MX2012010247A - Powder coating having anodized look. - Google Patents

Abstract

A powder coating composition comprises the following ingredients: (a) a binder resin, (b) a solvent soluble dye, (c) a matting effect compound, and (d) less than 10 wt. % of a pigment or dye that is not soluble in a solvent, based on the total weight of powder coating composition. When cured, the powder coating composition has an anodized look. A substrate having an anodized look is also provided, which has an ADE-index above 3.

Description

DUST COVER THAT HAS AN APPEARANCE ANODIZED Description of the invention The present invention relates to a powder coating composition which will result, when cured, in a special effect coating, i.e., a coating having an anodized appearance.

Powder coating compositions are solid compositions generally comprising a solid film-forming resin, generally with one or more pigments and, optionally, one or more performance additives such as plasticizers, stabilizers, flow aids and extenders. The resins are generally thermosetting, incorporating, for example, a binder resin and a corresponding crosslinking agent (which may itself be another binder resin). Generally, the resins have a Tg, softening point or melting point of more than 30 ° C.

Conventionally, the manufacture of a powder coating comprises fusing-mixing the components of the composition. The melt-mix involves mixing at high speed, high intensity of dry ingredients and then heating the mixture to an elevated temperature - above the softening temperature of the resin but below the curing temperature - in a mixer continuous to form a molten mixture. The mixer preferably comprises a single screw or twin screw extruder since these serve to improve the dispersion of the other ingredients in the resin while the resin melts. The molten mixture is extruded, typically laminated into the sheet form, cooled to solidify the mixture and subsequently ground (pulverized).

Such a process is then generally followed by a sequence of particle size and separation operations - such as grinding, sorting, sifting, screening, cyclone separation, screening and filtration - which precede the application of the powder to a substrate and heating of this powder to fuse and melt the particles and to cure the coating. The main methods by which powder coatings are applied include fluidized bed and electrostatic fluidized bed processes and electrostatic spray processes in which the powder coating particles are electrostatically charged by a spray gun and directed onto a substrate connected to the powder coating. the earth.

Anodization is an electrochemical process in which a protective layer of aluminum oxide is formed on the surface of an aluminum sheet. This layer can be colored by dyeing the electrochemical bath. Anodization gives aluminum a deeper and more pronounced metallic appearance that is possible with organic coatings. An anodized surface is translucent, so the lower base metal remains visible, even after treatment.

This anodized appearance is desired for various applications and various substrates, not just aluminum substrates.

An anodized appearance can be measured in an objective way by determining the reflection along and through the observed texture. For each measurement the values L, a and b can be recorded and the color differences along and through the texture can be calculated using the standard color difference equation. When the reflection is measured in the iridescence angle (110 ° of the specular reflection) for a surface with an anodized appearance it is found that a? (along - through texture) is greater than 3. For non-anodized surfaces at low or high brightness it is found that a ?? (along - through the texture) is less than 2.

For the purpose of the present invention, a surface having an anodized appearance is a surface having an ADE index greater than 3, wherein the ADE index is defined as the? (along - through the texture) measured according to the method described above.

Currently, there are no coatings available, but the solvent based coatings and powder coatings, to produce a coating with an anodized appearance without the need to use the well-known electrochemical process.

In GB 1363741 various powder coating compositions are described. These compositions Powder coating when applied to a substrate and cure will not give an anodized appearance.

Various powder coating compositions are described in US 6800334. These powder coating compositions when applied to a substrate and cure will not give an anodized appearance.

Various powder coating compositions are described in EP 1347021. These powder coating compositions when applied to a substrate and cure will not give an anodized appearance.

Various powder coating compositions are described in JP 63243176. These powder coating compositions when applied to a substrate and cure will not give an anodized appearance.

Various powder coating compositions are described in WO 2007/060070. These powder coating compositions when applied to a substrate and cure will not give an anodized appearance.

Various powder coating compositions are described in JP 2006185525. These powder coating compositions when applied to a substrate and cure will not give an anodized appearance.

It was found that substrates with an anodized appearance can be obtained when a powder coating is applied and cured which contains transparent pigments and which is substantially free of any non-transparent pigment. None of the documents mentioned above describe such a combination and neither is teaching or suggestion that this combination could lead to powder coatings that can be used to generate such anodized appearance on a substrate.

Therefore, the present invention relates to a used powder coating composition, which comprises to. a binder resin, b. a solvent soluble dye, c. a compound of opacity effect, and d. less than 10% by weight of a pigment or dye that are not soluble in a solvent,% by weight based on the total weight of the powder coating composition.

In one embodiment of the invention the solvent soluble dye is a complex metal dye.

In a further embodiment of the invention the powder coating composition comprises an agent that improves the solubility of the dye in the binder resin.

In a further embodiment of the invention the agent that enhances the solubility of the dye in the binder resin comprises isocyanate groups.

In a further embodiment of the invention the agent that enhances the solubility of the dye in the binder resin comprises caprolactam blocking groups.

Another embodiment of the invention relates to a process for the manufacture of a substrate with an anodized appearance wherein a powder coating composition comprises a. a binder resin, b. a solvent soluble dye, c. a compound of opacity effect, and d. less than 10% by weight of a pigment or dye that is not soluble in a solvent,% by weight based on the total weight of the powder coating composition is applied to the substrate, the substrate is heated, and the powder coating It is cured.

Resins and crosslinking systems in the powder composition are not desired to limit the characteristics of the present invention. Accordingly, resins suitable for inclusion within the powder coating mixture include thermoplastic and thermosetting resins.

When used in powder coatings, the thermoplastic resins must fuse and flow to form a thin film within a few minutes at oven-drying temperatures of 120 ° C to 300 ° C without significant degradation. As a result, thermoplastic resins suitable for use in the practice of the present invention include polyamides, polyesters, cellulose esters, polyethylene, polypropylene, polyvinyl chloride [PVC], poly (vinylidene fluoride) [ PVF2, for its acronym in English], polyphenylsulphones and poly (tetrafluoroethylene) [PTFE, of which the polyphenylsulfones and PTFE are particularly preferred. All suitable thermoplastic resins are readily available from commercial sources. The thermosetting resins which are suitable for this invention include epoxy resins, polyurethanes, silicones, crystalline resins, polyesters (including unsaturated polyesters), acrylics, and hybrids such as epoxy-acrylic, polyester-acrylic, and epoxy-polyester. The glass transition temperature (Tg) of these resins must be high enough so that the particles do not fuse together or sinter at temperatures at which this would likely occur during transport and storage.

Preferably, the Tg is in the range of 45 ° to 120 ° C, within which interval a Tg greater than 55 ° is more preferred. EPOXY RESINS Suitable epoxy resins are those which contain the aliphatic or aromatic principal structures with oxirane functionality and are exemplified by: the diglycidyl ether condensation polymers resulting from the reaction of the epichlorohydrin with a bisphenol for example bisphenol A and bisphenol F in the presence of an alkaline catalyst; and, glycidyl ethers of novolac phenolic resins synthesized by reacting the novolac phenolic resin with epichlorohydrin in the presence of sodium hydroxide as a catalyst.

Generally epoxy resins must have: a weight epoxide equivalent (EEW, for its acronym in English) between 600 and 2000; an equivalent hydroxyl weight between 300 and 400; and, a melt viscosity in the range of 200 to 2000 centipoise (cps) at 150 ° C, preferably 300 to 1000 cps. The low melt viscosities of such resins can allow them to be extruded at temperatures less than 200 ° C.

Commercially available epoxy resins that are preferred for the purposes of this invention are bisphenol A epoxies sold under the trademarks ARALDITE® GT-7004, GT-7071, GT-7072, GT-6259 (Huntsman LLC) EPON® 1001 and 2042 (Shell Chemicals, Inc.).

A wide variety of hardening agents for epoxy resins is available depending on the process and properties required. Dicyandiamides modified and dicyandiamide substituted, solid dicarboxylic acids and their anhydrides are examples of these agents that can be used for the curing of epoxy resins. A curing agent in solid form is preferred for convenience in the formulation of epoxy resin-based powders as well as in the formulation of other resin-based powders in this invention.

Silicone resins The silicone resins for use in this invention should be: solid at room temperature; have a Tg greater than 55 ° C, preferably greater than 60 ° C; and a viscosity of between about 500 and about 10,000 cps at 150 ° C, preferably 2000 to 5000 cps.

Silicone resins suitable for use in this invention are described inter alia in U.S. Patent Nos. 3,170,890; 4,879,344; 3,585,065; and 4,107,148 whose descriptions are incorporated herein by reference. Examples of suitable silicone resins, commercially available are phenylsilicone SY-430 and metilsilicone MK (both products of Wacker Silicone, E.E.U.U.) and methylphenylsilicone 6-2230 (Dow Corning).

Polyester Resins with Hydroxy Function The hydroxy-functional polyesters suitable for use in the process of this invention are predominantly hydroxyl in functionality and should preferably be characterized as having: i) a hydroxyl number in the range of about 25 to about 50; ii) an acid number less than or equal to 15 but preferably in the range of about 1 to 2; and, iii) a Tg greater than 50 ° C.

Hydroxy-functional polyesters that meet these requirements are commercially available as RUCOTE® 107, CARGILL® 3000/3016, and CRYLCOAT® 3109. Likewise, however, such polyesters can be formed as the condensation products of polybasic carboxylic acids and polyhydric alcohols . As such, carboxylic acids useful for the preparation of such polyester resins include one or more of phthalic acid, tetra and hexahydrophthalic acids and their anhydrides, succinic acid, adipic acid, sebaceous acid, terephthalic and isophthalic acids, 1,3- and 1-acids. , 4-cyclohexane-dicarboxylic acid, and trimellitic anhydride, esters of such acids. In addition, suitable difunctional alcohols include isomers of ethylene, diethylene, propylene, 1,2- and 1,3-propylene glycol and trimethylene glycol and suitable dihydric alcohols include hexanediol, 1,3-, 1,2-, and 1,4- butanediols, neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol, 2-methyl-1,3-propanediol, 1,4-cyclohexanediol, trimethylolpropane, and mixtures thereof. The skilled reader will be aware of a number of such acids and alcohols and processes for carrying out the condensation of acids and alcohols. The hydroxyl-functional polyesters are curable through the hydroxyl groups with aliphatic and aromatic isocyanates and with aminoplasts. Isocyanate curing forms resins that are technically polyesters but when cured they are described as polyurethanes. Aminoplasts are oligomers that are the reaction products of aldehydes, particularly formaldehyde, with amino or amino group-bearing substances exemplified by melamine, urea, dicyandiamide, and benzoguanamine. It is preferable in many cases to employ aminoplast precursors such as hexamethylolmelamine, dimethylolurea, and their etherified forms, ie, modified with alkanols having from one to four carbon atoms. Hexametoxymethylmelamine and tetrametoxiglycoluril exemplify the etherified forms. Particularly preferred are the CYMEL® amino cross-linking agents available from American Cyanamid. Thus, a wide variety of commercially available aminoplasts and their precursors can be used to be combined with the hydroxyl-functional polyesters of this invention.

The aminoplast curing agents are typically provided in an amount sufficient to be reacted with at least one half of the hydroxyl groups of the polyester, ie, an amount of at least one half of the stoichiometric equivalent of the hydroxyl functionality. Those skilled in the art will choose the correct stoichiometric ratio and catalyst level to achieve the desired coating performance. Preferably, the amount of crosslinking agent is sufficient to substantially fully react with all of the hydroxyl functionality of the polyester, and crosslinking agents having nitrogen crosslinking functionality are provided in amounts of about 2 to about 12 equivalents of nitrogen crosslinking functionality. by hydroxyl functionality equivalent of polyester.

The acid catalysts can be used to modify the cure of the polyester with an aminoplast resin by lowering the required temperature or by raising the reaction rate or both. When it is desirable to decrease the speed at ambient storage temperatures, the acid catalyst can be blocked with an amine. The volatile amines that can escape from the curing film when the catalyst is unblocked by heat are suitable for this purpose. It is particularly desirable for the purposes of this invention to retard the complete curing of the composition. NACURE® 1557, an amine-blocked dinoniinaphthalenesulfonic acid available from King Industries, is an example of the blocked acid catalyst suitable for use in aminoplast curing of the powder coating composition of this invention.

The diisocyanates cure polyester resins with hydroxy function forming urethane bonds between the polymer chains at the hydroxyl group sites. The common aliphatic diisocyanates are exemplified by hexamethylene diisocyanate (HDI), di-cyclohexylmethane diisocyanate (sold as DESMODUR W® by Miles Chemical) and isophorone diisocyanate (IPDI). Toluene diisocyanate (TDI) is an example of a suitable aromatic diisocyanate. The low temperature reactivity of free diisocyanates can be reduced by adducing them with blocking agents selected from phenol, cresols, isononylphenol, amides such as epsilon-caprolactam, oximes such as methyl ethylketoxime and butanone oxime, compounds containing the active methylene group such as diethylmalonate, and isopropylidene malonate and acetoacetates, and sodium bisulfite. Examples of the blocked diisocyanates include isophorone diisocyanate blocked by caprolactam and hexamethylene diisocyanate blocked by caprolactam. Examples of commercially available curing agents of this type are the products 24-2400, 24-2430, and 24-2450 sold under the trademark of CARGILL. Another group of blocked curing agents is uretdiones which can be described as internally blocked.

Carboxi Functional Polyester Resins Carboxy functional polyesters are also suitable for the purposes of this invention. These can be made from the same acids and polyfunctional glycols as the polyesters with hydroxyl function but with an excess of the acids. The acid number is from about 10 to about 100. Suitable commercial products are: CRYLCOAT® 430, 3010 and 7617 (available from UCB); URALAC® 3400 and 3900; EL6500 or EL6700 or EL8800 available from Chan Sieh Enterprises Fast, curing of these carboxy functional polyesters can be achieved with polyepoxide curing agents such as triglycidyl isocyanurate (TGIC).

Additional alternative curing agents to TGIC include: Primidas, such as Primida XL552 and QM1260 which are hydroxyalkylamides available from EMS-Primid; Araldite PT910 gilcidilyester available from Ciba-Geigy; and Uranox available from DSM.

Unsaturated polyesters suitable for use in the practice of the invention include ethylenically unsaturated reaction products of a di- or polyfunctional organic acid and a di- or polyfunctional alcohol. The acid is typically unsaturated. Such polyester resins typically work best in combination with a second copolymerizable resin such as diallyl phthalate. Initiators may also need to be incorporated.

Acrylic Resins Preferred acrylic resins for powder coatings are copolymers of acrylates and / or alkyl methacrylates with glycidyl methacrylates and / or acrylates and olefinic monomers such as styrene. Functional glycidyl acrylic resins are sold by Mitsui Toatsu Chemicals, Inc. as ALMATEX® for which a carboxy terminated polymer can be used as a crosslinking agent. Acrylate and hydroxyalkyl methacrylate copolymers are also suitable for this invention.

Hybrid Resin Systems Hybrid resin systems, such as epoxy-acrylic and polyester-acrylic blends, are also suitable for this invention. However, where such a system is employed, it is preferably a polyester-epoxy hybrid. As is known in the art, polyester-epoxy hybrids comprise epoxy resins and carboxyl-terminated polyester resins and may also comprise a catalyst for conducting the curing reaction. Typically, the acid polyester has an equivalent weight between 600 and 4000 and the epoxy resin has an equivalent weight between 400 and 1100. Catalysts for the reaction of the epoxy acid include quaternary ammonium salts, quaternary phosphonium salts, phosphines, amines, imidazoles and metal salts. Amphoteric catalysts such as zinc oxide (Zn02) are effective in 1-5 parts per hundred parts by weight of the resins to improve the curing ratio and the physical properties of the product.

The powder coating composition according to the present invention also comprises a solvent soluble dye. Such dyes normally show good solubility in solvents such as alcohol, ketones, and glycol ether and ester solvents.

In one embodiment of the invention the solvent soluble dye is a metal complex dye. Metal complex dyes are also known as pre-metallized dyes. The metal complex dyes can be applied to dyeing fibers, both natural and synthetic fibers such as polyamide fibers and wool. Chemically speaking, metal complex dyes can be broadly classified into two classes. Metal complexes of 1: 1, where a dye molecule manages to coordinate with a single metal atom. In metal complexes of 1: 2, a metal atom is coordinated with double dye molecules. The dye molecules are typically a monoazo structure which may contain additional groups such as hydroxyl, carboxyl or amino groups. They can form strong coordination complexes with transition metal ions, such as Nickel, Chromium, Cobalt and Copper.

In one embodiment of the invention the solvent soluble dye is a metal complex dye of 1: 2.

Examples of solvent-soluble dyes that can be used in the coating compositions according to the present invention include metal complex dyes, fluorescent dyes, polymer-soluble dyes, and polystyrene dyes. An example of dyes that can be used in the coating compositions of the present invention are Savinil® type dyes supplied by Clariant.

It was found that such dyes show a good solubility in the binder resin, in particular when a polyester binder resin is used.

When a resin or a mixture of resins is used with mediocre or poor dye solubility, it was found that the solubility can be improved by using a compound having isocyanate groups. In another embodiment it was found that the solubility can be improved by using a compound with caprolactam groups. It is also possible to use a compound having isocyanate functionality and caprolactam functionality, for example a compound having isocyanate groups blocked with e-caprolactam. Examples of Compounds that can be used to improve the solubility of the dye in the binder resin include Vestagon® B1530 (a polyisocyanate blocked by e-caprolactam for example Degussa) and Vestagon® B1540 (a blocked uretdione compound, for example Degussa).

The coating composition according to the present invention also comprises an opacity compound. In combination with a soluble dye, an opacifying compound is an essential ingredient to achieve a cured powder coating with an anodized appearance.

In the context of the present application, an opacity effect compound is a compound that is added to the composition to achieve an opacity effect. In the composition according to various types of the opacity effect of the present invention the compounds can be used, such as: - a wax, or a mixture of waxes; - a second binder resin with a gel time that is different from the gel time of the binder resin that is already present in the composition; - a gloss reducer that reacts with the binder resin; - a hardener with different reactive groups, wherein the reactive groups show a different reactivity towards the binder resin; - a high amount of a filling with coarse particles.

Suitable waxes can be selected from the group consisting of polyamide wax and polyethylene wax. The waxes may have modifications, such as micronized or modified by PTFE. In general, the waxes have a melting temperature in the range of 100 to 160 ° C.

An example of the use of a second binder resin can be found in compositions comprising two different types of polyester resins, one type of polyester resin with a relatively short gel time, the other type of polyester resin with a relatively long gel time. long.

An example of a gloss reducing agent that reacts with the binder resin is Synthacryl 700, when used in combination with a polyester binder resin. Another example of such a compound is T-325, a resin-based tarnish agent, when used in a hybrid polyester / epoxy binder system.

An example of a hardener with different reactive groups is Vestagon B68, when used in combination with an epoxy resin.

Barium sulfate and calcium carbonate with coarse particles can be used in relatively high amounts to obtain a cured powder coating with a matte appearance.

In addition to the resin systems, the dye, and the opacifying effect compounds described above, the powder coating compositions may comprise other components that are conventionally known in the art. These may include: fillers, flow control agents, degassing agents, and antiblocking agents.

The powder coating composition according to the present invention contains less than 10% by weight of a pigment or dye that is not soluble in a solvent,% by weight based on the total weight of the powder coating composition.

In one embodiment, the powder coating composition according to the present invention is substantially free of any non-transparent pigment, but may contain small amounts of transparent pigments. High amounts of pigments can destroy the anodized / translucent appearance of the coating. In the context of the present invention, substantially free means that the composition contains less than 0.5% by weight of any non-transparent pigment, more particularly less than 0.1% by weight of any non-transparent pigment. In one embodiment, the composition does not contain any of the non-transparent pigments, but may contain small amounts of transparent pigments.

Examples of non-transparent pigments include inorganic pigments such as titanium dioxide, red and yellow iron oxides, chromium pigments and carbon black. Additional suitable additives for the powder coating composition may include: adhesion promoters; light stabilizers and UV absorbers; flow and leveling additives; brightness modifying additives; cratering agents; curing agents; texturizers; surfactants; wetting agents; antioxidants (in particular phosphites, blocked phenols and propionates); biocides; and, organic plasticizers.

Fillers can be used to reduce the cost and / or reinforce or modify the performance and appearance of the coatings. The fillers comprise glass particles, glass fibers, metal fibers, metal flakes and particles of mica or calcium metasilicate may be included in the powder coating compositions of this invention. Inorganic sulfates such as barites, carbonates such as chalk, and silicates such as talc are generally used.

Metals that include zinc-rich anticorrosive particulates can be added to the powder coating compositions to impart corrosion resistance to the underlying substrate.

The flow control agents may be present in the powder coating compositions in an amount of up to 3% by weight based on the weight of the composition. Such flow control agents, which improve the melt-flow properties of the compositions and help eliminate surface defects, typically include acrylics and fluorine-based polymers. Examples of commercially available flow control agents include: Resiflow® P-67, Resiflow® P-200 and Clearflow® (all available from Estron Chemical Inc., Calvert City, KY); BYK® 361 and BYK® 300 by BYK Chemie (Wallingford, CONN); Mondaflow® 2000 from Monsanto (St. Louis, MO); and, Acranal 4F of BASF.

The degassing agents can also be used in the powder coating compositions of the present invention in an amount between 0.1 and 5% by weight, based on the weight of the composition. Such degassing agents facilitate the release of gases during the curing process. Examples of commercially available degassing agents include: Benzoin available from Well Worth Medicines; and, Uraflow® B available from GCA Chemical Corporation (Brandenton, FLA).

The powder coating compositions may also comprise an anti-blocking agent (dry flow additive) in an amount of 0.05 to 1.0% by weight, based on the total weight of the composition. Examples of such additives include fumed silica, precipitated silica, smoked alumina, clay, talc and mixtures thereof.

Typical powder coating compositions according to the present invention can have the following ingredients: 40-95% by weight of a binder resin or a mixture of binder resins; 0. 2-2% by weight of a solvent-soluble dye; 0. 2-60% by weight of an opacity compound; 0-8% by weight of a curing agent; 0-25% by weight of an agent to improve the solubility of the dye; 0. 2-5% by weight of other ingredients the above weight% which is calculated on the basis of the total weight of the powder coating composition and the sum of all the ingredients in the powder coating composition by the addition of up to 100% by weight.

Typical powder coating compositions according to the present invention based on a polyester binder resin can have the following ingredients: 40 -. 40 -. 40-60% by weight of a first polyester resin; 40-60% by weight of a second polyester resin, having a different gel time than the first polyester resin, acting as an opacifying compound; 2 - . 2 - 8% by weight of a curing agent; 0. 2 - 2% by weight of a solvent soluble dye; 0. 2 - 5% by weight of other ingredients; the above weight% which is calculated on the basis of the total weight of the powder coating composition and the sum of all the ingredients in the powder coating composition by adding up to 100% by weight.

Typical powder coating compositions according to the present invention based on a hybrid binder resin can have the following ingredients: 30 -. 30 -. 30-50% by weight of a polyester resin; 30-50% by weight of an epoxy resin; 0. 2 - 2% by weight of a solvent soluble dye; 0. 2-5% by weight of an opacity compound; 0 - 8% by weight of a curing agent; 0 -. 0-25% by weight of an agent to improve the solubility of the dye; 0. 2 - 5% by weight of other ingredients the above weight% which is calculated on the basis of the total weight of the powder coating composition and the sum of all the ingredients in the powder coating composition by the addition of up to 100% by weight.

The powder coating according to the present invention can be applied over a wide range of applied film thickeners, typically from thin films of, for example, 30 microns or less to films of 50, 100, 150 or 200 microns. A typical minimum film thickness is 5 microns.

The powder coating according to the present invention can be applied by electrostatic spray equipment. Normally, the powder is sprayed under 60-80 KV in a film thickness between 40-60 microns. Unused dust can be collected and recycled through the application system.

The powder coating composition according to the present invention can be applied on a wide range of substrates, such as metal, wood, and plastic. The best results on substrates having an anodized appearance were found when the powder coating compositions were applied to an aluminum substrate.

ADE index The ADE index is an objective way to quantitatively describe a genuine anodized surface or a surface with an anodized appearance. The ADE index can be measured using devices that are capable of measuring color at discrete angles in a plane.

For this measure, for example, a X-rite MA68II portable multiple angle spectrophotometer can be used.

The ADE index can be measured by determining the reflection along and through the observed texture. For each measurement the values L, a and b are recorded and the color differences along and through the texture are calculated using the standard color difference equation. The reflection is measured in the iridescence angle (110 ° of the specular reflection) of the surface to be measured. The ADE index is ?? (along - through the texture). For a surface that has a genuine anodized object or for an object with an anodized appearance an ADE index greater than 3 was found. For non-anodized surfaces or surfaces that do not have an anodized appearance in low or high brightness an ADE index of less of 2.

In another embodiment, the invention relates to a substrate covered with a powder coating having an anodized appearance, which means that the covered surface has an ADE index of more than 3.

The powder coatings according to the present invention show a number of advantageous properties when subjected to various mechanical or chemical tests known to an expert. The properties have been listed in the table below: All percentages given in the following examples are percentages by weight, based on the weight of the total composition, unless expressly stated otherwise.

Examples In the examples described below the following ingredients are used: Examples 1-6 The following powder coating compositions of polyester resin were prepared.

These compositions were sprayed on aluminum panels and cured for 10-15 minutes at 200 ° C. After curing all the panels showed a brightly colored anodized appearance. When measured according to the method described above, all the coated panels showed an ADE index of more than 3.

Hybrid systems of Examples 7-12 The following hybrid polyester / epoxy compositions were prepared: These compositions were sprayed onto the aluminum panels and cured for 10-15 minutes at 200 ° C. After curing all the panels showed a brightly colored anodized appearance. When measured according to the method described above, all the coated panels showed an ADE index of more than 3.

Claims (11)

1. A powder coating composition comprising to. a binder resin, b. a solvent soluble dye, c. a compound of opacity effect, and d. less than 10% by weight of a pigment or dye that are not soluble in a solvent,% by weight based on the total weight of the powder coating composition.

2. The powder coating composition of claim 1, wherein the solvent soluble dye is a metallic complex dye.

3. The powder coating composition of claim 1 or 2, comprising an agent that improves the solubility of the dye in the binder resin.

4. The powder coating composition of claim 3, wherein the agent that improves the solubility of the dye in the binder resin comprises isocyanate groups.

5. The powder coating composition of claim 3 or 4, wherein the agent that improves the solubility of the dye in the binder resin comprises blocking groups of caprolactam.

6. The powder coating composition of claim 1, characterized in that the composition is substantially free of any non-transparent pigment.

7. A powder coating composition comprising 40 -. 40-95% by weight of a binder resin or a mixture of binder resins; 0. 2 - 2% by weight of a solvent soluble dye; 0. 2 - 60% by weight of an opacity compound; 0 -. 0 - 8% by weight of a curing agent; 0 -. 0-25% by weight of an agent to improve the solubility of the dye, 0. 2 - 5% by weight of other ingredients; which is substantially free of any non-transparent pigment, the above weight% which is calculated on the basis of the total weight of the powder coating composition and the sum of all the ingredients in the powder coating composition by adding up to 100% by weight.

8. A process for the manufacture of a substrate with an anodized appearance, wherein a powder coating composition according to any of claims 1-7 is applied to the substrate, the substrate is heated, and the powder coating is cured.

9. A substrate that has an anodized appearance when coated with a powder coating composition according to any of claims 1-7.

10. The substrate of claim 9, characterized in that the substrate is an aluminum substrate.

11. A substrate coated with a powder coating, the coated surface having an ADE index of more than 3.