A low temperature curing powder coating composition and articles formed therefrom

Abstract

The present invention relates to a low temperature curing powder coating composition and articles formed therefrom. The powder coating composition comprises a polyester resin, a tri-glycidyl isocyanurate (TGIC) curing agent, a beta-hydroxyalkylamide (HAA) curing agent, and a leveling agent, wherein the leveling agent is a solid form of a polymeric material having a melting point of less than 100°C and a melt viscosity of less than 2000 mPa-s, the melt viscosity being determined at 200°C using a Brookfield viscometer. The above-described powder coating composition can be cured at a temperature of 140°C or less without the need for adding any curing accelerators. Moreover, the surface of the coating formed from the above-described powder coating composition is substantially free of pores.

Description

Technical Field

[0001] This invention relates to a powder coating composition, and more particularly to a powder coating composition suitable for low-temperature curing that uses a combination of TGIC and HAA as a curing agent, and articles formed therefrom. Background Technology

[0002] Powder coatings are widely used to provide decorative and / or protective coatings on substrates. Powder coatings have a completely different form from conventional coatings; they exist as fine powders and do not use solvents. Powder coatings are characterized by being harmless, highly efficient, resource-saving, and environmentally friendly. After years of development, powder coatings have made significant progress, and their application areas have expanded year by year.

[0003] Polyester-based powder coatings are among the most common thermosetting powder coatings on the market. They are generally formulated with polyester resin as the base material and triglycidyl isocyanate (TGIC) as the curing agent. Due to their good compatibility with existing coating varieties and low raw material and production costs, this type of powder coating has a promising future. However, the curing temperature of this polyester-based powder coating is usually high, which inevitably increases energy consumption and reduces the production speed.

[0004] Therefore, there is a market demand for polyester resin-based powder coating compositions that are suitable for curing at low temperatures (especially at 140°C or lower). Summary of the Invention

[0005] On one hand, the present invention 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 solid polymer material with a melting point below 100°C and a melt viscosity below 2000 mPa·s, the melt viscosity being measured at 200°C using a Brookfield viscometer. Preferably, the melting point of the leveling agent is in the range of 40 to 100°C, and / or the melt viscosity of the leveling agent is in the range of 800 to 2000 mPa·s, the melt viscosity being measured at 200°C using a Brookfield viscometer.

[0006] In a preferred embodiment of the 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 below 60°C, and the second polyester resin having a melt viscosity as low as 3000 mPa·s, the melt viscosity being measured at 200°C using a Brookfield melt viscometer.

[0007] On the other hand, the present invention provides an article comprising a substrate; and a coating formed by a powder coating composition according to a first aspect of the invention, directly applied onto the substrate. Preferably, the substrate comprises 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 invention, a polyester resin is used as the base material, and a combination of triglycidyl isocyanate (TGIC) and β-hydroxyalkylamide (HAA) is used as the curing agent. This is combined with a leveling agent having specific melt properties to form a powder coating composition suitable for low-temperature (e.g., at 140°C or lower) curing. This also solves the problem of pinholes on the surface of the coating (especially thick coatings) caused by the use of HAA curing agents, resulting in coatings formed from this powder coating composition, even those up to 120 micrometers thick, having a substantially pore-free surface. Preferably, in the powder coating composition according to the invention, using 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 performance of the powder coating composition formulated therefrom and the coating properties of the resulting coating.

[0009] The inventors of this invention have surprisingly discovered that, in the formulation of powder coating compositions, using a combination of triglycidyl isocyanurate (TGIC) and β-hydroxyalkylamide (HAA) as a curing agent not only facilitates low-temperature curing and reduces the amount of curing accelerator required, but also significantly improves the storage stability of the resulting powder coating composition—something that was difficult to foresee before this application. Furthermore, the inventors have surprisingly discovered that, in the formulation of powder coating compositions, the additional addition of weather-resistant polyester containing 5% active polyester component as a curing accelerator not only lowers the curing temperature and increases the curing speed of the resulting powder coating composition, but also does not adversely affect the weather resistance of the resulting coating as conventional curing accelerators do; on the contrary, it improves the leveling and weather resistance of the coating.

[0010] Details of one or more embodiments of the present invention are set forth in the following description. Other features, objects, and advantages of the invention will become clear from the description and claims.

[0011] definition

[0012] In this document, unless otherwise stated, the terms “a,” “this,” “at least one,” and “one or more,” as well as the absence of quantifiers, are used interchangeably. Thus, for example, a coating composition containing “a” additive can be interpreted as meaning that the coating composition contains “one or more” additives.

[0013] When a composition is described as including or comprising specific components, it is anticipated that optional components not covered by the present invention are not excluded from the composition, and that the composition may be constituted or composed of the components involved. Similarly, when a method is described as including or comprising specific process steps, it is anticipated that optional process steps not covered by the present invention are not excluded from the method, and that the method may be constituted or composed of the process steps involved.

[0014] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0015] When referring to "first polyester resin and second polyester resin," the term "glass transition temperature (Tg)" refers to the measured Tg of the respective resin. According to the present invention, the glass transition temperature of the polyester resin is measured using differential scanning calorimetry (DSC) according to ISO 11357.

[0016] When referring to "first polyester resin and second polyester resin," the term "acid value" (AV) refers to the measured AV of the respective resin. According to the present invention, the acid value (AV) (mg KOH / g polyester) of the polyester resin is measured by titration according to ISO 2114-2000. The acid value of the polyester resin is a measure of the amount of carboxylic acid groups in the polyester resin.

[0017] In the context of this paper, "viscosity" or its equivalent "melt viscosity" refers to the melt viscosity (in mPa·s) at 200 °C. Viscosity measurements were performed at 200 °C on a Brookfield CAP 2000+HViscometer. The applied shear rate was 21 s. -1 It uses a 19.05mm spindle (conical rotor CAP-S-05 (19.05mm, 1.8°)).

[0018] In the context of this invention, "polyester resin" refers to a polyester resin that mainly has carboxylic acid functional groups but does not exclude hydroxyl functional groups, wherein the acid value of the carboxylic acid functional polyester resin is significantly higher than its hydroxyl value.

[0019] When referring to the use of “curing accelerator”, the term “active polyester” means a polyester resin that can physically and / or chemically react with the components constituting the coating composition, particularly the curing agent component, including but not limited to polyester resins that undergo physical entanglement or chemical crosslinking.

[0020] In the context of this invention, the term "composition" means: a combination and / or mixture of different chemical substances and / or components that form a whole.

[0021] In the context of this invention, the term "powder" means: a substantially dry solid substance at room temperature and atmospheric pressure, reduced to a fine, loose particulate state, wherein the maximum particle size of a single particle at 23°C and atmospheric pressure is preferably up to 200 μm, more preferably up to 180 μm, even more preferably up to 160 μm, most preferably up to 150 μm, particularly up to 140 μm, more particularly up to 130 μm, most particularly up to 120 μm, etc. For example, at most 110 μm, at most 100 μm, at most 90 μm; the minimum particle size of a single particle at 23°C and atmospheric pressure is 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, for example at least 45 μm, for example at least 50 μm, for example at least 60 μm, for example at least 70 μm. Particles are defined as small objects that: a) have an average linear size as described herein and b) exhibit uniformity in their transport and performance. The method used to measure the particle size of the powder coating compositions of the present invention is sieving.

[0022] In the context of this invention, the term "curing" refers to the process of becoming "fixed" to form an irreversible cross-linked network (the so-called "cured form" or "cured composition"), wherein the material no longer flows, melts, or dissolves. In this document, the terms "curing" and "cross-linking" are used interchangeably.

[0023] In the context of this invention, the term "powder coating" refers to a cured powder coating composition in the form of a coating. A powder coating is obtained after the powder coating composition has been cured.

[0024] When referring to a “coating formed from a powder coating composition”, the phrase “substantially pore-free” means that the surface of the coating is smooth, for example, when observed with the naked eye, preferably by an optical microscope at 10x, 20x, or even 50x magnification, no pinholes can be found.

[0025] Unless the context clearly indicates otherwise, the plural form of terms used herein (e.g., polyester resin, curing agent, powder coating composition, component) may be interpreted as including the singular form, and vice versa.

[0026] In this invention, the numerical range defined by the endpoints includes all values ​​within that range. For example, the range of 1 to 5 encompasses the values ​​1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc. Moreover, the disclosed numerical range includes all subsets of the wider range. For example, the range of 1 to 5 includes subranges 1 to 4, 1.5 to 4.5, 1 to 2, etc.

[0027] The terms "preferred" and "ideally" refer to embodiments of the invention that provide certain benefits in certain circumstances. However, other embodiments may also be preferred in the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of the invention. Detailed Implementation

[0028] One aspect of this invention 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 polymer material in solid form with a melting point below 100°C and a melt viscosity below 2000 mPa·s, the melt viscosity being measured at 200°C using a Brookfield viscometer.

[0029] Low-temperature curing powder coating compositions are attracting increasing attention and are expected to be the preferred products in the future powder coating industry. Currently, low-temperature curing powder coating products on the market are generally immature, with significant room for improvement. Therefore, this invention provides a novel low-temperature curing powder coating composition. In the powder coating composition according to embodiments of the invention, polyester resin is used as the base material, and a combination of triglycidyl isocyanurate (TGIC) and β-hydroxyalkylamide (HAA) is used as the curing agent. By adding a leveling agent with specific melting properties, a powder coating composition suitable for low-temperature (e.g., at 140°C or lower) curing can be formed. Furthermore, the problem of pinholes appearing on the surface of coatings (especially thick coatings) caused by the use of HAA curing agents can be solved, resulting in coatings formed from this powder coating composition, even those with a thickness of up to 120 micrometers or more (e.g., 200 micrometers), having a surface that is essentially free of pores.

[0030] In embodiments of the invention, the polyester resin used as the base material can be a linear or branched polyester resin. Preferably, the polyester resin is a linear polyester resin with an average functionality of about 2, for example, formed by polycondensation of a dicarboxylic acid and a diol. Polyester resins with a linear structure are advantageous for formulating powder coating compositions with good leveling properties.

[0031] In embodiments of the present invention, the polyester resin is suitable for TGIC curing and / or HAA curing, and therefore can also be referred to as a carboxylic acid-functionalized polyester resin. In this invention, the acid value of the polyester resin is an important parameter, affecting the leveling properties and low-temperature curing performance of TGIC-cured and / or HAA-cured powder coatings formulated therefrom. Therefore, the acid value of the polyester resin according to the present invention is selected in the range of 32-38 mg KOH / g resin, preferably in the range of 32-36 mg KOH / g resin.

[0032] In some embodiments of the present invention, the polyester resin may contain a certain amount of hydroxyl value in addition to carboxylic acid functional groups. However, considering that the polyester resin of the present invention is cured by TGIC and / or HAA, its hydroxyl value (OHV) does not exceed 10 mg KOH / g resin, preferably up to 8 mg KOH / g resin, more preferably up to 6 mg KOH / g resin, even more preferably up to 4 mg KOH / g resin, and most preferably up to 3 mg KOH / g resin.

[0033] In some embodiments of the invention, the polyester resin may have a glass transition temperature (Tg) within a specific range. The glass transition temperature can be measured according to ISO 11357 by differential scanning calorimetry (DSC) at a heating rate of 5°C / min. The inventors of the present invention have surprisingly discovered that the presence of a polyester resin with a specific glass transition temperature in a powder coating composition can significantly improve the low-temperature curing properties of the coating, enabling the powder coating composition formulated therefrom to cure at temperatures as low as 140°C. Preferably, the polyester resin has a glass transition temperature as low as 60°C, and more preferably a glass transition temperature of 55-58°C.

[0034] In some embodiments of the invention, the polyester resin may have a specific melt viscosity, which is measured using a Brookfield viscometer at 200°C. The inventors of the invention have surprisingly discovered that the presence of a polyester resin with a specific melt viscosity in a powder coating composition can significantly improve the leveling properties of the coating, resulting in a higher gloss. Preferably, the polyester resin has a melt viscosity as low as 3000 mPa·s, and more preferably in the range of 2000 mPa·s to 2500 mPa·s.

[0035] The inventors of this invention have surprisingly discovered that, in the formulation of the powder coating composition according to the invention, the low-temperature curing properties and film-forming properties of the powder coating composition can be further adjusted by regulating the combination of polyester resins. Therefore, in some preferred embodiments according to the invention, the polyester resin can be a combination of a first polyester resin and a second polyester resin. Preferably, the first polyester resin can have a glass transition temperature below 60°C, and more preferably, a glass transition temperature in the range of 55-58°C. Optionally, the melt viscosity of the first polyester resin can be in the range of 5000 mPa·s to 35000 mPa·s, the melt viscosity being measured at 200°C using a Brookfield melt viscometer. Preferably, the second polyester resin can have a melt viscosity as low as 3000 mPa·s, and more preferably, a melt viscosity in the range of 1500 mPa·s to 2500 mPa·s, the melt viscosity being measured at 200°C using a Brookfield melt viscometer. Optionally, the glass transition temperature of the second polyester resin can be below 65°C, preferably in the range of 55 to 63°C. In some embodiments of the present invention, the acid values ​​of both the first polyester resin and the second polyester resin are in the range of 32-38 mg KOH / g resin.

[0036] The inventors of this invention have surprisingly discovered that, in the powder coating composition according to the invention, selecting a combination of a first polyester resin having the aforementioned specific glass transition temperature and a second polyester resin having the aforementioned 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.

[0037] In a preferred embodiment of the invention, the powder coating composition comprises at least 80% by weight of polyester resin based on the total weight of the powder coating composition. Preferably, the polyester resin is present in an amount ranging from 80% to 90% by weight relative to the weight of the powder coating composition, more preferably, the polyester resin is present in an amount ranging from 85% to 90% by weight relative to 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, more preferably in the range of 1:1.3 to 1.3:1.

[0038] As an example, the polyester resin may be commercially available or prepared as needed. In some embodiments of the invention, the polyester resin may be Kinte NH-9362, commercially available from Keenon Corporation, or Allnex 4430, commercially available from Allnex.

[0039] In embodiments of the invention, a combination of triglycidyl isocyanurate (TGIC) and β-hydroxyalkylamide (HAA) is used as a curing agent in the formulation of the powder coating composition. As described herein, a "curing agent" refers to a compound that can be used as a crosslinking agent for acid-functionalized or carboxyl-terminated polyester resins. Typically, this type of curing agent or crosslinking agent can include epoxy-functionalized compounds, amides, substituted alkylamides, diamides, etc. However, in the formulation of the powder coating composition according to the invention, the curing agent is specifically a combination of TGIC and HAA. TGIC is a triazine compound having reactive epoxy functional groups, which is considered in the art to be a preferred curing agent for acid-functionalized resins (e.g., acrylic resins, polyester resins, etc.). HAA has four active hydroxyl groups in its molecular structure and undergoes a dehydration condensation reaction with carboxyl groups. The inventors of this invention have surprisingly discovered that using a combination of triglycidyl isocyanurate (TGIC) and β-hydroxyalkylamide (HAA) as a curing agent in the formulation of the powder coating composition according to the invention not only facilitates low-temperature curing and reduces the amount of curing accelerator, but also significantly improves the storage stability of the resulting powder coating composition. For example, the powder coating composition can be stored at 30°C for 6 months, or even at 24°C for 6-12 months, without any agglomeration and / or crosslinking.

[0040] In a preferred embodiment of the invention, the powder coating composition comprises, based on the total weight of the powder coating composition, 5 to 8% by weight, preferably 6 to 8% by weight, of TGIC curing agent and 1 to 3% by weight, preferably 1.5 to 3% by weight, of HAA curing agent.

[0041] As is well known, HAA-type curing agents have advantages such as low dosage, low curing temperature, and non-toxicity in the formulation of polyester powder coating compositions. However, these curing agents inevitably cause pinhole problems in the coating film due to their high volatility. The inventors of this application have surprisingly discovered that by using polyester resin as a base material and a combination of triglycidyl isocyanurate (TGIC) and β-hydroxyalkylamide (HAA) as curing agents in the formulation of powder coating compositions, and by adding a leveling agent with specific melting properties, the problem of pinholes appearing on the surface of coatings (especially thick coatings) caused by the use of HAA curing agents has been solved. This results in coatings formed from this powder coating composition, even those with a thickness of up to 120 micrometers or more (e.g., 200 micrometers), having a surface that is essentially free of pores. In embodiments of the invention, the leveling agent is a polymer material in solid form having a melting point below 100°C and a melt viscosity below 2000 mPa·s. In some embodiments of the invention, the melting point of the leveling agent is in the range of 40 to 100°C. In some other embodiments of the invention, the melt viscosity of the leveling agent is in the range of 800 to 2000 mPa·s, and the melt viscosity is measured at 200°C using a Brookfield viscometer.

[0042] Without being bound by any theory, the inventors speculate that leveling agents with the aforementioned specific melting properties have low melting points, low melt viscosity, and good fluidity, which can delay the curing process; and they can provide excellent wetting properties and release air. This leveling agent acts as a bridge between the pigment and the resin, anchoring the pigment at one end and making it compatible with the resin at the other, reducing the surface tension difference between them. Therefore, during the curing process of the powder coating composition, the small molecules generated by the reaction have sufficient time to escape, allowing pinhole defects on the coating surface to be restored.

[0043] In the coating composition according to the invention, any leveling agent known in powder coating compositions having the above-described melting properties can be used. As an example, the leveling agent is selected from one or more of polyacrylates, silicone-modified polyacrylates, polysiloxanes, hydrogenated castor oil, and polyvinyl butyral, preferably from one or more of polyacrylates, silicone-modified polyacrylates, and polysiloxanes, and more preferably from polyacrylates.

[0044] In a preferred embodiment of the invention, the powder coating composition comprises, based on the total weight of the powder coating composition, 0.1 to 2% by weight, preferably 0.5 to 1.5% by weight, a leveling agent.

[0045] As an example, the leveling agent may be commercially available or prepared as needed. In some embodiments of the invention, the leveling agent may be Resinflow PL-200, commercially available from Estron Chemical.

[0046] In one embodiment of the invention, the powder coating composition according to the invention further comprises a weather-resistant polyester containing 5% active polyester component as a curing accelerator. As the name suggests, a curing accelerator is an additive that promotes the curing of the powder coating composition, preferably contributing to a low curing temperature. Currently, the mainstream curing accelerators used in powder coating compositions are usually low-molecular-weight compounds. While the use of such additives can improve the curing performance of the coating, it inevitably affects the weather resistance of the film. The inventors of the present invention have surprisingly discovered that by additionally adding a weather-resistant polyester containing 5% active polyester component as a curing accelerator to the formulation of the powder coating composition, not only can the curing temperature of the resulting powder coating composition be reduced and the curing speed increased, but it also does not adversely affect the weather resistance of the resulting coating as conventional curing accelerators do; on the contrary, it can improve the leveling and weather resistance of the coating. For example, in some embodiments of the invention, the powder coating composition containing the above-mentioned curing accelerator can be cured at a temperature of 130°C or lower and exhibits good coating weather resistance.

[0047] In a preferred embodiment of the invention, the powder coating composition comprises, based on the total weight of the powder coating composition, 0.5% by weight or less of a curing accelerator, preferably 0.1% by weight or less. In some embodiments of the invention, the powder coating composition is substantially free of any curing accelerator, preferably free of any curing accelerator.

[0048] As an example, the curing accelerator may be commercially available or prepared as needed. In some embodiments of the invention, the curing accelerator may be a product with the brand name ADDITOL P966.

[0049] In embodiments of the invention, the powder coating composition according to the invention may optionally include additional additives that do not adversely affect the powder coating composition or the cured coating obtained therefrom. Suitable additives include, for example, those agents that improve the processability or manufacturing properties of the composition, improve specific functional properties or characteristics (such as adhesion to a substrate) of the waterborne coating composition or the cured coating obtained therefrom, or reduce costs. Examples of additives suitable for 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 contain colorants, such as pigments or dyes. The amounts of each optional component are sufficient to achieve their intended purpose, but preferably, such amounts do not adversely affect the powder coating composition or the cured coating obtained therefrom. According to the invention, the total amount of the additional additives is from 0% by weight to about 5% by weight relative to the total weight of the powder coating composition, preferably 0.1-5% by weight.

[0050] In a preferred embodiment of the invention, the powder coating composition comprises, based on the total weight of the powder coating composition,

[0051] At least 80% by weight of the polyester resin,

[0052] 5 to 8% by weight of TGIC curing agent,

[0053] 1 to 3% by weight of HAA curing agent,

[0054] 0.1 to 2% by weight of the leveling agent,

[0055] 0 to 0.5% by weight of curing accelerator, and

[0056] 0 to 5% by weight of additional additives, wherein the additional additives are selected from one or more of benzoin, wetting agents, defoamers, and pigments.

[0057] Furthermore, the present invention also provides a method for preparing a powder coating composition, comprising the following steps:

[0058] a) All the polyester resin, TGIC curing agent, HAA curing agent, leveling agent and optional additives according to the invention used for manufacturing powder coatings are premixed and pulverized in a premixer;

[0059] b) The pre-mixed and pulverized raw materials are melted and extruded through an extruder;

[0060] c) Cool and compress the molten extruded material into tablets;

[0061] d) The flakes are crushed by a pulverizer and sieved to obtain powder particles of suitable size, which is the powder coating.

[0062] The obtained powder particles are sprayed onto a suitable substrate using an electrostatic spray gun and then cured in an oven at a specific temperature. After curing, a powder coating is obtained. The powder coating can be a primer, topcoat, or intermediate coating. When heating the powder coating composition to cure it, the heating can be carried out at a specific temperature and sustained for a suitable time to cure the powder coating composition of the present invention. Heating of the powder coating composition can be performed using conventional methods, such as a convection oven and / or (N)IR lamp, and / or infrared laser and / or microwave equipment.

[0063] In some embodiments of the invention, the powder coating composition according to the invention can be cured at a temperature of 140°C or lower, preferably at a temperature of 130°C or lower.

[0064] In some embodiments of the invention, the powder coating composition according to the invention can be cured at 140°C or lower without the addition of any curing accelerator.

[0065] In some embodiments of the invention, the surface of the coating formed by curing the powder coating composition according to the invention is substantially free of pores.

[0066] Therefore, the present invention also provides an article comprising a substrate partially or wholly 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. Those skilled in the art will select and determine suitable materials as the substrate according to actual needs. The substrate may be, for example, glass, ceramic, wood, fiber cement board, or metal (e.g., aluminum, copper, or steel).

[0067] This invention also relates to polyester resins and powder coatings as described herein in powder coating, in-mold powder coating, 3D printing, automotive applications (automotive parts, agricultural machinery, composite structures, ceramic structures, etc.), marine applications (ships), aerospace applications (aircraft, helicopters, composite structures, ceramic structures, etc.), medical applications (artificial joints, nets, woven or nonwoven sheets, strips, ribbons, cords, cables, tubular products such as ligament substitutes, composite structures, ceramic structures, etc.), protective applications (bulletproof equipment, bulletproof vests, bulletproof helmets, bulletproof vehicles, composite structures, ceramic structures, etc.), and sports / recreation applications (fencing, skating, skateboarding, skis, slings in sports parachutes, paragliding, kites, kite flying, etc.). Applications include: kite strings, mountaineering equipment, composite structures, ceramic structures, etc.; architectural applications (windows, doors, (false) walls, cables, etc.); bottle applications; household applications (home appliances, white goods, furniture, computer casings, etc.); mechanical applications (can and bottle handling machine parts, moving parts of textile machines, bearings, gears, composite structures, ceramic structures, computer casings, etc.); can applications; roll applications; energy applications (for example, wind, tidal, or solar generators); textile applications (for example, fabrics, which can be very broad, from impregnation-technical textiles to, for example, all composite materials, both as coatings and as adhesives for composite materials); and electrical applications (for example, cabinets for wires or distribution panels).

[0068] Test methods

[0069] Unless otherwise indicated, the following test methods are used in the following embodiments.

[0070] melt viscosity

[0071] Melt viscosity refers to the melt viscosity (in Pa·s) at 200°C according to ISO 3219. Viscosity was measured at 200°C using a Brookfield CAP 2000+H Viscometer. The applied shear rate was 21 s⁻¹. -1 It uses a 19.05mm spindle (conical rotor CAP-S-05 (19.05mm, 1.8°)).

[0072] gloss

[0073] This test is used to measure the gloss of the cured coating. A gloss meter is used to evaluate the gloss at 20° and 60° according to ISO 2813.

[0074] Impact resistance

[0075] Impact resistance is a test of the degree of deformation of a coating under high-speed load. Impact resistance is evaluated using an impact tester according to GB / T1732-93.

[0076] Weather resistance

[0077] Weather resistance was measured by testing the resulting coating under a xenon lamp for 3350 hours.

[0078] Storage stability

[0079] This test is used to measure the stability of powder coating compositions during storage. Storage stability is evaluated according to ISO 8130-8.

[0080] Example

[0081] The present invention is described in more detail below through examples. These examples are merely illustrative and should not be construed as limiting the scope of protection of the present invention, as various modifications and variations will be apparent to those skilled in the art within the scope of the present invention. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight, and all reagents used in the examples are commercially available and ready for use without further processing.

[0082] Raw materials:

[0083] First polyester resin: a polyester resin with a glass transition temperature below 60°C, commercially purchased from KinteNH-9362 by Qingtian Company;

[0084] Second polyester resin: Polyester resin with a viscosity of less than 3000 mPa·s, commercially available from Allnex, Allnex 4430;

[0085] TGIC: General Industrial Products;

[0086] HAA: General Industrial Products;

[0087] Leveling agent: Resinflow PL-200, purchased from Estron Chemical;

[0088] Curing accelerator: ADDITOL P966, commercially available from Allnex;

[0089] Additional additives: standard industrial products.

[0090] Component proportions and properties of powder coating compositions

[0091] The powder coating composition was prepared according to the dosages in Table 1 below and sprayed onto degreased, iron-phosphated steel strips using an electrostatic spray gun. The strips were then baked and cured in an oven. The performance of the powder coating was tested after curing.

[0092] Table 1:

[0093]

[0094]

[0095] As can be seen from the results in Table 1 above, in the powder coating composition according to the present invention, using polyester resin as the base material, a combination of triglycidyl isocyanurate (TGIC) and β-hydroxyalkylamide (HAA) as the curing agent, and combining it with a leveling agent having specific melt properties, a powder coating composition suitable for low-temperature (e.g., at 140°C or lower) curing can be formed, and the problem of pinholes appearing on the surface of the coating (especially coatings with a thickness of up to 120 micrometers or more (e.g., 200 micrometers)) caused by the use of HAA curing agent can be solved. Moreover, as shown in 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 performance of the powder coating composition formulated therefrom and the coating performance of the resulting coating. Furthermore, as shown in Example 3, the additional addition of a curing accelerator to the above-mentioned powder coating composition can significantly reduce the curing temperature while maintaining good weather resistance.

[0096] In comparison, the curing temperature of the powder coating composition using TGIC alone in Comparative Example 1 was significantly higher than that of the powder coating composition according to the present invention; although the powder coating composition using a combination of TGIC and HAA as curing agents in Comparative Example 2 had a lower curing temperature, the coating surface had pinholes and the gloss was significantly reduced.

[0097] Although the present invention has been described with reference to numerous embodiments and examples, those skilled in the art will recognize that other embodiments can be designed based on the disclosure of the present invention without departing from the scope and spirit of the invention.

Claims

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 solid polymer material with a melting point below 100°C and a melt viscosity below 2000 mPa·s. The melt viscosity was measured at 200°C using a Brookfield viscometer. in, Relative to the total weight of the powder coating composition, the powder coating composition comprises, At least 80% by weight of the polyester resin, 5 to 8% by weight of TGIC curing agent, 1 to 3% by weight of HAA curing agent, 0.1 to 2% by weight of the leveling agent, 0 to 0.5% by weight of curing accelerator, and Additional additives: 0 to 5% by weight.

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

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

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

5. The powder coating composition according to any one of claims 1 to 3, wherein, The leveling agent is selected from one or more of polyacrylate, silicone-modified polyacrylate, and polysiloxane.

6. The powder coating composition according to any one of claims 1 to 3, wherein, The leveling agent is selected from polyacrylate.

7. The powder coating composition according to any one of claims 1 to 3, 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 below 60°C and the second polyester resin having a melt viscosity as low as 3000 mPa·s, the melt viscosity being measured at 200°C using a Brookfield melt viscometer.

8. The powder coating composition of claim 7, wherein, The first polyester resin has a glass transition temperature in the range of 55-58°C, and the second polyester resin has a melt viscosity in the range of 1500 mPa·s to 2500 mPa·s, the melt viscosity being measured at 200°C using a Brookfield melt viscometer.

9. The powder coating composition of claim 7, wherein, The melt viscosity of the first polyester resin is in the range of 5000 mPa·s to 35000 mPa·s, and the melt viscosity is measured at 200°C using a Brookfield melt viscometer.

10. The powder coating composition of claim 7, wherein, The glass transition temperature of the second polyester resin is not higher than 65°C.

11. The powder coating composition of claim 7, wherein, The glass transition temperature of the second polyester resin is in the range of 55 to 63°C.

12. The powder coating composition according to claim 7, wherein, The acid values ​​of both the first polyester resin and the second polyester resin are in the range of 32-38 mg KOH / g resin.

13. The powder coating composition according to any one of claims 1 to 3, further comprising a weather-resistant polyester containing 5% active polyester component as a curing accelerator, wherein the amount of the curing accelerator is 0.5% by weight or less relative to the total weight of the powder coating composition.

14. The powder coating composition according to any one of claims 1 to 3, wherein, The powder coating composition does not contain any curing accelerator.

15. The powder coating composition according to any one of claims 1 to 3, wherein, The powder coating composition is cured at 140°C or lower.

16. The powder coating composition according to any one of claims 1 to 3, wherein, The powder coating composition is cured at 130°C or lower.

17. The powder coating composition according to any one of claims 1 to 3, wherein, The powder coating composition is cured at 140°C or lower without the addition of any curing accelerator.

18. The powder coating composition according to any one of claims 1 to 3, wherein, The surface of the coating formed by curing the powder coating composition is substantially free of pores.

19. An article comprising Substrate; and A coating formed by the powder coating composition of any one of claims 1-18, applied directly onto the substrate.

20. The article of manufacture as claimed in claim 19, wherein, The substrate includes metal substrate, wood substrate, plastic substrate, glass substrate, ceramic substrate, or a combination thereof.

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