MXPA97000969A - Coatings with polyuret powder - Google Patents

Abstract

The present invention relates to a coating powder composition in the form of a intimate mixture, in a finely divided form, comprising: A. a mixture of resins comprising: 1. about 10 to 40 weight percent of a polyester resin having a glass transition temperature of at least 55 ° C, a hydroxyl number of about 190 to 320, and an inherent viscosity of about 0.1 to 0.5 dl / g determined at 25 ° C in a mixture (60/40) by weight of phenyl / tetrachloroethane at a concentration of 0.5 g / 100 ml, said polyester comprising: a. diacid radicals comprising at least 50 mole percent of isophthalic acid radicals; and b. diol radicals comprising about 50 to 100 mole percent of tris (hydroxyethyl) isocyanurate radicals; and 2. about 60 to 90 weight percent of a polyester resin comprising at least 70 mole percent of terephthalic acid radicals and 2,2-dimethyl-1,3-propanediol and having a Tg of 55 to 85 ° C, a hydroxyl index of 30 to 80, and an inherent viscosity of about 0.1 to 0.3 dl / g; . an effective crosslinking amount of a polyisocyanate blocks

Description

COATINGS WITH POLYURETHANE POWDER This invention belongs to the field of coatings with thermosetting powders. More particularly, this invention relates to a mixture of a certain polyester having a high hydroxyl number and a Tg (vitreous transition temperature) with a polyester having a low hydroxyl number. These compositions possess a good stability against the formation of a hard sediment and the polyurethane coatings formed therefrom have an increased hardness, while maintaining a good storage capacity, that is to say they possess stability to the formation of hard sediment.

BACKGROUND OF THE INVENTION Plastic materials used in the manufacture of powder coatings are classified broadly as thermosetting or thermoplastic. In the application of thermoplastic powder coatings, heat is applied to the coating on the substrate to melt the particles of the powder coating and thereby allow the particles to flow together and form a smooth coating. Thermosetting coatings, compared to coatings derived from thermoplastic compositions, are generally tougher, more resistant to solvents and detergents, have better adhesion to metal substrates and do not soften when exposed to elevated temperatures. However, the curing of thermosetting coatings has presented problems in obtaining coatings which, in addition to the desirable characteristics set forth above, have good uniformity and flexibility. Coatings prepared from thermosetting powder compositions, upon application of heat, can be cured or fixed prior to the formation of a smooth coating, resulting in a relatively rough finish, which is referred to as an "orange peel" surface. The problem of the "orange peel" surface has caused the thermosetting coatings to be applied from organic solvent systems which are inherently undesirable due to environmental and safety problems that can be caused by the evaporation of the solvent system. Solvent-based coating compositions also have the disadvantage of relatively low utilization, ie, in some forms of application, only 60 percent or less of the solvent-based coating composition applied is puts in contact with the article or substrate that is covered. According to this, a substantial portion of solvent-based coatings can be scattered since the part that does not come into contact with the article or substrate being coated can obviously not be recovered. The technical bulletins of the RUCÓTE 103 polymer (Ruco) describe an increasing hardness by mixing RUCÓTE 107 with a high hydroxyl index RUCÓTE 103 resin to provide 5 coatings having improved hardness. U.S. Patent No. 5,229,470 describes coatings of low-gloss polyurethane powders prepared by mixing hydroxyl polyesters having a gel-time difference of at least three minutes. The US Pat. No. 3,211,585 discloses polyesters comprising the reaction product of a polymeric ester of a polycarboxylic acid from the group consisting of terephthalic acid, isophthalic acid and isocyanurate of tris (hydroxyethyl), with 10-40 % of an organic polyisocyanate that is useful for coating electrical conductors US Pat. No. 3,249,578 discloses polyesters prepared from tris (hydroxyethyl) isocyanurate used to coat electrical conductors US Patent No. 3,646,374 describes 0-polyester-imide resins comprising tris (hydroxyethyl) isocyanurate used for coating and electrical insulation of core members of dynamo-electric machines US Patent No. 4,476,279 describes an enamel for coil wire comprising an organic solvent solution of 'low viscosity and high solids content of a polyester-tris (isocyanurat or hydroxyethyl) which has a hydroxyl number of 216 to 316, and a hydroxyl to carboxyl group ratio of 1.65 to 2.0: 1. The present invention, as described below, relates to new coatings of polyurethane powders having a high hardness upon curing and good stability to hard sediment formation during storage. Prior to the present invention, the polyurethane coatings of Q. ' "High hardness was prepared by mixing two types of polyester resins having low and high hydroxyl rates.This is usually done by preparing resins having high hydroxyl rates due to the increased use of a polyalcohol such as trimethylolpropane; however, this method lowers the Tg of the composition and therefore reduces stability against the formation of hard sediments. It has now been found that a polyester resin with a high hydroxyl number and high Tg based on isophthalic acid and tris (hydroxyethyl) isocyanurate can be obtained. This resin can be mixed with polyester resins having low hydroxyl numbers to produce coating powder compositions having good stability against hard sediment formation and coatings having high hardness after application by electrostatic spraying and curing. This invention relates to powder coatings having both a high hardness and a good stability against the formation of hard sediment. The powder coating compositions are based on a mixture of polyester resins having a low hydroxyl number with a polyester having a high hydroxyl number comprising tris (hydroxyethyl) isocyanurate as the polyalcohol radical. The present invention provides a coating powder composition in the form of an intimate mixture, in finely divided form, comprising: A. a mixture of resins comprising 1. about 10 to 40 weight percent of a polyester resin which it has a vitreous transition temperature of at least 55 ° C, a hydroxyl number of about 190 to 320, and an inherent viscosity of about 0.1 to 0.5 dl / g determined at 25 ° C in a mixture (60 / 40 in weight) of phenol / tetrachloroethane at a concentration of 0.5 g / 100 ml; the aforementioned polyester comprising: a. diacid radicals comprising at least 50 mole percent of isophthalic acid radicals; and b. diol radicals consisting of about 50 to 100 mole percent of tris (hydroxyethyl) isocyanurate radicals; and 2. about 60 to 90 weight percent of a polyester resin consisting of at least 70 mole percent of terephthalic acid and 2,2-dimethyl-1,3-propanediol radicals and having a Tg of 55 to 85 ° C, a hydroxyl number of 30 to 80, and an inherent viscosity of about 0.1 to 0.3 dl / g; and B. an effective crosslinking amount of a blocked polyisocyanate. In the above composition, it is preferred that the resin component A (1) consists of at least 75 mole percent of isophthalic acid radicals and from about 75 to about 100 mole percent of tris (hydroxyethyl) isocyanurate radicals. It is further preferred that the resin component A (1) consists of at least 90 mole percent of isophthalic acid radicals and from about 80 to about 100 mole percent of tris (hydroxyethyl) isocyanurate radicals and that component A is present in a range of about 15 to 25 weight percent and component B is present in a range of about 75 to 85 weight percent. These new powder coating compositions exhibit markedly better stability against hard sediment formation than other known polyurethane powder coating compositions having high hardness. The effectiveness of this powder is evidenced in the comparison of powder coatings based on mixtures of low-hydroxyl resin with (1) resins high in typical hydroxyl 5 and (2) resins high in hydroxyls containing isocyanurate of tris ( hydroxyethyl) described herein. After three days at 40 ° C, powder coatings formulated with (1) showed poor stability to hard sediment formation while coatings formulated with (2) ÍC, showed a good stability to hard sediment formation. The high hydroxyl resins of this invention (component A (1)) can be produced using well-known polycondensation methods. The resin of component A (l) preferably has a hydroxyl number of about 190 to 320, more preferably 200 to 300, and comprises repeating radicals, alternating dicarboxylic acid radicals and diols where the diacid radicals comprise at least 50 mole percent isophthalic acid . Up to 50 moles percent of diacid radicals can be radicals of various aliphatic, alicyclic and aromatic diacids, preferably terephthalic acid. More preferably, the Tg is from about 70 to about 90 ° C.

The polyalcohol radicals of the component resin A (1) are derived from tris (hydroxyethyl) isocyanurate or from a mixture of tris (hydroxyethyl) isocyanurate, trimethylolpropane, and 2,2-dimethyl-1,3-propanediol. These polyalcohol radicals can also include up to 10 mol percent of other diols. The low-hydroxyl resins (component A (2)) are typical polyester resins for powder coatings comprising mainly terephthalic acid as diacid radical and 2,2-dimethyl-1,3-propanediol as the diol radical. The polyester has a Q "" hydroxyl number in the range of 30 to 80, an acid number of less than 15, and a Tg greater than 55 ° C. These resins are commercially available, for example, as RUCOTE 107 polyester. The blocked polyisocyanate compounds of the compositions of this invention are known compounds and can be obtained from commercial sources or can be prepared according to published methods. When heated to cure the coatings of the compositions, the compounds are deblocked and the isocyanate groups react with the hydroxyl groups present in the amorphous polyester to crosslink the polymer chains and thus cure the compositions to form tough coatings. Examples of the blocked polyisocyanate crosslinking component include those based on isophorone diisocyanate blocked with e-caprolactam, which is commercially available as Hüls 1530 and CARGILL 2400, or toluene 2,4-diisocyanate blocked with e-caprolactam, found in the trade as CARGILL 2450, and hexamethylene diisocyanate blocked with phenol. The most easavailable blocked polyisocyanate crosslinking agents or compounds, and therefore preferred, are those commonly known as isophorone diisocyanate blocked with e-caprolactam, for example, those described in U.S. Patent Nos. 3,822,240, 4,150,211 and 4,212,962, which are incorporated herein by reference. However, the products marketed as isophorone diisocyanate blocked with e-caprolactam may consist mainly of the diisocyanate of isophorone monomer, difunctional, blocked, ie, a mixture of cis and trans isomers of isocyanate of 3-isocyanate-methyl-3, 5, 5-trimethylcyclohexyl, the blocked difunctional dimer thereof, the trifunctional trimer blocked therefrom or a mixture of the monomeric, dimeric and / or trimeric forms. For example, the blocked polyisocyanate compound used as the crosslinking agent may be a mixture consisting mainly of the diisocyanate of difunctional isoform monomer blocked with e-caprolactam, and the trifunctional trimer blocked with e-caprolactam of isophorone diisocyanate. The description made here of the crosslinking agents as "polyisocyanates" refers to compounds containing at least two isocyanate groups which are blocked, ie reacted, with another compound, for example e-caprolactam. The reaction of the isocyanate groups with the blocking compound is reversible at elevated temperatures, for example, normally approximately 150 ° C, and higher, temperature at which the isocyanate groups are available to react with the hydroxyl groups present as free hydroxy groups in the polyester to form urethane linkages. Alternatively, the blocked polyisocyanate can be an effective crosslinking amount of a 1,3-diazetidino-2,4-dione dimer adduct of isophorone diisocyanate and a diol having the structure OO 1 \ II OCN-R1- -X-R'-NH-COR ^ OC-NH-R1- XR * -NCO n where: R1 is a 1-methylene-1,3,3-trimethyl-5-cyclohexyl radical divalent, that is, a radical that has the structure R2 is an aliphatic, cycloaliphatic, araliphatic or aromatic divalent radical of a diol; and X is a 1,3-diazetidin-2,4-dioneryl radical, that is, a radical having the structure 0p - N N- 0 where the ratio of NCO groups to OH in the adduct formation is approximately 1: 0.5 to 1: 0.9, the molar ratio of diazetidinedione to diol is from 2: 1 to 6: 5, the content of free isocyanate groups in the adduct is not more than 8 weight percent and the adduct has a molecular weight of about 500 to 4000 and a melting point of approximately 70 to 130 ° C. The 1,3-diazetidin-2,4-dione dimer adducts of isophorone diisocyanate and a diol are prepared according to the process described in Patent No. 4,413,079, incorporated herein by reference, by reaction of the diazetidine dimer of isophorone diisocyanate, preferably free of isocyanurate trimers of isophorone diisocyanate, with diols in a ratio of reactants giving as isocyanate: hydroxyl ratio a ratio of about 1: 0.5 to 1: 0.9, preferably 1: 0, 6 to 1: 0.8. The adduct preferably has a molecular weight of 1450 to 2800 and a melting point of about 85 to 120 ° C. The preferred diol reagent is 1,4-butanediol. This adduct is commercial with the name of Hüls BF1540. The amount of blocked polyisocyanate crosslinking compound present in the compositions of this invention may vary depending on several factors such as those mentioned here above with respect to the amount of component (A) that is used. Typically, the amount of crosslinking compound that will effectively crosslink the polymers to produce coatings with a good combination of properties is in the range of about 5 to 30 weight percent, preferably 15 to 25 weight percent, based on the total weight of components (A) and (B). The coating powder compositions of this invention can be prepared from the compositions described herein, by dry blending and subsequent mixing of the melt of the component (A) and the crosslinking compound, together with other additives of which are commonly used. in the powder coatings, and then grinding the solidified mixture to a certain particle size, for example, an average particle size in the range of about 10 to 300 microns, suitable for producing powder coatings. For example, the ingredients of the powder coating composition can be dry mixed and then the melt mixed in a ZSK twin screw extruder between 90 ° C and 130 ° C, granulated and finally ground. The melt mixture should be carried out at a sufficiently low temperature to prevent unblocking of the polyisocyanate crosslinking compound and thus prevent premature crosslinking. Typical additives that may be present in powder coating compositions include benzoin, flow aids or flow control agents that favor the formation of a smooth, shiny surface, stabilizing agents, pigments and dyes. The powder coating compositions preferably contain a flow aid, which is also known as a flow control agent or leveling agent, to enhance the surface appearance of the cured coatings of the powder coating compositions. These flow auxiliaries typically comprise acrylic polymers and are commercially available from various suppliers, for example MODAFLOW from Monsanto Company and ACRONAL from BASF. Other agents of '"" flow control that can be used include Modarez MFP SYNTHRON, EX 486 from Troy Chemical, BYK 360P from BYK Mallinkrodt and PERENOL F-30-P from Henkel. An example of a specific flow aid is an acrylic polymer having a molecular weight of about 17,000 and containing 60 mole percent of 2-ethylhexyl methacrylate radicals and about 40 mole percent of ethyl acrylate radicals. The amount of flow aid present may preferably be in the range of about 0.5 to 4.0 weight percent, based on the total weight of the resin component, and the crosslinking agent. The powder coating compositions can be deposited on various metallic and non-metallic substrates (eg, thermoplastic or thermoset composites) using known powder deposition techniques such as by means of spray gun, electrostatic deposit or by deposit from a fluidized bed. In fluidized bed sintering, a preheated article is immersed in an air suspension of the powder coating. The particle size of the powder coating composition is usually in the range of 60 to 300 microns. The powder is kept in suspension by passing air through the porous bottom of the fluidized bed chamber. The articles to be coated are preheated to approximately 121 ° to 205 ° C (approximately 250-400 ° F) and then contacted with a fluidized bed of the coating powder composition. The contact time depends on the thickness of the coating to be produced and typically is 1 to 12 seconds. The temperature of the coated substrate causes the powder to flow and melt to form a smooth, uniform, continuous, crater-free coating. The temperature of the preheated article also effects crosslinking of the coating composition and results in the formation of a tough coating having a good combination of properties. By this method, coatings having a thickness between 200 and 500 microns can be produced. The compositions can also be applied using an electrostatic process where a coating composition of powders having a particle size of less than 100 microns, preferably of about 15 to 50 microns, is blown by means of compressed air into an applicator in which load with a voltage of 30 to 100 kV by high voltage direct current. The charged particles are then sprayed onto the article attached to the ground to be covered, to which the particles adhere due to their electrical charge. The coated article is heated so that the powder particles melt and cure. Coatings of 40 to 120 microns thick can be obtained. Another method of applying coating powder compositions is the electrostatic fluidized bed process which is a combination of the two methods described above. For example, annular or partially annular electrodes are mounted in the feed air to a fluidized bed so that an electrostatic charge such as 50 to 100 kV is produced. The article to be covered, either heated, for example between 121 ° C and 205 ° C, or cold, is briefly exposed to the fluidized powder. The coated article can then be heated to effect crosslinking if the article has not been preheated to a temperature high enough to cure the coating upon contact of the coating particles with the article. The coating powder compositions of this invention can be used to coat articles of various shapes and sizes constructed of heat-resistant materials such as glass, ceramics and various metallic materials. The compositions are especially useful for producing coatings on articles made of metals and metal alloys, particularly steel articles. It is also possible to coat many thermoplastic and thermosetting resin compositions with the compositions of the present invention. Other examples of formulation methods, additives and powder coating application methods can be found in "User's Guide to Powder Coatings", 2nd edition, Emery Miller, editor, Society of Manufacturing Engineers, Dearborn, (1987). The compositions and coatings of this invention are further illustrated with the examples given below. All inherent viscosities are determined at 25 ° C in a mixture (60/40) by weight of phenol / tetrachloroethane at a concentration of 0.5 g / 100 ml. The acid and hydroxyl numbers are determined by volume and are expressed in them as mg of KOH consumed per gram of polymer. Vitreous transition temperatures (Tg) are determined by differential scanning calorimetry (DSC) in the second heating cycle at a scanning rate of 20 ° per minute after the sample has been heated so that it is quickly melted and cooled by below the glass transition temperature of the polymer. Molecular weights were determined by gel permeation chromatography (GPC) on a Perkin-Elmer instrument with tetrahydrofuran as mobile phase and solvent. The values are given in polystyrene equivalents. The brightness at 60 degrees is measured using a brightness meter (Gardner Laboratory, Inc. Model GC-9095) according to ASTM D-523. The pencil hardness of a coating is that which corresponds to the hardest pencil that fails to make a cut in the coating according to ASTM 3363-74 (re-approved in 1980). The results are expressed according to the following scale: (the softest) 6B, 5B, 4B, 3B, 2B, B, HB, F, H, 2H, 3H, 4H, 5H, 6H (the hardest). Impact resistance was determined using an Impact Tester from Gardner Laboratory, Inc. A weight is dropped into a slide tube from a specified height to strike a punch having a 1.5 cm hemispherical protrusion (5 / 8 inches) in diameter that is carried to the front (coated face) or to the back of the panel. The highest impact that does not crack the coating in pounds-inch is recorded. The stability against the formation of hard sediment was determined by filling two thirds of a wide-mouth flask of 0.09 1 (4 oz.) With the powder sample. Cover the bottle and place the closed container in a constant temperature oven at 40 ° C. The sample is removed from the powder after 72 hours and allowed to cool to room temperature. The bottle is then gently poured and the form in which the powder flows is noted. The stability to hard sediment formation is classified as good, if the powder flows freely or is classified as poor if the powder flows with difficulty. As an alternative method to measure stability to hard sediment formation, the following procedure was used: The stability to hard sediment formation was determined by weighing 60 grams of powder in a 0.09 1 (4 oz) wide-mouth flask that was cover later. The flask is then placed in an oven at constant temperature at 0 ° C for 72 hours. To evaluate the physical stability, the powder sample is then removed from the oven and left to stand for 1 hour at room temperature. The bottle is uncovered and a long blade is used to make three cuts in parallel lines in the powder followed by two additional cuts perpendicular to the three original cuts. Each cut should reach the bottom of the container completely to give 12 blocks of powder. The blocks are then poured into a sieve of 80 tared mesh and shaken for 1 minute. The stability to hard sediment formation is calculated by dividing the weight of the powder passing through the sieve by the weight of the original sample multiplied by 100. This test is then cited as "EVTECH Method". EXPERIMENTAL SECTION Example 1 A three-necked, round bottom flask of 2000 ml capacity, equipped with a stirrer, a short distillation column and an inlet tube for nitrogen, was charged with isophthalic acid (424.5 g, 2561 moles), terephthalic acid (106.5 g, 0.6411 mol), tris (hydroxyethylene) isocyanurate (1084.5 g, 4.147 mol), and 1.5 g of butylstannoic acid. The glycol was introduced into the flask and heated to 150 ° C over 45 minutes. The monomers of the acid and catalyst were added and the reaction was heated to 210 ° C over 30 minutes. The reaction was then maintained, under nitrogen, at 210 ° C for 6 hours with stirring to produce a low melt viscosity polymer. The polymer had an inherent viscosity of 0.14 dl / g, a hydroxyl number of 228, an acid number of 11, a vitreous transition temperature, Tg, by DSC, of 82 ° C, and an average molecular weight of number 4200.

Example 2 A coating powder composition was prepared with the following materials: 618.0 g RUCOT 107, a polyester based mainly on terephthalic acid and 2,2-dimethyl-1,3-propanediol; 109.0 g Polyester of Example 1; 272.0 g HULS 1530 crosslinker; 5.0 g Benzoin 10.0 g Flow aid MODAFLOW III; and 500.0 g Ti02, R960 (DuPont) The above material was melt blended in a ZSK-30 twin-screw extruder at 110 ° C, ground in a Bantam mill, which was fed with a stream of liquid nitrogen, and it was classified through a sieve of 170 meshes on a KEK centrifugal sieve. The finely divided powder coating composition thus obtained had an average particle size of about 50 microns. This coating powder composition was electrostatically applied to one side of a 7.5 cm by 22.5 cm (3 by 9 inch) panel as described above. The coating was cured (i.e., reticulated) by heating the coated panel at 177 ° C in an oven for 20 minutes. The coating on the panel had a brightness index at 60 degrees of 94, pencil hardness of 4H, a Gardner Impact of 160 pounds-inch (29.2 kg-cm), and good stability against hard sediment formation. The result of the EVTECH Method test indicated a stability to the formation of 99% hard sediment.

Comparative Example 1 A coating powder composition was prepared from the following materials: 608.0 g Polymer RUCÓTE 107, a polyester based primarily on terephthalic acid and 2,2-dimethyl-1,3-propanediol with an hydroxyl of approximately 48; 107.0 g RUCÓTE 107, a polyester based mainly on isophthalic acid and trimethylolpropane with a hydroxyl number of about 270; 285.0 g HULS 1530 crosslinker 5, 0 g Benzoin 10.0 g Flow aid MODAFLOW III; and 500.0 g Ti02, R960 (DuPont) Using the procedure of Example 2, these panels were coated with this composition and the coatings were cured and evaluated. The coatings had a brightness at 60 degrees of 94, a pencil hardness of 4H, a Gardner impact of 160 pounds-inch (29.2 kg-cm), and poor stability to hard sediment formation. The result of the EVTECH Method test was 80%.

Claims (10)

1. CLAIMS 1. A powder coating composition in the form of an intimate mixture, in a finely divided form, comprising: A. a resin mixture comprising 1. about 10 to 40 weight percent of a polyester resin that it has a vitreous transition temperature of at least 55 ° C, a hydroxyl number of about 190 to 320, and an inherent viscosity of about 0.1 to 0.5 dl / g determined at 25 ° C in a mixture (60 / 40 in weight) of phenol / tetrachloroethane at a concentration of 0.5 g / 100 ml; the aforementioned polyester comprising: a. diacid radicals comprising at least 50 mole percent of isophthalic acid radicals; and b. diol radicals comprising about 50 to 100 mole percent of tris (hydroxyethyl) isocyanurate radicals; and 2. about 60 to 90 weight percent of a polyester resin comprising at least 70 mole percent of terephthalic acid radicals and 2,2-dimethyl-1,3-propanediol and having a Tg of 55 to 85 ° C, a hydroxyl number of 30 to 80, and an inherent viscosity of about 0.1 to 0.3 dl / g; and B. an effective crosslinking amount of a blocked polyisocyanate.
2. 2. The coating composition according to claim 1, wherein the component resin (1) has a hydroxyl number of about 200 to 300.
3. 3. The coating powder composition according to claim 1, wherein the blocked polyisocyanate is selected from the group consisting of isophorone diisocyanate blocked with e-caprolactam, toluene 2,4-diisocyanate blocked with e-caprolactam, and hexamethylene diisocyanate blocked with phenol.
4. 4. A coating powder composition in the form of an intimate mixture, in a finely divided form comprising: A. a resin mixture comprising 1. about 10 to 40 weight percent of a polyester resin having a temperature of vitreous transition of at least 55 ° C, a hydroxyl number of about 190 to 320, and an inherent viscosity of about 0.1 to 0.5 dl / g determined at 25 ° C in a mixture (60/40 by weight) of phenol / tetrachloroethane at a concentration of 0.5 g / 100 ml; the aforementioned polyester comprising: a. diacid radicals comprising at least 75 mole percent radicals of isophthalic acid; and b. diol radicals comprising about 75 to 100 mole percent of tris (hydroxyethyl) isocyanurate radicals; and 2. about 60 to 90 weight percent of a polyester resin comprising at least 70 mole percent of terephthalic acid radicals and 2, 2-dimethyl-l, 3-propanediol and having a Tg of 55 a 85 ° C, a hydroxyl number of 30 to 80, and an inherent viscosity of about 0.1 to 0.3 dl / g; and B. an effective crosslinking amount of a blocked polyisocyanate.
5. 5. The coating powder composition according to claim 4, wherein the blocked polyisocyanate is selected from the group consisting of isophorone diisocyanate blocked with e-caprolactam, toluene 2,4-diisocyanate blocked with e-caprolactam, and hexamethylene diisocyanate blocked with phenol.
6. 6. A coating powder composition in the form of an intimate mixture, in a finely divided form, comprising A. a mixture of resins comprising 1. about 15 to 25 weight percent of a polyester resin having a temperature of vitreous transition of at least 55 ° C, a hydroxyl number of about 190 to 320, and an inherent viscosity of about 0.1 to 0.5 dl / g determined at 25 ° C in a mixture (60/40 by weight) of phenol / tetrachloroethane at a concentration of 0.5 g / 100 ml; the aforementioned polyester comprising: a. diacid radicals comprising at least 90 mole percent of isophthalic acid radicals; and b. diol radicals comprising about 80 to 100 mole percent of tris (hydroxyethyl) isocyanurate radicals; and 2. about 75 to 85 weight percent of a polyester resin comprising at least 70 mole percent of terephthalic acid and 2, 2-dimethyl-1,3-propanediol radicals and having a Tg of 55 to 85 ° C, a hydroxyl number of 30 to 80, and an inherent viscosity of about 0.1 to 0.3 dl / g; and B. an effective crosslinking amount of a blocked polyisocyanate.
7. 7. The coating powder composition according to claim 9, wherein the blocked polyisocyanate is selected from the group consisting of isophorone diisocyanate blocked with e-caprolactam, toluene 2, -diisocyanate blocked with e-caprolactam, and hexamethylene diisocyanate blocked with phenol.
8. 8. A molded or shaped article coated with the cured composition of claim 1.
9. 9. A molded or shaped article coated with the cured composition of claim 4.
10. 10. An article molded or formed with the cured composition of claim 6.