10% by weight. If the unsaturated polyesters have a hydroxyl functionality, then the hydroxyl number is usually within a range of 5 to 100 mg KOH / gram of resin. If the unsaturated polyester has an acid functionality, then the acid number is usually from about 1 to 80 mg KOH / gram of resin. In a preferred embodiment, the base resin A) comprises a relatively polar, solid, non-crystalline, unsaturated polyester resin with maleate or fumarate unsaturations. Accordingly, the reactive crystalline material is preferably supplied by the crosslinker resin B). Generally, all non-crystalline resins useful herein should have a glass transition temperature (Tg) greater than 90 ° F, preferably within the range of about 110 to 150 ° F, which is high enough for conventional melt processing and so that the powders remain solid and do not become blocked or synthesized during storage at room temperature. However, the glass transition temperature is still sufficiently low for the powders to pass their softening point and flow freely at the temperature required to preserve temperature sensitive substrates, usually between about 170 ° F and 300 ° F, and preferably between approximately 170 ° F and 250 ° F. The unsaturated base resins A) work best in combination with copolymerizable crosslinker resins B) (also known as curing agents) having ethylenic unsaturation, and preferably having two sites of unsaturation per molecule. Examples of such crosslinker resins include oligomers having vinyl ether, vinyl ester, allyl ether, allyl ester, acrylate or methacrylate, ethylenically unsaturated groups, even though vinyl ether groups are usually preferred. These materials are usually available as crystalline resins. Examples of suitable vinyl ether crosslinker resins include crystalline oligomers of vinyl ether-terminated urethane, this oligomer can be prepared by well-known techniques, as for example by the reaction of hydroxyl-functional vinyl ethers, such as, for example, hydroxybutylvinyl ether, with crystalline diisocyanates, such as for example hexamethylene diisocyanate, hydrogenated methylene bis (cyclohexyl) diisocyanate, or biurets or uretdiones thereof . Another suitable vinyl ether crosslinker is a crystalline ester oligomer terminated with vinyl ether. This crystalline material can also be prepared by conventional methods, such as, for example, by the condensation of hydroxyl-functional vinyl ethers, such as, for example, hydroxybutylvinyl ester, with crystalline carboxylic acids (or their anhydrides), such as, for example, ophthalmic anhydride. Other suitable crosslinkers include resins having acrylate or methacrylate groups, such as urethanes terminated with dimethacrylate. Again, these materials are usually crystalline resins which can be conventionally formed by the reaction of hydroxyl-functional (meth) acrylates, such as for example hydroxyethyl methacrylate and hydroxypropyl methacrylate, with crystalline isocyanates. Allyl ester crosslinkers are also frequently used, such as, for example, the product of the reaction of allyl alcohol and crystalline carboxylic acids (or their anhydrides), typically ophthalmic anhydride.

Standard crystalline allyl ether crosslinkers include the product of the reaction of an allyl ether such as for example allyl propoxylate, and a crystallizing hydrogenated methylene diisocyanate.

The crosslinker resins B) of particular interest here are solid materials also due to the fact that good powder stability and good processing capacity in the melted state are more easily achieved. The solid crosslinker resins typically have a weight average molecular weight (Mw) which is within a range of about 200 to 1000, and preferably between about 300 and 800. Obviously, if these resins are in the liquid state, as is the case of many of the other materials used in the UV-curable powder other than the base resin, they can be converted into solid by absorption in an inert silica-type filler, such as, for example, fumed silica, before use, as is well known in the art. In a preferred embodiment, the crosslinker resin B) comprises a solid, relatively non-polar crystalline vinyl ether-terminated urethane resin. As described above, the reactive crystalline ingredient is preferably supplied by the crosslinker resin B), with the base resin A) preferably supplying the non-crystalline reactive material. Generally, all crystalline resins useful herein should have a melting point (Tm) greater than the glass transition point of the non-crystalline resins, and preferably greater than 180 ° F to about 300 ° F. This allows an efficient melt processing of the powders using conventional equipment, and this ensures at the same time that the crystalline structures remain intact after processing in the melted state, which gives the powders the desired powder stability and the resistance of the powder. blocking. In addition, the melting temperature is below the flow temperature required for the preservation of temperature sensitive substrates. A person with certain knowledge in the art will note that the proportions between unsaturated base resin and unsaturated copolymerizable crosslinker resin in UV-curable coatings and powder will depend on the choice of materials used. Typically, such materials are employed in stoichiometric equivalent amounts to allow the crosslinking to proceed to its substantial completion, even if an excess of any of them may be employed, if desired. In general, if the crosslinker is a urethane oligomer terminated with vinyl ether and the base resin is an unsaturated polyester with maleate or fumarate unsaturations, as preferred, the crosslinker is employed in an amount that is within a range of 0.5-1.5 equivalents of vinyl ether unsaturation at 1.0 equivalent of polyester unsaturation, preferably 1.0 to 1.0 equivalents. To obtain the desired low viscosity melt flow behavior at temperatures between 170 ° F and 300 ° F, preferably between 170 ° F and 250 ° F, the amount of crystalline resin, which is supplied by the base resin A) or by the crosslinker resin B) present in the ultraviolet radiation curable powders is generally within ranges between about 10 and 50% by weight of the total amount of A) plus B), and preferably between about 15 and 25% by weight the remainder being a non-crystalline resin. Below about 10% by weight, the desired flow behavior at the lower melting temperatures can not be achieved. Above 50% by weight, recrystallization rates generally can not be controlled effectively. Photoinitiators C) of standard free radicals are also incorporated in the curable powders with ultraviolet radiation to initiate the photopolymerization of the ethylenically unsaturated compounds. Examples of suitable alpha dissociation photoinitiators include benzoin, benzoin ethers, benzyl ketals, such as, for example, benzyl dimethyl ketal, acyl phosphines, such as, for example, diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide, arylketones, such as, for example, 1-hydroxycyclohexylketone, etc. Examples of suitable hydrogen abstraction photoinitiators include Michler's ketone, etc. Examples of suitable cationic photoinitiators include diaryliodonium salts and copper synergists, etc. Usually the amount of photoinitiator present is within a range between about 0.1 and 10 phr, and preferably between about 1 and 5 phr. In accordance with this invention, for the purpose of reducing or eliminating clouding and maintaining a consistent smooth shiny appearance when the powder coating, after having been melted and having fluid for curing, is cured in the melted state at temperatures below the Normal recrystallization point of the crystalline resin component supplied by A) or B), preferably supplied by D), a recrystallization or cloudy inhibitor D) is used in the resin system of the powder composition. In general, the recrystallization inhibitor D) comprises another crystalline resin mutually compatible with the generally incompatible crystalline and non-crystalline resins provided by A) and B). When incorporated into the powder composition, it can be observed visually that the recrystallization inhibitor interrupts the recrystallization of the crystalline resin species supplied by A) or B) in the coating and prevents the visible development of clouding in the coating formed when it is cured. at temperatures that normally cause such cloudy. The recrystallization inhibitors D) of particular interest here are solid materials as well. More particularly, this material is a solid crystalline oligomer having portions compatible with the crystalline and non-crystalline coreactive materials supplied by A) and B). The crystalline oligomer typically has a weight average molecular weight (Mw) which falls within a range between about 200 and 1000, and preferably between about 300 and 800. The melting point (Tm) must also fall within the range described above for crystalline materials, i.e., a Tm greater than the glass transition temperature of the non-crystalline resins, and preferably greater than 180 ° F to about 300 ° F. It may also contain unsaturated groups that participate in curing with UV radiation, even though it typically does not contain such unsaturated groups. This component can also be characterized in that it can not be recrystallized from a clear fusion as shown by DSC in contrast to the crystalline component supplied by A) or B) which is susceptible to clouding. In a preferred embodiment, where the non-crystalline resin is an unsaturated polyester base resin A) and the crystalline resin is a urethane crosslinker resin finished with vinyl ether B), the recrystallization inhibitor D) is preferably a crystalline oligomer containing one or more portions compatible with the non-crystalline, relatively polar unsaturated polyester, such as for example aryl, for example benzyl, substituted aryl, sulfone, ether, glycidyl ether, hydroxyl, ester, and the like which make component D) becomes compatible with the base resin A), and an aliphatic crystal structure and a molecular weight (Mw) close to the molecular weight of the crystalline crosslinker resin B) which makes the component D) compatible with the crystalline crosslinker resin B). More preferably, the recrystallization inhibitor D) consists of a crystalline epoxy oligomer having by definition a glycidyl ether portion and which may contain other portions that appear in the above list as well. It may also contain unsaturated functionalities even when typically only saturated functionalities are present. Preferably, the molecular weight (Mw) of these crystalline epoxy oligomers is less than 800. Crystalline epoxy resins of the aforementioned character can be prepared by well known techniques, such as by means of the glycidylation of an alcohol containing the functional groups before mentioned and known to have limited rotation with epichlorohydrin. Examples of suitable crystalline epoxide resins useful in the practice of this invention include, but are not limited to, tetramethyl bisphenol diglycidyl ether, triglycidyl isocyanurate, dihydroxydiphenylsulfon diglycidyl ether (bisphenol S diglycidyl ether), 2,5-di-t-butylbenzene-1,4-diblicidyl ether. , isophthalate, diglycidyl, epoxypropoxydimethylbenzyl acrylamide, hydroquinondiglycidyl ether, 2,5-di-t-butylhydroquinone diglycidyl ether, as well as diglycidyl ester of terephthalic acid, etc. As mentioned above, it is also possible to supply the recrystallization inhibitor D) with unsaturated groups that will participate in the curing reaction with UV radiation proceeding primarily through the unsaturated groups. An example of a suitable coreactive recrystallization inhibitor includes a crystalline vinyl ether containing one or more of the aforementioned portions, such as, for example, butanol-4-ethylene-oxy-benzoate. While we do not wish to be bound by any particular theory, we believe that the recrystallization inhibitor inhibits the recrystallization of the other crystalline components by making the other crystalline component more compatible with the non-crystalline resin. In this more compatible mixture, the other crystalline resin component appears visually separated and is recrystallized from the melted coating powder less completely than in the absence of the recrystallization inhibitor. The amount of recrystallization inhibitor D) employed will obviously depend on the amount of reactive crystalline resin contained in the ultraviolet-curable powder composition. The amount is generally within a range of about 0.1 to 100% by weight of the total amount of the crystalline resin supplied from A) or B), and preferably between about 1 and 50% by weight. Other ingredients, such as standard catalysts, can also be used to increase the crosslinking speed, such as, for example, transition metal compounds based on a fatty acid or oil, or tertiary amines. Cobalt soaps such as for example cobalt octoate, cobalt neodecanoate, cobalt naphthenate, and cobalt octadecanoate, are especially preferred. If employed, the amount of catalyst present is typically less than about 1.0 phr, and preferably lies within a range of about 0.1 to 0.5 phr. In addition, initiators of thermal free radicals, such as for example organic peroxide and azo compounds can also be used in combination with the photoinitiators. The presence of thermal initiators together with photoinitiators aids curing close to the substrate, particularly when thicker, opaque, pigmented film coatings are desired. Examples of suitable peroxide initiators and azo include diacyl peroxide, such as for example benzoyl peroxide, azobis (alkylnitrile) peroxy compounds, peroxy ketals, such as for example 1,1-bis (t-butyl peroxy) -3,3, 5-trimethylcyclohexane, peroxy esters, dialkylperoxides, hydroperoxides, ketone peroxides, etc. if used, the amount of thermal initiator present is usually within a range of about 0.1 to about 10 phr, and preferably between about 1 and 5 phr. Common additives such as pigments and fillers, flow control agents, dry flow additives, anti-pitting agents, surfactants, texture agents, light stabilizers, etc., can also be used. For example, UV curable powders made in accordance with this invention can be clear coatings (ie, not pigmented or filled) or may contain up to about 200 phr, usually up to about 120 phr, of traditional fillers and / or pigments for a desired opacity and / or color. Examples of suitable fillers include calcium carbonate, barium sulfate, wollastonite, mica, china clay, diatomaceous earth, benzoic acid, low molecular weight nylon, etc. Examples of suitable pigments include inorganic pigments, such as for example titanium dioxide, and organic pigments such as, for example, carbon black, etc. The other common additives mentioned above are typically present in a total amount of up to about 15 phr. Examples of typical flow control agents include acrylic resins, silicone resins, etc. Examples of typical dry flow additives include fumed silica, alumina oxide, etc. Examples of typical agents against the formation of depressions include benzoin, benzoin derivative, phenoxy plasticizers and low molecular weight phthalate, etc. Examples of typical surfactants include acetylene diol, etc. Examples of typical texture forming agents include organophilic clays, crosslinked rubber particles, multiple crosslinkers, etc. Examples of typical light stabilizers include hindered amines, hindered phenols, etc. The UV curable coatings powders employed in this invention are produced by conventional melt-mixing techniques. The components are mixed dry between them, and then the melt is mixed in a single screw or double screw extruder with heating above the melting of the resin system. The extruded composition is rapidly cooled and cut into flakes, milled in a mill with cooling, and, as necessary, the particles are sized according to size. The average particle size is typically between about 20 and 60 microns. Gaseous or supercritical carbon dioxide can be charged to the extruder to lower the extrusion temperatures. This is particularly desirable with powders containing crystalline resins. These powders tend to present drastic viscosity reductions above the melting point (Tm) of the crystalline materials, which in turn undesirably reduces the amount of cutting and mixing action that occurs in the extruder, causes longer processing time while the crystalline materials are expected to be recrystallized and the powder hardens, and also reduces the shelf stability of the powder produced due to the destruction of the crystal. Thus, the extrusion is preferably carried out at temperatures above the glass transition point of the non-crystalline resins but below the melting temperature of the crystalline components for an efficient melt processing and for a desired stability in storage. . Once the dry, free flowing, ultraviolet curable powders containing the crystalline resins are produced, they are ready for application in a substrate to be coated. The curable powders with ultraviolet radiation are applied in a conventional manner, for example, electrostatically, on the substrate. Electrostatic spray booths are used which house series of spray guns for corona discharge or triboelectric and a recovery system to recycle the remaining dust in the powder feed system. The applied powders are then exposed to a sufficient amount of heat to melt and flow in a smooth, continuous melted film on the substrate. The substrate can be heated at the time of application (preheated) and / or subsequently (subsequent heating) to effect melting and flow. The heating can be carried out in convection, infrared ovens, or a combination of both, even when infrared ovens are preferred. In the initial melting step, the UV curable powders employed in this invention have the ability to melt and flow in exceptionally smooth films very quickly (eg, in about 5-190 seconds) at very low melting temperatures (e.g. , between 170 and 300 ° F), making these powders suitable for coating a plurality of heat sensitive substrates. Usually, the flow viscosity is also very low (for example, about 100-4000 cones and plates) which helps to produce extremely smooth coating at the desired flow temperatures.

Immediately after the melting and powder flow, the melted powder coating is exposed to an ultraviolet light that, almost instantaneously, cures and hardens the film in a glossy and uniformly smooth coating, without clouding, lasting, attractive in the totality of the substrate. Standard ultraviolet light sources are suitable for coating curing, such as standard medium pressure mercury vapor lamps, iron-doped mercury vapor lamps, and / or gallium-doped mercury vapor lamps, for example, H-, D- and / or V- lamps of 600-watt fusion. Radiation with electronic rays can be used instead of ultraviolet radiation, if desired. The hardening of the coating requires a period of about 1 il-second to 10 seconds, and typically is less than about 3 seconds. The thickness of the coating that can be obtained is typically between about 0.5 and 25 mils, and more commonly between about 1 and 10 mils. The gloss of the cured coating (measured on a Gardner glossiness scale of 60 °) is desirably about 50 or more, preferably about 70 or more without visually significant decrease in gloss level and smoothness in the film when cure at temperatures at which the crystalline ingredient supplied by A) or B) would normally separate and recrystallize in the absence of the recrystallization inhibitor D). The ultraviolet curable powder coatings in this invention are especially suitable for heat sensitive substrates. They are also suitable for traditional substrates resistant to heat. Examples of typical heat sensitive substrates include wood, such as hardwood, hardwood boards, laminated bamboo, composite wood, such as particle board, electrically conductive particle board, high density, medium or low fiber board. , artificial board, laminated bamboo, and other substrates that contain a significant amount of wood. These substrates can be filled or protected with UV radiation liquids, powder preparation agents, or coatings carried in solvent or water in order to improve the smooth character and reduce the required film structures. Other heat-sensitive substrates include plastics such as ABS, PPO, SMC, polyolefins, polycarbonates, acrylics, nylons, and other copolymers which usually twist or degas when coated and heated with traditional thermal curable powders, together with paper , cardboard and heat-resistant composites and components that have a heat-sensitive appearance, and especially those with a variable mass, etc. Examples of typical heat-resistant substrates include metal, steel, other alloys, glass, ceramics, carbon and graphite. This invention will be described in more detail below through specific examples. EXAMPLES 1-2 Curing of unsaturated polyester powder coating curable with ultraviolet radiation The following ingredients were mixed and extruded together in the manner provided to produce UV curable powder coatings in accordance with the present invention which can form a glossy finish smooth without consistent clouding when cured with ultraviolet radiation at variable high and low temperatures, together with traditional ultraviolet curable powder coating that can not obtain such results and serves as a control. INGREDIENTS PHR CONTROL EXAMPLE 1 EXAMPLE 2 MIXING IN DRY UNTIL HOMOGENEITY Uralac XP-31251 (Non-crystalline) 80 80 80 Uralac ZW-3307P2 (crystalline) 20 20 20 Epon RSS-14073 (crystalline) - 5 Ciba RD 97-2754 (crystalline) - - 5 Lucerin TPO 2 2 2 Resiflow P-676 2 2 2 Shepard Black7 6 6 6 LOAD THE EXTRUDER AND EXTRUDE TO A 180 ° F LIGHTING TEMPERATURE COOL THE EXTRUDED PRODUCT AND FORM IN LASKS AND THEN ADD OXIDE aluminum C8 0.2 0.2 0.2 LOADING TO THE MILL AND MOLLING UNTIL GETTING A DUST TO SCREEN MESH 140 1 Uralac XP 3125 is an unsaturated polyester resin, amorphous, solid which is believed to be based on fumaric or maleic acid, terephthalic acid, and 1,6-hexanediol, sold by DSM Resins. The individual resin has a glass transition temperature of approximately 125 ° F. 2 Uralac ZW-3307P is a crystalline, solid, divinyl ether urethane crosslinker resin, which is believed to be based on hexamethylene diisocyanate 4- hydroxybutyl vinyl ether, sold by DSM Resins. The resin individually has a melting temperature of about 223 ° F and a recrystallization point of about 176 ° F. 3 Epon RSS-1407 is a crystalline epoxy resin composed of tetramethyl bisphenol diglycidyl ether, sold by Shell Chemical. The resin individually has a melting temperature of about 221 ° F. 4 Ciba RD 97-275 is a crystalline epoxy resin composed of bisphenol S diglycidyl ether, sold by Ciba Polymers. The resin individually has a melting temperature of about 257 ° F. 5 Lucerin TPO is a solid photoinitiator composed of diphenyl (2,4,6-trimethyl-benzoyl) phosphine oxide sold by BASF. 6 Resiflow P-67 is a solid acrylic flow control agent sold by Estron Chemical. 7 Shepard Black is a black spinel copper chromite pigment, sold by Shepard Color. 8 Aluminum oxide C is a dry flow additive composed of aluminum oxide, sold by Degussa. Each powder formulation above was applied electrostatically by a corona discharge spray gun on two separate steel panels preheated to different temperatures, ie, 170 ° F and 250 ° F. The panels were coated at these temperatures in order to simulate what happens in a heat sensitive part that has thick sections and thin sections that are heated to different temperatures depending on the mass of the part. The applied powders were allowed to fuse as a result of the residual heat provided by the preheating until a smooth continuous melt coating film will be formed. Immediately after the fusion, while the film was still melted, the panels were cured by exposure to ultraviolet radiation. The cured coatings all had a film thickness comprised between 2.2 mils and 3.0 mils. The coating conditions and the performance results appear in the following table CONTROL Preheating (15 minutes) 175 ° F 250 ° F Energy application 100 kV corona gun Cured with UV radiation (1 sec) D 600 watt lamp Substrate Panel Q Overcast temperature at 170 ° F 242 ° F UV curing Cloudy Cloudy No cloudy mottling Uniformity Texturized non-peel Orange Brightness at 60 ° 72 90 MEK resistance (50 Floating light Double no) detachment peel EXAMPLE 1 Preheat (15 minutes) 175 ° F 250 ° F Application Energy 100 kV corona gun Cured with UV radiation (1 sec) D 600 watt lamp Substrate Panel Q Coating temperature at 168 ° F 241 ° F cured with UV radiation Cloudy No Cloudy Uniformity shell without shell Orange noOrange table Gloss at 60 ° 82 94 Resistance MEK (50 float no desnointing Double) detachment detachment EXAMPLE 2 Preheat (15 minutes) 175 ° F 250 ° F Energy application 100 kV corona gun Cured with UV radiation (1 sec) D 600 watt lamp Substrate Panel Q Coating temperature at 168 ° F 242 ° F cured with UV radiation Cloudy No Cloudy Orange peel shell uniformity non-orange Lightweight table Brightness at 60 ° 77 94 Resistance MEK (50 floating no des- no Double) detachment detachment The above results confirm that the incorporation of a more compatible crystalline resin into the powder composition together with the crystalline crosslinker resin prevents the visible development of a clouding on the surface of the coating when cured at temperatures at which the crystalline crosslinker resin it would recrystallize normally in the absence of the other crystalline ingredient. This allows the production of cured coatings with a smoother glossy appearance, especially in the case of a heat sensitive part, with variable mass despite having sections of the cured part at different temperatures above and below the usual recrystallization temperature. Example 3 Curing of unsaturated acrylated polyester powder coatings curable with ultraviolet radiation. The following ingredients were mixed and extruded together in the same manner as that offered in Examples 1-2 to produce another curable powder coating with ultraviolet coating according to this invention which can form a smooth glossy finish free from consistent clouding when cured with ultraviolet radiation both at high temperatures and at low temperatures, together with a coating with curable dust with traditional ultraviolet radiation that can not provide these results and serves as a control. PHR INGREDIENTS CONTROL EXAMPLE 3 Crylcoat E52521 (non-crystalline) 80 80 Uralac Z -3307P (crystalline) 20 20 Epon RSS-1407 (crystalline) - 5 Lucerin TPO 2 2 Resiflow P-67 2 2 Shepard Black 6 6 Aluminum oxide C 0.2% 0.2% Pie de Table 1 Crylcoat E5252 is a solid amorphous, unsaturated acrylated polyester resin. The resin individually has a glass transition temperature of about 140 ° F. Each powder formulation was tested in the same manner as that given in Examples 1-2. The coating conditions and the performance results appear in the following table. CONTROL Preheating (15 minutes) 175 ° F 250 ° F Powder application 100 kV corona gun Cured with UV radiation (1 sec) D 600 watt lamp Substrate Panel Q Coating temperature at Usually the same as curing with UV radiation in examples 1-2 Cloudy very Cloudy Cloudy very mottled light Cascara regularity from no Naranj to cascara Light orange Shine at 60 ° 24 86 MEK resistance (50 light float denyon Double) detachment detachment EXAMPLE 3 Preheat (15 minutes) 175 ° F 250 ° F Powder application 100 kV corona gun Cured with UV radiation (1 sec) D 600 watt lamp Substrate Panel Q Coating temperature at Usually the same as curing with UV radiation in examples 1-2 Cloudy No No Cloudy Cloudy Shell regularity of none Orange moderate spring of orange Brightness at 60 ° 66 86 MEK Resistor (50 Lightweight float des no Double) detachment detachment from the foregoing it will be noted that this invention is an invention well adapted to fulfill all the purposes and objects set forth above together with other advantages that are apparent and inherent. Since many variations of the invention can be made without departing from its scope, the invention is not intended to be limited to the embodiments and examples presented, which are considered merely exemplary. Accordingly, reference should be made to the appended claims to assess the real spirit and the full scope of the invention, on which exclusive rights are claimed.

Claims (11)

1. CLAIMS A non-cloudy ultraviolet curable powder coating composition comprising a mixture of particles forming a film of: A) an unsaturated base resin; B) an unsaturated crosslinker resin copolymerizable with the base resin; and, C) a photoinitiator, wherein the combination of components A) plus B) comprises a mixture of at least one crystalline resin capable of clouding and at least one non-crystalline resin, and wherein the composition further comprises D) a recrystallization inhibitor or cloudy comprising at least one other crystalline resin that reduces or eliminates cloud formation in the cured coating formed from the powder composition. The composition of claim 1, wherein the base resin A) comprises a non-crystalline unsaturated polyester resin, the crosslinker resin B) comprises a crystalline unsaturated oligomer having one or more groups of vinyl ether, vinyl ester, allyl ether, allyl ester, acrylate or methacrylate copolymerizable with the base resin, and recrystallization or cloudy inhibitor D) comprises a crystalline oligomer having one or more aryl, sulfone, ether, glycidyl ether, hydroxyl or ester groups. The composition of claim 1, wherein the base resin A) comprises a non-crystalline unsaturated polyester resin with maleate or fumarate unsaturations and a glass transition temperature from about 90 ° F to about 150 ° F, the crosslinker resin B) comprises a crystalline vinyl ether-terminated urethane oligomer with a Tm of from about 180 ° F to about 300 ° F, and the recrystallization or cloudy inhibitor D) comprises a crystalline epoxy oligomer with a Tm of about 180 ° F to about 300 ° F. The composition of claim 3, wherein the recrystallization or cloudy inhibitor is selected from the group consisting of tetramethylbisphenol diglycidyl ether, triglycidyl isocyanurate, bisphenol S diglycidyl ether, 2,5-di-t-butylbenzen-1, 4 diglycidyl ether, diglycidyl isophthalate, epoxypropoxy-dimethylbenzyl acrylamide, hydroquinondiglycidyl ether, 2,5-di-t-butyl-hydroquinone diglycidyl ether, and diglycidyl terephthalic acid ester. The composition of claim 3, wherein the recrystallization or cloudy inhibitor is tetramethylbisphenol diglycyl ether. The composition of claim 3, wherein the recrystallization or cloudy inhibitor is bisphenol S diglycidyl ether. The composition of claim 3, wherein the crystalline vinyl ether oligomer crosslinker is employed in a stoichiometric equivalent amount in relation to said non-crystalline unsaturated polyester base resin within a range comprised between about 0.5 and 1.5. The composition of claim 7, wherein the crystalline epoxy oligomer recrystallization or clouding inhibitor is employed in an amount of between about 0.1 and 100% by weight relative to the total amount of crystalline resin supplied by B). 9. The composition of claim 1, wherein the crystalline resin supplied by A) or B) is used in an amount comprised between 10 and 50% by weight in relation to the total amount of resin supplied by A) plus B). The composition of claim 9, wherein the recrystallization or clouding inhibitor is employed in an amount of between about 0.1 and 100% by weight relative to the total amount of crystalline resin supplied by A) or B). The composition of claim 1, wherein the powder composition, after it has been melted and flowable, can be cured in its melted state at temperatures of about 170 ° F without the crystalline materials being recrystallized to visually significant levels. The composition of claim 11, wherein the cured coating has a uniform 60 ° Gardner gloss of about 50 or more. A non-cloudy ultraviolet curable powder coating composition comprising a mixture of particles forming a film of: A) a non-crystalline unsaturated polyester resin with a glass transition temperature of about 90 ° F about 150 ° F; B) a crystalline vinyl ether functionality crosslinker resin with a Tm from about 180 ° F to about 300 ° F copolymerizable with the base resin; C) a photoinitiator; and D) a recrystallization or cloudy inhibitor comprising a crystalline epoxy resin with a Tm from about 180 ° F to about 300 ° F, where the incorporation of the recrystallization or cloudy inhibitor D) reduces or eliminates cloud formation in the coating cured formed. The composition of claim 13, wherein the recrystallization or cloudy inhibitor is free of unsaturated functional groups. The composition of claim 13, wherein the recrystallization or cloudy inhibitor is selected from the group consisting of tetramethylbisphenol diglycidyl ether, triglycidyl isocyanurate, bisphenol S diglycidyl ether, 2,5-di-t-butylbenzen, 1,4-diglycidyl ether, diglycidyl isophthalate, epoxypropoxy-dimethylbenzyl acrylamide, hydroquinondiglycidyl ether, 2,5-di-t-butyl hydroquinondiglycidyl ether, and diglycidyl terephthalic acid ester. The composition of claim 15, wherein the recrystallization or cloudy inhibitor is tetramethylbisphenol diglycidyl ether. The composition of claim 15, wherein the recrystallization or cloudy inhibitor is bisphenol S diglycidyl ether. The composition of claim 15, wherein the base resin is an unsaturated polyether with fumarate unsaturations, maleate, or acrylic unsaturations. The crosslinker resin is a urethane oligomer terminated with vinyl ether. The composition of claim 13, wherein the crystalline vinyl ether crosslinker is employed in an amount of stoichiometric equivalent in relation to said unsaturated polyester base resin of between about 0.5 and 1.5. The composition of claim 19, wherein the crystalline epoxy resin recrystallization inhibitor is employed in an amount of between about 0.1 and 100% by weight relative to the total amount of the crystalline resin supplied by B). The composition of claim 13, wherein the powder composition after having melted and after being flowable can be cured in its melted state at temperatures of about 170 ° F without the crystalline materials being recrystallized at visually significant levels. A substrate on which the powder coating composition of claim 1 is applied and cured. A heat sensitive substrate on which the powder coating composition of claim 1 is applied and cured.