Metal effect pigment preparation for powder coatings

Abstract

The invention relates to a metal effect pigment preparation in a granulate form in powder coatings, wherein the metal effect pigment preparation has metal effect pigments which have optionally one or more metal oxide and / or metal hydroxide and / or metal oxide hydrate layers on a metal core, a binder selected from a cellulose, a cellulose derivative, a starch, a starch derivative, or mixtures thereof, and a surface-active additive. The invention additionally relates to a method for producing the powder coatings.

Description

[0001] Metallic effect pigment preparation for powder coatings

[0002] The invention relates to the use of a metallic effect pigment preparation in granulate form in powder coatings and to a process for producing powder coatings.

[0003] Metallic effect pigments, such as aluminum effect pigments, are frequently used in coatings, paints, printing inks, cosmetics, or plastics to add color and create a metallic effect. The main function of metallic effect pigments is the directed reflection of light by parallel-aligned pigment platelets.

[0004] In recent years, powder coatings have become increasingly popular due to their inherently low volatile organic compound ("VOC") content, which significantly reduces emissions of volatile organic compounds into the atmosphere during application and curing. These environmentally friendly and versatile powder coatings can be used in numerous applications – generally for metal coating, household appliances, facade coating, furniture coating, or automotive coating. Powder coatings used as primers or single-layer topcoats are almost entirely recyclable. Powder coatings typically contain binders, pigments, fillers, and crosslinking agents, as well as optional additives. They are in finely divided form and are usually applied electrostatically to various substrates and cured by baking or radiant energy.

[0005] Powder coatings can be produced in a mixing process with subsequent extrusion and intensive grinding by comminuting the extrudate. However, this method is not suitable for effect pigments, as the shear forces in the extruder and during intensive mixing can damage or destroy the effect-generating platelet-shaped structure, which can negatively impact the gloss and appearance of the pigments. Effect pigments such as metallic effect pigments are therefore often subsequently added to the base powder coating (so-called dry-blend process). A disadvantage of this process, however, is that the different charging behavior and different specific weights of the individual coating components can lead to a separation of pigment and powder coating binder during coating application, which impairs the optical quality of the applied powder coating.In addition, the recyclability of such powder coatings with metallic pigments is no longer given for powder coatings produced using this process.

[0006] Another method for powder coating production is the so-called bonding process, in which the pigment is fixed to the particles of the base coat (powder coating binder) by heating. Heating a mixture of powder coating and metallic pigment to the glass transition temperature of the powder coating binder creates a physical bond between the metallic pigment particles and the powder coating particles.

[0007] In the bonding process (as well as in the dry blend process), the metallic effect pigments are often used as fine-particle powder, which leads to high dust levels.

[0008] JP 2003213157 A discloses a metallic pigment for a powder coating composition with a high metallic luster. This aluminum pigment, which can be used in single-layer or multi-layer powder coatings, is coated with at least one resin component containing a fluorinated alkyl group. The coated aluminum effect pigments disclosed therein are used in the powder coating by dry blending or bonding and are in non-dust-free powder form.

[0009] EP 2 896661 A1 relates to a powder coating in particulate and cured form with effect pigments, as well as to a process for producing powder coating with effect pigments that are at least 50% wetted by a viscous coating mass. An extruder is used to produce a film-forming, homogeneous thermoplastic coating mass from the starting materials, in particular comprising binders, additives, colorants, and / or fillers. This coating mass is ground after leaving the extruder, with the effect pigments being added in an end region of the extruder and dispersed in the viscous coating mass. The composition of the finished powder coating is identical to the composition used to coat the effect pigments.EP 3 144 352 describes a powder coating comprising at least one base powder coating and at least one effect powder coating with effect pigments, wherein the effect pigments are dispersed in a melt of transparent effect powder coating. In both cases, the formulation freedom is limited.

[0010] EP 3 500 630 describes a particulate pigment composition for powder coatings, in which the pigment is coated with a thermosetting resin with an acid number of 10 to 50 mg KOH / g resin. To produce the pigment composition, the resin is typically dissolved in a solvent, particularly an organic solvent, and then mixed with the pigment to be coated in paste form in an organic solvent. Consequently, organic solvents, particularly aromatic solvents in the examples, must be used in the production process. Furthermore, the storage stability of the pigment composition with a reactive thermosetting resin is subject to certain limitations.

[0011] The present invention is based on the object of providing a metallic effect pigment preparation for use in powder coatings, wherein the metallic effect pigment preparation is in granular form and can thus be dosed dust-free. This improves handling and occupational safety. Furthermore, in a preferred embodiment, the metallic effect pigment preparation should be producible in an aqueous system—without the use of organic solvents.

[0012] This object is achieved by the use of a metallic effect pigment preparation in a powder coating according to claim 1, and a process for producing a powder coating according to claim 10. Further features, embodiments and advantages emerge from the subclaims and the description. One aspect of the invention relates to the use of a metallic effect pigment preparation in powder coatings, characterized in that the metallic effect pigment preparation is in granulate form and comprises the following components: a) 60 - 98 wt. %, based on the total weight of the metallic effect pigment preparation, of at least one metallic effect pigment with a metallic core, which optionally has one or more metal oxide and / or metal hydroxide and / or metal oxide hydrate layers, b) 1 - 30 wt.-%, based on the total weight of the metallic effect pigment preparation, of at least one binder selected from cellulose, cellulose derivative, starch, starch derivative or mixtures thereof, c) 1 - 30 wt.%, based on the total weight of the metallic effect pigment preparation, of a surface-active additive, and d) less than 3 wt.%, based on the total weight of the metallic effect pigment preparation, of residual moisture, wherein the residual moisture comprises water and organic solvents.

[0013] Components a) to d) amount to 100 wt.%.

[0014] A further aspect of the invention relates to a process for producing a powder coating, which comprises the following steps: a) producing a metallic effect pigment preparation by mixing a metallic effect pigment with a metallic core, which optionally has one or more metal oxide and / or metal hydroxide and / or metal oxide hydrate layers, with at least one binder selected from cellulose, cellulose derivative, starch, starch derivative or mixtures thereof, and a surface-active additive, compacting the resulting mixture in granular form, optionally drying the compacted mixture, wherein the metallic effect pigment preparation is in granular form and comprises the following components:

[0015] A) 60 - 98 wt.%, based on the total weight of the metallic effect pigment preparation, of at least one metallic effect pigment with a metallic core, which optionally has one or more metal oxide and / or metal hydroxide and / or metal oxide hydrate layers,

[0016] B) 1 - 30 wt.%, based on the total weight of the metallic effect pigment preparation, of at least one binder selected from cellulose, cellulose derivative, starch, starch derivative or mixtures thereof,

[0017] C) 1 - 30 wt.%, based on the total weight of the metallic effect pigment preparation, of a surface-active additive, and

[0018] D) less than 3 wt.%, based on the total weight of the metallic effect pigment preparation, residual moisture, wherein the residual moisture comprises water and organic solvents, b) mixing the metallic effect pigment preparation obtained in step a) in granulate form together with a powder coating binder and optionally further components of a powder coating, and c) bonding the mixture obtained in step b).

[0019] A further aspect of the invention relates to the powder coating thus obtained.

[0020] Surprisingly, the metallic effect pigment preparation used according to the invention can be homogeneously incorporated in granular form into a powder coating without causing pigment aggregation or inhomogeneities in the powder coating, which would negatively affect the optical properties of the metallic pigments. Due to the binder based on cellulose, starch, or derivatives thereof, and the water-soluble additive, the metallic effect pigment preparation according to the invention exhibits no significant dust formation despite low residual moisture. This improves handling and occupational safety. The resulting powder coating produces a coating with excellent optical properties such as gloss. Surprisingly, after bonding, the effect pigments are very uniformly aligned on the surface. The metallic effect pigment preparation used according to the invention is versatile in many powder coating systems.A further advantage of a preferred embodiment with a water-soluble binder is that the metallic effect pigment preparation is produced with the water-soluble cellulose derivative binder in an aqueous system without the need to use organic solvents.

[0021] The terms "metallic effect pigment" and "metallic pigment" are used synonymously within the scope of the present invention. A metallic effect pigment is understood to be a pigment having a metallic core, which is preferably platelet-shaped and optionally has one or more metal oxide and / or metal hydroxide and / or metal oxide hydrate layers. The average diameter of the metallic core is typically 1-250 pm, preferably 2-150 pm, in particular 5-100 pm. The thickness of the platelets is usually in the range of about 4 nm - 2 pm, preferably 15 - 200 nm, in particular 30 to 140 nm or 60 to 120 nm. The ratio of diameter to thickness is generally 1500:1 - 20:1, preferably 1000:1 - 100:1, in particular 500:1 - 200:1. This ratio of diameter to thickness is referred to as the form factor. The metallic effect pigments can be obtained by grinding (so-called cornflake or silver dollar, orvery thin metallic effect pigments produced by grinding) or by VMP / PVD processes.

[0022] A metallic effect pigment preparation is understood to be a metallic effect pigment composition.

[0023] A water-soluble binder is defined here as one that dissolves at least 10 g of the binder in 1 L of demineralized water at 20 °C and 1 bar pressure. A non-water-soluble binder is defined here as one that dissolves less than 10 g of the binder in 1 L of demineralized water at 20 °C and 1 bar pressure.

[0024] A surface-active additive is a substance that has the ability to reduce the surface tension of water. A non-ionic surface-active additive is a substance that has no ionic functional groups, while an ionic additive has one or more ionic functional groups. A surface-active additive can also be referred to as a surfactant. A cellulose derivative is a chemical derivative of cellulose. Possible modifications include methylation (to methylcellulose), ethylation, hydroxypropylation, etc. Cellulose derivatives can have various degrees of polymerization and substitution patterns. A starch derivative is a chemical derivative of starch. Modifications can be carried out using physical, enzymatic, or chemical processes (e.g., esterification).

[0025] Bonding is a process in which the metallic effect pigment is fixed to the particles of the basecoat (powder coating binder) by heating. Heating a mixture of powder coating and metallic pigment to the glass transition temperature of the powder coating binder creates a physical bond between the metallic pigment particles and the powder coating particles. In the bonding process, the powder coating is heated to its glass transition point or higher by applying energy, e.g., through external heat sources or high shear forces.

[0026] A metallic effect pigment preparation in granular form is understood to be a metallic effect pigment preparation that is in the form of a free-flowing, coarse-grained material. The granules are preferably cylindrical (with diameters of approximately 0.5 mm to approximately 5 mm and lengths of approximately 1 mm to approximately 8 cm) or spherical (with diameters of approximately 0.05 to approximately 5 mm).

[0027] The metallic effect pigment preparation used according to the invention comprises 60-98% by weight of at least one metallic effect pigment, based on the total weight of the metallic effect pigment preparation. In a preferred embodiment, the metallic effect pigment preparation according to the invention contains 70-95% by weight, more preferably 75-93% by weight, in particular 80 to 91% by weight of at least one metallic effect pigment, based on the total weight of the metallic effect pigment preparation. The metallic effect pigment preparation used according to the invention further comprises 1-30% by weight, based on the total weight of the metallic effect pigment preparation, of at least one water-soluble binder which is a cellulose derivative, preferably 3-25% by weight, more preferably 4-15% by weight, in particular 5-10% by weight of at least one cellulose derivative.

[0028] As a further component, the metallic effect pigment preparation of the present invention comprises 1-30 wt.% of a surface-active additive, based on the total weight of the metallic effect pigment preparation, preferably 1.5-20 wt.%, in particular 2-15 wt.%, in particular 2.5-10 wt.%.

[0029] A further advantage of the metallic effect pigment preparation used according to the invention is its low residual moisture content and its presence in granular form. According to the invention, the metallic effect pigment preparation contains less than 3% by weight, based on the total weight of the metallic effect pigment preparation, of residual moisture, wherein the residual moisture comprises water and organic solvents. The metallic effect pigment preparation according to the invention preferably contains less than 2.5% by weight of residual moisture, in particular less than 2% by weight of residual moisture.

[0030] The granular form of the pigment preparation can be obtained using various processes and can have different size ranges. The granules are preferably in cylindrical form (with diameters of about 0.5 mm to about 5 mm and lengths of about 0.1 cm to about 8 cm). The granules in cylindrical form of the metallic effect pigment preparation usable according to the invention preferably have a diameter of 1 to 3 mm and a length of 0.5 to 7 cm, more preferably a diameter of 1.5 to 2.5 mm and a length of 1 to 5 cm. Such granules can be produced by conventional processes such as extrusion, punch pressing (press with a punch and punch plate), or extrusion, in particular also low-pressure extrusion through a basket extruder, optionally with subsequent drying (at about 20°C to 150°C) and comminution with, for example, a rotating knife.Granules in spherical form (with diameters of about 0.05 to about 5 mm, in particular 1 to 3 mm) can be obtained by spray and fluidized bed granulation or with a granulating plate, optionally with subsequent sieving.

[0031] The pigment preparations in granular form that can be used according to the invention are characterized by good abrasion resistance, good metering properties, and freedom from dust. They can be easily incorporated into powder coatings using the bonding process and are highly compatible there, resulting in powder coatings with high gloss. Furthermore, it was shown (in SEM images) that the effect pigments in the bonded coating align very evenly on its surface, significantly more orderly than in a pigment preparation in powder form without the binders according to the invention. Surprisingly, powder coatings made from the metallic effect pigment preparation used according to the invention with binders based on cellulose, starch, or their cellulose / starch derivatives in granular form exhibited a significantly higher gloss than powder coatings with the corresponding metallic effect mixture without these binders and in powder form.

[0032] Commercially available powder coatings can be used, particularly those based on polyurethane, epoxy, polyester / epoxy, polyester / polyamide, polyester, or acrylate systems. Carbonyl-functional polyesters (PES) are particularly preferred. The powder coatings can be transparent (e.g., AL96 from DuPont) or opaque, particularly black with a high gloss. Powder coatings contain binders and usually fillers and crosslinking agents, as well as optional additives and pigments.

[0033] The metallic effect pigment of the invention is preferably an aluminum or iron effect pigment, more preferably an aluminum effect pigment.

[0034] The metallic effect pigment can consist of the metallic core alone. In another embodiment, the metallic effect pigment has one or more metal oxide and / or metal hydroxide and / or metal oxide hydrate layers on the metallic core. Furthermore, it is preferred that in the metallic effect pigment preparation used according to the invention, the metal oxide and / or metal hydroxide and / or metal oxide hydrate layer is selected from the group consisting of oxides, hydroxides or oxide hydrates of the elements silicon, vanadium, molybdenum, chromium, titanium, iron, aluminum, tin and mixtures thereof. In a preferred embodiment, the one or more layer(s) is / are a metal oxide layer, in particular a metal oxide layer or two or three metal oxide layers made of different metal oxides. In a preferred embodiment, the layer is an SiO2 layer.In another preferred embodiment, the metal core has an SiO2 layer and an iron oxide layer thereon. The layer thickness of the metal oxide, metal hydroxide, and / or metal oxide hydrate layer according to the invention is 3-270 nm (total layer(s) thickness). In one embodiment, the layer thickness is 7-100 nm, particularly preferably 10 to 50 nm. In another embodiment, the layer thickness is preferably 150-270 nm, particularly preferably 260 nm. The optional metal oxide and / or metal hydroxide and / or metal oxide hydrate layer can be modified with surface modifiers such as optionally functionalized silanes, for example alkyl-, alkoxy-, primary amino-, secondary amino-, epoxy-, isocyano-, mercapto-, azido-, (meth)acryl-, vinyl-, or hydroxyl-functionalized silanes.Furthermore, the metal oxide and / or metal hydroxide and / or metal oxide hydrate layer can be coated with a polymer layer for stabilization, for example based on polyacrylates or polymethacrylates, polyurethanes, polyesters, epoxides or polyolefins, optionally modified with silanes.

[0035] The binder is selected from cellulose, cellulose derivatives, starch, starch derivatives, or mixtures thereof, and can be water-soluble or insoluble. Starch (usually a mixture of amylose and amylopectin) can be used in the form of potato starch, corn starch, and wheat starch. This is a water-soluble binder. Starch derivatives can be produced by physical, enzymatic, or chemical processes (e.g., esterification) and, depending on the modification, can be water-soluble or insoluble. Cellulose is a water-soluble binder that can be used according to the invention. A cellulose derivative can be used as a water-soluble binder. Hydroxypropyl methyl cellulose (e.g. Methocel (DuPont), VIVAPHARM HPMC (JRS)), hydroxypropyl cellulose (e.g. Klucel H (Ashland), Klucel E (Ashland)), hydroxyethyl cellulose (e.g. Tylose HEC (SE Tylose GmbH)), methyl hydroxy ethyl cellulose (e.gTylose MHEC (SE Tylose GmbH)).

[0036] The surface-active additive is preferably a nonionic surface-active additive. Preferred nonionic additives include polyglycol, polyvinyl butyral (PVB) and / or polyvinylpyrrolidone (PVP) or polysiloxanes (e.g., Getren (Evonik)); particular preference is given to a polyglycol. The polyglycol is preferably a polyethylene glycol or polypropylene glycol, in particular a polyethylene glycol with an average molar mass of 200-600 g / mol, preferably 300-500 g / mol, more preferably 380-420 g / mol. A particularly preferred polyethylene glycol ether is PEG 400 (PCC Chemax Inc.). In this embodiment, the metallic effect pigment preparation used according to the invention contains less than 500 ppm, preferably less than 20 ppm, of phosphorus, based on the total weight of the metallic effect pigment preparation.In the prior art, metallic effect pigment preparations often contain larger amounts of phosphorus through the use of organic phosphates, phosphonates, or phosphites, which need not be used in this embodiment of the present invention. This has the advantage that environmentally hazardous phosphorus compounds, such as, in particular, organic phosphates and phosphonates, can be dispensed with.

[0037] Ionic surface-active additives can also be used according to the invention. Preferred ionic additives include alkyl sulfates (e.g., Chemsulf (PCC Chemax Inc.), Rewopol (Evonik), ROSULfan E (PCC Chemax Inc.)), alkyl sulfosuccinates (e.g., PLANTAPON SUS (BASF), TEXAPON SB 3 KC (BASF), Genapol SBE (Clariant), Rewopol SB (Evonik)), alkylbenzene and paraffin sulfonates (e.g., Marlon A (Sasol Chemicals), Marlopon AT (Sasol Chemicals)), and secondary alkanesulfonates (e.g., MERSOLAT H (Lanxess)). Further preferred are alkyl ether sulfates (e.g. SUL- FOROKanol (PCC Chemax Inc.), ROSULfan OD (PCC Chemax Inc.), EXOsoft MG (PCC Chemax Inc.)), alkyl carboxylates (e.g. Tween 20 (Croda)), benzalkonium chloride (e.g. BTC 1218-50 (ADBAC)), taurides (e.g. Igepon TK (Nantong Tailida Chemical Industry)), or amine oxides (e.g. Tegotens (Evonik)). Also usable as ionic additives are organophosphorus compounds such as phosphates, phosphonates, phosphites or phosphoric acid esters (e.g.Servoxyl (KLK Oleo)). The cellulose or starch binder in the metallic effect pigment preparation used according to the invention has the particular task of ensuring homogeneous incorporation and adhesion to the powder coating in the bonding process. The metallic effect pigments are then present in a non-agglomerated form, attached to the powder coating binder.

[0038] In a preferred embodiment, the metallic effect pigment preparation used according to the invention comprises 88-92% by weight, preferably 90% by weight, of an SiO2-coated aluminum effect pigment, as well as 5-8% by weight, preferably 6% by weight, of a hydroxypropyl methylcellulose and 2-4% by weight, preferably 3% by weight, of a non-ionic wetting agent based on polyethylene glycol, and 1-2% by weight of residual moisture. This metallic effect pigment preparation is in granular form, preferably as cylindrical granules with a diameter of 1.5 to 2.5 mm and a length of 0.5 to 6 cm, in particular 1 to 5 cm.

[0039] In another preferred embodiment, the pigment preparation used according to the invention comprises 78-82% by weight, preferably 80% by weight, of an aluminum effect pigment coated with SiO2, as well as 8-12% by weight, preferably 10% by weight, of a hydroxypropyl methylcellulose and 8-12% by weight, preferably 9% by weight, of a non-ionic wetting agent based on polyethylene glycol, and 1-2% by weight of residual moisture.

[0040] A further aspect of the invention relates to a process for producing a powder coating, which comprises the following steps: a) producing a metallic effect pigment preparation by mixing a metallic effect pigment with a metallic core, which optionally has one or more metal oxide and / or metal hydroxide and / or metal oxide hydrate layers, with at least one binder selected from cellulose, cellulose derivative, starch, starch derivative or mixtures thereof, and a surface-active additive, compacting the resulting mixture in granular form, optionally drying the compacted mixture, wherein the metallic effect pigment preparation is in granular form and comprises the following components:

[0041] A) 60 - 98 wt.%, based on the total weight of the metallic effect pigment preparation, of at least one metallic effect pigment with a metallic core, which optionally has one or more metal oxide and / or metal hydroxide and / or metal oxide hydrate layers,

[0042] B) 1 - 30 wt.%, based on the total weight of the metallic effect pigment preparation, of at least one binder selected from cellulose, cellulose derivative, starch, starch derivative or mixtures thereof,

[0043] C) 1 - 30 wt.%, based on the total weight of the metallic effect pigment preparation, of a surface-active additive, and

[0044] D) less than 3 wt.%, based on the total weight of the metallic effect pigment preparation, residual moisture, wherein the residual moisture comprises water and organic solvents, b) mixing the metallic effect pigment preparation obtained in step a) in granulate form together with a powder coating binder and optionally further components of a powder coating, and c) bonding the mixture obtained in step b).

[0045] The compaction of the mixture to produce the metallic effect pigment preparation in granulate form is preferably carried out by conventional processes such as extrusion, perforation pressing (press with a ram and perforated plate), or extrusion, in particular also low-pressure extrusion through a basket extruder, optionally with subsequent drying (at about 20°C to 150°C, for example above 40°C, preferably between 55 and 65°C), and comminution with, for example, a rotating knife. Granules in spherical form (with diameters of about 0.05 to about 5 mm, in particular 1 to 3 mm) can be obtained via spray and fluidized-bed granulation or with a granulating disc, optionally with subsequent sieving. Bonding can be carried out in commercially available apparatus currently known in the field of technology (e.g.Equipment from Lödige & Pappenmeier, Zeppelin-Henschel, Hosokawa, Plas-Mec, or Mixaco) is used to combine the metallic effect pigment preparation with the powder coating. By introducing energy, e.g., from external heat sources or high shear forces, the powder coating binder is heated to the glass transition point or higher, and then mixed with the metallic effect pigment preparation. Typical glass transition temperatures are in the range of 50-70°C, particularly between 55 and 65°C. The amount of metallic effect in the powder coating is usually between 0.5 and 4% by weight, preferably 1 to 3% by weight.

[0046] The present invention further relates to a powder coating comprising at least one powder coating binder and at least one metallic effect pigment preparation as defined in any one of claims 1 to 7 and above, and to a substrate coated therewith.

[0047] The present invention also relates to the use of the powder coatings according to the invention for coating substrates containing metal, metal foils, plastic, glass, glass fibers, composite materials, ceramics, wood, concrete, textile materials, and wood-based materials. Preferred substrates for coating with the powder coatings according to the invention are, in particular, pretreated and / or cleaned / degreased aluminum alloys or steel and its alloys.

[0048] It is understood that the features mentioned above and those to be explained below can be used not only in the specified combinations, but also in other combinations or on their own, without departing from the scope of the present invention. The advantages of features or combinations of several features mentioned are merely exemplary and can be used alternatively or cumulatively.

[0049] The following examples and comparative examples further illustrate the invention and demonstrate its advantages. Examples of metallic effect preparations usable according to the invention:

[0050] Example 1 : Granule production

[0051] 30 g of Methocel E5 Premium LV binder (hydroxypropyl methylcellulose (methoxyl content: 28.0–30.0%; hydroxypropoxyl content: 7.0–12.0%; viscosity 2% in water at 20°C: 4.0–6.0 cP), Dupont) were dissolved in 100 mL of cold water. 16.3 g of this solution were homogenized together with 2.1 g of PEG 400 (polyethylene glycol, average molar mass: 380–420 g / mol) and 120.68 g of filter cake (Aquamet ST-IL 10600 / 50, silver dollar coated with SiO2 in isopropanol (sales product of Schlenk)). The homogenized mixture thus contained 63 g of the SiO2-coated aluminum pigment. It was pressed into granules with a diameter of approximately 2 mm and a length of approximately 1-5 cm using a press with a punch and perforated plate. The granules were then dried in a drying cabinet at 60°C for 5 hours. The resulting granules comprised 89.6% by weight of aluminum pigment, 6.5% by weight of a water-soluble binder, 2.6% by weight of the binder.-% of a surface-active additive and 1.3 wt.% residual moisture.

[0052] Example 2: Granule production

[0053] 30 g of the binder Methocel E5 Premium LV (hydroxypropyl methylcellulose (methoxyl content: 28.0-30.0%; hydroxypropoxyl content: 7.0-12.0%; viscosity 2% in water at 20°C: 4.0-6.0 cP), Dupont) were dissolved in 100 mL of cold water. 16.3 g of this solution were homogenized together with 2.1 g of PEG 400 (polyethylene glycol, average molar mass: 380-420 g / mol) and 90 g of aluminum powder (Powdal 8500 01, silver dollar coated with SiO2 (sales product of Schlenk)). The homogenized mixture thus contained 90 g of the SiO2-coated aluminum pigment. It was pressed into granules with a diameter of approximately 2 mm and a length of approximately 1-5 cm using a press with a punch and perforated plate. The granules were then dried in a drying cabinet at 60°C for 5 hours. The resulting granules comprised 89.6 wt.% aluminum pigment, 6.5 wt.% of a water-soluble binder, 2.6 wt.% of a surface-active additive, and 1.3 wt.% of the binder.-% residual moisture. Comparative example of metallic effect composition:.

[0054] Comparative example 3: Metallic effect powder

[0055] Aquamet ST-IL 10600 / 50 (sold by Schlenk) is dried in an oven at 120°C for 5 hours to obtain a powder from the isopropanol paste. This powder is referred to below as Comparative Example 3.

[0056] Comparison example 4: Powdal 8500 01 (sales product of Schlenk)

[0057] Characterization of metallic effect pigment preparations

[0058] Test for dust-freeness and dimensional stability of the granules:

[0059] To test the dust-free nature of the pigment preparation, a defined amount of granules (3 g) is filled into a plastic container and shaken on a shaker (GFL 3006) for 0.5 h at a shaking frequency of 300 min -1shaken. The granules are then removed from the plastic container, and the remaining abrasion is weighed using an analytical balance. The percentage abrasion is thus determined.

[0060] Determination of the residual solvent content of the granules:

[0061] To determine the residual solvent content of the metallic effect pigment preparation, a weighing boat made of thin aluminum foil is placed on the Sartorius Ultramat MA35. The weight of the weighing boat is tared, and 2 g of the metallic effect pigment preparation is added. The lid of the Ultramat is then closed, and the metallic effect pigment preparation is heated to 120°C. During this time, the weight of the metallic effect pigment preparation is continuously determined. When no further weight loss can be recorded, the solids content of the metallic effect pigment preparation is determined in percent from the initial weight and the remaining weight of the metallic effect pigment preparation. The residual moisture content of the metallic effect pigment preparation corresponds to the value resulting from subtracting the solids from 100%. Data of the metallic effect pigment preparations

[0062] Table 1: Assessment of dust-freeness, stability and environmental impact of the granules.

[0063] The measured values ​​in Table 1 demonstrate good dimensional stability of inventive examples 1 and 2, which exhibit hardly any abrasion after prolonged mechanical stress. A further advantage of inventive examples 1 and 2 is the high metal content, which leads to a low incorporation of binder into the coating formulation and a lower consumption of metallic effect pigment preparation. In addition, the environmental compatibility of inventive examples 1 and 2 is also very good, and no organic solvents are required to dissolve the binder.

[0064] Application of metallic effect pigment preparation in powder coating

[0065] To apply the metallic effect pigment preparation in powder coating, it must be bonded.

[0066] For this purpose, inventive example 1 (metallic effect pigment preparation in granular form) is compared with its starting material, Aquamet ST-IL 10600 / 50 (a commercial product from Schlenk) in powder form (Comparative Example 3). Furthermore, inventive example 2 (metallic effect pigment preparation in granular form) is compared with its starting material, Powdal 8500 01 (a commercial product from Schlenk) (Comparative Example 4).

[0067] Bonding procedure:

[0068] In the bonding process, the metallic effect pigment preparation or pigment powder is mixed with the corresponding powder coating (transparent in PES-PRIMID or PES-PRIMID black high-gloss). The material mixture is then brought to the glass transition temperature of the powder coating and heated 2°C above the DSC end set point. This is done with constant mixing motion to ensure complete dispersion of the powder coating-pigment mixture. The pigmentation level of the metallic effect pigment preparation in the powder coating is 3% for the transparent PES-PRIMID system and 1% for the black high-gloss PES-PRIMID system. After reaching a specified temperature above the DSC end set point, the mixture is cooled as quickly as possible to prevent a curing reaction. Before the powder is applied, a protective sieve is also carried out using a sieve with a mesh size of 100 μm to remove any agglomerates.

[0069] Powder coat application:

[0070] A Gema powder gun is used to apply the bonded powder coating. The bonded transparent PES-PRIMID powder coating is applied to a sheet metal panel using the following gun parameters (20% powder cloud, 2.5 Nm / cm^3, 60 mA, 90 kV) and then cured at 180 °C for 20 minutes. The bonded black high-gloss PES-PRIMID powder coating is also applied to a sheet metal panel using the following gun parameters (20% powder cloud, 2.5 Nm / cm^3, 60 mA, 90 kV) and then cured at 180 °C for 20 minutes.

[0071] Optical inspection of the coating:

[0072] The optical properties were measured as follows:

[0073] The BYK micro-gloss 60° device is used to measure gloss. Scanning electron microscope images of the powder coatings:

[0074] The samples are prepared by cutting the powder-coated sheets into small pieces and embedding them in Technovit 4000 (from Külzer Technik). The edge of the sheet is then ground and polished. The sample is placed in a scanning electron microscope (Auriga 40 from ZEISS), and images of Example 1 according to the invention (Figure 1) and Comparative Example 3 (Figure 2) are acquired using the following settings: Working distance = 7.9 mm; Magnification = 500x; Voltage = 12 kV; Stage at T = 0.0°; Tilt Angle = 36.0°; Brightness = 51.0%; Contrast = 73.9%; Tilt Correction = Off; FIB Image - SEM; Detector - NTS BSD. The image colors are then inverted for better visibility of the pigments. Thus, the pigments are shown as black and the powder coating matrix as white.

[0075] Table 2: Measurement values ​​of powder coating application, bonded in the transparent PES-PRIMID system

[0076] Table 3: Measurement values ​​of powder coating application, bonded in the black high gloss PES-PRIMID system

[0077] Here, it can be seen that inventive example 1 exhibits a significantly higher gloss than comparative example 3, both in the black high-gloss PES-PRIMID system and especially in the transparent PES-PRIMID system. Inventive example 2 exhibits an equivalent gloss in the transparent PES-PRIMID system. This results from the better arrangement of the pigments on the coating surface, which can be seen in the SEM images (Figures 1 and 2).

[0078] Furthermore, the dust-free dosing of the granulate form of Examples 1 and 2 according to the invention significantly reduces dust exposure during the bonding process compared to the comparative examples. Handling, storage stability, and occupational safety are significantly improved by using the metallic effect preparation according to the invention.

Claims

Claims 1. Use of a metallic effect pigment preparation in powder coatings, characterized in that the metallic effect pigment preparation is in granular form and comprises the following components: a) 60 - 98 wt.%, based on the total weight of the metallic effect pigment preparation, of at least one metallic effect pigment with a metallic core, which optionally has one or more metal oxide and / or metal hydroxide and / or metal oxide hydrate layers, b) 1 - 30 wt.%, based on the total weight of the metallic effect pigment preparation, of at least one binder selected from cellulose, cellulose derivative, starch, starch derivative or mixtures thereof, c) 1 - 30 wt.%, based on the total weight of the metallic effect pigment preparation, of a surface-active additive, and d) less than 3 wt.%, based on the total weight of the metallic effect pigment preparation, of residual moisture, wherein the residual moisture comprises water and organic solvents.

2. Use according to claim 1, characterized in that the metallic effect pigment is an aluminum effect pigment.

3. Use according to one of the preceding claims, characterized in that the metal oxide and / or metal hydroxide and / or metal oxide hydrate layer is selected from the group consisting of oxides, hydroxides or oxide hydrates of the elements silicon, vanadium, molybdenum, chromium, titanium, iron, aluminum, tin and mixtures thereof.

4. Use according to one of the preceding claims, characterized in that the binder is a water-soluble binder, preferably hydroxypropyl methylcellulose.

5. Use according to one of the preceding claims, characterized in that the surface-active additive is an ionic surface-active additive.

6. Use according to one of claims 1 to 4, characterized in that the surface-active additive is a non-ionic surface-active additive, preferably a polyglycol, polyvinyl butyral (PVB) and / or polyvinylpyrrolidone (PVP).

7. Use according to claim 6, characterized in that the polyglycol is a polyethylene glycol or polypropylene glycol, preferably a polyethylene glycol with an average molar mass of 200 - 600 g / mol.

8. Use of a metallic effect pigment preparation as defined in any one of claims 1 to 7 for producing powder coatings by bonding the metallic effect pigment preparation in granulate form with powder coating binder.

9. Powder coating comprising at least one powder coating binder and at least one metallic effect pigment preparation as defined in any one of claims 1 to 7.

10. A process for producing a powder coating, comprising the following steps: a) producing a metallic effect pigment preparation as defined in any one of claims 1 to 7, by mixing a metallic effect pigment with a metallic core, which optionally has one or more metal oxide and / or metal hydroxide and / or metal oxide hydrate layers, with at least one binder selected from cellulose, cellulose derivative, starch, starch derivative or mixtures thereof, and a surface-active additive, compacting the resulting mixture in granular form, optionally drying the compacted mixture, b) mixing the metallic effect pigment preparation obtained in step a) in granulate form together with powder coating binder and optionally further components of a powder coating, and c) bonding the mixture obtained in step b).

11. A method according to claim 10, wherein during bonding the mixture is heated to a temperature around the glass transition temperature of the powder coating binder.

12. Use of powder coatings according to claim 9 for coating substrates containing metal, metal foils, plastic, glass, glass fibers, composite materials, ceramics, wood, concrete, textile material, wood materials.

13. Coated substrate, characterized in that the substrate is coated with a Powder coating according to claim 9 or produced by a process according to claim 10.

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