MXPA99009305A - Powder coating composition containing lamellar pigment and resin - Google Patents

Abstract

A pigment in the form of platelets made of a reflective metal or of pearlescent type is mixed with a sticky viscous liquid. The resulting pigment can be combined with a powdery film-forming composition which can be applied by electrostatic coating.

Description

COMPOSITION OF POWDER COATING CONTAINING LAMINAR AND RESIN PIGMENT BACKGROUND OF THE INVENTION The application of color coatings on various substrates by an electrostatic coating process is well known. For example, many automotive finishes are applied by this method. The composition applied by this process is an electrically charged powder mixture of a film-forming polymer and a pigment or pigments of the desired color. The preparation of these powder coating compositions for application by spray applicators for powder coating has presented a problem in the past with flake pigments. Pigments that are composed of platelets of a metallic material depend on their laminar structure for maximum apparent effect. Examples of these platelets include metal flakes such as aluminum flakes, bronze flakes and stainless steel flakes and natural or synthetic pearlescent pigments, exemplified, for example, by natural pearlizing mica or mica coated with metal oxide, such as mica. coated with titanium dioxide, mica coated with reduced titanium dioxide and mica P1568 / 99MX coated with iron oxide and glass flakes coated with titanium and / or fierce and aluminum flake coated with iron. In the course of the manufacture of the powder coating compositions containing said metallic or pearlescent pigments, the laminar structure is destroyed during the extrusion or milling processes that are used. As a result, the resulting finish exhibits a reduced luster effect. In order to avoid the above problems, the industry has dry-mixed the pigments and the polymer powder, that is, the carrier or vehicle powder is mechanically mixed with the pigments. Unfortunately, the pigment and the powder coating particles normally develop a different magnitude of charge, so that there is a shift in color when the powder coating composition is sprayed electrostatically onto a substrate. In addition, the pigments tend to separate from the powder in the volume of the powder spray composition that does not bind to the substrate and recover, making it difficult to reuse the recovered material. An adhesion process was developed to overcome the problems encountered as a result of the dry mixing process. In the bonding or bonding process, the powder base and the pigment are mixed together and then heated to a P 15 68/9 9IIX sufficient to soften the surface of the powder particles, so that the pigment particles can be bound to the surface of the dust particles. The process works well for corona electrostatic charging and alleviates problems with the reuse of overspray powder. Unfortunately, it also leaves two distinctly different surfaces in the final mixture, namely, the powder surface and the "outer" surface of the laminar pigment that is bonded to the powder. This one does not work or works well for triboelectric loading tática. This process also requires additional processing steps to prepare the powder coating composition and must also be specially adapted to each selected combination of pigment and powder base. U.S. Patent No. 5,378,275, discloses a water-based paint composition containing mica pigment which is the combination of a water-soluble or water-dispersible film-forming polymer and a mica-containing pigment. The mica pigment may be mica flakes or mica flakes coated with metal oxide, which have been uniformly coated with a melamine resin to form a suspension and then volatilized to the remaining organic solvent. The melamine resin must be used in an amount of at least equal weight to the P1568 / 99MX of the mica flakes or otherwise satisfactory results in terms of dispersibility, water resistance and adhesion can not be obtained. U.S. Patent Nos. 4,116,628 and 4,205,997 disclose powdered pearlescent pigment compositions which are coated by a solid polymer different from sticky or sticky polymers, in order to protect the pigment before use. The polymer content can be about 1-25% by weight and the product can be produced by various methods including forming a suspension followed by spray drying. The coating causes the pigment to lose its luster, that is, its pearlizing power, but the luster can be restored by removing the coating prior to incorporation into the coating composition. In U.S. Patent No. 5,268,197 a coating of organic and inorganic particles is disclosed, such as pigment particles and coloring particles with a plastic dispersion. The dispersion is that of a polymer based on a vinyl mopomer, a phosphorus-containing compound and certain "(meth) acrylates, itaconates, fumarates or maleates." Coated particles can be formed by a spray drying step and the resulting product P1568 / 99MX can be mixed with plastics without forming agglomerates. In US Pat. No. 3,980,607 a powder coating composition is disclosed in which synthetic resins, hardeners and pigments such as, for example, metallic alloys and mica for metallic appearance coatings are prepared by a process in the that the individual components are mixed in a finely divided state under a protective gas atmosphere and the mixture is plasticized with homogenization at a temperature at which the viscosity of the synthetic resin is higher than the drop viscosity. The hardenable synthetic resin can be a melamine resin and the resulting powder can be sprayed electrostatically. DE 43 17 019 A1 discloses a coating of pearlescent pigments, for example, based on mica coated with titanium dioxide or with iron oxide or metal oxides of the plate type with substituted or unsubstituted melamine resins, such as melamine acrylate. . EP 0 096 283 A2 discloses the process of processing pearlescent pigments, such as mica coated with metal oxide with an adhesion enhancing agent, wherein the agent comprises a polymer compatible with the organic solvent and a surfactant. EP 755 986 A2 discloses a coating of P 156 8/9 9I1X metallic flakes or inorganic flakes such as mica or glass with a polymer. US Pat. No. 3,843,571 A1 discloses the coating of pigments comprising metallic flakes or mica flake coated with titanium dioxide, the flakes are mixed with a typical hot melt in a two-roll mill and also comprises a polymer. It is the object of the present invention to provide a novel process for preparing pigments that can be incorporated into powder coating compositions suitable for electrostatic corona and tribo applications and with the pigments and powder coating compositions produced in this manner. These and other objects of the invention will be apparent to those skilled in the art from the following detailed description.

SUMMARY OF THE INVENTION This invention relates to a platelet pigment with metallic content for a powder coating composition and with powder coating compositions including said pigments. More particularly, the metal platelets are provided with a viscous surface layer of polymer or other tacky liquid material. When this treated pigment is mixed with powder coating compositions, the powder P1568 / 99MX joins the surface of the pigment reducing to. minimum in this way the color separation. The pigment is also encapsulated by the powder in order to present a single surface. The coating also results in a better charge on those pigment particles which do not bind to the powder materials, ie, they accept a charge that is closer to the charge of the surfaces of the powder coating particles than the particles of the powder. pigment not coated.

DESCRIPTION OF THE INVENTION A lamellar pigment, which is a platelet-type pigment, is provided with a viscous surface layer of material according to the present invention. Platelets can be fabricated from a reflective metal, such as aluminum flake, bronze flake, stainless steel flake or any natural or synthetic pearlescent pigment. Natural nacreous pigments include natural nacreous pigments and the synthetic pigments include mica pigments coated with metal oxide, glass flakes coated with titanium and / or iron, aluminum scales coated with iron and micas coated with reduced titanium. Commercially, the synthetic pigments that are found more frequently are the micas coated with titanium dioxide and the micas P1568 / 99MX coated with iron oxide. Any of these laminar pigments can be treated in accordance with the present invention. The lamellar pigments are provided with a viscous surface coating of sticky material, which is preferably a polymer or a monomer. Any liquid material can be used in the present invention, which provides a coating that is viscous, that is, adherent or sticky, at room temperature, stable at room temperature or storage temperature (if it is different) and that Neither does it adversely affect the appearance of the pigment to the conditions of use. This last requirement is a function of the particular pigment from which it will be coated, the characteristics of the material itself, the degree to which it is cured, the amount used, etc. "Materials that provide a dry film, such as alkyds or those that react with oxygen, will be used.The selection of the appropriate material can be made by conducting one or more routine screening experiments." Suitable materials include, but are not limited to, acrylic resins such as those sold under the Acryloid WR-97, materials characterized as reactive diluents, such as glycidyl esters of netidecanoic acid, by P1568 / 99MX example, those sold under the registered trademark Glydexx N-10, polyester resins, high boiling petroleum distillate and similar solvents such as those sold under the trademark Magiesol 52, Magiesol 500 and Exxprint 795, polyisocyanate resins, such as those sold under the registered trademark Desmodur N-75, typing phenols such as dioctyl phthalate, dibutyl phthalate, di-isodecyl phthalate and di-isononyl phthalate, dispersing agents such as those sold under the trademark Solsperse 28000 and the non-ionic silane agent sold under the name Silquest A-1230 and the like. Preferred materials for use as the surface coating in the present invention are melamine resins available in commercial form. These melamine resins are, in general, alkoxy methylol melamines such as methoxy methylol melamine, n-butoxy methylol melamine, isobutoxy methylol melamine, methoxy butoxy methylol melamine and the like, as well as their condensation products. Examples of commercially available products include those sold under the trademarks Cymel 301, 303, 325 and 327. Material, such as melamine or the like, is generally used in the form of a pulp or solution either in water or in an organic vehicle. It is preferred to use pulps or solutions P1568 / 99MX based on water, because they do not harm the environment, are generally safer for workers and are generally available commercially at a relatively low cost. However, vehicles based on organic compounds, such as aromatic compounds that include toluene and xylene, alcohols that include ethanol, isopropanol and butanol, ketones such as acetone, methyl isobutyl ketone and methyl ethyl ketone, esters including ethyl acetate and ethyl butyrate, petroleum compounds such as petroleum naphtha and mineral spirits, as well as cellosolve, carbitol and similar materials can also be used. The coated lamellar pigments were prepared simply by dispersing the solid laminar material in the solution or pulp of the viscous material to thereby form a pulp. In general, the pulp will contain approximately 0.1 to 10% material and, preferably, approximately 0.5 to 5% material. In general, the lamellar pigment will constitute about 5 to 75% by weight, preferably, about 20 to 35% by weight of the weight of the pulp containing the pigment. It is also preferred to agitate the mixture to a sufficient degree so that all surfaces of the pigment are exposed. After the agitation continues for a P1568 / 99 X suitable time, which is generally about 0.2-5 hours and, preferably, about 0.5-2 hours, recovers the coated pigments. The recovery may be by spray drying the suspension using any conventional spray drying procedure, provided that the resulting coating remains viscous and the pigment particles remain separated. Alternatively, the viscous liquid can be distributed over the surface of the pigment by means of mechanical mixing. Special care should be taken to use sufficient mixing to distribute the sticky liquid as long as it does not damage the pigment plate type structure.A tape mixer with high intensity choppers is preferred.The resulting coated pigment can then be incorporated into a composition of Conventional powder coating for electrostatic application by dry drying When the coated pigments are mixed with the powder coating composition by drum mixing, for example, the powder particles are attached to the pigment particles by means of the coating In addition, the surface coating of pigment platelets tends to perform a surface charge that is similar to the P1568 / 99MX charges powder coated particle surfaces even if bonding does not occur. In order to further illustrate the invention, several examples are set forth below. In these, as with the rest of this specification and claims, all parts and percentages are by weight and all temperatures in degrees centigrade unless otherwise indicated.

EXAMPLE 1 A mixing vessel was filled with 750 parts of deionized water. To the water was added dropwise the 100% solid melamine resin, soluble in water, Cymel 301 with stirring in a total amount of 5 parts and then mixing was continued using an air propellant for 5 minutes. To the resulting solution, 250 parts of a mica coated with commercially available titanium dioxide were added and mixing continued with the air propellant for a further 10 minutes. After this, the resulting pigment pulp was spray dried using an inlet temperature of 275 ° C and an outlet temperature of 85 ° C. The treated pigment was incorporated at a concentration of 5% in a commercial polyester powder coating composition (Corvel Clear No. 23-9030 from Morton International) by P1568 / 99 X drum mixing. After this, the mixture was sprayed onto a metal substrate panel using a corona charging gun at 75kv voltage and the resulting substrate was baked at 204 ° C (400 ° F) for 10 minutes. For comparative purposes, the above procedure was repeated using mica coated with uncoated titanium dioxide. The comparison of the two coated substrates showed that "the film formed with the coated pigment exhibited a better luster, indicating that there was more pigment in the substrate panel and a better appearance." The treated pigment was also incorporated into the coating composition. Polyester powder was mixed by drum at a concentration of 10%, then sprayed using a 75kv corona barrel on a metal panel.The treated sample sprayed uniformly and consistently produced a flawless panel.For comparative purposes, the same pigment without the viscous treatment was incorporated to 10% in the same powder coating composition in polyester in the same way and sprayed in the same way.The resulting panel had a regular appearance _ with several defects. The ratio of charge to mass of the resultant plate-type powder / pigment mixture was measured P1568 / 99 X using a Kleber barrel. In this instrument, the powder coating is transported through a Teflon tube and the load transferred from the powder to the Teflon is measured. The composition of polyester powder per se (ie, without pigment) had a "charge" of 0.60 μ coulombs / gram. A mixture of polyester and 5% of the pigment to be treated had a charge of 0.35 μg / g while "the mixture containing the treated pigment had a loading of 0.67 μg / g." The untreated pigment pigment had a charge ratio of mass of 0.82 μc / g, while the treated pigment had a proportion of 1.3 μc / g.The similarity of the charge of the non-pigmented polyester (0.60) and the mixture containing the treated pigment (0.67) is indicative of the pigment that it is encapsulated by the polymer, so that essentially it is only one type of surface that occurs in the powder coating composition.

EXAMPLE 2 Example 1 was repeated, with the exception that "the mica pearl pigment coated with iron oxide replaced the mica pigment coated with titanium dioxide.

EXAMPLE 3 A mixing vessel was filled with 600 parts of deionized water and the pH was adjusted to 8.0 P1568 / 99MX using dilute ammonium hydroxide. A thermoset acrylic polymer (Acryloid WR-97) reducible in water with stirring in a total amount of 5 parts was added dropwise and mixing was continued for ten minutes. Then, 350 parts of a commercially available titanium dioxide coated mica pearl pigment (Exterior Mearlin Sparkle, Engelhard Corp.) was added to the resulting mixture and stirred for one hour. The pigment pulp was spray dried using an inlet temperature of 275 ° C and an outlet temperature of 95 ° C. The treated pigment can be incorporated into a powder coating composition and applied using the methods described, inter alia, in Example 1.

EXAMPLE 4 Example 3 was repeated, except that the treated pigment was mica coated with titanium dioxide treated with chromium hydroxide.

EXAMPLE 5 Example 3 was repeated, except that the coated pigment was a mica pearl pigment coated with titanium dioxide with chromium-free exterior quality.

P1568 / 99MX EXAMPLE 6 An eight-liter V-shaped tumbler mixer was fitted with a cutting blade with high rotational speed and loaded with 2,000 parts of commercially available titanium dioxide-coated mica pigment (Magnapearl). 1100, Engelhard Corp.). 40 parts of a 1: 1 mixture of melamine resin: phthalate ester (Cymel 324: Jaylex DINP) were atomized onto the pigment and the combination was mixed for 30 minutes as the twisting blade rotated. The treated pigment can be incorporated into a powder coating composition and applied using the methods described, inter alia, in Example 1. EXAMPLE 7 1,000 parts of a mica coated with dioxide were introduced into a four liter high intensity batch mixer. of titanium available commercially (Exterior Mearlin Super Sparkle, Engelhard Corp.). With the mixer running at 3,500 rpm, 20 parts of a 2: 1 mixture of melamine resin (Cymel 301): butyl carbitol were atomized in the mixing chamber which was then left running for four more minutes and the pigment was recovered covered. The treated pigment can be incorporated into a powder coating composition and applied S1568 / 99MX using the procedures described, among others, in Example 1.

EXAMPLE 8 Example 1 was repeated, except that the aluminum flakes replaced the mica pigment coated with external titanium dioxide.

EXAMPLE 9 klO A mixing vessel was filled with 560 parts of mineral spirits and 240 parts (based on 100% pigments) of aluminum flake coated with iron oxide (Paliochrome L-2020, BASF). The resulting pulp was stirred for 30 minutes. minutes and then 6 parts of 100% solid melamine resin (Cymel 303) were added dropwise. The mixture was stirred for an additional thirty minutes, dried by aperspersion and the pigment-melamine product was collected. The treated pigment can be incorporated into a powder coating composition and applied using the methods described, inter alia, in Example 1.

EXAMPLE 10 In a 4 liter high-batch batch mixer, one thousand parts of mica coated with reduced titanium oxide were introduced (Paliocrom P1568 / 99MX L-6000). With the mixer running at 3,500 rpm, 20 parts of a 1: 1 mixture of melamine resin and butyl carbitol were drip added. Mixing continued for another 10 minutes. The treated pigment can be incorporated into a powder coating composition and applied using the methods described, inter alia, in Example 1.

, EXAMPLE 11 A thousand parts of mica coated with exterior grade titanium dioxide (Engelhard Corp.) were placed in a batch 4 liter high intensity blender. With the mixer operating at 15 3,000 rpm, 20 parts of a 1: 1 mixture of non-ionic silane dispersing agent were drip added.

(Silquest A-1230) and butyl carbitol. The mixing i continued for another 5 minutes. The treated pigment can be incorporated into a powder coating composition and applied using the methods described, inter alia, in Example 1. Various changes and modifications can be made to the products and processes of the present invention. invention, without departing from the scope thereof. It is intended that the various embodiments illustrated in this specification exemplify the invention although not intended to limit it.

P1568 / 99MX

Claims (17)

1. NOVELTY OF THE INVENTION Having described the present invention, | considered as a novelty and, therefore, property is claimed as contained in the following 5 CLAIMS. 1. A pigment containing a sheet metal having a sticky surface layer thereon.
2. 2. The pigment according to claim 1, wherein the sticky layer comprises a polymer.
3. 3. The pigment according to claim 1, wherein the sticky layer comprises a melamine.
4. 4. The pigment according to claim 3, wherein the pigment containing lamellar metal 15 comprises a metal flake or a metallic flake pigment coated with oxide.
5. The pigment according to claim 1 or 3, wherein the sheet metal containing pigment comprises a mica pigment coated with metallic oxide.
6. 6. The pigment of claim 5, wherein the sheet metal containing pigment comprises a mica pigment coated with titanium oxide or iron oxide.
7. 7. The pigment according to claim 1, wherein the pigment containing sheet metal comprises a metallic flake pigment.
8. 8. The pigment according to claim 1, P15S8 / 99MX wherein the sticky layer comprises a solvent and a material selected from the group consisting of a. polymer, melamine, ti ficante piles, reactive diluent and mixtures thereof.
9. 9. A powder coating composition comprising a mixture of a particulate resin carrier and a particulate pigment in which the pigment is the pigment of one of claims 1 to 5.
10. 10. A method for preparing a particulate pigment for compositions powder coating comprising combining a lamellar metal containing pigment with a liquid sticky surface layer material and recovering the resulting combination to form the tacky surface layer on the pigment.
11. The method according to claim 10, wherein the combination is by dry blending.
12. The method according to claim 10, wherein the sticky material is a polymer and the recovery is by spray drying.
13. The method according to claim 11, wherein the sticky polymer is a melamine and the recovery is by spray drying.
14. 14. The method according to claim J.3, wherein the sheet metal containing pigment comprises a metallic flake pigment.
15. 15. The method according to claim 10 or P1568 / 99 X 13, wherein the pigment containing lamellar metal comprises a mica pigment coated with metal oxide.
16. 16. The method according to claim 15, wherein the metal-containing pigment comprises a mica pigment coated with titanium oxide or iron oxide.
17. 17. The method according to claim 10, wherein the sheet metal containing pigment comprises a metal flake mica pigment. P1568 / 99MX