Powder coating composition comprising a dry-

Abstract

The present invention relates to a powder coating composition comprising a first powder coating component dry-blended with a second powder coating component. The first powder coating component comprises a curable resin and the second powder coating component comprises a powdered organic polymer or resin having a particle size distribution in which a Dv90 value and / or a Dv50 value is less than a Dv90 value and / or a Dv50 value of the first powder coating component. In addition, a Dv90 value of the second powder coating component is 50 [mu] m or less and / or a Dv50 value of the second powder coating component is 30 [mu] m or less.

Description

Field of the Invention

[0001] The present invention relates to a powder coating composition comprising dry-mixed components, a substrate coated with the powder coating composition and a method for coating a substrate with the powder coating composition. Background of the Invention

[0003] Powder coating compositions are solid compositions that typically comprise a solid film-forming (binder) polymer or a mixture of different solid film-forming polymers. These compositions may also comprise other components, such as pigments, extenders and one or more performance additives such as plasticizers, stabilizers, degassing agents and flow aids. Film-forming polymers are typically thermosetting polymers that cure when heated, typically in the presence of a crosslinking agent, which may itself be a polymer. These polymers typically have a glass transition temperature (Tg), softening point or melting point in excess of 30°C.

[0004] The manufacture of powder coating compositions generally involves melt mixing the components of the composition. Melt mixing involves high speed, high intensity mixing of dry ingredients in a continuous compounding machine such as a single or twin screw extruder, and then heating the mixture to a temperature above the softening temperature of the uncured polymer but below the curing temperature to form a molten mixture. The extruded molten mixture is rolled into a sheet, cooled to solidify the mixture, crushed into flakes, and then pulverized into a fine powder. The powder is then typically subjected to a series of particle screening and separation operations, such as grinding, grading, sieving, screening, cyclone separation, screening and filtering.

[0005] The powder coating composition so obtained is then applied to a substrate and heated to melt and fuse the particles and cure the coating. The powder coating composition may be applied by a fluidized bed process in which the substrate is preheated and immersed in a fluidized bed of powder causing the powder to fuse and adhere to the substrate upon contact with the hot surface, by an electrostatic fluidized bed process, or by an electrostatic spray process in which the powder coating particles are electrostatically charged by electrodes or electrostatic spray guns within a fluidized bed and directed for deposition onto a grounded substrate.

[0006] Powder coating compositions are usually formulated as so-called one-component compositions prepared by melt mixing all the ingredients together. It is believed that melt mixing of all the ingredients is required to mix the film-forming compounds (curable resin and curing additives), pigments and performance additives very intimately with one another so that they can coalesce and cure to form a coherent coating having integrity and the desired properties. Occasionally, small amounts, usually up to 1% by weight, of solid additives are dry blended with the powder coating particles formed by melt mixing, especially to improve flow properties (so-called dry flow agents).

[0007] Other particulate additives, such as matting agents such as silica, extenders, color pigments, biocidal pigments and corrosion inhibiting pigments are often incorporated into the powder coating particles during the melt mixing process. As a result, the particulate additives are embedded in the resin, which may adversely affect its function. The amount of particulate additives that can be added to the melt mixing step is limited from a processability perspective. In addition, large amounts of particulate additives will result in an unacceptable reduction in surface flow during the curing of the powder coating.

[0008] Pigments with metallic effect, such as metal flakes or mica flakes, are not usually added during the melt-mixing step, since the pigment flakes will be crushed during the subsequent grinding step, which would be detrimental to the metallic effect. Such flakes are therefore usually added to the powder coating composition in a so-called bonding step. This bonding step is known in the art and generally comprises: heating the powder coating particles (obtained by melt-mixing as described above) to a temperature near the glass transition temperature, but below the solidification temperature of any base polymer in the powder coating particles, under an inert atmosphere; adding the pigment flakes with metallic effect to the heated powder coating particles under stirring while maintaining this temperature, until the pigment flakes are bonded to the powder coating particles, generally for 10-20 minutes; and cooling the powder coating composition.

[0009] However, the bonding step is time-consuming and energy-consuming and is limiting in terms of batch size and the amount of pigment that can be used. In addition, the bonding process tends to break up the pigment flakes.

[0010] Pigments with metallic effects can be dry-blended with powder coating particles. However, these compositions generally show poorer stability in spray application, reduced flowability and poorer surface appearance due to flake agglomeration and uneven coverage of metallic flakes.

[0011] WO 00 / 01774 discloses a powder coating composition comprising film-forming polymer powder coating particles having a standard particle size distribution, dry-mixed therewith at least one appearance-modifying additive and a further additive comprising wax-coated silica or consisting of aluminum oxide together with aluminum hydroxide. The appearance-modifying additive in WO 00 / 01774 may be a colored polymer material in an amount of up to 10% by weight, a fine powder of a glass-reducing polymer material, a polymer texture additive or a mica pigment or other gloss pigment.

[0012] There is a need for powder coating compositions in various aesthetic effects or various functions where the aesthetic effects or functions can be controlled while avoiding processability problems. SUMMARY OF THE INVENTION

[0014] It has now been found that functional particulate additives, such as pigments with metallic effects or other functional pigments, which would not normally pass the melt mixing step without affecting functionality or can be added in amounts, can be dry blended with powder coating components, even in relatively high amounts, without adversely affecting processability while still achieving a coherent film with the desired film properties. This can be achieved by adding or dry blending specific types of particulate additives with the powder coating component.

[0015] Thus, the present invention provides a powder coating composition comprising a first powder coating component dry mixed with a second powder coating component, wherein the first powder coating component comprises a curable resin and the second powder coating component comprises a powdered organic polymer or resin.

[0016] The particle size distributions of the first and second powder coating components are different. The second powder coating component has a D v 90 and / or D v The second powder coating component has a D value of 50 μm or less. v 90 and / or 30μm or less D v 50 value.

[0017] In a second aspect, the present invention provides a method for coating a substrate with the powder coating composition.

[0018] In a third aspect, the present invention provides a substrate coated with the powder coating composition.

[0019] In a fourth aspect, the present invention provides a method for producing the powder coating composition. DETAILED DESCRIPTION OF THE INVENTION

[0021] The powder coating composition of the present invention comprises a first powder coating component, which may be abbreviated as "first component" below. The first component comprises one or more curable resins. The first component may also be referred to as "binder".

[0022] The powder coating composition further comprises a second powder coating component, which may be abbreviated as "second component" in the following.

[0023] The first and second powder coating components are each comprised of particles. The individual powder particles in each powder coating component may comprise one or more materials.

[0024] The powder coating composition may include one or more curing additives for curing the one or more curable resins. These may be incorporated into the powder particles of the first powder coating component, or they may be incorporated into the powder particles of the second powder coating. Alternatively, they may be dry mixed separately with the first and second powder coating components. The powder coating composition typically includes one or more curing additives in the first powder coating component.

[0025] The curing additive mentioned herein refers to a compound capable of curing the curable resin, such as a curing agent cross-linked with the curable resin, or a compound that affects the curing reaction rate, such as a curing catalyst, a free radical initiator such as a thermal free radical initiator or a photoinitiator, a accelerator or an inhibitor. The curing catalyst mentioned herein refers to a compound that catalyzes the cross-linking reaction between the curable resin and the cross-linking curing agent or catalyzes the self-cross-linking reaction in the case of a self-cross-linkable curable resin.

[0026] The one or more curing additives for curing the curable resin preferably comprise a curing agent and / or a curing catalyst crosslinked with the curable resin. The crosslinking curing agent can be the resin itself, such as an epoxy resin crosslinked with a carboxyl functional polyester resin, or a polyamine resin crosslinked with an epoxy resin.

[0027] The term "curing system" can be used to include the curable resin and one or more curing additives. It should be understood that in the case of a curing system with a curable resin and a curing agent that is the resin itself, either of the two resins can be considered as the curable resin or the curing additive.

[0028] [First powder coating component]

[0029] When the powder particles of the first powder coating component contain more than one material, they can be obtained by melt mixing the constituent components in a compounder such as an extruder. When melt mixing is used, the powder particles of the first powder coating component contain a polymer that can be softened, i.e. melted, in a compounder. The polymer can be the curable resin and / or a curing agent for the curable resin that is the resin itself. Other powder coating ingredients such as pigments, extenders or performance additives, such as melt flow agents, degassing agents or dispersants, may also be optionally included.

[0030] The first powder coating composition typically comprises all of the curable resin and the one or more curing additives.

[0031] The powder particles of the first powder coating component are larger than those of the second powder coating component. v 90 and / or D v 50 particle size distribution is larger than those of the second component. In an embodiment, the first powder coating component has D v 90 is at most 150 μm and D v 50 is at most 75 μm, for example D v 90 is at most 120 μm and D v 50 is a particle size distribution of at most 50 μm, such as at most 40 μm. In other embodiments, D v 90 not less than 30μm and D v50 is not less than 20 μm. Therefore, Example D v 90 ranges include 20-150μm, 20-75μm, 20-50μm, 30-150μm, 30-75μm and 30-50μm.

[0032] D v 90 is the particle size value at which 90% of the total volume of particles has a particle size lower than this value, and D v 50 is the particle size value at which 50% of the total volume of particles has a particle size below this value. v 90 or D v A typical method for 50 is laser diffraction according to ISO 13320, which in embodiments may use the Mie model.

[0033] In an embodiment, the first powder coating component comprises so-called "bonded" powder coating particles. This means that the binder-containing first powder coating component particles contain not only the binder material and other components in any particles formed by melt mixing and extrusion, but also particles of one or more additives that are subsequently bonded to these particles. The bonding of additive particles (e.g., pigment particles) to binder-containing particles is known in the art and is typically achieved by: heating the powder coating composition under an inert atmosphere to a heating temperature near the glass transition temperature, but below the curing temperature of any binder polymer in the powder coating composition; adding the additive (e.g., solid pigment) to the heated powder coating composition under stirring while maintaining the heating temperature until the additive is bonded to the powder coating particles, typically after 10-20 minutes; and cooling the powder coating composition.

[0034] The term "cure system" may be used to describe the combination of a curable resin and one or more curing additives known to be suitable for powder coating compositions.

[0035] Suitable curable resins are, for example, carboxyl-functional resins such as carboxyl-functional polyesters, polyester-amides or (meth)acrylate-based resins; amine-functional resins such as polyamides or polyester-amide resins; hydroxy-functional resins such as hydroxy-functional polyesters; epoxy-functional resins (including glycidyl-functional resins); anhydride-functional resins; and resins having unsaturated bonds such as unsaturated polyesters.

[0036] Curing additives such as crosslinking curing agents or curing catalysts for curing such curable resins are well known in the art. Suitable curing additives for curing carboxyl functional resins are, for example, β-hydroxyalkylamides or polyisocyanates such as triglycidyl isocyanurate.

[0037] The first powder coating component comprises a curable resin. In one embodiment, the curable resin is a carboxyl functional polyester, a carboxyl functional polyacrylate, a hydroxyl functional polyester or a hydroxyl functional polyacrylate. In embodiments, it is a carboxyl or hydroxyl functional polyester. Any of these may be applied in combination with one or more curing additives selected from β-hydroxyalkylamides or polyisocyanates such as triglycidyl isocyanurate. Preferably, the curable resin is a carboxyl functional polyester or a hydroxyl functional polyester and the one or more curing additives comprise a β-hydroxyalkylamide as a crosslinking agent.

[0038] In other embodiments, this curing system can be suitably epoxy-polyester system or epoxy-amine system.In epoxy-polyester curing system, these one or more curing additives are epoxy resin and this curable resin is polyester resin with crosslinkable functional group.This epoxy resin is crosslinked with the functional group on this polyester resin.In epoxy-amine curing system, these one or more curing additives are polyamine resin and this curable resin is epoxy resin.This polyamine resin is used as the curing agent of crosslinking this epoxy resin.

[0039] In one embodiment, the curing system is capable of curing at a temperature below 160°C.

[0040] [Second powder coating component]

[0041] The powder coating composition comprises a dry-mixed second powder coating component. The second component is or comprises particles of an organic polymer or resin. When the particles comprise other components or additives, the content of the organic polymer is generally at least 60% by weight, such as at least 70% by weight.

[0042] In an embodiment, the organic polymer or resin of the second component is chemically different from the curable resin of the first component. The powder particles comprising the organic polymer or resin have a v 90 and / or D v 50 is less than the particle size distribution of the first powder coating component. In an embodiment, D v 90 is 50 μm or less, for example 40 μm or less, such as 30 μm or less, 25 μm or less. In an embodiment, D v 90 is at least 3 μm, for example at least 5 μm. In an embodiment, D v The 90 value may fall within the range of 3-50 μm, 3-40 μm, 3-30 μm or 3-25 μm. In an embodiment, the particle size distribution also or alternatively has a D of 30 μm or less, such as 20 μm or less, such as 10 μm or less. v 50. In other embodiments, D v 50 value is at least 1 μm and D vThe 50 value may range from 1-30 μm, 1-20 μm or 1-10 μm.

[0043] Particles having such properties can be produced by jet milling and therefore in embodiments they are so-called jet milled powders.

[0044] In an embodiment, the second powder coating component has a particle size distribution such that D v 90 and D v 50 ratio is in the range of 1.5-4.0.

[0045] In embodiments, the second powder coating component is the most negatively charged powder coating component relative to the first powder coating component and also relative to any other dry-blended components of the coating composition. Generally speaking, smaller organic particles tend to have a higher charge / mass ratio than larger organic particles. The use of certain additives can also modify this charge / mass ratio difference.

[0046] In embodiments, the second powder coating component comprises one or more polymers or resins selected from polyesters, polyurethanes, polyureas, epoxy resins, polycarbonates, any combination of two or more thereof, and polymers or resins having the characteristics of any two or more thereof. The polymer is typically a functional polymer and / or a curable polymer so that it can form a chemical bond with the material in the first powder coating component. For example, the organic polymer can be a hydroxyl or carboxyl functional organic polymer. In other embodiments, it can be a curable polymer, so that the second powder coating component comprises both the organic polymer and a curing agent / hardener or crosslinking agent.

[0047] In embodiments, the organic polymer is selected from polyesters and polyurethanes.In embodiments, the second powder coating component comprises an organic polymer and a hardener / curing agent, ie a polyester and an isocyanate, or a polyester and a hydroxyalkylamide such as a beta-hydroxyalkylamide.

[0048] In embodiments, the powder coating composition comprises the second powder coating component in the range of 0.1-25 wt%, preferably 0.2-15, more preferably 0.3-8.0 wt%.

[0049] [additive]

[0050] The powder coating composition may include one or more additives different from the second powder coating component. In embodiments, these may be selected from stabilizers, leveling agents, anti-settling agents, matting agents, rheology modifiers, preservatives, flexibilizers, surfactants, UV light absorbers, light stabilizers, amine synergists, waxes, adhesion promoters, fillers, pigments, flow control agents, degassing agents and antioxidants.

[0051] The total amount of these additional components may be in the range of 0-40 wt%, such as 0-35 wt% or 0-30 wt%. When any of such additional components are present, their minimum concentration (individually or cumulatively) in the powder coating composition is typically at least 0.05 wt%, such as at least 0.1 wt%.

[0052] Each additive may have an average particle size (D v 50).

[0053] Any one or more of these additives may be incorporated into the first powder coating component, for example by being included in the extrudate with the curing system ingredients or bonded to the particles of the first powder coating component. Alternatively or additionally, they are dry blended separately from the first and second powder coating components as additional dry blended powder coating components.

[0054] The additional dry-blended powder coating components (i.e. in addition to the first and second powder coating components) may be inorganic particulate components. For example, they may be selected from inorganic particulate materials that provide functionality to the powder coating composition, such as inorganic color pigments, inorganic effect pigments such as metallic effect pigments, biocidal pigments, anticorrosive pigments, extenders, opacifying pigments, conductive or antistatic pigments, infrared absorbing pigments, radiation shielding pigments, glass flakes, anti-wear agents or any combination of two or more thereof.

[0055] The total amount of additional components dry blended may be up to 35 wt%, for example up to 30 wt% or up to 25 wt%.

[0056] [Improved Effect]

[0057] A particular advantage of the present invention is that additional dry-mixed components can be incorporated at higher concentrations than previously possible without causing inhomogeneities in the resulting coating. This means that it is not always necessary to melt-mix or bond them to the binder-containing particles. This is particularly advantageous for additives (e.g. effect pigments) which are typically bonded to the first powder coating particles, as it avoids the need for a separate heating step. In addition, a higher total amount of effect pigments (and / or other additive particles) can be included in the powder coating composition. For example, bonded effect pigments can typically only be included in a concentration of up to 5 or 6 wt.-% based on the amount of the first powder coating component (i.e., the binder-containing particles). In the present invention, embodiments may include much higher concentrations (e.g., up to 35 wt.-%) based on the total weight of the powder coating composition. In addition, it is sometimes not possible to incorporate components such as effect particles during melt mixing and extrusion because they may be damaged and deformed.

[0058] The invention is particularly useful for coatings containing effect pigments, such as metallic, pearlescent, lustrous or glamorous effect pigments. These are generally based on platelet-like inorganic particles, such as mica or metal particles. For the sake of brevity, these may be abbreviated herein as "effect particles".

[0059] To avoid separation problems, such effect particles generally tend to be bonded to or otherwise incorporated into the binder-containing particles of the curing system. Otherwise, if simply dry-mixed, they tend to easily separate from the rest of the composition. For example, they may preferentially stick to the walls of a storage container or spray equipment. In addition, they may also preferentially migrate to substrate surfaces, particularly grounded substrates, causing reduced adhesion to the rest of the powder coating particles. This may also result in non-uniformity in color or appearance, such as a "frame" effect around substrate defects.

[0060] In the present invention, the use of a second powder coating component avoids these effects, significantly reduces the adhesion of additional dry-mixed particles (e.g., effect particles) to the walls of the reservoir or equipment and provides a much more uniform and consistent deposition during spray application, giving improved uniformity in both color and other appearance effects (e.g., metallic or sparkling effects from metallic effect particles). It also avoids loss of adhesion of the powder particles.

[0061] Thus, in embodiments, the powder coating composition comprises one or more effect pigments, for example inorganic effect pigments (such as metallic effect pigments or pearlescent effect pigments) as dry-blended additional powder coating components. In other embodiments, the first powder coating component additionally comprises one or more bound effect pigments.

[0062] In an embodiment, the powder coating composition comprises one or more effect pigments in a total concentration in the range of 1.0-35 wt%, such as 3.0-30 wt%, for example 7-30 wt%, based on the total weight of the powder coating composition. In an embodiment, the upper limit is 20 wt% or less. The total effect pigment concentration includes the sum of dry blended effect pigments and any effect pigments bonded or melt mixed with the first powder coating component.

[0063] The effect pigment particles may be dry blended with the powder particles of the first and second powder coating components. In other embodiments, at least a portion of the effect pigment is bonded to the particles of the first powder coating component. In embodiments, at least 1 wt%, such as at least 3 wt%, of the effect pigment is dry blended based on the total weight of the powder coating composition. In embodiments, the amount of dry blended effect pigment may be up to 35 wt%, such as up to 25 wt%. Thus, the range of dry blended effect pigment may be in the range of 1-35 wt%, such as 3-35 wt%, 1-25 wt%, or 3-25 wt%. In embodiments, the upper limit is 20 wt% or 15 wt%.

[0064] In an embodiment, the effect pigment is a metallic effect pigment, which may optionally be a metal or a metal alloy. In an embodiment, the metal may be selected from aluminum, aluminum alloys, stainless steel, copper, tin, bronze and brass. The metal may be in the form of flakes and may be selected to produce various metallic effects, including those referred to as "metallic", "effect", "gloss", "charm" or "pearlescent" effects. The metallic effect pigment may also be a non-metallic compound, for example selected from mica and borosilicates.

[0065] In embodiments, the effect pigment particles may be coated, for example with silica or other inert inorganic materials to improve chemical resistance and durability. Alternatively, the particles may be coated with a plastic material used for similar purposes, such as an acrylic plastic material, PFTE or a thermosetting plastic material. In other embodiments, the particles may be provided in a polymer or plasticizer that is compatible with the film-forming binder of the powder coating composition. In other embodiments, the effect pigment particles may be coated with a colorant such as a metal oxide pigment, for example iron oxide, to provide special color effects.

[0066] Effect pigments such as metallic effect pigments are well known and commercially available. Suitable examples of commercially available metallic effect pigments include Standart PU aluminum powder (available from Eckart) and SILBERCOTE PC X (available from Silberline).

[0067] Such metal effect pigments are generally in the form of flakes or plate-like particles, powders or granules. In embodiments, they are flakes or plate-like particles. In embodiments, the metal effect pigments are coated or uncoated aluminum flakes. In other embodiments, they are plate-like inorganic oxide or mixed oxide particles (such as mica or borosilicates as described above). The volume average particle size (D v 50) may be in the range of 10-100 μm, such as in the range of 15-50 μm.

[0068] [Inorganic particulate component]

[0069] Separately from any effect pigments, the powder coating composition may in embodiments comprise at least one dry-mixed inorganic particulate additional component. In other embodiments, the inorganic particulate additional component consists of inorganic components i), ii) and iii), wherein:

[0070] - component i) is uncoated alumina or uncoated silica;

[0071] - component ii) is aluminum hydroxide and / or aluminum oxyhydroxide; and

[0072] - Component iii) is silicon dioxide.

[0073] The dry-blended inorganic particulate additive comprises a first silica and a second silica, wherein the first silica is a surface-treated silica having a negative tribocharge and the second silica is an uncoated silica or a surface-treated silica having a positive tribocharge.

[0074] Thus, if component i) is uncoated silica, component iii) does not contain uncoated silica. If component i) is uncoated alumina, component iii) contains the first silica and the second silica. If component i) is uncoated silica, component iii) contains surface-treated silica having a negative triboelectric charge. Preferably, component iii) contains the first silica and the second silica.

[0075] Silica, which has a negative triboelectric charge, is itself triboelectrically negatively charged by contact with other foreign particles, but imparts a negative charge on the powder coating particles upon mixing due to particle-particle adhesion and encapsulation of powder particles.

[0076] Silica, which has a positive triboelectric charge, itself becomes positively triboelectrically charged by contact with other dissimilar particles, but imparts a positive charge on the powder coating particles upon mixing due to particle-particle adhesion and encapsulation of powder particles.

[0077] The charge imparted by silica on the powder coating particles can be determined by mixing the silica with particles of the powder coating component and then determining on which electrode (negative or positive) the mixture preferentially deposits.

[0078] Suitable types of inorganic particulate additional components are described, for example, in WO 2021 / 245043, WO 2021 / 245044, WO 2021 / 245045 and WO 2021 / 245046.

[0079] The dry-blended inorganic particulate additives may be surface treated with organic compounds to modify their surface properties.

[0080] The various components of the powder coating composition are usually dry mixed together in a powder drum or other suitable mixing apparatus. The components may be added to one another simultaneously or separately.

[0081] Without wishing to be bound by any theory, it is believed that the second powder coating component has a more negative triboelectric charge than the other powder coating components, and thus it preferentially binds to the substrate surface, particularly the grounded surface which tends to be positively charged. This prevents the other dry-blended powder coating components from separating from each other and improves the uniformity of their distribution. One way to achieve this is to ensure that its particle size (i.e., its D v 90 and D v 50 value) is less than at least the first powder coating component and in embodiments less than all other dry-blended powder coating components.

[0082] The terms coated and surface treated in connection with the particles of the powder coating composition are used interchangeably herein.

[0083] [Paint application]

[0084] The substrate may be any substrate suitable for powder coating, such as metal, wood, plastic or a substrate comprising any of these materials. In an embodiment the substrate is a metal substrate.

[0085] The substrate surface may be treated prior to application of the powder coating composition to remove any contaminants and / or to improve the corrosion resistance of the substrate.Such surface treatments are well known in the art and are typically applied to surfaces to be coated with powder coatings.

[0086] The powder coating composition of the present invention can be applied as a topcoat over a first layer of powder coating composition. In this case, the first layer can be a powder coating composition different from those described herein. Thus, in one embodiment, the substrate is coated with a first layer of a first powder coating composition and then coated with a second layer of the powder coating composition of the present invention.

[0087] The powder coating composition can be applied by any application technique known in the art, such as fluidized bed application or spray application, preferably corona gun spray application.

[0088] The invention will now be illustrated by the following non-limiting examples. Example

[0089] [First powder coating component (binding particles)]

[0090] The powder coating particles (used as the first powder coating component) are prepared by melt mixing and extruding the constituent components (except the effect pigments) and then grinding the cooled hardened extrudate to form melt extruded particles. The effect pigments are then bonded to these "melt extruded particles" as described above to form "bonded particles".

[0091] The main ingredients used to form the bonded particles are listed in Table 1 and the amounts used are listed in Table 2.

[0092] Table 1 - Main components of bonded particles (first powder coating component)

[0093]

[0094] Table 2 - Composition of the bonded particles (first powder coating component)

[0095]

[0096] [1] Total amount of surface modifier, degassing agent, antioxidant and rheology modifier [second powder coating component]

[0097] These are jet mill particles comprising an organic polymer / resin and a crosslinker in the ratios shown in Table 3. They are dry blended with the other powder coating ingredients to form the powder coating composition.

[0098] Table 3 - Properties of polymer particles (second powder coating component)

[0099] Components 2A 2B Resin Polyester Polyester Resin content (weight %) 94.1 74.2 Crosslinking agent (wt%) 3.3[1] 13.5[2] Dv50(μm) 3.50 5.12 Dv90(μm) 5.77 7.65

[0100] [1]β-Hydroxyalkylamide (HAA)

[0101] [2] Cycloaliphatic polyuretdione

[0102] [Inorganic particulate component]

[0103] These are blends of various inorganic oxides and hydroxides which are subsequently dry blended with the other powder coating ingredients to form the powder coating composition. The relevant details are listed in Table 4.

[0104] Nano-sized particles were prepared by dry blending alumina and aluminum hydroxide together and blending in a high shear Waring blender for 3 minutes. Silica (if used) was then added to the blender and the contents were mixed under high shear for an additional minute.

[0105] Table 4 - Properties of Inorganic Particulate Components (Weight %)

[0106] Components 3A 3B 3C Aluminum hydroxide 90 68 60 Alumina 10 22 20 Fumed Silica - 10 20

[0107] [Powder coating composition]

[0108] These were formed by dry blending the above components in the amounts shown in Table 5. Dry blending was performed using a laboratory scale turbine mixer operated at 500 rpm for 5 minutes.

[0109] Table 5 - Powder coating composition (wt%)

[0110]

[0111]

[0112] *Comparative ratio

[0113] [Test 1—Coating Uniformity]

[0114] The steel panels were coated using a handheld corona spray gun at 40 kV and 80 kV. The coating uniformity was checked for appearance. The changes in color consistency and consistency of the sparkle effect were also checked for each panel at different voltages.

[0115] Inventive Examples 2 and 4-8 all show very good coating uniformity and high coverage of the panels at different voltages, including at the edges of the panels. There are also no differences in color and sparkle effects between the panels coated at different voltages.

[0116] On the other hand, Comparative Examples 1 and 3 showed poor coating consistency at both voltages, with little or no coverage at the edges of the panels, and often large non-uniform areas across the panel. The color and sparkle also varied widely between panels coated at different voltages.

[0117] [Test 2—Electrostatic Adhesion]

[0118] The panels were coated using a hand-held corona spray gun at 60 kV and 80 kV. The edge of each panel was then tapped three times on the floor of the spray booth and the extent of coating loss was observed.

[0119] Inventive Examples 2 and 4-8 showed very little loss of the powder coating from each panel, with the vast majority remaining on each panel. Comparative Examples 1 and 3, on the other hand, showed significant loss of the powder coating from each panel, with large patches of exposed substrate.

[0120] [Test 3—Contamination]

[0121] A visual inspection of the powder coating blending equipment was performed to see how much contamination from mica-based effect pigments occurred. Contamination with effect pigments is problematic when the equipment needs to be used with different colored powder coatings or coatings with different effect pigments.

[0122] Inventive Examples 2 and 4-8 produced very little contamination from effect pigments. There was a thin coating of fine particles from the second powder coating component, but this contamination was easily removed by blowing compressed air on the surface. Comparative Examples 1 and 3, on the other hand, left a large amount of effect pigment on the surface, which was not easily removed even after compressed air treatment.

[0123] The spraying equipment was also visually inspected. For the inventive examples, there was again little to no contamination with effect pigments. In relation to the mixing vessel, there was a thin coating of some fine particles of the second powder coating component in the grounded area of ​​the fluidized bed portion of the spraying equipment and also on the walls of the spray booth. However, this was easily removed using compressed air. In contrast, the comparative examples left a large amount of effect pigment deposits on the grounded part and perforated plates of the fluidized bed unit of the spraying equipment. Furthermore, the effect pigments were seen to preferentially deposit on the walls and floor of the spray booth. Table 6 summarizes the coating properties of the powder coating examples.

[0124] Table 6 - Coating properties

[0125]

Claims

1. A powder coating composition comprising a first powder coating component dry mixed with a second powder coating component, wherein the first powder coating component comprises a curable resin and the second powder coating component comprises a v 90 value and / or D v 50 value is less than the D of the first powder coating component v 90 value and / or D v 50 and wherein the D of the second powder coating component v 90 value is 50 μm or less and / or the D v The value 50 is a powdered organic polymer or resin having a particle size distribution of 30 μm or less.

2. A powder coating composition according to claim 1 comprising one or more curing additives for curing the curable resin.

3. A powder coating composition according to claim 2, wherein one or more curing additives are present in the first powder coating component.

4. A powder coating composition according to any one of claims 1 to 3, wherein the particles of the first powder coating component have a v 90 is at most 150 μm and / or a particle size distribution with a Dv50 of at most 75 μm.

5. A powder coating composition according to claim 4, wherein the particles of the first powder coating component have a particle size distribution according to one or more of the following: -D up to 150μm or 120μm v 90 value; - D of at least 30 μm or at least 40 μm v 90 value; -D in the range of 30-150μm or 40-120μm v 90 value; - D up to 75μm, 50μm or 40μm v 50 value; - D of at least 20 μm or 30 μm v 50 value; - D in the range selected from 20-75 μm, 20-50 μm, 20-40 μm, 30-75 μm, 30-50 μm and 30-40 μm v 50 value.

6. A powder coating composition according to any one of claims 1 to 5, wherein the particles of the second powder coating component have a particle size distribution according to one or more of the following: - D up to 40μm, 30μm or 25μm v 90 value; - D of at least 3μm or 5μm v 90 value; - D in the range selected from 3-50 μm, 5-40 μm, 5-30 μm and 5-25 μm v 90 value; - D up to 25μm, 20μm or 10μm v 50 value; - D of at least 1 μm v 50 value; - A Dv50 value in a range selected from 1-30 μm, 1-25 μm, 1-20 μm and 1-10 μm.

7. A powder coating composition according to any one of claims 1 to 6, wherein the first powder coating component comprises: (i) a curable resin selected from carboxyl and hydroxyl functional polyester resins and a curing additive selected from β-hydroxyalkylamides and polyisocyanates; (ii) a curable resin selected from cross-linkable polyesters and a curing additive selected from epoxy resins; or (iii) a curable resin selected from epoxy resins and a curing additive selected from polyamine resins.

8. A powder coating composition according to any one of claims 1 to 7, wherein the second powder coating component comprises one or more organic polymers or resins selected from polyesters and polyurethanes.

9. A powder coating composition according to any one of claims 1 to 8, additionally comprising one or more additives.

10. A powder coating composition according to claim 9, wherein at least a portion of the one or more additives are dry blended as an additional powder coating component.

11. A powder coating composition according to claim 9 or 10, wherein at least one additive is an effect pigment, at least a portion of which is dry-blended as an additional powder coating component.

12. A powder coating composition according to claim 11, wherein the effect pigments are inorganic.

13. A powder coating composition according to any one of claims 1 to 12, wherein the tribocharge of the second powder coating component is more negative than the tribocharge of the first powder coating component and also any dry-blended additional powder coating components.

14. A substrate coated with a powder coating composition according to any one of claims 1 to 13.

15. A method of coating a substrate, comprising applying a powder coating composition according to any one of claims 1 to 13 to a surface of the substrate and curing the powder coating composition.

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