A matt powder coating composition, its preparation and use

Abstract

The application discloses a matt powder coating composition, which comprises the following raw materials: a high-activity polyester resin, a high-levelling polyester resin, a curing crosslinking agent and a matt agent; the acid value of the high-activity polyester resin is 60-80 mgKOH / g, the reactivity at 160 DEG C is 120-300 s, and the melt viscosity at 160 DEG C is less than or equal to 10000 mPa.s; the acid value of the high-levelling polyester resin is 40-60 mgKOH / g, the reactivity at 160 DEG C is 480-900 s, and the melt viscosity at 160 DEG C is less than or equal to 5000 mPa.s. The low-temperature curing matt powder coating composition of the application can be fully cured under the curing condition of 160 DEG C, and the coating after curing not only can obtain ideal matt effect, but also can obtain excellent appearance flatness and delicateness, and in addition, the coating has good physical and chemical properties such as impact resistance, bending resistance and chemical resistance.

Description

Technical Field

[0001] This invention belongs to the field of powder coating technology, specifically relating to a matte powder coating composition, its preparation method, and its application. Background Technology

[0002] Thermosetting powder coatings, as an environmentally friendly coating with zero VOC emissions, offer advantages such as low overall cost, low energy consumption, convenient application, and excellent performance, and are rapidly replacing traditional solvent-based coatings in the coating of metal substrates. The rapid economic growth in China over the past decade has driven the booming development of the automotive industry. Under the requirements of environmental policies, more and more automotive parts are using powder coatings, with matte powder coatings being the primary method for primer application on aluminum wheel rims. Currently, powder coatings for aluminum wheel rims generally require relatively high curing temperatures (180-200℃) to ensure sufficient curing. Excessively high curing temperatures can reduce the toughness of aluminum wheel rims, posing certain safety hazards. Therefore, aluminum wheel rim manufacturers hope to lower the curing temperature of powder coatings to 150-160℃. Lower curing temperatures not only improve the safety of aluminum wheel rims but also save energy and reduce production costs for enterprises.

[0003] In addition to meeting basic protective performance requirements, powder coatings for aluminum wheels also place extremely high demands on decorative performance. They require not only a good matte finish (gloss level not exceeding 30%) but also excellent surface leveling (PC I leveling grade ≥ 7). While existing low-temperature curing powder coatings can achieve curing temperatures below 160℃, they suffer from poor matte finish and poor surface leveling after matte coating, failing to meet the requirements for aluminum wheel coating. Because the mechanisms of low-temperature curing, matte finish, and leveling used in existing technologies are mutually inhibiting or conflicting, low-temperature curing high-leveling matte powder coating compositions are currently lacking in the market. Summary of the Invention

[0004] To overcome the problems existing in the prior art, one objective of the present invention is to provide a matte powder coating composition. A second objective of the present invention is to provide a method for preparing the above-mentioned matte powder coating composition. A third objective of the present invention is to provide applications of the above-mentioned matte powder coating composition. A fourth objective of the present invention is to provide a metal substrate.

[0005] Existing technologies primarily address the issues of low-temperature curing, matte finish, and leveling by employing a single polyester. However, due to the interdependent or contradictory mechanisms among these three properties, existing technologies fundamentally fail to achieve a balance between all three. This invention addresses the incompatibility of low-temperature curing, matte finish, and leveling by blending two polyesters with different performance characteristics. The highly reactive polyester provides excellent reactivity and matte finish at low temperatures, while the high-leveling polyester resin offers excellent leveling performance at low temperatures. Furthermore, the high-leveling polyester resin exhibits lower reactivity than the highly reactive polyester. The powder coating prepared from this blend exhibits a reaction system with multiple curing rates during curing. This difference in curing rate disrupts the continuity of the coating film, further enhancing the matte finish. Adding a certain amount of matting agent to the powder formulation further increases the complexity of the curing reaction, ultimately resulting in an ideal matte finish.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A first aspect of the present invention provides a matte powder coating composition comprising the following raw materials: a highly active polyester resin, a high-leveling polyester resin, a curing crosslinking agent, and a matting agent;

[0008] The highly reactive polyester resin has an acid value of 60-80 mgKOH / g, a reactivity of 120-300 s at 160℃, and a melt viscosity of ≤10000 mPa.s at 160℃.

[0009] The high-level polyester resin has an acid value of 40-60 mgKOH / g, a reactivity of 480-900 s at 160℃, and a melt viscosity of ≤5000 mPa.s at 160℃.

[0010] The molecular structural formula of the highly reactive polyester resin is:

[0011]

[0012] The molecular structural formula of the high-level polyester resin is:

[0013]

[0014] Among them, R1, R2, R3, R4, R5, R 1 R 2 R 3 R 4 R 5 R 6 Each independently represents either the unsubstituted or substituted C. 1-20 Alkyl or C 6-20 Aryl;

[0015] The mass ratio of the highly active polyester resin to the highly leveling polyester resin is (1-4):1.

[0016] Preferably, the highly active polyester resin is prepared from the following raw materials: polyol 1, polyacid 1, acidifier 1, esterification catalyst, and crosslinking catalyst; the polyol 1 is an aliphatic and / or alicyclic diol; the polyacid 1 is an aromatic diacid and an aliphatic diacid; the acidifier 1 is an aromatic polyacid anhydride; the molar ratio of the polyol 1 to the polyacid 1 is 1:(1-1.3); the molar ratio of the polyol 1 to the acidifier 1 is 1:(0.05-0.2).

[0017] More preferably, the highly active polyester resin is prepared from raw materials comprising the following molar amounts: 90-110 parts of polyol 1, 100-125 parts of polyacid 1, 10-20 parts of acidifier 1, 0.05-0.2 parts of esterification catalyst, and 2-4 parts of crosslinking catalyst.

[0018] More preferably, the acid hydrolysant 1 is selected from trimellitic anhydride, pyromellitic anhydride or a combination thereof.

[0019] This invention utilizes highly reactive anhydrides with ≥3 functional groups for terminal carboxylation to obtain the highly reactive polyester resin. The highly reactive anhydrides at the ends of the polyester main chain can not only improve the reactivity of the polyester, but also increase the crosslinking density of the coating film, thereby endowing the coating film with good mechanical properties.

[0020] More preferably, the polyol 1 is selected from at least one of neopentyl glycol, ethylene glycol, diethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, pentanediol, hexanediol, and 1,4-cyclohexanediol.

[0021] More preferably, the polyol 1 is composed of neopentyl glycol and other aliphatic and / or alicyclic polyols, and the molar ratio of neopentyl glycol to the other aliphatic and / or alicyclic polyols is (1-4):1.

[0022] More preferably, the polyol 1 is composed of neopentyl glycol, ethylene glycol, diethylene glycol, and 2-methyl-1,3-propanediol, wherein the molar percentage of neopentyl glycol is 50-80 mol%.

[0023] More preferably, the aromatic dicarboxylic acid in the polycarboxylic acid 1 is selected from at least one of terephthalic acid, isophthalic acid, phthalic anhydride, and pyromellitic acid, and the aliphatic dicarboxylic acid in the polycarboxylic acid 1 is selected from at least one of succinic acid, adipic acid, glutaric acid, and 1,4-cyclohexanedicarboxylic acid.

[0024] More preferably, the molar ratio of aromatic dicarboxylic acid to aliphatic dicarboxylic acid in the polycarboxylic acid 1 is (4-20):1.

[0025] Preferably, the high-level polyester resin is prepared from the following raw materials: polyol 2, polyacid 2, acidifier 2, esterification catalyst, and crosslinking catalyst; the polyol 2 is an aliphatic and / or alicyclic diol and an aliphatic triol; the polyacid 2 is an aromatic diacid; the acidifier 2 is an aromatic diacid and an aliphatic diacid; the mass ratio of the polyol 2 to the polyacid 2 is 1:(0.85-1); the mass ratio of the polyol 2 to the acidifier 2 is 1:(0.1-0.25).

[0026] More preferably, the high-level polyester resin is made from raw materials comprising the following molar amounts: 90-110 parts of polyol 2, 85-100 parts of polyacid 2, 10-23 parts of acidifier 2, 0.05-0.2 parts of esterification catalyst, and 0.4-0.8 parts of crosslinking catalyst.

[0027] More preferably, the aliphatic dicarboxylic acid in the acid hydrolysate 2 is selected from at least one of succinic acid, adipic acid, and glutaric acid.

[0028] This invention utilizes a dicarboxylic acid for terminal carboxylation to obtain the high-leveling polyester resin. The dicarboxylic acid at the end of the polyester main chain can control the reactivity of the polyester and reduce the reaction rate with the curing agent, allowing the powder coating to have sufficient time to melt and level during the curing process, thereby giving the coating film good leveling properties. At the same time, the addition of a small amount of triol can ensure that the curing system can form a certain spatial network structure, giving the coating film certain mechanical properties.

[0029] More preferably, the aliphatic and / or alicyclic diol in the polyol 2 is selected from at least one of neopentyl glycol, ethylene glycol, diethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, pentanediol, hexanediol, and 1,4-cyclohexanediol, and the aliphatic triol in the polyol 2 is selected from at least one of trimethylolpropane, trimethylolethane, and pentaerythritol.

[0030] More preferably, the polyol 2 is composed of neopentyl glycol, other aliphatic and / or alicyclic polyols and aliphatic triols.

[0031] More preferably, the polyol 2 is composed of neopentyl glycol, ethylene glycol, diethylene glycol, 2-methyl-1,3-propanediol, and trimethylolpropane, wherein the molar percentage of neopentyl glycol is 40-70 mol%.

[0032] More preferably, the polybasic acid 2 is selected from at least one of terephthalic acid, isophthalic acid, and phthalic acid.

[0033] More preferably, the esterification catalyst is selected from at least one of monobutyltin oxide, monobutyltin chloride, and tetrabutyl titanate.

[0034] More preferably, the crosslinking catalyst is selected from at least one of benzyltrimethylammonium chloride, triphenylphosphine, triphenylethylphosphine bromide, and tert-butylamine.

[0035] More preferably, the highly reactive polyester resin is prepared by a method comprising the following steps:

[0036] A1: Polyol 1, polyacid 1 and esterification catalyst are mixed and esterification reaction is carried out to obtain esterification product 1;

[0037] A2: Add acidifying agent 1 to the esterification product 1 and carry out acid hydrolysis reaction to obtain acidification product 1;

[0038] A3: Acidification product 1 is reacted with a crosslinking catalyst to obtain a highly active polyester resin.

[0039] More preferably, in A1, the acid value of the esterification product 1 is 15-26 mg KOH / g.

[0040] More preferably, in A1, the reaction temperature of the esterification reaction is 230-245℃.

[0041] More preferably, in A1, the esterification reaction is carried out under a protective atmosphere.

[0042] More preferably, A1 further includes: vacuum polycondensation of the esterified product 1.

[0043] More preferably, in A2, the reaction temperature of the acidolysis reaction is 215-225℃.

[0044] More preferably, in A2, the acid value of the acidification product 1 is 60-80 mg KOH / g.

[0045] More preferably, in A3, the reaction temperature is 170-190°C.

[0046] More preferably, the high-leveling polyester resin is prepared by a method comprising the following steps:

[0047] B1: Polyol 2, polyacid 2 and esterification catalyst are mixed and esterification reaction is carried out to obtain esterification product 2;

[0048] B2: Add acidifying agent 2 to the esterification product 2 and carry out acid hydrolysis reaction to obtain acidification product 2;

[0049] B3: Acidification product 2 reacts with a crosslinking catalyst to obtain a high-level polyester resin.

[0050] More preferably, in B1, the acid value of the esterified product 2 is 8-26 mg KOH / g.

[0051] More preferably, in B1, the reaction temperature of the esterification reaction is 230-245°C.

[0052] More preferably, in B1, the esterification reaction is carried out under a protective atmosphere.

[0053] More preferably, in B2, the reaction temperature of the acidolysis reaction is 220-235°C, and the reaction temperature of the acidolysis reaction is lower than that of the esterification reaction.

[0054] More preferably, B2 further includes: vacuum polycondensation of the acidified product 2.

[0055] More preferably, in B2, the acid value of the acidification product 1 is 55-70 mg KOH / g.

[0056] More preferably, in B3, the reaction temperature is 170-190°C.

[0057] Preferably, the curing crosslinking agent is an epoxy resin curing agent.

[0058] More preferably, the epoxy resin curing agent is a bisphenol A type epoxy resin.

[0059] More preferably, the bisphenol A type epoxy resin has a softening point of 70-95℃ and an epoxy equivalent of 650-950 g / mol.

[0060] Preferably, the mass ratio of the highly active polyester resin to the curing crosslinking agent is 1:(1-2.5).

[0061] Preferably, the matting agent is selected from one or a combination of physical matting agents, chemical matting agents, etc.

[0062] Preferably, the mass ratio of the highly active polyester resin to the matting agent is 1:(0.1-0.2).

[0063] Preferably, the matte powder coating composition further includes at least one of a leveling control agent, a degassing agent, and pigments / fillers.

[0064] More preferably, the polyester resin composition for matte powder coating comprises the following raw materials in parts by weight: 150-400 parts of high-activity polyester resin, 80-160 parts of high-leveling polyester resin, 250-500 parts of curing crosslinking agent, 20-50 parts of matting agent, 10-15 parts of leveling control agent, 2-6 parts of degassing agent, and 50-350 parts of pigments and fillers.

[0065] More preferably, the pigments and fillers are selected from at least one of titanium dioxide, iron oxide, zinc oxide, metal hydroxides, metal powders, sulfides, sulfates, carbonates, silicates, carbon black, talc, kaolin, barite, iron blue, lead blue, organic red, and organic violet.

[0066] The second aspect of the present invention provides a method for preparing the matte powder coating composition of the first aspect, comprising the following steps: mixing the components, extruding and kneading, and grinding to obtain the matte powder coating composition.

[0067] A third aspect of the invention provides the application of the matte powder coating composition described in the first aspect in the protection of workpiece surfaces.

[0068] Preferably, the matte powder coating composition is used in the surface protection of metal workpieces.

[0069] Preferably, the matte powder coating composition is used in the surface protection of aluminum workpieces.

[0070] A fourth aspect of the present invention provides a metal substrate, the surface of which is coated with a coating formed by curing the low-temperature curing matte powder coating composition of the first aspect.

[0071] Preferably, the metal substrate is prepared by the following steps: depositing a low-temperature curing powder coating composition onto the substrate using an electrostatic or triboelectric spray gun, or depositing the low-temperature curing powder coating composition onto the substrate using fluidized bed technology, and then heating and melting to form a coating.

[0072] More preferably, the curing temperature is 150-160°C.

[0073] The beneficial effects of this invention are:

[0074] (1) This invention provides a matte powder coating composition, which uses two polyesters with different performance characteristics to solve the problem that low-temperature curing, matting and leveling cannot be achieved at the same time. The high-activity polyester can provide good reactivity and matting performance at low temperature, while the high-leveling polyester resin can provide good leveling performance at low temperature. At the same time, the high-leveling polyester resin has lower reactivity than the high-activity polyester. The powder coating prepared by the two polyesters has a reaction system with multiple curing rates during curing. This difference in curing rate can disrupt the continuity of the coating film, which is beneficial to further improve the matting effect of the system. After adding a certain amount of matting agent to the powder formulation, the addition of matting agent will further increase the disorder of the curing reaction. At this time, the coating film can obtain an ideal matte effect.

[0075] (2) Compared with the prior art, the low-temperature curing matte powder coating composition of the present invention can achieve full curing under curing conditions of 160°C. The cured coating can not only obtain an ideal matte effect (coating gloss not higher than 30%), but also obtain excellent appearance smoothness (PCI leveling grade ≥ 7) and fineness. In addition, the coating has good physical and chemical properties such as impact resistance, bending resistance and chemical resistance, while conventional polyester / epoxy low-temperature curing powder coatings cannot achieve both matte and appearance leveling. Detailed Implementation

[0076] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials used in the following embodiments can be obtained from conventional commercial channels or prepared and isolated through simple synthesis; unless otherwise specified, the processes employed are conventional processes in the art.

[0077] Example 1

[0078] This embodiment provides a highly reactive polyester resin, the synthesis steps of which are as follows:

[0079] First stage: Mix the polyol and esterification catalyst according to the proportions in Example 1 in Table 1, heat until melted, then add the polyacid, purge with nitrogen and gradually raise the temperature to 235°C to carry out the esterification polycondensation reaction until the acid value of the reactants is 15-20 mg KOH / g.

[0080] Second stage: The temperature of the reactor was lowered to 230℃, and the esterification polycondensation reaction was carried out under vacuum of -0.094MPa for 120min. After the vacuum was released, the acid value of the polycondensation product was measured to be 5-10mgKOH / g.

[0081] Third stage: After the temperature of the reactor is further reduced to 225℃, trimellitic anhydride is added to carry out the acidification reaction until the acid value of the reactants is measured to be 63.8 mgKOH / g;

[0082] Fourth stage: After further reducing the reaction temperature to 190℃, add the crosslinking catalyst and stir for 25 minutes before discharging the material, which is then labeled HAPE1.

[0083] Example 2

[0084] This embodiment provides a highly reactive polyester resin, the synthesis steps of which are as follows:

[0085] First stage: Mix the polyol and esterification catalyst according to the proportions in Example 2 in Table 1, heat to melt, then add polyacid, purge with nitrogen and gradually raise the temperature to 238°C to carry out esterification polycondensation reaction until the acid value of the reactants is 18-24 mg KOH / g KOH / g.

[0086] Second stage: The temperature of the reactor was lowered to 230℃, and the esterification polycondensation reaction was carried out under vacuum of -0.094MPa for 100min. After the vacuum was released, the acid value of the polycondensation product was measured to be 8-14mgKOH / g.

[0087] Third stage: After the temperature of the reactor is further reduced to 220℃, trimellitic anhydride is added to carry out the acidification reaction until the acid value of the reactants is 66.1mgKOH / g;

[0088] Fourth stage: After further reducing the reaction temperature to 185℃, add the crosslinking catalyst and stir for 25 minutes before discharging the material, which is recorded as HAPE2.

[0089] Example 3

[0090] This embodiment provides a highly reactive polyester resin, the synthesis steps of which are as follows:

[0091] First stage: Mix the polyol and esterification catalyst according to the proportions in Example 3 in Table 1, heat until melted, then add the polyacid, purge with nitrogen and gradually raise the temperature to 240°C to carry out the esterification polycondensation reaction until the acid value of the reactants is 20-25 mg KOH / g.

[0092] Second stage: The temperature of the reactor was lowered to 230℃, and the esterification polycondensation reaction was carried out under vacuum of -0.094MPa for 90 minutes. After the vacuum was released, the acid value of the polycondensation product was measured to be 10-15mgKOH / g.

[0093] Third stage: After the temperature of the reactor is further reduced to 215℃, trimellitic anhydride is added to carry out the acidification reaction until the acid value of the reactants is measured to be 68.4 mgKOH / g;

[0094] Fourth stage: After the reaction temperature is lowered to 185℃, the crosslinking catalyst is added and stirred for 25 minutes before the material is discharged, which is recorded as HAPE3.

[0095] Example 4

[0096] This embodiment provides a highly reactive polyester resin, the synthesis steps of which are as follows:

[0097] First stage: Mix the polyol and esterification catalyst according to the proportions in Example 4 in Table 1, heat to melt, then add polyacid, purge with nitrogen and gradually raise the temperature to 243°C to carry out esterification polycondensation reaction until the acid value of the reactants is 22-26 mgKOH / g.

[0098] Second stage: The temperature of the reactor was lowered to 230℃, and the esterification polycondensation reaction was carried out under vacuum of -0.094MPa for 80 minutes. After the vacuum was released, the acid value of the polycondensation product was measured to be 11-17 mgKOH / g.

[0099] Third stage: After the temperature of the reactor is further reduced to 220℃, trimellitic anhydride and pyromellitic anhydride are added to carry out the acidification reaction until the acid value of the reactants is 73.3 mgKOH / g.

[0100] Fourth stage: After further reducing the reaction temperature to 185℃, add the crosslinking catalyst and stir for 25 minutes before discharging the material, which is recorded as HAPE4.

[0101] Example 5

[0102] This embodiment provides a highly reactive polyester resin, the synthesis steps of which are as follows:

[0103] First stage: Mix the polyol and esterification catalyst according to the proportions in Example 5 in Table 1, heat until melted, then add the polyacid, purge with nitrogen and gradually raise the temperature to 245°C to carry out the esterification polycondensation reaction until the acid value of the reactants is 23-28 mgKOH / g.

[0104] Second stage: The temperature of the reactor was lowered to 230℃, and the esterification polycondensation reaction was carried out under vacuum of -0.094MPa for 90min. After the vacuum was released, the acid value of the polycondensation product was measured to be 14-18mgKOH / g.

[0105] Third stage: After the temperature of the reactor is further reduced to 215℃, trimellitic anhydride and pyromellitic anhydride are added to carry out the acidification reaction until the acid value of the reactants is 76.4mgKOH / g.

[0106] Fourth stage: After the reaction temperature is lowered to 180℃, the crosslinking catalyst is added and stirred for 25 minutes before the product is discharged, which is recorded as HAPE5.

[0107] The raw materials and their quality at each stage are shown in Table 1.

[0108] Table 1. Input amounts of each raw material (unit: mol)

[0109]

[0110] Example 6

[0111] This embodiment provides a high-leveling polyester resin, the synthesis steps of which are as follows:

[0112] First stage: Mix the polyol and esterification catalyst according to the proportions in Example 6 in Table 2, heat to melt, then add polyacid, purge with nitrogen and gradually raise the temperature to 232°C to carry out esterification polycondensation reaction. After the material is clear, the acid value of the reactants is detected to be 8-12 mgKOH / g.

[0113] Second stage: After the reactor temperature is lowered to 230℃, acid hydrolysis agent is added and reacted for 150 minutes. After the material is clear, the acid value of the reactant is measured to be 55-59 mgKOH / g.

[0114] The third stage: The temperature inside the reactor was maintained at 230℃, and the acidified product was subjected to vacuum polycondensation reaction at a vacuum degree of -0.095Mpa for 90min. After the vacuum was released, the acid value of the polycondensation product was measured to be 45.1mgKOH / g.

[0115] Fourth stage: After further reducing the reaction temperature to 185℃, add the crosslinking catalyst and stir for 25 minutes before discharging the material, which is then labeled HLPE1.

[0116] Example 7

[0117] This embodiment provides a high-leveling polyester resin, the synthesis steps of which are as follows:

[0118] First stage: Mix the polyol and esterification catalyst according to the proportions in Example 7 in Table 2, heat to melt, then add polyacid, purge with nitrogen and gradually raise the temperature to 235°C to carry out esterification polycondensation reaction. After the material is clear, the acid value of the reactants is detected to be 10-14 mgKOH / g.

[0119] Second stage: After the temperature of the reactor is lowered to 230℃, the acid hydrolysis agent is added and the reaction is carried out for 180 minutes. After the material is clear, the acid value of the reactant is measured to be 57-61 mgKOH / g.

[0120] The third stage: The temperature inside the reactor was maintained at 230℃, and the acidified product was subjected to vacuum polycondensation reaction at a vacuum degree of -0.095Mpa for 100min. After the vacuum was released, the acid value of the polycondensation product was measured to be 47.3mgKOH / g.

[0121] Fourth stage: After the reaction temperature is lowered to 185℃, the crosslinking catalyst is added and stirred for 25 minutes before the material is discharged, which is recorded as HLPE2.

[0122] Example 8

[0123] This embodiment provides a high-leveling polyester resin, the synthesis steps of which are as follows:

[0124] First stage: Mix the polyol and esterification catalyst according to the proportions in Example 8 in Table 2, heat to melt, then add polyacid, purge with nitrogen and gradually raise the temperature to 238°C to carry out esterification polycondensation reaction. After the material is clear, the acid value of the reactants is detected to be 13-18 mgKOH / g.

[0125] Second stage: After the temperature of the reactor is lowered to 230℃, the acid hydrolysis agent is added and the reaction is carried out for 180 minutes. After the material is clear, the acid value of the reactant is measured to be 60-64 mgKOH / g.

[0126] The third stage: The temperature inside the reactor was maintained at 230℃, and the acidified product was subjected to vacuum polycondensation reaction at a vacuum degree of -0.095Mpa for 120min. After the vacuum was released, the acid value of the polycondensation product was measured to be 49.8mgKOH / g.

[0127] Fourth stage: After further reducing the reaction temperature to 185℃, add the crosslinking catalyst and stir for 25 minutes before discharging the material, which is recorded as HLPE3.

[0128] Example 9

[0129] This embodiment provides a high-leveling polyester resin, the synthesis steps of which are as follows:

[0130] First stage: Mix the polyol and esterification catalyst according to the proportions in Example 9 in Table 2, heat to melt, then add polyacid, purge with nitrogen and gradually raise the temperature to 240°C to carry out esterification polycondensation reaction. After the material is clear, the acid value of the reactants is detected to be 16-21 mgKOH / g.

[0131] Second stage: After the temperature of the reactor is lowered to 230℃, the acid hydrolysis agent is added and the reaction is carried out for 180 minutes. After the material is clear, the acid value of the reactant is measured to be 62-65 mgKOH / g.

[0132] The third stage: The temperature inside the reactor was maintained at 230℃, and the acidified product was subjected to vacuum polycondensation reaction at a vacuum degree of -0.095Mpa for 150min. After the vacuum was released, the acid value of the polycondensation product was measured to be 52.8mgKOH / g.

[0133] Fourth stage: After further reducing the reaction temperature to 185℃, add the crosslinking catalyst and stir for 25 minutes before discharging the material, which is then labeled HLPE4.

[0134] Example 10

[0135] This embodiment provides a high-leveling polyester resin, the synthesis steps of which are as follows:

[0136] First stage: Mix the polyol and esterification catalyst according to the proportions in Example 10 in Table 2, heat until melted, then add polyacid, purge with nitrogen and gradually raise the temperature to 240°C to carry out esterification polycondensation reaction. After the material is clear, the acid value of the reactants is tested to be 20-25 mg KOH / g.

[0137] Second stage: After the temperature of the reactor is lowered to 230℃, the acid hydrolysis agent is added and the reaction is carried out for 180 minutes. After the material is clear, the acid value of the reactant is measured to be 64-68 mgKOH / g.

[0138] The third stage: The temperature inside the reactor was maintained at 230℃, and the acidified product was subjected to vacuum polycondensation reaction at a vacuum degree of -0.095Mpa for 180min. After the vacuum was released, the acid value of the polycondensation product was measured to be 55.2mgKOH / g.

[0139] Fourth stage: After further reducing the reaction temperature to 185℃, add the crosslinking catalyst and stir for 25 minutes before discharging the material, which is then labeled HLPE5. The raw materials and their quantities used in each stage are shown in Table 2.

[0140] Table 2. Input amounts of each raw material (unit: mol)

[0141]

[0142]

[0143] In Tables 1 and 2 above:

[0144] The acid value was tested according to GB / T6743-2008;

[0145] Melt viscosity: ICI cone-plate viscosity measured at 160°C according to ASTM D4287-88;

[0146] Reactivity: refers to the time required for the resin and curing agent to react to form a gel, determined at 160℃ according to GB / T 16995-1997.

[0147] Examples 11-20

[0148] The obtained high-activity polyester and high-leveling polyester were mixed with curing crosslinking agent, matting agent, leveling control agent, degassing agent and pigments and fillers in the amounts specified in Tables 3 and 4 and formulated into powder coatings.

[0149] Powder coatings are prepared by the following method: First, different components are dry-mixed, then homogenized in melt form using a twin-screw extruder at a base temperature of 90-120°C, then the homogenized mixture is cooled and ground in a grinding tank, and then the powder is sieved to obtain a particle size of 10-90 μm, denoted as powder 5 to powder 14.

[0150] Comparative Examples 1-4

[0151] The obtained high-activity polyester and high-leveling polyester were mixed with curing crosslinking agent, matting agent, leveling control agent, degassing agent and pigments and fillers in the amounts specified in Table 3 and formulated into powder coatings.

[0152] Powder coatings are prepared by the following method: First, different components are dry-mixed, then homogenized in melt form using a twin-screw extruder at a base temperature of 90-120°C, then the homogenized mixture is cooled and ground in a grinding tank, and then the powder is sieved to obtain a particle size of 10-90 μm, denoted as comparative powder 1 to comparative powder 4.

[0153] Table 3

[0154]

[0155]

[0156] Table 4

[0157] Powder 7 Powder 8 Powder 9 Powder 10 Powder 11 Powder 12 Powder 13 Powder 14 HAPE1 180 / / / / / / 246 HAPE2 / 220 / / / 200 / / HAPE3 / / 280 / / 286 / HAPE4 / / / 360 / / / / HAPE5 / / / / 160 / / / HLPE1 150 / / / / / / 84 HLPE2 / 144 / / / 120 / / HLPE3 / / 120 / / / 114 / HLPE4 / / / 90 / / / / HLPE5 / / / / 144 / / / E-12 280 316 360 420 316 370 482 452 PM228 332 254 165 46 323 244 44 133 GLP588 14 12 11 10 13 12 10 11 701 6 6 6 6 6 6 6 6 Benzoin 4 4 4 4 4 4 4 4 PE520 6 6 6 6 6 6 6 6 carbon black 8 8 8 8 8 8 8 8 3390 20 30 40 50 / / / / X-8 / / / / 20 30 40 50

[0158] In the table:

[0159] E-12 is an epoxy resin curing agent, manufactured by Sinopec Hunan Petrochemical Co., Ltd.

[0160] PM228 is a type of barium sulfate, manufactured by Guangdong Xinmei Nanotechnology Co., Ltd.

[0161] GLP588 is a leveling agent, manufactured by Ningbo Nanhai Chemical Co., Ltd.

[0162] 701 is a brightening agent, manufactured by Ningbo Nanhai Chemical Co., Ltd.

[0163] Benzoin is a degassing agent; Ningbo Nanhai Chemical Co., Ltd.

[0164] PE520 is a wax powder, manufactured by Clariant Chemicals (China) Co., Ltd.

[0165] 3390 is a physical matting agent, produced by Guangzhou Zehe Chemical Materials Research and Development Co., Ltd.

[0166] X-8 is a chemical matting agent. One part of X-8 requires three parts of E-12 epoxy resin. (Guangzhou Zehe Chemical Materials Research and Development Co., Ltd.)

[0167] Experimental Analysis

[0168] The powders obtained in Examples 11-20 and Comparative Examples 1-4 were deposited on cold-rolled steel with a thickness of 0.5 mm using an electrostatic spray gun. At a film thickness of 60-80 μm, the panel was transferred to a hot air circulating oven and cured at 160°C for 15 minutes to obtain the cured coating. The performance test results of the coating are shown in Table 5.

[0169] Table 5

[0170]

[0171] In Table 5:

[0172] Column 1: Indicates the powder formulation identification number;

[0173] Column 2: Indicates the curing temperature / time of the powder coating;

[0174] Column 3: Indicates 60° gloss, tested according to GB / T9754-2007;

[0175] Column 4: Indicates the PCI leveling grade of the coating appearance. Specifically, the leveling grade of the coating to be tested is determined by visually comparing it with the PCI leveling grade reference board (0-10 grades). This is a common leveling grade determination method in the industry.

[0176] Column 5: Indicates the positive and negative impact strength, tested according to GB / T1732-2020, and records the highest impact that will not cause the coating to crack, in kg.cm;

[0177] Column 6: Indicates coating adhesion, tested according to GB / T9286-2021;

[0178] Column 7: Indicates the hardness of the coated pencil, tested according to GB / T6739-2022;

[0179] Column 8: Indicates the T-bend performance of the coating, tested in accordance with GB / T 30791-2014.

[0180] The test results in Table 5 clearly show that, compared to powders 1-2, which use a single high-activity polyester to achieve a lower matte gloss at low temperatures, the coating appearance is poor, with PCI leveling grades all <5. Conversely, powders 3-4, which use a single high-leveling polyester, achieve a leveling grade >8 at low temperatures, but have higher gloss and poorer mechanical properties. In contrast, powders 5-14, prepared by blending two polyesters, exhibit excellent matte effects at low temperatures, with gloss levels below 30% and leveling grades above 7. Furthermore, the coatings demonstrate good impact resistance, adhesion, hardness, and T-bend performance, meeting the requirements for aluminum wheel coating.

[0181] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A matte powder coating composition, characterized in that, The raw materials include: highly reactive polyester resin, high-leveling polyester resin, curing crosslinking agent, and matting agent; The highly reactive polyester resin has an acid value of 60-80 mgKOH / g, a reactivity of 120-300s at 160℃, and a melt viscosity of ≤10000mPa·s at 160℃. The high-leveling polyester resin has an acid value of 40-60 mgKOH / g, a reactivity of 595-900 s at 160℃, and a melt viscosity of ≤5000 mPa·s at 160℃. Reactivity: refers to the time required for the resin to react with the curing crosslinking agent to gel, determined at 160℃ according to GB / T 16995-1997; The mass ratio of the highly active polyester resin to the high-leveling polyester resin is (1-4):1; The preparation method of the matte powder coating composition includes the following steps: mixing the components, extruding and kneading, and grinding to obtain the matte powder coating composition; The highly active polyester resin is prepared from the following raw materials: polyol 1, polyacid 1, acidifier 1, esterification catalyst, and crosslinking catalyst; the polyol 1 is an aliphatic and / or alicyclic diol; the polyacid 1 is an aromatic diacid and an aliphatic diacid; the acidifier 1 is an aromatic polyacid anhydride; the molar ratio of the polyol 1 to the polyacid 1 is 1:(1-1.3); the molar ratio of the polyol 1 to the acidifier 1 is 1:(0.05-0.2). The high-level polyester resin is prepared from the following raw materials: polyol 2, polyacid 2, acidifier 2, esterification catalyst, and crosslinking catalyst; the polyol 2 is an aliphatic and / or alicyclic diol and an aliphatic triol; the polyacid 2 is an aromatic diacid; the acidifier 2 is an aromatic diacid and an aliphatic diacid; the molar ratio of the polyol 2 and the polyacid 2 is 1:(0.85-1); the molar ratio of the polyol 2 and the acidifier 2 is 1:(0.1-0.25). The highly reactive polyester resin is prepared by a method comprising the following steps: A1: Polyol 1, polyacid 1 and esterification catalyst are mixed and esterification reaction is carried out to obtain esterification product 1; A2: Add acidifying agent 1 to the esterification product 1 and carry out acid hydrolysis reaction to obtain acidification product 1; A3: Acidification product 1 is reacted with a crosslinking catalyst to obtain a highly active polyester resin; The high-level polyester resin is prepared by a method comprising the following steps: B1: Polyol 2, polyacid 2 and esterification catalyst are mixed and esterification reaction is carried out to obtain esterification product 2; B2: Add acidifying agent 2 to the esterified product 2 and carry out acid hydrolysis reaction to obtain acidified product 2; B3: Acidification product 2 reacts with a crosslinking catalyst to obtain a high-level polyester resin.

2. The matte powder coating composition according to claim 1, characterized in that, The acidifier 1 is selected from trimellitic anhydride, pyromellitic anhydride or a combination thereof; And / or, the aromatic dicarboxylic acid in the acidifying agent 2 is selected from at least one of terephthalic acid, isophthalic acid, phthalic acid, and naphthalic acid, and the aliphatic dicarboxylic acid in the acidifying agent 2 is selected from at least one of succinic acid, adipic acid, and glutaric acid.

3. The matte powder coating composition according to claim 1, characterized in that, The polyol 1 is selected from at least one of neopentyl glycol, ethylene glycol, diethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, pentylene glycol, hexanediol, and 1,4-cyclohexanediol. And / or, the aliphatic and / or alicyclic diols in polyol 2 are selected from at least one of neopentyl glycol, ethylene glycol, diethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, pentanediol, hexanediol, and 1,4-cyclohexanediol, and the aliphatic triols in polyol 2 are selected from at least one of trimethylolpropane and trimethylolethane.

4. The matte powder coating composition according to claim 2, characterized in that, The aromatic dicarboxylic acid in the polycarboxylic acid 1 is selected from at least one of terephthalic acid, isophthalic acid, and phthalic anhydride, and the aliphatic dicarboxylic acid in the polycarboxylic acid 1 is selected from at least one of succinic acid, adipic acid, glutaric acid, and 1,4-cyclohexanedicarboxylic acid. And / or, the polyacid 2 is selected from at least one of terephthalic acid, isophthalic acid, and phthalic acid.

5. The matte powder coating composition according to claim 2, characterized in that, The esterification catalyst is selected from at least one of monobutyltin oxide, monobutyltin chloride, and tetrabutyl titanate; And / or, the crosslinking catalyst is selected from at least one of benzyltrimethylammonium chloride, triphenylphosphine, triphenylethylphosphine bromide, and tert-butylamine.

6. The matte powder coating composition according to claim 1, characterized in that, The curing crosslinking agent is an epoxy resin curing agent; And / or, the matting agent is selected from one or a combination of physical matting agents, chemical matting agents.

7. The matte powder coating composition according to claim 1, characterized in that, The matte powder coating composition further includes at least one of a leveling control agent, a degassing agent, a pigment, a dye, and a filler.

8. The use of the matte powder coating composition according to any one of claims 1 to 7 in the protection of workpiece surfaces.

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