Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
  • C09D5/03—Powdery paints
  • C09D5/031—Powdery paints characterised by particle size or shape
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
  • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
  • C09C1/0015—Pigments exhibiting interference colours, e.g. transparent platelets of appropriate thinness or flaky substrates, e.g. mica, bearing appropriate thin transparent coatings
  • C09C1/0021—Pigments exhibiting interference colours, e.g. transparent platelets of appropriate thinness or flaky substrates, e.g. mica, bearing appropriate thin transparent coatings comprising a core coated with only one layer having a high or low refractive index
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
  • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
  • C09C1/0081—Composite particulate pigments or fillers, i.e. containing at least two solid phases, except those consisting of coated particles of one compound
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
  • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
  • C09C1/62—Metallic pigments or fillers
  • C09C1/64—Aluminium
  • C09C1/644—Aluminium treated with organic compounds, e.g. polymers
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
  • C09D5/03—Powdery paints
  • C09D5/033—Powdery paints characterised by the additives
  • C09D5/035—Coloring agents, e.g. pigments
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
  • C09D7/40—Additives
  • C09D7/60—Additives non-macromolecular
  • C09D7/61—Additives non-macromolecular inorganic
  • C09D7/62—Additives non-macromolecular inorganic modified by treatment with other compounds
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/60—Particles characterised by their size
  • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K9/00—Use of pretreated ingredients
  • C08K9/02—Ingredients treated with inorganic substances
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
  • C09C2200/00—Compositional and structural details of pigments exhibiting interference colours
  • C09C2200/10—Interference pigments characterized by the core material
  • C09C2200/1054—Interference pigments characterized by the core material the core consisting of a metal
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
  • C09C2200/00—Compositional and structural details of pigments exhibiting interference colours
  • C09C2200/40—Interference pigments comprising an outermost surface coating
  • C09C2200/402—Organic protective coating
  • C09C2200/405—High molecular weight materials, e.g. polymers

Definitions

• metallic powder coatings which are also referred to as effect powder coatings, in particular RAL 9006, RAL 9007, DB coatings or iron mica coatings
• the powder coating present in powder form is weighed with effect pigments and additives in the correct ratio and homogenized in a subsequent mixing process.
• effect basic powder coating based on resin, on polyester/Primid ® , polyester/epoxy mixtures, on pure epoxy, or on polyurethane resins is used as a powder coating.
• pigments based on aluminum flakes, on natural or synthetic mica, or on glass can be used as an effect factor. According to the respective requirements, these pigments are single- or multi-coated, thereby rendering them resistant to weathering and/or chemicals.
• mica pigments pearlescent or interference pigments
• metallic-effect pigments metallic-effect pigments
• the mixing process can be performed as a simple mixing process in a mixer with low peripheral speed and short residence time, wherein binding agents, additives etc. and the metallic pigments particles are dry-blended.
• the disadvantage here is that such dry blends, among other factors due to the difference in specific weights and electrostatic charging behavior, result in a segregation of metallic pigment and binding agent during the powder coating process.
• the recyclability of such a powder coating comprising metallic pigments is no longer given for powder coatings produced according to this method.
• a physical bonding of the metallic pigment particles to the powder coating particles can be achieved by heating a mixture of powder coating and metallic pigment until the glass transition temperature of the powder coating is achieved.
• the bonding method thus effects an adhesion of the metallic pigment particles to the surface of the powder coating particles by introducing energy, e. g. by means of external heat sources or high shearing forces, and a resulting heating of the powder coating to the glass transition point or higher .
• EP 2 896 661 A1 relates to a powder coating composition in particulate and cured form comprising effect pigments as well as to a method for preparing a powder coating composition comprising effect pigments.
• a film-forming, homogeneous, thermoplastic coating mass is produced from the starting materials, in particular comprising binding agents, additives, coloring agents and/or bulking agents, by means of an extruder, and the resulting coating mass is ground after leaving the extruder, wherein the effect pigments are added in an end region of the extruder and dispersed in the viscous coating mass.
• the effect pigments are thereby wetted and coated with the film-forming coating mass, wherein at least 50 %, especially at least 75 %, and preferably at least 90 % of the surface of the effect pigment particles are wetted with the coating mass.
• the composition of the final powder coating composition is identical to the composition used for coating the effect pigment particles.
• DE 10 2007 006 820 A1 relates to metallic-effect pigments having a homogeneous synthetic resin layer, wherein said synthetic resin coating comprises polyacrylate and/or polymethacrylate as well as organofunctional silane.
• the synthetic resin layer is applied onto the metallic-effect pigment particles by means of in situ polymerization to form a layer.
• WO 2005/063897 A2 discloses chemically and mechanically resistant metallic-effect pigments coated with oligomeric and/or polymeric binding agents which can be cross-linked chemically and/or under the influence of, e. g., UV or IR radiation.
• the metallic-effect pigments can be embedded in a polymeric film.
• the binding agents are still curable or polymerizable, due to which said metallic pigments are used in powder coatings.
• the coated metal pigments are provided in the form of a powder which has a particle size d50 of less than 190 pm and wherein said metal pigments are corrosion-resistant after curing in a powder coating.
• the binding agents can be slightly grafted, but they will not cure.
• the metallic pigment may be coated with the same binding agent system, in which it will be embedded and processed later on - for example in a powder coating.
• the metallic-effect pigments are produced by dispersing the metallic pigment particles in a solution or dispersion of an oligomeric and/or polymeric binding agent in an organic solvent and subsequent spraying or by spraying a solution or dispersion of an oligomeric and/or polymeric binding agent in an organic solvent onto metallic pigment particles being swirled a gas stream, followed by drying the metallic pigment particles that are coated with said binding agent in a moving gas stream.
• US 2006/189718 A1 relates to a method of producing a powder coating composition wherein in a first step a pigment composition comprising flake-like, color effect pigment particles and a polymeric binder is provided, said pigment composition having an initial particle size distribution with fine particles and wherein in a second step the pigment composition is mixed and heated to a temperature to achieve a second particle size distribution substantially without fine particles and wherein in a third step the pigment composition from the second step is cooled to produce the powder coating composition.
• a powder coating composition comprising non-leafing pigment particles, flake-like, color effect pigment particles, and a polymeric binder, wherein the powder coating composition has a particle size distribution determined as a function of particle count having two count modes, in particular located between 10 and 50 pm is disclosed.
• the disclosed powder coating compositions may further comprise organic coloring pigments, inorganic filler pigments or both. Effect powder coatings produced by the disclosed method are said to have an improved uniformity in appearance.
• the closest state-of-the-art is represented by our own EP 3 144 352, which discloses a powder coating composition comprising at least one base powder paint B and at least one effect powder coating A having effect pigments, wherein the effect pigments in the effect powder coating A are encased at least in part by a powder coating matrix which hardens transparently.
• Such powder coating comprises a combination of a milled premix, which has effect pigment particles dispersed in a melt of at least one transparent powder coating, and a powder coating, which forms the basis of the effect coating.
• effect pigment particles are already encased by a transparent powder coating matrix when being mixed with the base powder coating, the shear forces acting on the effect pigment are at such a low level that most of the effect pigments will not be subjected to any substantial reduction in particle size.
• the document further discloses milling the effect powder coating A having effect pigments to a powder coating with a D50 smaller than 80 pm.
• Powder coatings providing a distinctive effect (a so-called sparkling effect) , which is particularly pronounced in dark basic shades, are provided by the composition according to EP 3 144 352. Due to the high contrast between lighter, brilliant effect pigments and the dark basic color, the slightest differences in effect concentration are easily discernible, especially in the finished object, in particular when a plurality of coated components are mounted directly adjacent to one another and aligned end to end. In the case of larger components, undesirable clouds or bandings have often shown (due to locally increased pigment concentration) in prior art coatings. In addition, coatings performed on different coating systems or with different system settings and part geometries could sometimes yield different coating results and shade/effect formations. These variations in shade are not desirable and will most likely be complained about by contractors or architects, even though they merely represent an optical defect and do not impair the protective effect of the powder coating.
• the proportion of recycling powder is very important in effect powder coatings.
• the powder which does not adhere to the object will be suction-filtered and passed on to a cyclone.
• the fine fraction is separated from the rest and suctioned off by means of rotation and gravity forces.
• the rest is then collected in a metering system and/or is recycled to the fresh powder in defined amounts and thus re-introduced into the coating process.
• effect powder coatings prepared by the dry blending method there is a risk that the fine metallic-effect pigment particles will be separated and suctioned off through the cyclone. This is reflected in the so- called effect drift, which renders the shade of the effect powder coating less and less metallic over time.
• the problem underlying the present invention is the manufacture of unique and more brilliant effect powder coatings than already disclosed in the closest state-of-the-art, whose appearance or effect characteristics are only insignificantly influenced by gun type, equipment setting, proportion of recycling powder and part geometry. Additionally, it is desirable to reduce the pigment content of the coating composition as compared to the closest state-of-the-art compositions without altering the brilliant effects of the coating. Reduction of pigment load improves the ease of production and the cost efficiency of the coating composition. These absolutely process-safe and pronounced metallic effects should have an improved special depth effect and should be suitable for use in highly weather-resistant systems with its effects being improved over both effect powder coatings of the closest state-of-the-art and those of wet paints. Furthermore, the present invention relates to such a powder coating containing effect pigments prepared according to the present invention in a milled premix.
• substrates coated with the metallic powder coatings according to the present invention also show significantly less color variations within a defined area .
• a powder coating composition comprising at least one opaque basic powder coating B and at least one effect powder coating A comprising effect pigments, wherein the effect pigment particles present in the effect powder coating A are, at least partially, coated with a transparent, curable or thermoplastic powder coating matrix and wherein the effect powder coating A is ground so that less than 70 % by weight, preferably less than 60 % by weight, more preferably less than 50 % by weight, and most preferably less than 40 % by weight, of the effect powder coating A have a grain size of below 90 pm, as measured by sieve analysis.
• a powder coating composition is generally used which in most cases exclusively consists of resins/curing agents (a curable / thermosetting powder coating composition) and required additives (e. g. for film degassing) . If in the following reference is made to a "cured" or "curable” powder coating, this term is understood to comprise also thermoplastic powder coatings.
• the cured powder coating film has a high transparency ( translucency) .
• a transparent powder coating is preferably used which, in case of a layer thickness of 15 pm of the cured film, still has sufficient transparency to keep visible the underlying coating layers or substrates.
• a transparent powder coating may contain dyes or a certain amount of color pigments under the proviso that the cured coating film remains transparent in accordance with the above definition.
• the transparent powder coating A is free of color pigments and/or dyes, thus being a clear powder coating. It is further clear for a person skilled in the art that any powder coating that is not considered as transparent in accordance with the above definition is considered as opaque.
• melt or "melted” is used, it is understood to comprise as well a softening of the respective material up to a point where stirring further ingredients into the respective material is possible. Thus, complete melting of the respective material is sometimes not necessary to carry out the processes of present invention, it might be enough to soften the material up to a point were thorough mixing with other materials is possible.
• the term “melt” or “melted” should not be understood as the first-order phase transition of a single crystalline compound from the solid to the liquid state at a well-defined temperature according to the teachings of classical thermodynamics.
• At least 5 % by weight, preferably at least 7 % by weight, more preferably at least 10 % by weight, and most preferably at least 15 % by weight of the effect powder coating A are ground to a grain size of more than 125 pm.
• at least 15 % by weight, preferably at least 20 % by weight, more preferably at least 25 % by weight, and most preferably at least 30 % by weight of the effect powder coating A are ground to a grain size of more than 125 pm.
• between 25 and 40 % by weight, preferably between 30 and 40 % by weight of the effect powder coating A are ground to a grain size of more than 125 pm, e.g.: 35% by weight or 40% by weight.
• At least 3 % by weight of the effect powder coating A are ground to a grain size of more than 212 pm.
• the shear forces acting on the effect pigment particles in effect powder coating A during production are kept so low that most of the effect pigment particles are not subjected to a substantial reduction in particle size. From a technical point of view, this can be achieved by melting or softening the transparent powder coating, for example in a heated stirred reactor, and stirring at least one effect pigment into or extruding the effect pigment with the melt/softened material, wherein the transparent effect powder coating A, which is obtained by cooling and subsequent coarse grinding and optionally sieving to a grain size as mentioned above, is then blended with an opaque, preferably colored basic powder coating B.
• Other technical embodiments are also conceivable within the scope of the present invention.
• d50 120 pm
• At least one effect pigment is added to a melt of transparent powder coating through at least one side feeder during an extrusion process, wherein the effect powder coating A, which is obtained from said powder coating melt by means of cooling and subsequent coarse grinding and optionally sieving to a grain size as mentioned above, is subsequently mixed with a basic powder coating B.
• side feeder implies the addition of a substance (according to the prior art usually an additive or effect pigment, see for example information material provided by the extruder manufacturer Leistritz Extrusionstechnik GmbH (Germany) "Master_V_07_GB/17.09.13 Masterbatch) ) at a position in the extruder process section other than the initial section of the extruder (premix feeder in barrel 1) .
• the effect pigment is forcibly conveyed laterally into the extruder and incorporated into the melt in a certain proportion to the transparent powder coating premix. Due to the arrangement of the side feeder along the process section and the implemented screw configuration it is possible to influence the shear force acting on the pigment particles in the extruder. A low shear force acting within the extruder results in minimal damage to the effect pigment particles.
• the use of screw elements which only serve the purpose of mixing or conveying the extruder melt allows for a reduction of shear forces down to a level intended according to the present invention, while at the same time providing a sufficient homogenization/dispersion .
• the shear force is kept as low as possible by means of special screw configurations, for example the exclusive use of conveying elements, in order to cause only minimal damage to (or destruction of) the one or more types of pigments, in particular effect pigments.
• a transparent effect powder coating A can be prepared by adding at least one effect pigment through at least one side feeder into the melt of a subsequently transparently curing powder coating during an extrusion process and the coarse grinding and optionally sieving of the cooled melt to a grain size as mentioned above, wherein the effect powder coating A is then mixed with at least one further powder coating B, the so-called basic powder coating.
• the basic powder coating B can be a single colored powder coating that contains no effect pigments or a powder coating that contains effect pigments and has been prepared by means of dry blending, bonding or extrusion.
• the basic powder coating B may comprise different powder coating materials, e.g.
• the basic powder coating B may be a thermosetting or thermoplastic powder coating composition or a mixture thereof, wherein however thermosetting powder coatings compositions are being preferably used .
• the effect powder coating A can be prepared in an extruder by adding effect pigment to a transparent powder coating melt via a side feeder. Downstream from the point of addition through the side feeder, only low shear forces are exerted by the extruder shaft. Subsequently to the extrusion process, the effect powder coating is cold-rolled, crushed and coarse ground to grains having a grain size as mentioned above, optionally with an additional sieving step.
• the powder coating according to the present invention can then be produced by preparing and weighing raw materials, including the transparent effect powder coating A and the basic powder coating B, followed by mixing the two powder coatings.
• the powder coating according to the present invention can then be additionally refined with effect pigment in a further process step, which can in particular be performed by means of a bonding method.
• the powder coating according to the present invention comprises the coarse ground grains of effect powder coating A having a grain size as mentioned above in admixture with the basic powder coating B in a mass ratio of 1 to 50 % of effect powder coating A and 50 to 99 % of basic powder coating B, particularly preferably 5 to 30 % of effect powder coating A and 70 to 95 % of basic powder coating B.
• the inventive powder coating comprises the coarse ground grains of effect powder coating A having a grain size as mentioned above in admixture with the basic powder coating B in a mass ratio of 10 to 30% of effect powder coating A and 70 to 90 % of basic powder coating B, particularly preferably 10 to 25 % of effect powder coating A and 75 to 90 % of basic powder coating B.
• the powder coating according to the present invention can be prepared by means of a so-called dry blending or bonding method. Within the scope of the present invention, it is also possible to mix the coarse ground effect powder coating A having a grain size as mentioned above with the basic powder coating B during the melt phase .
• basic powder coating B is milled and optionally sieved to obtain a distribution dso of below 80 pm, preferably below 60 pm and even more preferably below 45 pm. In an especially preferred embodiment, the distribution dso of the basic powder coating B is 36 pm. In some embodiments a topcut (by sieving) of 120 pm, more preferably 90 pm is employed, resulting in a basic powder coating B that is free of particles above 120 pm (topcut at 120 pm) or preferably above 90 pm (topcut at 90 pm) .
• the basic powder coating B features a PSD, wherein dio is between 5 and 20 pm, preferably between 8 and 15 pm, dso is between 20 and 60 pm, preferably between 30 and 45 pm and dgo is between 60 and 120 pm, preferably between 60 and 90 pm, even more preferably between 60 and 80 pm.
• the effect powder coating A is ground more coarsely than the basic powder coating B. It was found to be particularly advantageous in case the dso value of effect powder coating A is at least 15 pm, preferably at least 25 pm more preferably at least 30 pm and most preferably at least 35 pm larger than the d50 value of basic powder coating B. Further it was found to be advantageous in case the d9o value of effect powder coating A is at least 30 pm, preferably at least 50 pm more preferably at least 70 pm and most preferably at least 90 pm larger than the d-9-q- value of basic powder coating B.
• effect powder coating A and basic powder coating B favor the formation of sufficiently large and isolated channels of effect powder coating A surrounded by basic powder coating B upon curing without deteriorating the processability of the composition upon application. Further, the hiding powder of the coating may be improved. This is achieved as the smaller particles of basic powder coating B may evenly distribute around the larger particles of the effect powder coating A upon application and subsequent curing.
• the powder coating composition comprises at least one opaque basic powder coating B and at least one effect powder coating A comprising effect pigment particles, wherein the effect pigment particles present in the effect powder coating A are, at least partially, coated with a transparent, curable or thermoplastic powder coating matrix and wherein at least 8 % by weight of the composition has a grain size of at least 90 pm and/or at least 6 % by weight of the composition has a grain size of at least 100 pm and/or at least 4 % by weight of the composition has a grain size of at least 112 pm and/or at least 3 % by weight of composition has a grain size of at least 125 pm as measured by sieve analysis.
• At least 12 % by weight, preferably at least 15 % by weight and more preferably at least 20 % by weight of the composition has a grain size of at least 90 pm and/or if at least 8 % by weight, preferably at least 10 % by weight and more preferably at least 13 % by weight of the composition has a grain size of at least 100 mpi and/or if at least 6 % by weight, preferably at least 8 % by weight and more preferably at least 10 % by weight of the composition has a grain size of at least 112 pm and/or if at least 5 % by weight, preferably at least 6 % by weight of composition has a grain size of at least 125 pm as measured by sieve analysis.
• the powder coating composition as described above may be obtained from embodiments or by suitable combination of embodiments, in particular of the effect powder coating A, the basic powder coating B and the production process for A and B, as described within the present application.
• effect coatings as disclosed within the present application are obtained from such compositions. It was found by the inventors that such inventive coating compositions provide for particularly pronounced effects, in particular metallic and or sparkling effects, in particular characterized by a strong depth effects, a brilliant effect and especially by featuring said effects irrespectively of the viewing angle. Further, such inventive compositions showed particularly pronounced recyclability and process stability upon application. Finally, the pigment content could be exceptionally reduced as compared to state of the art coatings, resulting in economic and environmental benefits.
• any extruder type available on the market such as a single- or multi screw extruder, can be used, provided it has a side feeder.
• the parameters to be adjusted such as screw configurations, torque and throughput, can be selected in a flexible manner depending on the powder coating system employed and the powder coating properties to be adjusted, with the proviso that the shear forces acting downstream from the addition point of the effect pigment particles through the side feeder be kept correspondingly low.
• the side feeder for the addition of effect pigments in the rear half, preferably the rear third of the extruder.
• the method of preparing powder coatings according to the present invention has proven particularly advantageous for the substitution of prior art powder coatings which are classified as category C according to OFI (Austrian Research Institute for Chemistry and Technology) instruction sheet No. 44.
• these are powder coatings exhibiting a very distinctly visible sparkle effect.
• such an effect can be achieved by mixing aluminum effect pigments having a dso of about 35 pm in the form of so-called silver dollars with a dark basic color.
• Said silver dollar pigments are made of a special aluminum grit and milled according to the respective size classification.
• pigments are obtained that are characterized by their round to oval shape and a smooth surface.
• These pigments generally have a very high sparkling degree, i.e. the pigment exhibits a low scattering, but a strong reflection of light.
• the higher the contrast between the effect pigments (light, silver) and the basic color the more difficult these effect coatings are in terms of manufacturing and handling by the end user.
• the powder coatings according to the present invention behave similarly to single colored powder coatings. Phenomena common in large components, such as clouds or banding, will not occur, nor will the typical brightening of edges in different profiles and sizes, which is caused by an accumulation of effect pigments at the edges. This constitutes a marked improvement over the prior art effect powder coatings .
• Specific substrates to be coated with the powder coatings according to the present invention are, in particular, pre-treated and/or purified/degreased aluminum alloys or steel and its alloys.
• Other substrates, such as wood and MDF, are in principle also conceivable.
• the inventive powder coatings are not limited to any specific substrate as the compositions of effect powder coating A and/or basic powder coating B may be adjusted accordingly .
• the powder coatings according to the present invention are characterized in that effect pigments contained in the coating are surrounded at least in part by a transparent powder coating matrix and at least one channel formed from said transparent matrix leads from at least one effect pigment to the surface of the coating, at least 10 % of said channels having a maximal cross section as determined by electron microscopy of at least 150 pm, preferably at least 160 pm, more preferably at least 180 pm and especially preferably at least 200 pm .
• At least 20 %, preferably at least 30 %, more preferably at least 35 % and most preferably at least 40 % of said channels have a maximum cross section of at least 150 pm, preferably at least 160 pm, more preferably at least 180 pm and especially preferably at least 200 pm .
• the channels having a maximal cross section as determined by electron microscopy of at least 150 pm contain on average at least 3, preferably at least 4, more preferably at least 5 effect pigments per channel.
• SEM electron microscope
• a channel in the finished coating layer is defined as a continuous area of transparent material surrounded by opaque material. Inclusions of opaque material within one and the same channel are possible, as long as the transparent cured powder coating is not completely interrupted.
• the powder coating according to the present invention may be characterized in that the sparkle intensity measured at measurement angles of 15°, 45° and 75° differs by at most 30% from the maximum value.
• Powder coating according to the present invention provides for an improved effect image better than the one according to the closest state-of-the-art, that is also substantially independent of the respective viewing angle. This independence of the viewing angle can be determined not only visually, but also by measurement.
• the samples were analyzed using the colorimeter "BYKmac" by BYK, Germany. Relevant in this context are the values SI (sparkle intensity) and SA (sparkle area), which are determined at three different measuring angles.
• the measurement values show that the sparkle intensity measured on coatings produced with the powder coating according to the present invention is at all three measurement angles very high and even higher than on coatings produced according to closest state-of-the-art (EP 3 144 352 A) . There is only a slight difference between the measured angles (max. 30 % below the maximum value) .
• Table 1 Comparing Sparkle Intensity SI of a coating made using a powder coating composition according to closest state-of-the- art (EP 3 144 352 A) with a coating made using a powder coating composition according to the present invention, both using LUXAN CFX 393D as effect pigment) .
• the pigment load and powder coating compositions of the basic powder coatings B and the effect powder coatings A were chosen identically.
• This reflection between different effect pigment particles in combination with the varying orientation of said pigments within the coating may also improve the independence of the effect appearance of the respective viewing angle. Also, not only the effect pigment particles located at the surface of the powder coating, but also a plurality of effect pigment particles located deep inside the powder coating can become visible to the observer. This effect creates, on the one hand, the above-mentioned independence of the viewing angle, and on the other hand an increased and enhanced visually perceptible 3D or depth effect of the powder coating according to the present invention.
• Photomicrographs of cross-section polishes of powder coating layers prepared with the powder coating according to the present invention substantiate the above theory of broader channel formation by employing coarser particles of a transparent powder coating matrix.
• binding agents for use in the powder coatings according to the present invention include saturated and unsaturated systems.
• the latter may be cross-linked, inter alia radically by UV irradiation and/or by means of thermal initiators such as peroxides.
• thermal initiators such as peroxides.
• saturated polyesters play the most significant role.
• carboxyl- functional polyester resins which have a functionality of 2 or higher are mentioned here. These can be cross-linked with organic compounds that are capable of reacting with the carboxyl groups of the polyester to produce a covalent bond and can optionally be mixed with conventional pigments, bulking agents and additives.
• TGIC as curing agents for carboxyl-functional polyester resins
• PrimidR QM-1260 bis [N, N ' -di- (b- hydroxypropyl ) ] adipamide
• a special feature of these curing agents is their, according to current knowledge, toxicological harmlessness.
• TGIC as curing agents for carboxyl-functional polyester resins
• the glycidyl esters of aromatic or cycloaliphatic dicarboxylic acids a suitable commercially available curing agent with an analogous chemical structure is, e.g., AralditR PT 910 ( terephthalic acid triglycidyl ester/trimellitic acid triglycidyl ester, about 75:25) available from CIBA Spezialitatenchemie GmbH, Germany.
• the presence of the trifunctional trimellitic acid ester in AralditR PT 910 is to be considered as advantageous in comparison with pure diglycidyl esters with respect to the cross-linking density of baked coatings.
• Polyester resins for preparing weather- resistant powder coatings which are cured by means of polyepoxides and/or b-hydroxyalkylamides , generally have an acid number in the range of 15 to 70 mg KOH/g polyester and a hydroxyl number of less than ( ⁇ ) 10 mg KOH/g polyester.
• They essentially consist of units of aromatic dicarboxylic acids, such as terephthalic acid and isophthalic acid, in addition to which minor amounts of aliphatic and/or cycloaliphatic dicarboxylic acids, such as adipic acid and/or cyclohexanedicarboxylic acid, are optionally used, and of aliphatic diols, particularly preferably branched, such as neopentyl glycol, in addition to minor amounts of linear and/or cycloaliphatic diols.
• lactones lactones
• modification of such resins by the use of di- and trimeric fatty acids. Besides that, smaller amounts of tri- or higher functional and optionally monofunctional compounds may also be employed.
• the size of the pigments depends on the desired effect and can vary between 3 pm and 200 pm, preferably between 20 pm and 130 pm and more preferably between 35 pm and 90 pm.
• the weight proportion of the effect pigments in relation to the total weight of effect powder coating A can amount to between 1 % and 40 % by weight, in particular between 2 % and 20 % by weight and further in particular between 5 % and 15 % by weight. In some embodiments, the weight proportion of the effect pigments in relation to the total weight of effect powder coating A can amount to between 0.25 % and 40 % by weight, in particular between 0.5 % and 20 % by weight and further in particular between 1 % and 15 % by weight.
• effect pigments preferably three types of pigments are used, namely aluminum pigments), mica pigments and glass flakes (e.g. Luxan pigments manufactured by Eckard GmbH in Hartenstein, Germany) . Brass and copper pigments may also be used. According to particularly preferred embodiment of the invention, glass flakes are used as effect pigments.
• the present invention is in no way limited to the above mentioned effect pigments.
• Effect pigments are subdivided into metallic-effect pigments and special-effect pigments.
• Metallic-effect pigments are based on platelets made of metal, especially aluminum. Light is reflected by the metallic surface, which is perceived by the observer as a metallic effect.
• Important metallic-effect pigments are aluminum, brass and copper platelets.
• Pearlescent pigments and interference pigments are summarized under the term special-effect pigments.
• Pearlescent pigments are effect pigments consisting of transparent platelets having a high refractive index. They produce a pearl-like effect by multiple reflection.
• Interference pigments are effect pigments whose coloring effect is based entirely or predominantly on interference. Interference pigments can be based on transparent or non transparent platelets.
• Most commonly used in the industry are mica pigments coated with metal oxide, which are classified as pearlescent or interference pigments according to type and thickness of coating.
• the most important interference pigments are platelet-shaped titanium dioxide, platelet-shaped organic pigments, metal oxide mica pigments, aluminum oxide flakes, Ca/Al borosilicate flakes, silica flakes, metal flakes coated with metal oxide or multilayer pigments. Many of these pigments are additionally coated with metal oxides (e.g. titanium dioxide) .
• the color effect can be influenced by the thickness of the oxide coating.
• Exemplary commercial names are Iriodin ® , Mira
• Pigments based on natural mica are generally produced from naturally occurring muscovite mica by means of grinding, fractionating, cleaning and re-coating, drying and calcination.
• the effect of the pigments is based on the principle of regular reflection in the case of metallic-effect pigments and on regular reflection and interference in the case of pearlescent pigments .
• the average diameter of the effect pigment particles dispersed in the powder coating according to the present invention amounts to at least 90 % of the average diameter of the original effect pigment particles.
• the effect pigments usually have a diameter of about 3 to 100 pm while the thickness of each plate is less than 5 pm.
• the platelets may consist of one or more layers.
• the carrier material can be crystalline (e. g. mica) or amorphous (glass or silica platelets) . In order to achieve a good effect image, the particles must have the highest possible surface smoothness .
• Metallic-effect pigments are further subdivided into leafing or non-leafing pigments.
• leafing pigments orient themselves to the surface in the cured film, thereby generating a strong metallic sheen. This effect is not scratch- or smear-proof, however, due to which in most cases an overcoat with a protective clear coating is required.
• Non-leafing pigments will distribute evenly in the film matrix upon application, wherein only a portion of the pigments will be oriented to the surface, which constitutes protection against abrasion and chemical attacks. Their effect, however, is less brilliant and metallic than the effect obtained with leafing pigments.
• these disadvantages of non-leaving pigments as generally known in the state of the art may, at least partially, be overcome, with the present invention due to the fact that also pigments, that are deep inside a channel become visible. Further, the presence and random orientation of more than one effect pigment per channel, which may be realized for certain embodiments of the present invention, results in the reflection and scattering of the incoming light, which provides for the high independence of the metallic and sparkling effects of the viewing angle.
• FIG. 2 to 6 Images of cross-section polishes are shown in Figures 2 to 6, each in comparison with an example according to the closest state-of-the-art.
• the black lined areas without any visible particles consist of the above-mentioned transparent powder coating matrix. These channels can extend up to 80 pm deep into the powder coating layer and render visible even those pigment particles that are embedded deep inside the powder coating layer (in these photographs, the effect pigment particles appear as bright areas due to illumination) .
• the light areas are cross-sections through the substrate.
• each channel of the coating according to the present invention contains more effect pigments when directly compared to a coating according to the closest state-of- the-art .
• the sieve analysis was carried out using a vibratory sieve shaker (AS 300 control, Retsch) .
• a sieve stack consisting of 4 screen trays with decreasing mesh sizes from 125 pm ( 1 ) , 112 pm(2),
• the powder coating material is applied onto an aluminum panel followed by a suitable curing step.
• the sample was embedded upright in a polymer matrix. To ensure good conductivity of the sample, the sample must protrude at both ends.
• layer (channel) analysis and good image quality one side of the protruding ends is ground smooth, then polished and carefully cleaned. Then the cross-cut of the panel with the cured coating thereon is analyzed under a scanning electron microscope JEOL IT 100.
• Particle Size Distribution (dio, dso, dgo) :
• a specific value for d x indicates an amount x % of the particles of the powder coating material.
• the PSD of the powder coating materials is determined by using a Scirocco 2000 machine commercially available from Malvern Instruments GmbH employing a laser diffraction method and following the instructions of the user manual.
• the powder coating according to the present invention can, for example, consist of two components, wherein one component is the transparent effect powder coating A and the other component is an opaque colored basic powder coating B.
• a transparent and colorless powder coating was prepared from 900 parts of Crylcoat ® 4642-3 or an equivalent polyester, 47 parts of Primid ® XL-552, 5 parts of Richfos ® 626, 3 parts of benzoin, 5 parts of Worlee ® Add 902, 5 parts of Licowax C Micropowder PM and 2 parts of Tinuvin ® .
• this premix is metered into a twin-screw extruder (e. g. ZSK 27), molten with a screw configuration that is suitable for powder coating production and then dispersed.
• twin-screw extruder e. g. ZSK 27
• effect pigment e.g.: aluminum powder PCU 5000 or LUXAN CFX 393D
• the screw configuration downstream from the side feeder is exemplarily shown in Figure 7.
• the temperatures inside the extruder was kept at less than 120 °C.
• the liquid extrudate is cold-rolled and crushed in an impact pin mill in order to obtain ground powder coating, which optionally can be sieved (all percentages in % by weight) :
• effect powder coating lb (effect pigment: PCU 5000) was prepared identical to la but the milling conditions were slightly modified to obtain an even coarser effect powder coating as compared to la:
• effect powder coating lc (effect pigment: LUXAN CFX 393D) was prepared identical to la but the milling conditions were slightly modified to obtain an even coarser effect powder coating as compared to la:
• the opaque, colored basic powder coating B was essentially prepared in the same manner as described above and, in addition to the above raw materials, also contains color pigments and bulking agents, but no metallic/effect pigments.
• the basic powder coating B may also contain effect pigments.
• the basic powder coating B is milled less coarsely than the effect powder coating A.
• effect powder coating A la, lb or lc
• colored, opaque basic powder coating B were mixed in a ratio of 20 to 80 by means of dry blending.
• the mixing was conducted in either a dry blend mixer or a bonding mixer.
• a typical inventive powder coating composition that was obtained by mixing the opaque basic powder coating B and effect powder coating lb or lc (sieved, 212 pm) in a ratio of 20:80 (A:B) was classified by sieve analysis:
• Powder coatings on suitable substrates were made using the described coating composition.
• the coating was applied by conventional methods (e.g.: corona or tribo spray guns) under conditions well-known to a person skilled in the art.
• the curing conditions depend strongly on the chemistry of the coating compositions and can be easily adjusted by a person skilled in the art.
• the coating was cured for 10 minutes at 200 °C in a conventional convection oven.
• Figure 7 shows an extruder screw which is fitted with mixing elements downstream from the point of addition via side feeder.

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• 2019
  • 2019-04-26 EP EP19171360.1A patent/EP3730556A1/de not_active Withdrawn
• 2020
  • 2020-04-24 WO PCT/EP2020/061414 patent/WO2020216880A1/en unknown
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