A low temperature curing powder coating and preparation method thereof

Abstract

The present application discloses a low-temperature curing powder coating and a preparation method thereof, and relates to the field of powder coatings. A low-temperature curing powder coating comprises 45-55 parts by weight of carboxyl polyester, 42-48 parts by weight of bisphenol A epoxy resin, 1.25-1.36 parts by weight of polyvinyl pyrrolidone coated modified curing accelerator and 3.5-4.5 parts by weight of pigments and fillers; the carboxyl polyester is prepared from raw material components including 25-30 parts by weight of aromatic diols, 11.2-13.8 parts by weight of aromatic dibasic acids, 28-34 parts by weight of long-chain aliphatic dibasic acids, and 0.01-0.05 parts by weight of catalysts. The present application can reduce the curing temperature of the powder coating to 120°C. For a coating of conventional thickness, the surface of the coating is smooth and flat, and the adhesion strength to the substrate is good, which is conducive to the coating of heat-sensitive materials such as wood, plastics, etc.; at the same time, it can also prevent the problem of poor stability and easy agglomeration of the powder coating.

Description

Technical Field

[0001] The present application relates to the field of powder coatings, and in particular to a low-temperature curing powder coating and a preparation method thereof. Background Art

[0002] Powder coatings are powder coatings that use resin base materials and curing agents as film-forming materials, supplemented with fillers, pigments and other functional additives. Powder coatings have basically no VOC emissions and are currently generally regarded as environmentally friendly coatings.

[0003] Among them, carboxyl polyester / epoxy resin powder coating is one of the common powder coatings, which is mainly made by reacting carboxyl polyester and epoxy resin. However, the curing temperature of common carboxyl polyester / epoxy resin powder coating is above 170°C, and the curing time is more than 10 minutes, which not only has high energy consumption, but also is not conducive to the coating of heat-sensitive substrates such as wood and plastic.

[0004] Among them, adding a curing accelerator can reduce the curing temperature of carboxyl polyester / epoxy resin powder coatings, but the curing accelerator is easy to cause pre-crosslinking of carboxyl polyester and epoxy resin, resulting in the extrusion, leveling and storage stability of the powder coating being affected. Therefore, it is difficult to obtain a powder coating that can be cured at low temperature (below 140°C) and has a smooth coating surface. Summary of the invention

[0005] In order to improve the problem in the related art that it is difficult to obtain a powder coating that can be cured under low temperature conditions (below 140°C) and has a smooth coating surface, the present application provides a low-temperature curing powder coating and a preparation method thereof.

[0006] In the first aspect, the present application provides a low temperature curing powder coating adopting the following technical solution:

[0007] A low-temperature curing powder coating comprises, based on raw materials, 45-55 parts by weight of carboxyl polyester, 42-48 parts by weight of bisphenol A epoxy resin, 1.25-1.36 parts by weight of polyvinyl pyrrolidone-coated modified curing accelerator and 3.5-4.5 parts by weight of pigments and fillers; the carboxyl polyester is prepared from raw material components including 25-30 parts by weight of aromatic diols, 11.2-13.8 parts by weight of aromatic dibasic acids, 28-34 parts by weight of long-chain aliphatic dibasic acids and 0.01-0.05 parts by weight of catalysts.

[0008] The difference between this application and the related art is that:

[0009] 1. The carboxyl polyester used in the low-temperature curing powder coating in the present application is obtained by esterification and polycondensation of aromatic diols, aromatic dibasic acids and long-chain aliphatic dibasic acids in a specific ratio. A specific ratio of long-chain aliphatic dibasic acids is introduced into the modified carboxyl polyester, which improves the flexibility and regularity of the carboxyl polyester, reduces the melt viscosity of the carboxyl polyester, and increases the activity of the end group, which is beneficial to reduce the curing temperature of the carboxyl polyester / bisphenol A epoxy resin powder coating and can prevent the problem of excessive viscosity of the powder coating from adversely affecting the leveling property of the powder coating.

[0010] 2. The present application adopts polyvinyl pyrrolidone-coated modified curing accelerator to replace the conventional curing accelerator, which can not only promote the curing of carboxyl polyester / bisphenol A epoxy resin powder coating to further reduce the curing temperature of carboxyl polyester / bisphenol A epoxy resin powder coating, but also prevent the powder coating from being pre-crosslinked and cured, resulting in poor stability and easy agglomeration of the powder coating.

[0011] Among them, the present application can reduce the curing temperature of carboxyl polyester / bisphenol A epoxy resin powder coating to 120°C through the combination of specific carboxyl polyester, bisphenol A epoxy resin and polyvinyl pyrrolidone coated modified curing accelerator. For coatings of conventional thickness (above 40μm), the surface of the coating is smooth and flat, and has good adhesion to the substrate, which is conducive to the coating of heat-sensitive materials such as wood and plastic; at the same time, it can also prevent the powder coating from being pre-cross-linked and cured, resulting in poor stability and easy agglomeration of the powder coating.

[0012] Optionally, the epoxy monomer amount of the bisphenol A epoxy resin is 600-650 g / eq.

[0013] Optionally, the aromatic diol is at least one of p-terephthalylinol, hydroquinone bis(hydroxyethyl) ether, resorcinol bis(hydroxyethyl) ether, and 2,3,5,6-tetrafluoroterephthalylinol.

[0014] Preferably, the aromatic diol is a composition of 2,3,5,6-tetrafluorophenylenediol and hydroquinone bis(hydroxyethyl)ether or resorcinol bis(hydroxyethyl)ether, and the weight ratio of the 2,3,5,6-tetrafluorophenylenediol to hydroquinone bis(hydroxyethyl)ether or resorcinol bis(hydroxyethyl)ether is 1:(3-4).

[0015] When preparing the carboxyl polyester of the present application, the aromatic diol is preferably a composition of 2,3,5,6-tetrafluorophenylenediol and hydroquinone bis(hydroxyethyl) ether or resorcinol bis(hydroxyethyl) ether in a specific ratio, which is beneficial to further improve the leveling properties of the carboxyl polyester / bisphenol A epoxy resin powder coating, and can achieve uniform coating of a thin coating (less than 10 μm), and the coating has no defects such as orange peel and shrinkage cavities.

[0016] Optionally, the aromatic dibasic acid is at least one of terephthalic acid, isophthalic acid, and phthalic acid, and the long-chain aliphatic dibasic acid is at least one of undecanedioic acid, dodecanedioic acid, tridecanedioic acid, and tetradecanedioic acid.

[0017] When preparing the carboxyl polyester of the present application, adding an aromatic dibasic acid is beneficial to improving the weather resistance of the coating, and adding a long-chain aliphatic dibasic acid is beneficial to making the carboxyl polyester have better flexibility.

[0018] Preferably, the preparation method of the carboxyl polyester comprises the following steps:

[0019] After the aromatic diol, aromatic dibasic acid, 70-75% of the total mass of the long-chain aliphatic dibasic acid and the catalyst are uniformly mixed according to the proportion, the temperature is raised to 240-250° C. under nitrogen protection, and the reaction is carried out for 4-6 hours to obtain an esterification product;

[0020] Add the remaining long-chain aliphatic dibasic acid to the esterification product, react at 220-230° C. for 3-4 hours, then cool to 210° C., evacuate to a vacuum degree of -0.095 MPa, and maintain for 1.5-2 hours to obtain a carboxyl polyester.

[0021] In the present application, the carboxyl polyester prepared by the above method has good flexibility and regularity, reduces the melt viscosity of the carboxyl polyester, and improves the activity of the end group, which is beneficial to reduce the curing temperature of the carboxyl polyester / bisphenol A epoxy resin powder coating and can prevent the problem of excessive viscosity of the powder coating causing adverse effects on the leveling of the powder coating.

[0022] Optionally, the polyvinyl pyrrolidone coated modified curing accelerator is obtained by coating and modifying a curing accelerator with polyvinyl pyrrolidone, and the curing accelerator adopts at least one of ethyltriphenylphosphine bromide, benzyltrimethylammonium bromide, 2-thiolbenzothiazole zinc salt, and zinc acetylacetonate, and the weight ratio of the polyvinyl pyrrolidone to the curing accelerator is (4-5):1.

[0023] In the present application, polyvinyl pyrrolidone is coated on the outer peripheral side of the curing accelerator. When the temperature of the powder coating reaches 120°C, the polyvinyl pyrrolidone on the surface of the polyvinyl pyrrolidone-coated modified curing accelerator melts and breaks, and the curing accelerator is released, which promotes the reaction of the carboxyl polyester and the bisphenol A epoxy resin, so that the carboxyl polyester / bisphenol A epoxy resin powder coating can be rapidly cross-linked and cured at 120°C. At the same time, the weight ratio of polyvinyl pyrrolidone to the curing accelerator is controlled to be (4-5): 1, the coating integrity of the curing accelerator is good, and it does not affect the subsequent curing accelerator to play a promoting role, which can further improve the stability of the carboxyl polyester / bisphenol A epoxy resin powder coating.

[0024] Optionally, the curing accelerator is a composition of ethyltriphenylphosphonium bromide and 2-thiolbenzothiazole zinc salt in a weight ratio of (8-9):1.

[0025] In the present application, the curing accelerator in the polyvinyl pyrrolidone-coated modified curing accelerator adopts a composition of ethyl triphenylphosphine bromide and 2-thiolbenzothiazole zinc salt in a weight ratio of (8-9):1, which can effectively reduce the curing temperature of the carboxyl polyester / bisphenol A epoxy resin powder coating while further improving the weather resistance and adhesion fastness of the powder coating.

[0026] Preferably, the polyvinyl pyrrolidone is polyvinyl pyrrolidone K30.

[0027] In the present application, polyvinyl pyrrolidone is preferably polyvinyl pyrrolidone K30, which is beneficial to the uniform dispersion and coating integrity of the curing accelerator.

[0028] Optionally, the preparation method of the polyvinyl pyrrolidone coated modified curing accelerator comprises the following steps:

[0029] Mix polyvinyl pyrrolidone and water in a weight ratio of 1:(10-12) to obtain a coating solution;

[0030] Adding a curing accelerator to the coating solution, and ball-milling until uniformly dispersed to obtain a dispersion;

[0031] The dispersion is spray-dried to obtain a polyvinyl pyrrolidone-coated modified curing accelerator.

[0032] The present application adopts the above method to prepare a polyvinyl pyrrolidone coated modified curing accelerator, and can obtain a polyvinyl pyrrolidone coated modified curing accelerator with good coating integrity and good product stability.

[0033] Optionally, the catalyst is at least one of dibutyltin dilaurate and dibutyltin oxide.

[0034] Optionally, the pigment filler is at least one of titanium dioxide, nano-calcium carbonate, and nano-silicon dioxide.

[0035] In the second aspect, the present application provides a method for preparing a low temperature curing powder coating using the following technical solution:

[0036] A method for preparing a low-temperature curing powder coating comprises the following steps:

[0037] The carboxyl polyester, bisphenol A epoxy resin, polyvinyl pyrrolidone coated modified curing accelerator and pigment filler are uniformly mixed to obtain a premix;

[0038] The premix is ​​mixed, extruded, cold-cut and crushed at 100-110°C to obtain a low-temperature curing powder coating.

[0039] In the present application, carboxyl polyester, bisphenol A epoxy resin, polyvinyl pyrrolidone coated modified curing accelerator and pigment filler are firstly uniformly mixed and then mixed and extruded, which is beneficial to improve the uniformity of low temperature curing powder.

[0040] In summary, this application at least includes the following beneficial technical effects:

[0041] 1. The present application can reduce the curing temperature of carboxyl polyester / bisphenol A epoxy resin powder coating to 120°C by combining specific carboxyl polyester, bisphenol A epoxy resin and polyvinyl pyrrolidone coated modified curing accelerator. For coatings of conventional thickness (above 40 μm), the surface of the coating is smooth and flat, and has good adhesion to the substrate, which is conducive to the coating of heat-sensitive materials such as wood and plastic. At the same time, it can also prevent the pre-cross-linking and curing of the powder coating, which leads to poor stability and easy agglomeration of the powder coating.

[0042] 2. When preparing the carboxyl polyester of the present application, the aromatic diol is preferably a composition of 2,3,5,6-tetrafluorophenylenediol and hydroquinone bis(hydroxyethyl) ether or resorcinol bis(hydroxyethyl) ether in a specific ratio, which is beneficial to further improve the leveling property of the carboxyl polyester / bisphenol A epoxy resin powder coating, and can achieve uniform coating of a thin coating (less than 10 μm), and the coating has no defects such as orange peel and shrinkage cavities.

[0043] 3. The curing accelerator in the polyvinyl pyrrolidone-coated modified curing accelerator is a composition of ethyl triphenylphosphine bromide and 2-thiolbenzothiazole zinc salt in a weight ratio of (8-9):1, which can effectively reduce the curing temperature of the carboxyl polyester / bisphenol A epoxy resin powder coating while further improving the weather resistance and adhesion fastness of the powder coating. DETAILED DESCRIPTION

[0044] The following specific preparation examples, embodiments and comparative examples are provided to further illustrate the present application. Unless otherwise specified, the raw materials of the present application can be obtained from commercial sources.

[0045] Preparation Example of Carboxyl Polyester

[0046] [Preparation Example 1-1]

[0047] A carboxyl polyester comprising the following raw materials:

[0048] Aromatic diol: 25 kg. In this preparation example, the aromatic diol is 2,3,5,6-tetrafluorophenylenedimethanol;

[0049] Aromatic dibasic acid: 11.2 kg. In this preparation example, the aromatic dibasic acid is specifically terephthalic acid;

[0050] Long-chain aliphatic dibasic acid: 28 kg. In this preparation example, the long-chain aliphatic dibasic acid is specifically undecanedioic acid, wherein the long-chain aliphatic dibasic acid is added in two steps. In the first step, the amount added is 70% of the total weight of the long-chain aliphatic dibasic acid, and is added simultaneously with the aromatic diol, the aromatic dibasic acid, and the catalyst; in the second step, it is added after the esterification reaction is completed;

[0051] Catalyst: 0.01 kg. In this preparation example, the catalyst is specifically dibutyltin oxide.

[0052] In this preparation example, the preparation method of carboxyl polyester comprises the following steps:

[0053] Aromatic diol, aromatic dibasic acid, 70% of the total mass of long-chain aliphatic dibasic acid and catalyst are uniformly mixed according to a ratio, heated to 240°C under nitrogen protection, reacted for 6 hours, and an esterification product is obtained;

[0054] The remaining long-chain aliphatic dibasic acid was added to the esterification product, reacted at 220°C for 4 hours, then cooled to 210°C, evacuated to a vacuum degree of -0.095 MPa, and maintained for 1.5 hours to obtain a carboxyl polyester.

[0055] [Preparation Example 1-2]

[0056] A carboxyl polyester comprising the following raw materials:

[0057] Aromatic diol: 30 kg. In this preparation example, the aromatic diol is hydroquinone bis(hydroxyethyl) ether;

[0058] Aromatic dibasic acid: 13.8 kg. In this preparation example, the aromatic dibasic acid is specifically isophthalic acid;

[0059] Long-chain aliphatic dibasic acid: 34 kg. In this preparation example, the long-chain aliphatic dibasic acid is tetradecanedioic acid. The long-chain aliphatic dibasic acid is added in two steps. The first step is to add 75% of the total weight of the long-chain aliphatic dibasic acid, and add it together with the aromatic diol, aromatic dibasic acid, and catalyst; the second step is to add it after the esterification reaction is completed;

[0060] Catalyst: 0.05 kg. In this preparation example, the catalyst is specifically dibutyltin dilaurate.

[0061] In this preparation example, the preparation method of carboxyl polyester comprises the following steps:

[0062] Aromatic diol, aromatic dibasic acid, 75% of the total mass of long-chain aliphatic dibasic acid and catalyst are uniformly mixed according to a ratio, heated to 250°C under nitrogen protection, reacted for 4 hours, and an esterification product is obtained;

[0063] The remaining long-chain aliphatic dibasic acid was added to the esterification product, reacted at 230° C. for 3 h, then cooled to 210° C., evacuated to a vacuum degree of -0.095 MPa, and maintained for 2 h to obtain a carboxyl polyester.

[0064] [Preparation Example 1-3]

[0065] A carboxyl polyester, which differs from [Preparation Example 1-1] in that the aromatic diol is different.

[0066] In this preparation example, the aromatic diol is specifically hydroquinone bis(hydroxyethyl) ether.

[0067] [Preparation Example 1-4]

[0068] A carboxyl polyester, which differs from [Preparation Example 1-1] in that the aromatic diol is different.

[0069] In this preparation example, the aromatic diol is a combination of 2,3,5,6-tetrafluorophenylenedimethanol and hydroquinone bis(hydroxyethyl)ether, and the weight ratio of 2,3,5,6-tetrafluorophenylenedimethanol to hydroquinone bis(hydroxyethyl)ether is 3:1.

[0070] [Preparation Example 1-5]

[0071] A carboxyl polyester, which differs from [Preparation Example 1-1] in that the aromatic diol is different.

[0072] In this preparation example, the aromatic diol is a combination of 2,3,5,6-tetrafluorophenylenediol and hydroquinone bis(hydroxyethyl)ether, and the weight ratio of 2,3,5,6-tetrafluorophenylenediol to hydroquinone bis(hydroxyethyl)ether is 1:3.

[0073] [Preparation Example 1-6]

[0074] A carboxyl polyester, which differs from [Preparation Example 1-5] in that the aromatic diol is different.

[0075] In this preparation example, the aromatic diol is a combination of p-phenylenediol and hydroquinone bis(hydroxyethyl)ether, and the weight ratio of p-phenylenediol to hydroquinone bis(hydroxyethyl)ether is 1:3.

[0076] [Preparation Example 1-7]

[0077] A carboxyl polyester, which differs from [Preparation Example 1-5] in that the aromatic diol is different.

[0078] In this preparation example, the aromatic diol is a combination of 2,3,5,6-tetrafluorophenylenedimethanol and phenylenedimethanol, and the weight ratio of 2,3,5,6-tetrafluorophenylenedimethanol to phenylenedimethanol is 1:3.

[0079] Preparation example of polyvinyl pyrrolidone coated modified curing accelerator

[0080] [Preparation Example 2-1]

[0081] A polyvinyl pyrrolidone coated modified curing accelerator comprises the following raw materials:

[0082] Curing accelerator: 5 kg; in this preparation example, the curing accelerator is specifically ethyl triphenylphosphonium bromide;

[0083] Polyvinyl pyrrolidone: 20 kg; in this preparation example, polyvinyl pyrrolidone specifically adopts polyvinyl pyrrolidone K30;

[0084] Water: 200kg.

[0085] In this preparation example, the preparation method of the polyvinyl pyrrolidone-coated modified curing accelerator comprises the following steps:

[0086] Mixing polyvinyl pyrrolidone and water uniformly according to a weight ratio to obtain a coating solution;

[0087] Adding a curing accelerator to the coating solution, and ball-milling until uniformly dispersed to obtain a dispersion;

[0088] The dispersion is spray-dried to obtain a polyvinyl pyrrolidone-coated modified curing accelerator with a particle size range of 0.1-0.3 μm.

[0089] [Preparation Example 2-2]

[0090] A polyvinyl pyrrolidone-coated modified curing accelerator, which differs from [Preparation Example 2-1] in that: in this preparation example, the curing accelerator specifically uses 2-thiolbenzothiazole zinc salt.

[0091] [Preparation Example 2-3]

[0092] A polyvinyl pyrrolidone coated modified curing accelerator, which differs from [Preparation Example 2-1] in that: in this preparation example, the curing accelerator specifically adopts a combination of ethyltriphenylphosphine bromide and 2-thiolbenzothiazole zinc salt, wherein the weight ratio of ethyltriphenylphosphine bromide to 2-thiolbenzothiazole zinc salt is 1:1.

[0093] [Preparation Example 2-4]

[0094] A polyvinyl pyrrolidone coated modified curing accelerator, which differs from [Preparation Example 2-1] in that: in this preparation example, the curing accelerator specifically adopts a combination of ethyltriphenylphosphine bromide and 2-thiolbenzothiazole zinc salt, wherein the weight ratio of ethyltriphenylphosphine bromide to 2-thiolbenzothiazole zinc salt is 9:1.

[0095] Example

[0096] [Example 1]

[0097] A low temperature curing powder coating comprising the following raw materials:

[0098] Carboxyl polyester: 45 kg; in this embodiment, the carboxyl polyester is specifically the carboxyl polyester prepared in [Preparation Example 1-1];

[0099] Bisphenol A epoxy resin: 42 kg; in this embodiment, the bisphenol A epoxy resin is specifically bisphenol A epoxy resin BE-502, and the epoxy equivalent is 600-650 g / eq;

[0100] Polyvinyl pyrrolidone modified curing accelerator: 1.25 kg; In this embodiment, the polyvinyl pyrrolidone modified curing accelerator specifically adopts the polyvinyl pyrrolidone modified curing accelerator prepared in [Preparation Example 2-1];

[0101] Color filler: 3.5 kg; in this embodiment, the color filler is specifically nano calcium carbonate.

[0102] In this embodiment, the preparation method of the low temperature curing powder coating comprises the following steps:

[0103] The carboxyl polyester, bisphenol A epoxy resin, polyvinyl pyrrolidone coated modified curing accelerator and pigment filler are uniformly mixed to obtain a premix;

[0104] The premix is ​​kneaded, extruded, cold-cut and crushed at 100°C to obtain a low-temperature curing powder coating.

[0105] [Example 2]

[0106] A low temperature curing powder coating comprising the following raw materials:

[0107] Carboxyl polyester: 55 kg; in this embodiment, the carboxyl polyester is specifically the carboxyl polyester prepared in [Preparation Example 1-2];

[0108] Bisphenol A epoxy resin: 48 kg; in this embodiment, the bisphenol A epoxy resin specifically adopts bisphenol A epoxy resin BE-502, and the epoxy equivalent is 600-650 g / eq;

[0109] Polyvinyl pyrrolidone modified curing accelerator: 1.36 kg; In this embodiment, the polyvinyl pyrrolidone modified curing accelerator specifically adopts the polyvinyl pyrrolidone modified curing accelerator prepared in [Preparation Example 2-1];

[0110] Pigment and filler: 4.5 kg; in this embodiment, the pigment and filler is specifically titanium dioxide.

[0111] In this embodiment, the preparation method of the low temperature curing powder coating comprises the following steps:

[0112] The carboxyl polyester, bisphenol A epoxy resin, polyvinyl pyrrolidone coated modified curing accelerator and pigment filler are uniformly mixed to obtain a premix;

[0113] The premix is ​​kneaded, extruded, cold-cut and crushed at 110°C to obtain a low-temperature curing powder coating.

[0114] [Example 3]

[0115] A low temperature curing powder coating, which is different from [Example 1] in that the carboxyl polyester is different. In this example, the carboxyl polyester is the carboxyl polyester prepared in [Preparation Example 1-3].

[0116] [Example 4]

[0117] A low temperature curing powder coating, which is different from [Example 1] in that the carboxyl polyester is different. In this example, the carboxyl polyester is the carboxyl polyester prepared in [Preparation Example 1-4].

[0118] [Example 5]

[0119] A low temperature curing powder coating, which is different from [Example 1] in that the carboxyl polyester is different. In this example, the carboxyl polyester is the carboxyl polyester prepared in [Preparation Example 1-5].

[0120] [Example 6]

[0121] A low temperature curing powder coating, which is different from [Example 1] in that the carboxyl polyester is different. In this example, the carboxyl polyester is the carboxyl polyester prepared in [Preparation Example 1-6].

[0122] [Example 7]

[0123] A low temperature curing powder coating, which is different from [Example 1] in that the carboxyl polyester is different. In this example, the carboxyl polyester is the carboxyl polyester prepared in [Preparation Example 1-7].

[0124] [Example 8]

[0125] A low temperature curing powder coating, which is different from [Example 5] in that the polyvinyl pyrrolidone modified curing accelerator is different. In this example, the polyvinyl pyrrolidone modified curing accelerator is the polyvinyl pyrrolidone modified curing accelerator prepared in [Preparation Example 2-2].

[0126] [Example 9]

[0127] A low temperature curing powder coating, which is different from [Example 5] in that the polyvinyl pyrrolidone modified curing accelerator is different. In this example, the polyvinyl pyrrolidone modified curing accelerator is the polyvinyl pyrrolidone modified curing accelerator prepared in [Preparation Example 2-3].

[0128] [Example 10]

[0129] A low temperature curing powder coating, which is different from [Example 5] in that the polyvinyl pyrrolidone modified curing accelerator is different. In this example, the polyvinyl pyrrolidone modified curing accelerator is the polyvinyl pyrrolidone modified curing accelerator prepared in [Preparation Example 2-4].

[0130] Comparative Example

[0131] [Comparative Example 1]

[0132] A powder coating, which differs from [Example 1] in that the carboxyl polyester is different.

[0133] The difference between the carboxyl polyester used in this comparative example and the carboxyl polyester in [Preparation Example 1-1] is that the long-chain aliphatic dibasic acid is replaced by an equal amount of glutaric acid.

[0134] [Comparative Example 2]

[0135] A powder coating, which differs from [Example 1] in that:

[0136] The polyvinyl pyrrolidone modified curing accelerator is replaced by an equal amount of ethyl triphenylphosphine bromide.

[0137] Performance testing

[0138] Test 1: The powder coatings prepared in each embodiment and comparative example were sprayed on a PVC substrate, one group controlled the spray dry thickness at 5 μm, and the other group controlled the spray dry thickness at 40 μm. They were all dried at 120°C for 2 min, and then the surface of the coating was observed to see if there were problems such as orange peel and shrinkage cavities that affect the surface quality of the coating.

[0139] Test 2: The adhesion strength of the samples prepared in Test 1 was tested in accordance with GB / T 9286-2021.

[0140] Test 3: The samples prepared in Test 1 were subjected to weather resistance test, specifically referring to GB / T 1865-2009. The test temperature was 38°C, the exposure method was continuous, the cycle method referred to cycle A, and the number of cycles was 500. After the test, the evaluation was carried out in accordance with Section 4.2 of GB / T 1766-2008.

[0141] Test 4: The powder coatings prepared in each embodiment and comparative example were subjected to stability test. The test period was 180 days. The ambient temperature was maintained at 35° C. The powder coatings were observed to see if they had agglomeration problems. Test 1 was repeated.

[0142] Table 1

[0143]

[0144] Table 2

[0145]

[0146]

[0147] Table 3

[0148]

[0149] Table 4

[0150]

[0151]

[0152] Combining Examples 1-10 and the data in Tables 1-4, it can be seen that when the coating thickness is a conventional thickness (above 40 μm), the powder coating of the present application can be cured at 120°C to obtain a coating with a smooth surface, and the adhesion strength and weathering discoloration stability of the coating to the substrate are both good, and the powder coating is not prone to agglomeration during storage. However, when the coating thickness is thin (less than 10 μm), the preparation of carboxyl polyester preferably requires a composition with a weight ratio of 2,3,5,6-tetrafluorophenylenediol and hydroquinone bis(hydroxyethyl) ether or resorcinol bis(hydroxyethyl) ether of 1:(3-4) as the aromatic diol, otherwise it is difficult to obtain a coating with a smooth surface, and good adhesion strength and weathering discoloration stability of the coating to the substrate.

[0153] The difference between Comparative Example 1 and Example 1 is that different carboxyl polyesters are used. In the preparation of carboxyl polyester, glutaric acid is used in Comparative Example 1 instead of undecanedioic acid used in Example 1. Combining the data in Tables 1-4, it can be seen that when a dibasic acid with a carbon number of less than 10 is used to replace a long-chain aliphatic dibasic acid, the coating film obtained by curing the powder coating at 120° C. is prone to orange peel problems, and at the same time, the adhesion fastness and weathering color change stability of the coating film are also significantly affected.

[0154] The difference between Comparative Example 2 and Example 1 is that the curing accelerator in Comparative Example 2 is not subjected to coating modification. Combining the data in Tables 1-4, it can be seen that directly using a curing accelerator instead of the polyvinyl pyrrolidone coating modified curing accelerator in the present application is likely to cause pre-crosslinking of the carboxyl polyester and the bisphenol A type epoxy resin, which is not conducive to the stable storage of the powder coating. At the same time, it is also likely to cause the problem of poor leveling of the coating film, which is not conducive to obtaining a coating film with a smooth surface.

[0155] The difference between Example 3-7 and Example 1 is that different aromatic diols are used in the preparation of carboxyl polyester. Combining the data in Table 1-4, it can be seen that when the coating thickness is thin (less than 10 μm), the preparation of carboxyl polyester preferably requires a composition of 2,3,5,6-tetrafluorophenylenediol and hydroquinone bis(hydroxyethyl) ether or resorcinol bis(hydroxyethyl) ether in a weight ratio of 1:(3-4) as the aromatic diol, otherwise it is difficult to obtain a coating with a smooth surface and good adhesion to the substrate and weathering and discoloration stability.

[0156] The difference between Examples 8-10 and Example 5 is that different curing accelerators are used in the polyvinyl pyrrolidone-coated modified curing accelerator. Combined with the data in Table 1, it can be seen that the curing accelerator in the polyvinyl pyrrolidone-coated modified curing accelerator uses a composition of ethyl triphenylphosphine bromide and 2-mercaptobenzothiazole zinc salt in a weight ratio of (8-9):1, which can effectively reduce the curing temperature of the carboxyl polyester / bisphenol A epoxy resin powder coating while further improving the weather resistance and adhesion of the powder coating.

[0157] The embodiments of this specific implementation are all preferred embodiments of the present application, and are not intended to limit the protection scope of the present application. The same components are represented by the same symbols. Therefore, any equivalent changes made based on the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A low temperature curing powder coating, characterized in that: Calculated by raw materials, it includes 45-55 parts by weight of carboxyl polyester, 42-48 parts by weight of bisphenol A epoxy resin, 1.25-1.36 parts by weight of polyvinyl pyrrolidone coated modified curing accelerator and 3.5-4.5 parts by weight of pigments and fillers; The carboxyl polyester is prepared from raw material components including 25-30 parts by weight of aromatic diol, 11.2-13.8 parts by weight of aromatic dibasic acid, 28-34 parts by weight of long-chain aliphatic dibasic acid, and 0.01-0.05 parts by weight of catalyst; The aromatic diol is a composition of 2,3,5,6-tetrafluorophenylenedimethanol and hydroquinone bis-hydroxyethyl ether or resorcinol bis-hydroxyethyl ether, wherein the weight ratio of 2,3,5,6-tetrafluorophenylenedimethanol to hydroquinone bis-hydroxyethyl ether or resorcinol bis-hydroxyethyl ether is 1:(3-4); The long-chain aliphatic dibasic acid is at least one of undecanedioic acid, dodecanedioic acid, tridecanedioic acid, and tetradecanedioic acid; The polyvinyl pyrrolidone coated modified curing accelerator is obtained by coating and modifying a curing accelerator with polyvinyl pyrrolidone. The curing accelerator adopts at least one of ethyl triphenyl phosphine bromide, benzyl trimethyl ammonium bromide, 2-thiol benzothiazole zinc salt, and zinc acetylacetonate. The weight ratio of the polyvinyl pyrrolidone to the curing accelerator is (4-5):

1.

2. A low temperature curing powder coating according to claim 1, characterized in that: The aromatic dibasic acid is at least one of terephthalic acid, isophthalic acid and phthalic acid.

3. A low temperature curing powder coating according to any one of claims 1-2, characterized in that: The preparation method of the carboxyl polyester comprises the following steps: Aromatic diol, aromatic dibasic acid, 70-75% of the total mass of long-chain aliphatic dibasic acid and catalyst are uniformly mixed according to a ratio, heated to 240-250°C under nitrogen protection, reacted for 4-6 hours, and an esterification product is obtained; Add the remaining long-chain aliphatic dibasic acid to the esterification product, react at 220-230° C. for 3-4 hours, then cool to 210° C., evacuate to a vacuum degree of -0.095 MPa, and maintain for 1.5-2 hours to obtain a carboxyl polyester.

4. A low temperature curing powder coating according to claim 1, characterized in that: The curing accelerator is a composition of ethyl triphenylphosphine bromide and 2-thiol benzothiazole zinc salt in a weight ratio of (8-9):

1.

5. A low temperature curing powder coating according to claim 1, characterized in that: The polyvinyl pyrrolidone is polyvinyl pyrrolidone K30.

6. A low temperature curing powder coating according to claim 1, characterized in that: The preparation method of the polyvinyl pyrrolidone coated modified curing accelerator comprises the following steps: Mix polyvinyl pyrrolidone and water in a weight ratio of 1:(10-12) to obtain a coating solution; Adding a curing accelerator to the coating solution, and ball-milling until uniformly dispersed to obtain a dispersion; The dispersion is spray-dried to obtain a polyvinyl pyrrolidone-coated modified curing accelerator.

7. A method for preparing a low temperature curing powder coating according to any one of claims 1 to 6, characterized in that: The following steps are involved: Carboxyl polyester, bisphenol A epoxy resin, polyvinyl pyrrolidone coated modified curing accelerator and pigments and fillers are uniformly mixed to obtain a premix; The premix is ​​mixed, extruded, cold-cut and crushed at 100-110°C to obtain a low-temperature curing powder coating.

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