Powder coating composition, coated substrate, component and method of treating substrate

Abstract

The powder coating composition comprises a first component and a second component, the first component comprises a combination of high-hydroxyl-value polyester resin and low-hydroxyl-value polyester resin, the hydroxyl value of the high-hydroxyl-value polyester resin is 200-400 mgKOH / g, and the hydroxyl value of the low-hydroxyl-value polyester resin is 30-70 mgKOH / g; and the second component comprises an isocyanate curing agent. A coated substrate, a component, and a method of treating a substrate are also disclosed.

Description

Technical Field

[0001] The present invention relates to the field of coatings, and particularly to a powder coating composition, a coated substrate, a component, and a method for treating a substrate. Background Art

[0002] Powder coatings are solvent-free and volatile-free solid coatings, which have the advantages of being harmless to the environment, efficient, and low-cost. In recent years, with the continuous increase of environmental protection efforts at home and abroad and the continuous improvement of users' environmental protection awareness, the demand for powder coatings in various fields has become increasingly urgent. Powder coatings are currently widely used in fields such as automobiles, pipelines, household appliances, furniture, and aluminum profiles.

[0003] With the development of technology, various industrial products, household products, or digital products (such as various processing tools, automobiles, household appliances or tools, instruments / gauges, desktop computers, laptop computers, mobile phones, etc.) have gradually become indispensable tools in people's production and life. The outer shell coating of these products is an important part of their production process. The outer shell coating not only provides various decorations for the products, but also can protect the metal or plastic substrates used to form the outer shell, enhancing their hardness, scratch resistance, wear resistance, and service durability. In the prior art, many product outer shells are made of steel, aluminum, magnesium, or their alloys, but the existing powder coatings have deficiencies in aspects such as adhesion, leveling property, and weather resistance on the coating surface.

[0004] Therefore, it is necessary to develop a powder coating that combines good mechanical properties and appearance properties. Summary of the Invention

[0005] The inventors have conducted extensive research and developed a powder coating composition suitable for metal substrates. This coating composition can achieve a bright appearance effect, such as simulating high-brightness silver or even electroplated silver or other aesthetic appearance effects, and can also achieve good hardness, improved flatness, leveling property, adhesion, scratch resistance, weather resistance, and a comfortable hand feel similar to the touch of skin. Moreover, it improves the common problem of poor edge coverage (shrinking or bulging) during powder coating spraying and curing, and can be advantageously used for coating substrates made of, for example, steel, aluminum, magnesium, or any alloy thereof, such as components of various industrial products, household products, or digital products (such as laptop computers, etc.).

[0006] A powder coating composition comprising a first component and a second component, wherein the first component comprises a combination of a high hydroxyl value polyester resin and a low hydroxyl value polyester resin, the hydroxyl value of the high hydroxyl value polyester resin is 200 - 400 mgKOH / g, the hydroxyl value of the low hydroxyl value polyester resin is 30 - 70 mgKOH / g; and the second component comprises an isocyanate curing agent.

[0007] The present invention also provides a coated substrate, comprising a substrate and the powder coating composition coated on at least a part of the substrate.

[0008] The present invention further provides a component, comprising the above-mentioned coated substrate.

[0009] The present invention additionally provides a method for treating a substrate, comprising: spraying the powder coating composition onto at least a part of the substrate; and curing the coating composition.

[0010] The features and advantages of the present invention will be specifically presented in the following detailed description of the embodiments. Detailed Embodiments

[0011] In this application, unless otherwise clearly stated, the use of the singular includes the plural and the plural includes the singular. For example, although "a" resin is mentioned herein, one or more resins can be used.

[0012] In this application, the terms "comprising", "including" and "containing" etc. do not limit the present invention to exclude any variants or additions. In addition, although the present invention has described the coating composition, preparation method, etc. in terms of "comprising" etc., the coating composition, preparation method, etc. detailed herein can also be described as "consisting essentially of..." or "consisting of...". In this case, "consisting essentially of..." means that any additional components will not substantially affect the properties of the coating formed by the coating composition.

[0013] In this application, unless otherwise clearly stated, the use of "or" means "and / or", even though "and / or" can be explicitly used in some cases. Additionally, it should be understood that any numerical range listed herein is intended to include all sub-ranges contained therein. For example, the range of "1 to 10" is intended to include all sub-ranges between the recited minimum value of 1 and the recited maximum value of 10 (including the end values), i.e., all sub-ranges having a minimum value equal to or greater than 1 and a maximum value equal to or less than 10.

[0014] Except as in the examples or otherwise clearly stated, it should be considered that all numerical values representing the amounts of components etc. used in the specification and claims can be varied in all cases according to the term "about". Therefore, unless there is a contrary statement, the numerical parameters listed in the following specification and claims are approximate values and can be varied according to the performance desired by the present invention. At the very least, not to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be interpreted at least according to significant figures and ordinary rounding.

[0015] Although the numerical ranges and parameters that describe the broad scope of the present invention are approximations, the numerical values recited in the specific embodiments are recorded as accurately as possible. However, any numerical value inherently has a certain error, which is an inevitable result of the standard deviation in its corresponding measurement method.

[0016] In one aspect, the present invention relates to a powder coating composition comprising a first component and a second component, wherein the first component comprises a combination of a high hydroxyl value polyester resin and a low hydroxyl value polyester resin, the hydroxyl value of the high hydroxyl value polyester resin is 200 to 400 mgKOH / g, and the hydroxyl value of the low hydroxyl value polyester resin is 30 to 70 mgKOH / g; and the second component comprises an isocyanate curing agent.

[0017] As used herein, the term "powder coating" refers to a solid powder coating composed of components such as a resin, a curing agent, and other additives such as pigments, fillers, and / or auxiliaries. The "powder" refers to a substance dried at room temperature (i.e., 20 to 30 °C) and atmospheric pressure, which is in a fine and loose particulate state. Generally, the maximum size of a single particle in the powder coating does not exceed 200 μm, and the particle size can be obtained by sieving.

[0018] The powder coatings described herein can have medium gloss to low gloss. As used herein, the term "medium gloss" means that the coating can form a 60-degree angle gloss of 31% to 70% after coating and curing; the term "low gloss" means that the coating can form a 60-degree angle gloss of 3% to 30% after coating and curing. The glossiness value can be obtained by measuring with a commercially available glossmeter.

[0019] The powder coating composition according to the present invention also has excellent leveling properties. In some examples, the leveling property of the powder coating composition according to the present invention can even be comparable to the excellent leveling property of liquid coatings. As used herein, the "leveling property" of a powder coating refers to the flatness and smoothness of the coating formed on the surface of a substrate, which directly affects the surface gloss and color consistency of the coating. The higher the leveling grade, the better the flatness and smoothness of the coating on the substrate surface, and the higher the color consistency. Moreover, the leveling grade also directly affects the service life and weather resistance of the coating. Coatings with good leveling properties have better adaptability and stability to environmental and temperature changes, and can effectively extend the service life of the coating. In short, the leveling grade of powder coatings is one of the important criteria for evaluating the quality and surface smoothness of coatings. A suitable leveling grade can obtain better coating effects and service life, and help improve the quality and competitiveness of products. In some examples, the powder coating according to the present invention can have a leveling grade of ≥7, and suitably, can have a leveling grade of ≥8. As used herein, the "leveling grade" is rated with reference to the PCI standard panel, which is developed by the PCI Powder Coating Research Institute and produced by ACT. These panels are used to evaluate the smoothness of powder coatings and are regarded as the standard for the smoothness performance in the powder coating industry.

[0020] The powder coating composition according to the present invention is a thermosetting coating composition, that is, the coating composition irreversibly forms a coating film after curing, which does not melt upon reheating and is insoluble in solvents. Herein, the term "curing" means that at least a part of the components in the coating composition are polymerized and / or crosslinked, or are dried to form a hardened coating film. The coating composition according to the present invention can be cured by heating. For example, the powder coating composition can be cured by heating at 180 - 240 °C (e.g., by baking) for 8 - 20 min. As used herein, the term "curable" means that after heating (e.g., by baking) for the curing time under suitable conditions, the formed film layer has a MEK double rub value of at least 50 times, and suitably even has a MEK double rub value of at least 70 times. Suitably, the powder coating composition can be cured by heating at 200 - 220 °C (e.g., by baking) for 10 - 15 min. Suitably, the thickness range of the film cured from the powder coating composition can be 50 - 150 μm, for example, 60 - 90 μm.

[0021] The first component of the powder coating composition may include a combination of a high hydroxyl value polyester resin and a low hydroxyl value polyester resin. Among them, the hydroxyl value of the high hydroxyl value polyester resin may be 200-400 mgKOH / g, for example, 250-330 mgKOH / g; the hydroxyl value of the low hydroxyl value polyester resin may be 30-70 mgKOH / g, for example, 30-50 mgKOH / g. If the hydroxyl values of the above high hydroxyl value and / or low hydroxyl value polyester resins are too high or too low (that is, higher than the upper limit of the corresponding range or lower than the lower limit of the corresponding range), problems such as unstable gloss, poor leveling, and poor mechanical properties of the coating will occur.

[0022] Suitably, the high hydroxyl value polyester resin may have a number average molecular weight (M n ) of 2,000-3,000, such as an M n of 2,500; the low polyester resin may have a number average molecular weight (M n ) of 3,000-4,000, such as an M n of 3,500. The number average molecular weight M n can be measured by gel permeation chromatography using appropriate standards such as polystyrene standards. If the molecular weights of the above high hydroxyl value and / or low hydroxyl value polyester resins are too high or too low (that is, higher than the upper limit of the corresponding range or lower than the lower limit of the corresponding range), it may cause problems such as unstable gloss, poor leveling, and poor mechanical properties of the coating.

[0023] Suitably, the high hydroxyl value polyester resin may have an acid value of no more than 15 mgKOH / g, such as an acid value of no more than 10 mgKOH / g, for example, an acid value of no more than 8 mgKOH / g, for example, an acid value of no more than 2 mgKOH / g. The low hydroxyl value polyester resin may have an acid value of no more than 15 mgKOH / g, such as an acid value of no more than 10 mgKOH / g, for example, an acid value of no more than 8 mgKOH / g, for example, an acid value of no more than 6 mgKOH / g, for example, an acid value of no more than 2 mgKOH / g. As used herein, the term "acid value" refers to the milligrams of potassium hydroxide required to neutralize the free acid in 1 gram of resin. If the acid values of the above high hydroxyl value and / or low hydroxyl value polyester resins are too high (that is, higher than the upper limit of the corresponding range), it may cause unstable gloss and incomplete curing of the coating film.

[0024] Suitably, the glass transition temperature of the high hydroxyl value polyester resin may be 50-55 °C, and the glass transition temperature of the low hydroxyl value polyester resin may be 55-60 °C. The glass transition temperature can be measured by dynamic thermomechanical analysis (DMA) using a TA Instruments Q800 instrument, with measurement parameters: frequency of 10 Hz, amplitude of 5 mm, temperature ramp from -100 °C to 250 °C, T gDetermined as the peak of the tanδ curve according to ASTM D7028.

[0025] Suitably, at least one of the high hydroxyl value polyester resin and the low hydroxyl value polyester resin is super weather resistant, and preferably both of the high hydroxyl value polyester resin and the low hydroxyl value polyester resin are super weather resistant. As used herein, the term "super weather resistant" means that the resin is made into a powder coating according to the recommended standard formula, and after spraying and curing, the xenon lamp aging test is carried out in accordance with GB / T16422.2-2014, and the gloss retention rate is greater than or equal to 90% after 1000 hours; "meeting the super weather resistance requirements" means that the coating formed after spraying and curing of the coating is subjected to the xenon lamp aging test in accordance with GB / T 16422.2-2014, and the gloss retention rate is greater than or equal to 90% after 1000 hours.

[0026] Suitably, the range of the weight ratio of the high hydroxyl value polyester resin to the low hydroxyl value polyester resin can be 8-15:30-40. For example, the range of the weight ratio of the high hydroxyl value polyester resin to the low hydroxyl value polyester resin can be 1:2-1:5. When the weight ratio is lower than 1:5, that is, when the content of the high hydroxyl value polyester resin in the first component is too low, it may cause the coating film to be difficult to mat; when the weight ratio is higher than 1:2, that is, when the content of the high hydroxyl value polyester in the first component is too high, it may cause poor mechanical properties of the coating film.

[0027] The second component of the powder coating composition may include an isocyanate curing agent. The isocyanate curing agent may include monoisocyanate, diisocyanate and / or polyisocyanate. The "polyisocyanate" refers to a compound containing three or more isocyanate (-NCO) groups. The isocyanate included in the second component of the coating composition according to the present invention may include aliphatic isocyanate and / or alicyclic isocyanate. In some examples, the isocyanate curing agent may be a self-blocking polyisocyanate.

[0028] Suitably, the second component may include a combination of one isocyanate or multiple isocyanates. For example, the second component may be a combination of two or more isocyanate curing agents. Examples of isocyanate curing agents that can be used for polyester resins include but are not limited to: BF1320, BF1321, etc. purchased from Evonik of Germany. For example, a combination of BF1320 and BF1321 can be used. In some examples, the weight ratio of BF1320 to BF1321 can be any ratio combination. For example, in order to obtain a lower gloss, a higher proportion of BF1321 can be added; in order to obtain a higher gloss, a higher proportion of BF1320 can be added.

[0029] Suitably, the total NCO content of the isocyanate curing agent in the second component is 10-18 wt%, and the free NCO content is less than 1 wt%.

[0030] The weight ratio of the first component to the second component can be from 3:1 to 1:1, for example, from 5:2 to 2:1. When the weight ratio is lower than 1:1 or higher than 3:1, that is, when the content of the first component is too low or too high, it may cause problems such as unstable gloss, poor leveling, and poor mechanical properties of the coating.

[0031] In the powder coating composition of the present invention, the combination of a high hydroxyl value polyester resin and a low hydroxyl value polyester resin provides a good gloss effect; the combination of two curing agents helps to improve gloss stability; the polyester resin makes the powder coating composition have good weather resistance; the combination of the above components also provides a leveling property comparable to that of liquid coatings, thereby providing a powder coating with good comprehensive properties.

[0032] Suitably, the powder coating composition of the present invention may further comprise one or more selected from the group consisting of: a leveling agent, a rheological modifier, and a degassing agent. The leveling agent, rheological modifier, and degassing agent can further improve the leveling property and rheological properties of the powder coating composition, so that a smooth and flat surface can be obtained when it is sprayed onto the surface of the substrate, and it helps to improve the phenomenon of poor edge coverage (edge shrinkage or edge thickening). Based on the total weight of the coating composition, the amount of each of the leveling agent, rheological modifier, and degassing agent can be 0 to 5 wt% of the composition.

[0033] The powder coating composition of the present invention may also comprise wax. Examples of suitable waxes may be micronized waxes, for example, one or more of polyethylene wax (PE wax), polypropylene wax (PP wax), polytetrafluoroethylene wax (PTFE wax), polyamide wax (PA wax), etc. Adding wax powder in the powder coating composition can effectively reduce the coefficient of friction and improve the scratch resistance and hand feeling of the cured coating. Based on the total weight of the coating composition, the amount of the wax can be 0 to 5 wt% of the composition.

[0034] The powder coating composition of the present invention may further include a flash edge improving aid. As used herein, "flash edge" may also be referred to as "thick edge" or "powder build-up", which refers to the phenomenon that the powder coating accumulates near the edge of the sprayed board or workpiece during spraying, resulting in the edge of the formed coating film bulging and being significantly thicker than other parts. Adding a flash edge improving aid to the powder coating composition can further improve or eliminate the flash edge phenomenon of the powder coating. For example, adding a flash edge improving aid to the powder coating composition can make the coating formed by the powder coating not have obvious flash edges. As used herein, "obvious flash edge" means that the difference between the average thickness of the edge area and the average thickness of the central area of the coating formed by the powder coating is not more than 100% of the average thickness of the central area, for example, not more than 80%, not more than 60%, not more than 50%, not more than 40%, not more than 30% or not more than 20%, etc. Based on the total weight of the coating composition, the amount of the flash edge improving aid can be 0 - 5 wt% of the composition.

[0035] The powder coating composition of the present invention may further contain a pigment and filler (i.e., pigment and / or filler). The pigment and filler can impart color and / or visual effects to the powder coating, and / or improve the relevant mechanical properties of the powder coating, such as hardness, abrasion resistance, corrosion resistance, stability, etc. Generally, based on the total weight of the powder coating composition, the pigment and filler may be present in the composition in an amount of about 10 - 30 wt%.

[0036] The coating composition according to the present invention may further contain one or more other auxiliary components / auxiliaries. The other auxiliary components include, but are not limited to, one or more of anti-pollution agents, dusting agents, coupling agents, anti-caking agents, anti-scratch agents, antistatic agents, antibacterial agents, anti-aging agents, slip agents, flame retardants, viscosity modifiers, antioxidants, etc. When used, those skilled in the art can adjust the content of the other auxiliary components according to actual needs. Generally, based on the total weight of the powder coating composition, the amount of each of the other auxiliary components may not exceed 5 wt%, for example, the amount of one or more or all of them may not exceed 2 wt% each.

[0037] The present invention also provides a coated substrate, comprising: a substrate and the powder coating composition coated on at least a part of the substrate. Suitably, the substrate may include one or more selected from the group consisting of aluminum, magnesium, steel, titanium, nickel or any alloy thereof. For example, the substrate may be steel (stainless steel), magnesium, magnesium alloy, aluminum, aluminum alloy or magnesium aluminum alloy.

[0038] The substrate may be a metal component of various products. For example, the substrate may be a metal component of various industrial products, household products or digital products. Examples of suitable substrates may include, but are not limited to, metal tools (such as wrenches, screwdrivers, nuts, sockets, etc.), automotive parts, the housings or their components of household appliances (such as TVs, washing machines, refrigerators, kitchen appliances, etc.), the housings or their components of household tools (such as mop poles, metal trays, storage boxes, etc.), the housings or their components of instruments / gauges (such as various detection instruments or gauges, etc.), the housings or their components of digital products (for example, one or more of laptop computers, tablet computers, mobile phones and digital photo frames, etc.). Suitably, the substrate may be the housing or a partial housing component of a laptop computer, a tablet computer, a mobile phone, a photo frame, a mop pole, a metal tray, a metal tabletop, a washing machine, a refrigerator, a small kitchen appliance, or may be a component of any other suitable product, etc. For example, the substrate may be a product housing made of a metal material such as steel, aluminum, magnesium or their alloys, etc.

[0039] The present invention also provides a component comprising a substrate and a coating applied to at least a part of the substrate, wherein the coating is formed from the powder coating composition. Suitably, the film thickness of the coating may be 50 - 150 μm, for example, 60 - 90 μm.

[0040] Suitably, the coating on the component of the present invention may have medium gloss to low gloss. For example, the coating may have a 60° gloss of 3% - 70%. For example, the coating formed by a solid color coating may have a 60° gloss of 3% - 30%, for example, 3% - 20% of 60° gloss, for example, 5% - 15% of 60° gloss; the metallic color binding coating may have a 60° gloss of 3 - 70%, for example, 5% - 50% of 60° gloss, for example, 5 - 20% of 60° gloss, for example, 10% - 15% of 60° gloss. As used herein, the term "solid color coating" also referred to as solid color paint, refers to a coating film formed after curing of a powder coating that does not contain effect pigments such as aluminum powder mica; the term "metallic color binding coating" also referred to as metallic color paint, refers to a coating film formed after curing of a powder coating that contains effect pigments such as aluminum powder and / or mica. The 60° gloss refers to the gloss measured at a 60° angle using a gloss meter (such as a commercially available gloss meter).

[0041] Suitably, the coating of the present invention satisfies one or more of the following items:

[0042] I) Evaluated according to the PCI leveling grade, the leveling property ≥ 7 grades, for example, the leveling property ≥ 8 grades;

[0043] II) Measured according to ASTM D3359, the adhesion ≥ 5B;

[0044] III) As measured according to ASTM D3363, the hardness is ≥ 2H, for example, greater than 3H, or greater than 4H;

[0045] IV) No obvious flash;

[0046] V) The weather resistance meets the requirements of super weather resistance.

[0047] Suitably, the substrate may comprise one or more selected from the group consisting of: aluminum, magnesium, steel / stainless steel, titanium, nickel or any alloy thereof. For example, the substrate may be steel / stainless steel, magnesium, magnesium alloy, aluminum, aluminum alloy or magnesium-aluminum alloy.

[0048] The substrate may be a metal part of various products. For example, the substrate may be a metal part of various industrial products, household products or digital products. Examples of suitable substrates may include, but are not limited to, metal tools (such as wrenches, screwdrivers, nuts, sockets, etc.), automotive parts, the housings or their components of household appliances (such as televisions, washing machines, refrigerators, kitchen appliances, etc.), the housings or their components of household tools (such as mop poles, metal trays, storage boxes, etc.), the housings or their components of instruments / instruments (such as various detection instruments or meters, etc.), the housings or their components of digital products (for example, one or more of laptop computers, tablet computers, mobile phones and digital photo frames, etc.). Suitably, the substrate may be the housing or part of the housing components of a laptop computer, tablet computer, mobile phone, photo frame, mop pole, metal tray, metal tabletop, washing machine, refrigerator, small kitchen appliances, or may be a part of any other suitable product. For example, the substrate may be a product housing made of metal material such as steel, aluminum, magnesium or their alloys.

[0049] The present invention also provides a method for treating a substrate, comprising: spraying a powder coating composition onto at least a part of the substrate; and curing the coating composition. Suitably, the curing may be carried out by baking at 180 - 240 °C for 8 - 20 min. For example, the curing may be carried out by baking at 200 - 220 °C for 10 - 15 min.

[0050] Examples

[0051] The following examples are provided to further illustrate the present invention, but it should not be considered as limiting the present invention to the details described in the examples. Unless otherwise specified, all parts and percentages in the following examples are by weight.

[0052] Preparation of the two-component coating composition according to the present invention

[0053] Prepare the powder coating composition according to the present invention using the components and contents listed in Table 1 below, where Ex1 to Ex8 are solid color powder coating formulations, and Ex9 to Ex12 are metallic bonded powder coating formulations. The preparation method includes: mixing the components except for the externally added edge improvement aid together and stirring evenly at room temperature and atmospheric pressure, and then mixing the externally added edge improvement aid with the previously prepared mixture evenly before coating to obtain the desired powder coating composition. The units of the values listed in Tables 1 and 2 below are parts by weight.

[0054] Table 1. Solid Color Powder Coating Composition According to the Present Invention

[0055]

[0056] Table 2. Metallic Bonded Powder Coating Composition According to the Present Invention

[0057] Raw materials EX9 EX10 EX11 EX12 <![CDATA[High-hydroxyl resin a > 10.0 10.0 10.0 10.0 <![CDATA[Low-hydroxyl resin b > 40.0 40.0 40.0 40.0 <![CDATA[Curing agent c > 20.0 10.0 10.0 <![CDATA[Curing agent d > 10.0 20.0 10.0 <![CDATA[Leveling agent e > 1.0 1.0 1.0 1.0 <![CDATA[Degassing agent f > 0.3 0.3 0.3 0.3 <![CDATA[Rheological aid g > 0.5 0.5 0.5 0.5 <![CDATA[Wax powder h > 0.5 0.5 0.5 0.5 <![CDATA[Filler i > 26.7 26.7 26.7 6.2 <![CDATA[Hardening filler j > 20.0 <![CDATA[Flash improvement agent k > 0.3 <![CDATA[Colorant l > 1.0 1.0 <![CDATA[Colorant m > 1.0 1.0 <![CDATA[External addition of edge thickening improvement agent n > 0.2 <![CDATA[Binding aluminum powder o > 0.3 2 2 <![CDATA[Binding mica p > 0.1 Total 100.1 100.3 102.0 102.0

[0058] Note:

[0059] a High hydroxyl value polyester resin: ALBESTER SILKYMATT 6615, obtained from Synthomer, with a number average molecular weight of: 2500; hydroxyl value of: 270 - 300 mg KOH / g; acid value of ≤6 mg KOH / g;

[0060] b Low hydroxyl value polyester resin: ALBESTER SILKYMATT 6620, obtained from Synthomer, with a number average molecular weight of: 3500; hydroxyl value of: 38 - 48 mg KOH / g; acid value of: ≤4 mg KOH / g;

[0061] c Curing agent: BF1321, obtained from Evonik

[0062] d Curing agent: BF1320, obtained from Evonik

[0063] e Leveling agent: PL - 200;

[0064] f Degassing agent: Benzoin;

[0065] g Rheology aid: Hydrogenated castor oil;

[0066] h Wax: PE - 310 POLYETHYLENE;

[0067] i Filler: Barium sulfate

[0068] j Hardening filler: glass fiber

[0069] k Flash improvement aid: fumed silica or fumed alumina

[0070] l Colorant: carbon black

[0071] m Colorant: titanium white

[0072] n Externally added flash improvement aid

[0073] o Binding aluminum powder: PCU 1000, obtained from Eckart

[0074] p Binding mica: T260 - 23, obtained from Merck

[0075] Performance test

[0076] The above powder coating compositions Ex1 - Ex12 were respectively coated on aluminum substrates, and then baked at 200 - 220 °C for 10 - 15 minutes to obtain parts 1 - 12. Then the following tests were respectively carried out on the parts 1 - 12 and the coatings formed thereon:

[0077] 1. Gloss

[0078] Using a commercially available gloss meter, the gloss of the coating was detected at 60° according to ASTM D523. After testing, the gloss of the coatings formed by the powder coating compositions Ex1 - Ex12 was all between 3% and 70%. Among them, the gloss of the solid color coatings (Ex1 - Ex8) was between 3 and 30%; the gloss of the metallic color coatings (Ex9 - Ex12) was between 5 and 70%.

[0079] 2. Levelling

[0080] The ACT PCI standard sample was used to evaluate the levelling grade of the powder coating composition to detect its levelling performance. After testing, the levelling grades of the powder coating compositions Ex1 - Ex12 were all ≥ 7 levels. The ACT PCI standard sample used here was developed by the PCI Powder Coating Research Institute and produced by ACT, and was used to evaluate the smoothness of the powder coating and was regarded as the standard for the smoothness performance of the powder coating industry.

[0081] 3. Appearance

[0082] The surface of the formed coating was observed with the naked eye to detect its appearance. After testing, on the surfaces of the coatings formed by the powder coating compositions Ex1 - Ex12, there were no sand holes, no bubbles, no cracks, no local accumulation or protrusions, no edge shrinkage or flash, and the surface was smooth and flat.

[0083] 4. Hardness

[0084] The hardness of the coating was detected according to ASTM 3363. After testing, the hardness of the powder coating compositions Ex1 to Ex12 was greater than or equal to 2H, showing good hardness effects.

[0085] 5. Substrate Adhesion

[0086] The adhesion of the coating was determined according to the ASTM D3359 standard. After testing, the adhesion of the powder coating compositions Ex1 to Ex12 to the aluminum substrate was ≥5B.

[0087] 6. Weather Resistance

[0088] The weather resistance of the coating was tested according to GB / T 16422.2 - 2014. After testing for 1000 hours, the powder coating compositions Ex1 to Ex12 all met the requirements that the gloss retention rate ≥90% and the color difference ≤2.

[0089] 7. Flash Index

[0090] The powder coating was sprayed on an aluminum plate of 150mm * 75mm * 0.6mm and baked at 200°C for 10 minutes to cure it. Samples with an area of 1cm * 1cm were randomly taken from the edge part and the center part of the sample plate, embedded with resin, polished, and then the film thickness was measured using a microscope. The maximum film thickness of the edge sample was denoted as E1, and the film thickness of the center sample was denoted as M1. The flash index F1 was calculated by the following formula:

[0091]

[0092] The detection was carried out three times in parallel, and the calculated average value of F1 was taken to obtain the final flash index F. Generally, when the F value <50% is better, the F value of 50% - 100% is medium, and the F value >100% is poor.

[0093] The specific results are shown in Table 3 and Table 4 below:

[0094] Table 3: Performance Test Results of the Plain Powder Coating Composition of the Present Application

[0095]

[0096] Table 4: Performance Test Results of the Bound Metallic Color Powder Coating Composition of the Present Application

[0097]

[0098]

[0099] As can be seen from the above results, the powder coating composition of the present invention has good matting effect and leveling property, can form a smooth and flat coating without flash, has good adhesion to the substrate, high coating hardness, and excellent weather resistance.

Claims

1. A powder coating composition comprising a first component and a second component, wherein the first component comprises a combination of a high hydroxyl value polyester resin and a low hydroxyl value polyester resin, the hydroxyl value of the high hydroxyl value polyester resin is 200 - 400 mgKOH / g, and the hydroxyl value of the low hydroxyl value polyester resin is 30 - 70 mgKOH / g; and the second component comprises an isocyanate curing agent.

2. The powder coating composition according to claim 1, wherein the acid value of the high hydroxyl value polyester resin is less than 8 mgKOH / g, and the acid value of the low hydroxyl value polyester resin is less than 6 mgKOH / g.

3. The powder coating composition according to claim 1 or 2, wherein the weight ratio range of the high hydroxyl value polyester resin to the low hydroxyl value polyester resin is 8 - 15:30 - 40.

4. The powder coating composition according to any one of claims 1 - 3, wherein, The weight ratio range of the first component to the second component is from 3:1 to 1:

1.

5. The powder coating composition according to any one of claims 1 - 4, wherein the total NCO content of the isocyanate curing agent is 10 - 18 wt%, and the free NCO content is less than 1 wt%.

6. The powder coating composition according to any one of claims 1 - 5, wherein the isocyanate curing agent comprises a combination of two or more isocyanate curing agents.

7. The powder coating composition according to any one of claims 1 - 6, further comprising one or more selected from the group consisting of: a leveling agent, a rheology modifier, and a degassing agent.

8. The powder coating composition according to any one of claims 1 - 7, further comprising wax.

9. The powder coating composition according to any one of claims 1 - 8, further comprising a flash edge improving aid.

10. The powder coating composition according to any one of claims 1 - 9, which can be cured at 180 - 240 °C for 8 - 20 min.

11. The powder coating composition according to any one of claims 1 - 10, wherein the thickness range of the film cured from the powder coating composition is 50 - 150 μm.

12. A coated substrate comprising: a substrate and the powder coating composition according to any one of claims 1 - 11 coated on at least a part of the substrate.

13. The coated substrate according to claim 12, wherein the substrate comprises one or more selected from the group consisting of: aluminum, magnesium, stainless steel, titanium, nickel, or any alloy thereof.

14. The coated substrate according to claim 12 or 13, wherein the substrate is a metal component of industrial products, household products, or digital products.

15. The coated substrate according to any one of claims 12 - 14, wherein the substrate is a laptop computer housing.

16. A component comprising the coated substrate according to any one of claims 12 - 15.

17. The component according to claim 16, wherein the coating meets one or more of the following: i) Leveling property ≥ grade 7 as measured by PCI; ii) Adhesion ≥ 5B as measured by ASTM D3359; iii) Hardness ≥ 2H as measured by ASTM D3363; iv) No obvious flash; and v) Weather resistance meets the requirements of super weather resistance.

18. A method of treating a substrate, comprising: Spray the powder coating composition according to any one of claims 1-11 onto at least a part of the substrate; and Cure the coating composition.

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