MX2008007905A - Powder coating composition providing low gloss - Google Patents

Abstract

The present invention provides a powder coating composition comprising A) 30 to 90 wt%of at least one glycidyl-functionalised (meth)acrylic resin, B) 30 to 90 wt%of at least one carboxyl functionalised polyurethane resin, C) 0.01 to 10 wt%of at least one wax, and D) 0.05 to 30 wt%of at least one coating additive, and optionally pigment and/or filler, the wt%based on the total weight of the powder coating composition;the powder coating composition provides coatings with a very low gloss level (highly matt finish) and smoothness, a superior durability against aggressive substances and a very good adhesion on metallic substrates.

Description

POWDER COATING COMPOSITIONS THAT PROVIDE LOW BRIGHTNESS FIELD OF THE INVENTION The present invention is directed to a powder coating composition that provides a low gloss coating with improved durability, as well as improved adhesion to metal substrates.

BACKGROUND OF THE INVENTION In certain applications it is desirable that the powder coatings have a smooth appearance surface, but have a low luster or gloss. The control of the gloss, and especially the matting of the powder coatings and maintaining these superior technology properties of the coating are currently still difficult tasks. The use of matting agents to adjust the brightness to the desired level is well known, see WO 03/102048, U.S. 200.3 / 0134978, EP-A-1129788 and EP-A-0947254. Examples of these agents are waxes, silicas, glass beads and crystalline resins. These compositions commonly lead to coatings with a loss in technological properties. For example, hydrocarbon waxes and fluorocarbons are used to reduce the amount of powder coatings. When a coating containing wax is baked, the wax migrates to REF .: 193114 the coating / air interface where it forms a layer with reduced brightness. The disadvantages of this approach are that the wax softens the coating surface and reduces its resistance to color alteration, coloration and chemical attack. Other techniques for forming a matting effect are the use of dry mixtures of chemically incompatible powders or the use of different process conditions such as different curing conditions, as described for example in EP-A-0706834, DE-A- 2247779 and WO2002244289. EP-A-551734, U.S. 4374954, U.S. 4091049 and U.S. 4091048 disclose powder coating compositions which are based on acrylate resins containing glycidyl groups and dicarboxylic acids or their anhydrides as hardeners, and which are suitable for coating aluminum substrates, by the partial use of bonding agents. Variations of this approach are widely used. A disadvantage of this approach is that coating properties such as impact resistance or chemical resistance are affected.

Brief description of the invention The present invention provides a powder coating composition comprising A) 30 to 90% by weight of at least one (meth) acrylic resin functionalized with glycidyl, B) 30 to 90% by weight of at least one polyurethane resin functionalized with carboxyl, C) 0.01 to 10% by weight of at least one wax and D) 0.05 to 30% by weight of at least one coating additive, and optionally pigment and / or filler, the weight percentage is based on the total weight of the powder coating composition. The powder coating composition of this invention can improve coatings with a very low gloss level (highly matt finish) and smoothness. Surprisingly, the powder coating composition of this invention further provides coatings that have superior durability against aggressive substances, such as inorganic acids as well as a very good resistance to yellowing. Adhesion on metal substrates, for example aluminum substrates, is greatly improved. The compositions of this invention are especially suitable for exterior coatings.

DETAILED DESCRIPTION OF THE INVENTION The features and advantages of the present invention will be more readily understood by those of ordinary skill in the art from the reading of the following detailed description. Certain features of the invention, which are, for clarity, described above and below in the context of separate embodiments, may also be provided in combination with a single embodiment. Conversely, several characteristics of the invention that are, for brevity, described in the context of a single modality, they can also be provided separately or in any subcombination. In addition, references to the singular may also include the plural (for example, "a", "an" and "an" may refer to one, or to one or more) unless the context clearly specifies otherwise. Slight variations above and below the indicated intervals specified in this application can be used to achieve substantially the same results as the values within the ranges. Also, the description of these intervals is attempted as a continuous interval including each value between the minimum and maximum values. All patents, patent applications and publications mentioned herein are incorporated by reference in their entirety. The powder coating compositions of this invention contain one or more (meth) acrylic functionalized glycidyl resins A) as the binder resin with amounts in the range of 30 to 90% by weight, preferably 40 to 70% by weight. (Met) acrylic tries respectively to mean acrylic and / or methacrylic. Glycidyl functionalized (meth) acrylic resins can be produced in a conventional manner from glycidyl (meth) acrylic monomers as described, for example, in D.A. Bates, The Science of Powder Coatings, volumes 1 and 2, Gardiner House, London, 1990, pages 62-70, and as is known to a person skilled in the art. Examples of glycidyl functionalized (meth) acrylic resins are glycidyl functionalized acrylic resins or copolymers thereof, such as, for example, WorléeCryl® CP 550 (Worlee Chemie GbmH), Almatex® PD 7610®, Almatex® PD 7690 (Siber Hegner GmbH), Synthacryl®710 (Cytec Surface Specialties). Glycidyl functionalized (meth) acrylic resins have an epoxide equivalent weight (EEW) in a range of 300 to 2000, an epoxy equivalent weight determined by means of ADSAM142, a method code of the EEW test using a self-titrator ( Brinkman Metrohm 751 GPD Titrino) and known to those skilled in the art and a glass transition temperature Tg in a range of, for example, 30 to 80BC, preferably 40 to 70 Tg determined by means of differential scanning calorimetry (DSC). In this invention, glycidyl-functionalized acrylic resins with an EEW in the range of 400 to 800 are preferred. Glycidyl-functionalized (meth) acrylic resins can be partially replaced by additional resins such as, for example, diglycidyl ethers of bisphenol, novolac epoxy and other resins containing epoxy groups, in amounts in the range of less than 10% by weight, based on the total weight of the powder coating composition. As a hardener, the powder coating composition of this invention contains one or more polyurethane resins functionalized with carboxyl B) as a curing agent (entangling agent) with amounts in the range of 30 to 90% by weight, preferably 40 to 90% by weight. 70% by weight. These are carboxyl functionalized polyurethane resins which are preferably solid at room temperature. The carboxyl-functionalized polyurethane resins can be produced by, for example, reacting hydroxyl-functionalized polyurethanes with acid anhydrides. In addition, carboxyl-functionalized polyurethane resins can be produced by reacting diisocyanates or polyisocyanates or pre-polymers functionalized with isocyanate with hydroxyl carboxyl acids. The hydroxyl-functionalized polyurethanes can be prepared in a conventional manner as is known to the person skilled in the art. In particular, they can be produced by reacting polyisocyanates with excess polyols. The polyols suitable for the production of the polyurethanes are not only polyols in the form of low molar mass compounds defined by empirical and structural formulas, but also oligomeric or polymeric polyols with molar masses averaging, for example, up to 800, for example , corresponding to hydroxy-functional polyethers, polyesters or polycarbonates; however, polyols of low molar mass defined by an empirical and structural formula are preferred. Examples of useful polyols are the following diols: ethylene glycol, isomeric propane- and butane-diols, 1,5-pentanediol, 1,6-hexanediol, 1,10-decanediol, 1, 12-dodecanediol, neopentyl glycol, butylethyl propanediol, cyclohexanediols. isomeric, isomeric cyclohexanedimethanol, hydrogenated bisphenol A, tricyclodecanedimethanol and dimeric fatty alcohol as representatives of cycloaliphatic diols defined by empirical and structural formulas with a low molar mass in the range of 62 to 600 as well as polymeric (meth) acrylic telechelic diols, polyester diols, polyether diols, polycarbonate diols, each with a molar mass average in number, for example, up to 800 as representatives of oligomeric or polymeric diols. Additional examples of polyols are polyester polyols, polycarbonate polyols, polyether polyols, polylactone polyols and / or poly (meth) acrylate polyols. Examples of acid anhydrides are anhydrides of maleic acid, succinic acid, tetrahydrophthalic acid, hexahydrophthalic acid, methylhexahydrophthalic acid, trimellitic acid, pyromellitic acid and citric acid. Examples of diisocyanates are hexamethylene diisocyanate (HDI), tetramethylxylylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, cyclohexane diisocyanate, toluylene diisocyanate and diphenylmethane diisocyanate. Examples of polyisocyanates are those containing heteroatoms in the residue linking the isocyanate groups. Examples of these are polyisocyanates comprising carbodiimide groups, allophanate groups, isocyanurate groups, urethane groups, adiated urea groups or biuret groups. The polyisocyanates have an isocyanate functionality higher than 2, such as, for example, polyisocyanates of the uretidione or isocyanurate type produced by the di- and / or trimerization of the diisocyanates indicated in the previous paragraph. Further examples are polyisocyanates containing diuret groups produced by the reaction of the diisocyanates indicated in the preceding paragraph with water. Further examples are also polyisocyanates containing urethane groups produced by reaction with polyols. Polyisocyanate crosslinking agents known for isocyanate curing coating systems and based on hexamethylene diisocyanate, isophorone diisocyanate and / or dicyclohexylmethane diisocyanate are very highly suitable as polyisocyanates. Examples are the per se known derivatives of these diisocyanates comprising biuret, urethane, uretidione and / or isocyanurate groups. Examples thereof may be found among the products known by the name Desmodur® sold by Bayer Material Science. Examples of hydroxy carboxylic acids are hydroxysuccinic acid, 2-hydroxystearic acid or adducts of monoepoxides and dicarboxylic acids. All the number average molar mass data indicated in the present description are the number-average molar masses determined or determined by gel permeation chromatography (GPC; polystyrene entangled by divinylbenzene as the phase). immobile, tetrahydrofuran as the liquid phase, polystyrene standards). The carboxyl-functional polyurethane resin of component B) can be produced in the presence of organic solvents which, however, makes it necessary to isolate the polyurethane resin obtained in this way or remove the solvent therefrom. Preferably, the production of the polyurethane resin B is, however, carried out without solvent and without subsequent purification operations. Once the reaction carried out in the absence of solvent is complete and the reaction mixture has cooled, the carboxyl-functional polyurethane resin is obtained. The polyurethane assumes the form of a mixture exhibiting a molar mass distribution. The polyurethane requires treatment and can be used directly as component B). The carboxyl-functional polyurethane resins of component B) have an acid value in the range of 50 to 300, preferably 80 to 200. The acid value is defined as the number of mg of potassium hydroxide (KOH) required to neutralize the carboxyl groups of 1 g of the resin. The person skilled in the art selects the nature and proportion of the polyisocyanates and polyols for the production of polyurethane resins B) in such a way which polyurethane resins B) are obtained which are solid at room temperature. The hardener may be partially replaced by additional hardeners useful for the curing of epoxy resins, such as, for example, hardeners containing carboxyl groups, for example, polycarboxylic acids and / or the anhydrides thereof, hardeners containing amide or amine groups , for example, dicyandiamide and the derivatives thereof, in amounts in the range of less than 10% by weight, based on the total weight of the powder coating composition. The powder coating composition of this invention contains 0.01 to 10% by weight of at least one wax C) selected from the group consisting of polyamide wax, polyethylene wax and zinc stearate. These are waxes, such as, for example, Ceraflour 993 and Ceraflour 990 of BYK®, Micromide 528 and MPP-230F of Micro Powders®, Lanco TPW-279, Lanco 1394 F and Lanco PE 1544 of Lubrizol®. The waxes may have modifications, such as, be micronized or modified by PTFE, and have a melting temperature in the range of, for example, 105 to 150 ° C. The powder coating composition according to the invention may contain as additional components the conventional constituents in powder coating technology, such as additives, pigments and / or filled as those known to a person skilled in the art. The additives are, for example, degassing aids, flow control agents, planing agents, texturizing agents, fillers (extenders), photo-initiators, catalysts and dyes. Examples are flow control agents incorporated in the composition according to the invention by means of an inorganic carrier or by master mixing techniques known to a person skilled in the art. Compounds having antimicrobial activity can also be added to the powder coating compositions. The entanglement reaction can be further accelerated by the presence in the powder coating composition according to the invention of known thermally entangled catalysts. These catalysts are, for example, tin salts, phosphides, amines and amides. They can be used, for example, in amounts of 0 to 5% by weight, based on the total weight of the powder coating composition. The powder coating composition of this invention may contain transparent pigments and / or fillings (extenders), imparting color and / or imparting special effects. The suitable color imparting pigments are any coating pigment conventional of an organic or inorganic nature. Examples of inorganic or organic color imparting pigments are titanium dioxide, micronized titanium dioxide, carbon black, azo pigments and phthalocyanine pigments. Examples of pigments imparting special effects are metallic pigments, for example, made of aluminum, copper or other metals, interference pigments, such as metal pigments coated with metal oxides and coated mica. Examples of suitable excipients are silicon dioxide, aluminum silicate, barium sulfate and calcium carbonate. The constituents are used in conventional amounts known to the person skilled in the art, for example, 0.05 to 30% by weight, based on the total weight of each powder coating base, preferably 0.1 to 20% by weight. The powder coating composition according to this invention can be prepared by conventional manufacturing techniques used in the powder coating industry, such as extrusion and / or milling processes, known to a person skilled in the art. For example, the ingredients can be mixed together by dry mixing methods and can be heated to a temperature to melt the mixture, and the mixture is mixed.

Extrude The extruded material is then cooled on cooling rolls, broken and milled to create a fine powder, which can be classified up to the desired grain size, for example, up to an average particle size of 20 to 200 μm. The composition according to the invention can also be prepared by spraying from supercritical solutions, "non-aqueous dispersion" NAD processes or ultrasonic rest wave atomization processes. Moreover, the specific components of the powder coating composition according to the invention, for example, additives, pigments, fillers, can be processed with the finished powder coating particles after extrusion and grinding by a "binder" process. "using an impact fusion. For this purpose, the specific components can be mixed with the powder coating particles. During mixing, the individual powder coating particles are treated to soften their surface in such a way that the components adhere to them and bond homogeneously with the surface of the powder coating particles. The softening of the surface of the powder particles can be carried out by heat treatment of the particles up to a temperature, for example, the glass transition temperature Tg of the composition, in a range of, for example, 50 to 602C. After cooling the mixture of the desired particle size of the resulting particles can proceed by a sieving process. The powder coating composition of this invention can provide powder coatings with a very low gloss. The gloss of the finishes according to this invention is measured at an angle of 602C according to DIN 67 530 and can be adjusted in the range of 1 to 95 gloss units. Typically, a gloss unit (matte finish) has a brightness in the range of 1 to 30 gloss units. The powder coating composition of this invention can provide coatings having a gloss value of 10 gloss units and lower. The powder coating composition of this invention can be applied, for example, by electrostatic spraying, thermal or flame spraying, or fluidized bed coating methods, also coil coating techniques, all of which are well known to those skilled in the art. technique. The coating composition can be applied to, for example, metal substrates, non-metallic substrates, such as paper, wood, plastic, glass and ceramic, as a coating system or as a coating layer in a layer film construction. multiple In certain applications, the substrate to be coated may be preheated before the coating application, and then either heated after the application of the powder or not. For example, gas is commonly used for several heating steps, but other methods, for example, microwave, IR or NIR are also known. The powder coating compositions according to the invention can be applied directly on the substrate surface or on a layer of a primer which can be a liquid or powder based primer. The powder coating compositions according to the invention can also be applied as a coating layer of a multi-layer coating system based on liquid or powder coatings, for example, based on a transparent powder coating layer. or liquid applied on a base coat layer for imparting color and / or imparting special effects or a top layer of pigmented powder or liquid coating of a layer applied on a previous coating. The applied and melted powder coating layer can then be cured by thermal energy. The coating layer can, for example, be exposed by convective, gas and / or radiant heating, for example, infrared (IR) and / or near infrared (NIR) irradiation as known in the art, up to temperatures of, for example, 100SC to 3002C, preferably 150SC to 250fiC (target temperature in each case). The powder coating composition can also be cured by high energy irradiation known to a skilled person. Ultraviolet (UV) radiation or electron beam radiation can also be used as high energy radiation. UV radiation is preferred. The irradiation can proceed continuously or discontinuously. Double curing can also be used. "Double curing" means a method of curing the powder coating composition according to the invention wherein the applied composition can be cured, for example, both by UV irradiation and by thermal curing methods known to a skilled person. The present invention is further defined in the following examples. It should be understood that these examples are given by way of illustration only. From the above description and from these examples, one skilled in the art can evaluate the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make several changes and modifications of the invention to adapt it to various uses. and conditions. As As a result, the present invention is not limited by the illustrative examples shown herein, but rather is defined by the claims contained below. The following examples illustrate the invention.

EXAMPLES Example 1 Preparation of carboxyl-functionalized polyurethane resin B) Two hundred and sixty-eight parts by weight (ppw) of tri-cyclodecanoclimethanol and 279 ppw of methyl ethyl ketone are filled into a reactor with internal thermometer and stirrer, and heated to 75 aC. 205 ppw of isocyanurate HDI (Tolonate® HDI / 100, Rhone-Poulenc) are added in portions within 60 minutes maintaining the temperature at 75 SC within this time period. Then the reaction mixture is heated and maintained at 85-90SC until the NCO number is reached. Subsequently the batch is cooled to 75 SC and 248 ppw of hexahydrofonic acid anhydride are added in portions within 60 minutes maintaining the temperature at 752C within this time period. The reaction mixture is then heated and maintained at 84-90 ° C until the carboxyl number of 130 mg KOH / g solid resin is reached. Subsequently the solvent is removed by distillation at temperatures of 130-140aC. A colorless resin is obtained which has an acid value of 126 mg KOH / g solid resin, a Tg (determined by DSC) of 49-542C and a viscosity of (125SC) of 18 Pas.

Example 2 Preparation of powder coating compositions and application Powder coating compositions according to the invention (formulation 1 and formulation 2) are prepared according to the following ingredients: The ingredients of each formulation are mixed and extruded in a PR 46 extruder (signature: Buss AG) at 1202C. Each mixed and melted formulation is cooled and the resulting material is milled to a D50 value of 40 μm particle size distribution. The final powder composition of each formulation is applied to a metal foil by electrostatic spraying to a film thickness of 80 μm. Finally, the coating is cured in a convection oven at 145 ° C for 30 minutes.

Example 3 Testing the coatings Table 1 The results show a high adhesion to metal substrates surfaces and a very low desired gloss value of the coating. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (10)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. A powder coating composition characterized in that it comprises A) 30 to 90% by weight of at least one (meth) acrylic resin functionalized with glycidyl, B) 30 to 90% by weight of at least one polyurethane resin functionalized with carboxyl, C) 0.01 to 10% by weight of at least one wax and D) 0.05 to 30% by weight of at least one coating additive, and optionally pigment and / or filler, the percentage by weight is based on the total weight of the powder coating composition.

2. The composition according to claim 1, characterized in that it comprises A) 40 to 70% by weight of at least one (meth) acrylic resin functionalized with glycidyl, B) 40 to 70% by weight of at least one resin of polyurethane functionalized with carboxyl, C) 0.01 to 10% by weight of at least one wax and D) 0.05 to 30% by weight of at least one coating additive, and optionally pigment and / or filler, the weight percentage is based on the total weight of the powder coating composition.

The composition according to claims 1 and 2, characterized in that the glycidyl functionalized (meth) acrylic resin (A) has an epoxide equivalent weight (EEW) in a range of 300 to 2000, an epoxy equivalent weight determined by means of of ADSAM142 and a glass transition temperature Tg in a range of 30 to 802C, Tg determined by means of differential scanning calorimetry (DSC).

The composition according to claims 1 and 2, characterized in that the carboxyl-functional polyurethane resin B) has an acid value in the range of 50 to 300.

5. The composition according to claims 1, 2 and 4, characterized in that the carboxy functionalized polyurethane resin B) is a reaction product of hydroxyl-functionalized polyurethanes with acid anhydrides.

6. The composition according to claims 1, 2 and 4, characterized in that the carboxy functionalized polyurethane resin B) is a reaction product of isocyanate diisocyanates, polyisocyanates and / or prepolymers functionalized with hydroxyl carboxylic acids.

7. The composition according to claim 5, characterized in that the hydroxyl functionalized polyurethanes are prepared by reacting polyols with polyisocyanates, wherein the polyisocyanates contain functional groups selected from the group consisting of carbodiimide groups, allophanate groups, isocyanurate groups, urethane groups, urea adiada groups and biuret groups, and wherein the polyisocyanates have an isocyanate functionality higher than 2.

The composition according to claims 1 and 2, characterized in that the wax C) is selected from the group consisting of polyamide wax , polyethylene wax and zinc stearate having a melting temperature in the range of 105 to 150 ° C.

The composition according to claims 1 to 8, characterized in that it is for coating metallic substrates and non-metallic substrates as a coating system or as a coating layer in a multilayer film structure.

10. A substrate characterized in that it is coated with the coating composition according to claims 1 to 9 and cured.