Low temperature cure powder coating compositions and articles formed therefrom

Abstract

A low-temperature-cure powder coating composition and an article formed therefrom. The powder coating composition includes a polyester resin, a triglycidyl isocyanurate (TGIC) curing agent, a β-hydroxyalkylamide (HAA) curing agent, and a leveling agent, the leveling agent being a polymeric material in solid form having a melting point of less than 100°C and a melt viscosity of less than 2000 mPa·s when measured at 200°C using a Brookfield viscometer. The powder coating composition can be cured at a temperature of 140°C or less without the addition of any curing accelerator. Furthermore, the coating formed by curing the powder coating composition is substantially free of pores.

Description

[Technical Field]

[0001] This application relates to powder coating compositions, particularly low temperature cure powder coating compositions that use both TGIC and HAA as curing agents, and articles formed therefrom. [Background technology]

[0002] Powder coatings are widely used to provide decorative and / or protective coatings on substrates. Powder coatings are completely different from conventional coatings in that they exist in the form of a fine powder and do not use solvents. Powder coatings are non-toxic, highly efficient, resource-saving, and environmentally friendly. With the development of powder coatings, great progress has been made, and their application fields are expanding year by year.

[0003] Polyester-based powder coatings are one of the common thermosetting powder coatings available on the market, and are generally formulated with polyester resin as the base material and triglycidyl isocyanurate (TGIC) as the curing agent. These powder coatings have good development prospects due to their good compatibility with existing coating types and low raw material and manufacturing costs. However, the curing temperatures of these polyester-type powder coatings are usually high, which inevitably increases energy consumption and reduces the production rate of the coatings.

[0004] Therefore, under the national policy of energy conservation and emission reduction, there is a need in the market for polyester resin-based powder coating compositions that are suitable for curing at low temperatures (especially below 140°C). Summary of the Invention

[0005] In one aspect, the present application provides a powder coating composition comprising a polyester resin, a triglycidyl isocyanurate (TGIC) curing agent, a β-hydroxyalkylamide (HAA) curing agent, and a leveling agent, wherein the leveling agent is a polymeric material in solid form having a melting point less than 100° C. and a melt viscosity less than 2000 mPa·s when measured at 200° C. using a Brookfield viscometer. Preferably, the leveling agent has a melting point in the range of 40 to 100° C. and / or a melt viscosity in the range of 800 to 2000 mPa·s when measured at 200° C. using a Brookfield viscometer.

[0006] In a preferred embodiment of the present invention, the polyester resin comprises a mixture of a first polyester resin and a second polyester resin, the first polyester resin having a glass transition temperature of less than 60°C, and the second polyester resin having a melt viscosity as low as 3000 mPa·s when measured at 200°C using a Brookfield viscometer.

[0007] Alternatively, the present invention provides an article comprising a substrate and a coating formed from the powder coating composition according to the first aspect of the present invention applied directly to the substrate, preferably the substrate comprising a metal substrate, a wood substrate, a plastic substrate, a glass substrate, a ceramic substrate, or a combination thereof.

[0008] In the powder coating composition according to the present invention, a polyester resin is used as a base material, and both triglycidyl isocyanurate (TGIC) and β-hydroxyalkylamide (HAA) are combined as curing agents. By matching these two curing agents with a leveling agent having specific melting properties, the resulting powder coating composition can be made suitable for low-temperature curing (e.g., 140°C or less). This addresses the problem of pinholes appearing on the surface of coatings, especially thickly applied coatings, caused by the use of HAA curing agents. Therefore, coatings formed from such powder coating compositions are substantially free of pores on their surfaces, even for coatings with thicknesses of up to 120 micrometers or more. Preferably, in the powder coating composition according to the present invention, a combination of a first polyester resin having a specific glass transition temperature and a second polyester resin having a specific melt viscosity is selected as the polyester resin. This is particularly advantageous for further improving the low-temperature curing properties of the powder coating composition formulated therefrom and the coating properties of the resulting coating.

[0009] The present inventors have surprisingly found that the combination of triglycidyl isocyanurate (TGIC) and β-hydroxyalkylamide (HAA) as curing agents in powder coating compositions not only facilitates low-temperature cure performance and reduces the amount of cure accelerator, but also significantly improves the storage stability of the resulting powder coating compositions, a finding that was not foreseeable prior to the present application. Furthermore, the present inventors have surprisingly found that the addition of a weatherable polyester containing 5% active polyester component as a cure accelerator in the formulation of powder coating compositions not only lowers the cure temperature and increases the cure rate of the resulting powder coating compositions, but also does not adversely affect the weatherability of the resulting coatings, as occurs with conventional cure accelerators. Instead, this improves the leveling and weatherability of the resulting coatings.

[0010] The details of one or more embodiments of the invention are set forth in the specification below. Other features, objects, and advantages of the invention will become apparent from the specification and claims.

[0011] definition As used herein, "a," "an," "the," "at least one," and "one or more" are used interchangeably. Thus, for example, a coating composition that includes "an" additive can be interpreted to mean that the coating composition includes "one or more" additives.

[0012] Throughout this application, when a composition is described as having, including, or comprising particular components or fractions, or a process is described as having, including, or comprising particular process steps, it is contemplated that the composition or process disclosed herein may further include other components or fractions or steps, whether or not specifically referred to in the present invention, so long as such components or steps do not affect the basic and novel characteristics of the invention, but it is also contemplated that the composition or process may consist essentially of or consist of the recited components or steps.

[0013] For brevity, only certain ranges are explicitly disclosed herein. However, a range from any lower limit may be combined with any upper limit to recite a range not explicitly recited, and a range from any lower limit may be combined with any other lower limit to recite a range not explicitly recited, and similarly, a range from any upper limit may be combined with any other upper limit to recite a range not explicitly recited. Furthermore, a range includes every point or individual value between its endpoints, even if not explicitly recited. Thus, every point or individual value can serve as its own lower or upper limit in combination with any other point or individual value or any other lower or upper limit to describe a range not explicitly recited.

[0014] The term "glass transition temperature (Tg)" when used in connection with the "first polyester resin and the second polyester resin" refers to the measured Tg of the corresponding resin. According to the present invention, the glass transition temperature of the polyester resin is measured by DSC differential scanning calorimetry (DSC) according to ISO 11357.

[0015] The term "acid number" (AV) when used in connection with the "first polyester resin and the second polyester resin" refers to the measured AV of each resin. According to the present application, the acid number (AV) (mg KOH / g resin) of the lateral polyester resin is measured by titration according to ISO 2114-2000. The acid number of the polyester resin is a measure of the amount of carboxylic acid groups in the polyester resin.

[0016] In the context of this application, the term "viscosity" or equivalently "melt viscosity" refers to the melt viscosity (MPa.s) of the melt at 200°C, as measured in a Brookfield CAP 2000+H viscometer at 200°C. The applied shear rate is 21 s -1 and a 19.05 mm spindle, i.e., a conical spindle CAP-S-05 (19.05 mm, 1.8°), is used.

[0017] In the context of the present invention, the term "polyester resin" refers to a polyester resin having primarily carboxylic acid functionality but not excluding hydroxyl functionality, and is therefore called a carboxylic acid functional polyester resin, the acid number of which is significantly higher than its hydroxyl number.

[0018] The term "active polyester" when used in connection with "curing accelerator" refers to a polyester resin that can react physically and / or chemically with the components contained in the coating composition, particularly the curing agent, including, but not limited to, polyester resins that are capable of physical entanglement and chemical crosslinking.

[0019] In the context of the present invention, the term "composition" denotes a combination and / or mixture of different chemical substances and / or components forming a whole.

[0020] In the context of the present invention, the term "powder" denotes a solid material which is substantially dry at room temperature and atmospheric pressure and which has been reduced to a fine, loose particle state, the individual particles having a maximum particle size at 23°C and atmospheric pressure of preferably at most 200 μm, more preferably at most 180 μm, even more preferably at most 160 μm, most preferably at most 150 μm, particularly at most 140 μm, more particularly at most 130 μm, most particularly at most 120 μm, such as at most 110 μm, for example at most 100 μm, such as at most 90 μm, and the individual particles having a minimum particle size at 23°C and atmospheric pressure of preferably at least 10 μm, more preferably at least 15 μm, even more preferably at least 20 μm, most preferably at least 25 μm, particularly at least 30 μm, more particularly at least 35 μm, most particularly at least 40 μm, such as at least 45 μm, for example at least 50 μm, such as at least 60 μm, for example at least 70 μm. A particle is defined as a small body that a) has an average linear size as described herein and b) behaves as a single unit in terms of its transport and performance. The method used to measure the particle size of the powder coating composition of the present invention is sieve analysis.

[0021] In the context of the present invention, the term "curing" refers to a process by which a material becomes "set" to form an irreversible crosslinked network (the so-called "set form" or "cured composition") that does not flow, melt, or dissolve. As used herein, the terms "curing" and "crosslinking" are used interchangeably.

[0022] In the context of the present invention, the term "powder coating" denotes a cured powder coating composition in the form of a coating. A powder coating is obtained upon curing of a powder coating composition.

[0023] The phrase "substantially free of pores" when used in connection with a "coating formed from a powder coating composition" means that the surface of the coating is smooth, e.g., no pinholes are detectable with the naked eye or when viewed under an optical microscope, preferably at 10x, 20x, or even 50x magnification.

[0024] Unless the context clearly indicates otherwise, the plural forms of terms used herein (e.g., polyester resins, curing agents, powder coating compositions, components, etc.) may be construed as including the singular form of the term, and vice versa.

[0025] For purposes of the present invention, ranges of values ​​defined by endpoints include all values ​​within that range, e.g., a range of 1 to 5 encompasses the values ​​1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc. Furthermore, disclosed ranges of values ​​include all subset ranges within that broader range, e.g., a range of 1 to 5 includes the subranges 1 to 4, 1.5 to 4.5, 1 to 2, etc.

[0026] The terms "preferred" and "preferably" refer to embodiments of the invention that may offer certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] In one aspect, the present embodiment of the present application provides a powder coating composition comprising a polyester resin, a triglycidyl isocyanurate (TGIC) curing agent, a β-hydroxyalkylamide (HAA) curing agent, and a leveling agent, wherein the leveling agent is a polymeric material in solid form having a melting point less than 100°C and a melt viscosity less than 2000 mPa·s as measured at 200°C using a Brookfield viscometer.

[0028] Under national policies for energy conservation and emission reduction, low-temperature curing powder coating compositions are attracting increasing attention and are expected to become a preferred product in the powder coating industry in the future. Currently, low-temperature curing powder coating products are generally immature on the market, leaving ample room for improvement. To this end, the present invention provides a novel low-temperature curing powder coating composition. The powder coating composition according to an embodiment of the present invention uses a polyester resin as a base material, a combination of triglycidyl isocyanurate (TGIC) and a β-hydroxyalkylamide (HAA) as a curing agent, and further contains a leveling agent with specific melting properties. As a result, the resulting powder coating composition is suitable for low-temperature curing (e.g., 140°C or less) and can address the problem of pinholes appearing on the surface of coatings, especially thickly applied coatings, caused by the use of HAA curing agents. Therefore, coatings formed from such powder coating compositions are substantially free of pores on their surface, even at thicknesses of up to 120 micrometers or more, e.g., 200 micrometers.

[0029] In an embodiment of the present invention, the polyester resin serving as the base material may be a linear or branched polyester resin. Preferably, the polyester resin is a linear polyester resin having an average functionality of about 2, formed, for example, by polycondensation of a dibasic carboxylic acid and a diol. A polyester resin having a linear structure is advantageous for formulating a powder coating composition with good leveling properties.

[0030] In embodiments according to the present invention, the polyester resin is suitable for TGIC curing and / or HAA curing and therefore may also be referred to as a carboxylic acid-functionalized polyester resin. In the present invention, the acid number of the polyester resin is an important parameter for both the leveling performance and low-temperature cure characteristics of the TGIC-cured and / or HAA-cured powder coatings formulated therefrom. Therefore, the acid number of the polyester resin according to the present invention is selected within the range of 32 to 38 mg KOH / g resin, preferably within the range of 32 to 36 mg KOH / g resin.

[0031] In some embodiments according to the present invention, the polyester resin may have a hydroxyl value of some magnitude in addition to the carboxylic acid functionality. However, considering that the polyester resin of the present invention is cured using a TGIC cure and / or an HAA cure, the hydroxyl value (OHV) does not exceed 10 mg KOH / g resin, preferably 8 mg KOH / g resin or less, even more preferably 6 mg KOH / g resin or less, even more preferably 4 mg KOH / g resin or less, and most preferably 3 mg KOH / g resin or less.

[0032] In some embodiments according to the present invention, the polyester resin may have a glass transition temperature (Tg) within a specific range. The Tg can be measured by differential scanning calorimetry (DSC) according to ISO 11357 at a heating rate of 5°C / min. Surprisingly, the present inventors have found that the presence of a polyester resin having a specific Tg in a powder coating composition can significantly improve the low-temperature cure characteristics of the coating, such that powder coating compositions formulated therefrom can be cured at temperatures as low as 140°C. Preferably, the polyester resin has a Tg as low as 60°C, and preferably between 55 and 58°C.

[0033] In some embodiments according to the present invention, the polyester resin can have a specific melt viscosity as measured at 200°C using a Brookfield viscometer. Surprisingly, the present inventors have found that the presence of a polyester resin having a specific melt viscosity in a powder coating composition can significantly improve the leveling properties of the coating, resulting in a higher gloss coating. Preferably, the polyester resin has a melt viscosity as low as 3000 mPa·s, and preferably in the range of 2000 mPa·s to 2500 mPa·s.

[0034] The present inventors have surprisingly found that by adjusting the combination of polyester resins in formulating powder coating compositions according to the present invention, the low-temperature cure and film-forming properties of the powder coating compositions can be further tuned. Accordingly, in some preferred embodiments according to the present invention, the polyester resin may be a combination of a first polyester resin and a second polyester resin. Preferably, the first polyester resin has a glass transition temperature of less than 60°C, preferably in the range of 55-58°C. Optionally, the first polyester resin may have a melt viscosity of 5000 mPa·s to 35000 mPa·s, as measured at 200°C using a Brookfield melt viscometer. Preferably, the second polyester resin may have a melt viscosity as low as 3000 mPa·s, preferably in the range of 1500 mPa·s to 2500 mPa·s, as measured at 200°C using a Brookfield melt viscometer. Optionally, the second polyester resin may have a glass transition temperature of less than 65° C., preferably in the range of 55 to 63° C. In some embodiments according to the present invention, both the first polyester resin and the second polyester resin have an acid number in the range of 32 to 38 mg KOH / g resin.

[0035]

[0013] Surprisingly, the present inventors have found that selecting a combination of a first polyester resin having a specific glass transition temperature as described above and a second polyester resin having a specific melt viscosity as described above as the polyester resin in a powder coating composition according to the present invention is particularly advantageous for further improving the coating properties of the resulting coating as well as the low temperature cure properties of the powder coating composition formulated therefrom.

[0036] In a preferred embodiment according to the present invention, the powder coating composition comprises at least 80 wt. % polyester resin, based on the total weight of the powder coating composition. Preferably, the polyester resin is present in an amount ranging from 80 wt. % to 90 wt. % based on the weight of the powder coating composition, and more preferably, the polyester resin is present in an amount ranging from 85 wt. % to 90 wt. % based on the weight of the powder coating composition. Preferably, in embodiments where the polyester resin is a combination of a first polyester resin and a second resin, the weight ratio of the first polyester resin to the second polyester resin is in the range of 1:2 to 2:1, preferably in the range of 1:1.5 to 1.5:1, and more preferably in the range of 1:1.3 to 1.3:1.

[0037] By way of example, the polyester resin may be commercially available or may be prepared as desired. In some embodiments according to the present invention, the polyester resin may be Kinte NH-9362, commercially available from DynaSky, or Allnex 4430, commercially available from Allnex.

[0038] In an embodiment of the present invention, a combination of triglycidyl isocyanurate (TGIC) and a β-hydroxyalkylamide (HAA) is used as a curing agent in the formulation of a powder coating composition. As used herein, "curing agent" refers to a compound that can be used as a crosslinker for acid-functionalized polyester resins or carboxyl-protected polyester resins. Typically, this type of curing agent or crosslinker includes, for example, epoxy-functionalized compounds, amides, substituted alkylamides, bisamides, and the like. However, in the formulation of the powder coating composition of the present invention, the curing agent is specifically a combination of TGIC and HAA. TGIC is a triazine compound with reactive epoxy functionality and is considered in the art to be a preferred curing agent for acid-functionalized resins (e.g., acrylic resins, polyester resins, etc.), and HAA is a compound with four active hydroxyl groups in its molecular structure that undergoes a dehydration polycondensation reaction with carboxyl groups. Surprisingly, the present inventors have found that the use of a combination of triglycidyl isocyanurate (TGIC) and β-hydroxyalkylamide (HAA) as a curing agent in formulating powder coating compositions according to the present invention not only facilitates low-temperature curing and a reduction in the amount of curing accelerator, but also significantly improves the storage stability of the resulting powder coating compositions. For example, the powder coating compositions can be stored at a temperature of 40°C for 20 days or more, or at a temperature of 30°C for 6 months, or even at a temperature of 24°C for 6 to 12 months, without any aggregation and / or crosslinking.

[0039] In a preferred embodiment according to the present invention, the powder coating composition comprises 5-8 wt. %, preferably 6-8 wt. %, of a TGIC curing agent and 1-3 wt. %, preferably 1.5-3 wt. %, of an HAA curing agent, based on the total weight of the powder coating composition.

[0040] In formulating polyester-type powder coating compositions, HAA-type curing agents have the advantages of low dosage, low curing temperature, and non-toxicity, but their high volatility inevitably leads to the problem of pinholes appearing on the coating surface. Surprisingly, the inventors of the present application have discovered that the problem of pinholes on the surface of the resulting coating film, especially thick ones, caused by the use of HAA curing agents can be solved by formulating a powder coating composition using a polyester resin as the base material, a combination of triglycidyl isocyanurate (TGIC) and a β-hydroxyalkylamide (HAA) as the curing agent, and a leveling agent with specific melting properties. As a result, coatings formed from such powder coating compositions are substantially free of pores on their surface, even at thicknesses of up to 120 micrometers or more (e.g., 200 micrometers). In embodiments according to the present invention, the leveling agent is a solid-form polymeric material having a melting point below 100°C and a melt viscosity below 2000 mPa·s. In some embodiments according to the present invention, the leveling agent has a melting point in the range of 40 to 100°C. In another embodiment according to the present invention, the leveling agent has a melt viscosity in the range of 800 to 2000 mPa·s, the melt viscosity being measured at 200° C. using a Brookfield viscometer.

[0041] Without being bound by any theory, the inventors hypothesize that the leveling agent having the above specific melting properties has a low melting point, low melt viscosity, good fluidity, can delay the curing process, can provide good wetting and air release, and the leveling agent acts as a bridge between the pigment and the resin, fixing the pigment at one end and being compatible with the resin at the other end, thereby reducing the difference in surface tension between the pigment and the resin. As a result, during the curing process of the powder coating composition, the small molecules generated by the reaction have enough time to float up, making it possible to repair pinhole defects on the surface of the coating.

[0042] In the coating composition of the present invention, any leveling agent known from powder coating compositions having the above-mentioned melting properties can be used. For example, the leveling agent is one or more selected from polyacrylate, silicone-modified polyacrylate, polysiloxane, hydrogenated castor oil, and polyvinyl butyral, preferably polyacrylate, silicone-modified polyacrylate, and polysiloxane, more preferably polyacrylate.

[0043] In a preferred embodiment according to the present invention, the powder coating composition comprises 0.1 to 2 wt. %, preferably 0.5 to 1.5 wt. %, of a leveling agent, based on the total weight of the powder coating composition.

[0044] By way of example, the leveling agent may be commercially available or may be prepared as needed. In some embodiments according to the present invention, the leveling agent may be Resinflow PL-200, commercially available from Estron Chemical.

[0045] In an embodiment of the present invention, the powder coating composition further comprises a weatherable polyester containing 5% active polyester as a cure accelerator. As the name suggests, a cure accelerator is an additive that accelerates the curing of the powder coating composition, preferably contributing to enabling the powder coating composition to achieve a low curing temperature. The majority of curing accelerators currently available on the market for use in powder coatings are typically low-molecular-weight compounds, and while these additives can improve the curing performance of the coating, they inevitably affect the weatherability of the coating. Surprisingly, the present inventors have discovered that adding a weatherable polyester containing 5% active polyester as a cure accelerator to the powder coating composition not only lowers the curing temperature and increases the curing rate of the resulting powder coating composition, but also does not adversely affect the weatherability of the resulting coating, as conventional cure accelerators do. On the contrary, this can improve the leveling properties and weatherability of the coating. For example, in some embodiments of the present invention, powder coating compositions containing the above-described cure accelerator can be cured at temperatures of 130°C or less and exhibit good coating weatherability.

[0046] In preferred embodiments according to the invention, the powder coating composition comprises no more than 0.5 wt.%, preferably no more than 0.1 wt.%, of a cure accelerator, based on the total weight of the powder coating composition. In some embodiments according to the invention, the powder coating composition is substantially free of any cure accelerator, preferably free of any cure accelerator.

[0047] By way of example, the accelerator may be commercially available or may be prepared as needed. In some embodiments according to the present invention, the accelerator may be a product having grade number ADDITOL P966.

[0048] In embodiments according to the present invention, additional additives that do not adversely affect the powder coating composition or the cured coating obtained therefrom may be optionally included in the powder coating composition according to the present invention. Suitable additives include, for example, additives that improve the processability or manufacturability of the composition, additives that improve a specific functional property or characteristic (e.g., adhesion to a substrate) of the coating composition or the cured coating obtained therefrom, or additives that reduce costs. Examples of additives suitable for use in powder coating compositions include colorants, inorganic fillers, surfactants, flow control agents, heat stabilizers, preservatives, antioxidants, tackifiers, light stabilizers, leveling agents, defoamers, and combinations thereof. For example, the powder coating composition may include a colorant such as a pigment or dye. The amount of each optional component is sufficient to fulfill its intended purpose, but preferably, such amount does not adversely affect the powder coating composition or the cured coating obtained therefrom. The total amount of additional additives according to the present invention is from 0% to about 5% by weight, preferably from 0.1 to 5% by weight, based on the total weight of the powder coating composition.

[0049] In a preferred embodiment according to the present invention, the powder coating composition comprises, based on the total weight of the powder coating composition: at least 80% by weight of the polyester resin; 5 to 8 wt. % of the TGIC curing agent; 1 to 3 weight percent of the HAA curing agent; 0.1 to 2 wt % of the leveling agent; 0 to 0.5 wt. % of the curing accelerator; and 0-5 wt. % of said additional additives, wherein said additional additives are one or more selected from benzoin, wetting agents, antifoaming agents, and pigments.

[0050] The present invention further provides a method for preparing a powder coating composition, comprising the steps of: a) premixing and grinding in a premixer all of the polyester resins according to the present invention, the TGIC curing agent, the HAA curing agent, the leveling agent, and optionally additives for producing powder coatings; b) melt-extruding the premixed and milled ingredients through an extruder; c) cooling and pressing the melt-extruded material into flakes; d) crushing and sieving the flakes in a crusher to obtain powder particles of a suitable particle size, i.e., the powder coating composition.

[0051] The resulting powder particles are sprayed onto a suitable substrate using an electrostatic spray gun and placed in an oven at a specific temperature for curing. After curing, a powder coating is obtained. The powder coating may be a primer, a topcoat, or an intermediate coating. When the powder coating composition is cured by heating, the powder coating composition can be heated to a specific temperature and for a time suitable for curing the powder coating composition of the present invention. The powder coating composition can be heated using conventional methods such as a convection oven, and / or a (N)IR lamp, and / or an infrared laser, and / or a microwave device.

[0052] In some embodiments according to the present invention, powder coating compositions according to the present invention may be cured at temperatures of 140°C or less, preferably 130°C or less.

[0053] In some embodiments according to the present invention, powder coating compositions according to the present invention can be cured at temperatures up to 140° C. without the addition of any cure accelerators.

[0054] In some embodiments according to the present invention, the coating formed by curing the powder coating composition according to the present invention is substantially free of pores on its surface.

[0055] Therefore, the present invention also provides an article comprising a substrate partially or completely coated with a powder coating composition according to the present invention or a powder coating composition obtainable by the method according to the present invention. A person skilled in the art will select and identify a suitable material as the substrate based on actual needs. The substrate may be, for example, a glass, ceramic, wood, fiber cement board, or metal (e.g., aluminum, copper, or steel) substrate.

[0056] The present invention also relates to powder coatings, in-mold powder coatings, 3D printing, motorized vehicle applications (automotive parts, agricultural machinery, composite structures, ceramic structures, etc.), marine applications (ships, boats), aerospace applications (airplanes, helicopters, composite structures, ceramic structures, etc.), medical applications (artificial joints, nets, fabrics or nonwoven sheets, tapes, ribbons, tapes, cables, tubular products such as ligament substitutes, composite structures, ceramic structures, etc.), protective applications (ballistic devices, bulletproof vests, bulletproof undershirts, bulletproof helmets, bulletproof vehicles, composite structures, ceramic structures, etc.), sports / recreational applications (fencing, ice skating, skateboarding, snowboarding, slings in sports parachutes, paragliding, kites, kiteboarding kites, etc.). the use of the polyester resin or powder coating composition as described herein in applications such as: stringing, climbing equipment, composite structures, ceramic structures, etc.; architectural applications (windows, doors, (fake) walls, cables, etc.); bottling and filling applications; domestic applications (household appliances, white goods, furniture, computer housings, etc.); machinery applications (machine parts for can and bottle handling, moving parts for textile machinery, bearings, gears, composite structures, ceramic structures, computer housings, etc.); tank applications; coil applications; energy applications (e.g. for wind, tidal or solar generators); textile applications (e.g. as both a coating and a binder for composites, which can be very broad, ranging from impregnated industrial textiles to, for example, fully composite materials); and electrical applications (e.g. cabinets for electrical wiring or switchboards).

[0057] Test Method Unless otherwise stated, the following test methods are utilized in the examples below.

[0058] Melt Viscosity The melt viscosity was measured in Pa.s at 200°C according to ISO 3219. The viscosity was measured in a Brookfield CAP 2000+H viscometer at 200°C. The applied shear rate was 21 s -1 A 19.05 mm spindle, i.e., a conical spindle CAP-S-05 (19.05 mm, 1.8°), was used.

[0059] gloss This test was used to measure the gloss of the cured coating. The gloss was evaluated at 20° and 60° using a gloss meter according to ISO 2813.

[0060] Shock resistance Impact resistance was measured by the degree of deformation of the coating under high-speed loading and was evaluated using an impact tester in accordance with GB / T1732-93.

[0061] weather resistance The weather resistance of the resulting coating film was measured by subjecting it to a xenon lamp test for 3350 hours.

[0062] Storage stability This test was used to measure the stability of powder coating compositions during storage. Storage stability was assessed according to ISO 8130-8. [Example]

[0063] The following examples are intended to describe the present application in more detail and are for illustrative purposes only, as various modifications and variations will become apparent to those skilled in the art from the scope of the present application. Unless otherwise specified, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available and may be used without further treatment.

[0064] Raw materials: First polyester resin: a commercially available polyester resin with a glass transition temperature of less than 60°C from Kinte NH-9362 manufactured by DynaSky; Second polyester resin: Allnex 4430, a polyester resin having a viscosity of less than 3000 mPa·s, commercially purchased from Allnex; TGIC: General Industrial Products; HAA: General Industrial Products; Leveling agent: Resinflow PL-200 commercially available from Estron Chemical; Curing accelerator: ADDITOL P966 from Allnex; Additional additives: conventional industrial products.

[0065] Composition and properties of powder coating compositions Powder coating compositions were prepared according to the dosages in Table 1 below, sprayed onto degreased iron phosphate-treated steel slate using an electrostatic spray gun, and then baked in an oven to cure. After curing, the properties of the powder coatings could be tested.

[0066] [Table 1]

[0067] As can be seen from the results in Table 1 above, powder coating compositions according to the present invention use a polyester resin as the base material, a combination of triglycidyl isocyanurate (TGIC) and a β-hydroxyalkylamide (HAA) as the curing agent, and a leveling agent with specific melting properties. This allows for the formation of powder coating compositions suitable for low temperatures (e.g., below 140°C) and solves the problem of pinholes appearing on the surface of coatings with thicknesses up to 120 micrometers or more (e.g., 200 micrometers), which is caused by the use of an HAA curing agent. Furthermore, as can be seen from Example 2, selecting a combination of a first polyester resin with a specific glass transition temperature and a second polyester resin with a specific melt viscosity as the polyester resin is particularly advantageous for further improving the low-temperature curing properties of the powder coating composition formulated therefrom and the coating properties of the resulting coating. Furthermore, as can be seen from Example 3, the addition of a curing accelerator to the above powder coating composition significantly lowers the curing temperature and maintains good weather resistance.

[0068] In contrast, the curing temperature of the powder coating composition using only TGIC curing agent in Comparative Example 1 was significantly higher than that of the powder coating composition according to the present invention, and the powder coating composition using a combination of TGIC and HAA as a curing agent in Comparative Example 2 had a lower curing temperature, but the coating film was characterized by the occurrence of pinholes on its surface and a significantly reduced gloss level.

[0069] While the present invention has been described in terms of numerous embodiments and examples, those skilled in the art, having the benefit of this invention, will appreciate that other embodiments may be devised which do not depart from the scope and spirit of the invention disclosed herein.

Claims

1. 1. A powder coating composition comprising a polyester resin, a triglycidyl isocyanurate (TGIC) curing agent, a β-hydroxyalkylamide (HAA) curing agent, and a leveling agent, wherein the leveling agent is a polymeric material in solid form having a melting point of less than 100°C and a melt viscosity of less than 2000 mPa·s when measured at 200°C using a Brookfield viscometer.

2. 10. The powder coating composition of claim 1, wherein the leveling agent has a melting point in the range of 40 to 100°C.

3. 10. The powder coating composition of claim 1, wherein the leveling agent has a melt viscosity in the range of 800 to 2000 mPa·s as measured at 200° C. using a Brookfield viscometer.

4. 4. A powder coating composition according to any one of claims 1 to 3, wherein the levelling agent is one or more selected from polyacrylate, silicone modified polyacrylate, polysiloxane, hydrogenated castor oil and polyvinyl butyral, preferably one or more selected from polyacrylate, silicone modified polyacrylate and polysiloxane, more preferably polyacrylate.

5. 4. The powder coating composition of claim 1, wherein the polyester resin comprises a mixture of a first polyester resin and a second polyester resin, the first polyester resin having a glass transition temperature of less than 60°C, and the second polyester resin having a melt viscosity as low as 3000 mPa s when measured at 200°C using a Brookfield viscometer.

6. 6. The powder coating composition of claim 5, wherein the first polyester resin has a glass transition temperature in the range of 55 to 58°C, and the second polyester resin has a melt viscosity in the range of 1500 mPa s to 2500 mPa s when measured at 200°C using a Brookfield viscometer.

7. 6. The powder coating composition of claim 5, wherein the first polyester resin has a melt viscosity in the range of 5,000 mPa·s to 35,000 mPa·s when measured at 200° C. using a Brookfield viscometer.

8. 6. A powder coating composition according to claim 5, wherein the second polyester resin has a glass transition temperature of 65°C or less, preferably in the range of 55 to 63°C.

9. 6. The powder coating composition of claim 5, wherein both the first polyester resin and the second polyester resin have an acid number in the range of 32 to 38 mg KOH / g resin.

10. 4. The powder coating composition of claim 1, further comprising a weatherable polyester containing 5% active polyester component as a cure accelerator, present in an amount of 0.5% by weight or less, based on the total weight of the powder coating composition.

11. The powder coating composition of any one of claims 1 to 3, wherein the powder coating composition is substantially free of any cure accelerators.

12. The powder coating composition comprises, based on the total weight of the powder coating composition: at least 80% by weight of said polyester resin; 5-8 wt. % of the TGIC curing agent; 1 to 3 wt. % of the HAA curing agent; 0.1 to 2 wt. % of the leveling agent; 0 to 0.5 wt. % of the curing accelerator; 0-5 wt. % of additional additives; 12. The powder coating composition of any one of claims 1 to 11, comprising:

13. A powder coating composition according to any one of claims 1 to 12 which cures at a temperature of 140°C or less, preferably 130°C or less.

14. A powder coating composition according to any one of claims 1 to 12, which cures at a temperature of up to 140°C without the addition of any cure accelerator.

15. 13. The powder coating composition of any one of claims 1 to 12, wherein the coating formed by curing the powder coating composition is substantially free of pores.

16. An article, A substrate; a coating formed from the powder coating composition of any one of claims 1 to 15 applied directly to the substrate; and Including, goods.

17. 17. The article of claim 16, wherein the substrate comprises a metal substrate, a wood substrate, a plastic substrate, a glass substrate, a ceramic substrate, or a combination thereof.

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